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High Speed Catamarans and Multihulls pp 423–475 Cite as

Other High-Speed Multihull Craft

  • Liang Yun 4 ,
  • Alan Bliault 5 &
  • Huan Zong Rong 4  
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In previous chapters we introduced catamarans of a displacement or semiplaning type with some information on resistance for the planing hull form as used mainly by wave piercers. We explained that, owing to the catamaran demihull’s slender length/beam ratio aimed at reducing wave-making drag, such craft would not operate in the planing region as the Froude number Fr l remains below around 0.75, even for high service speed (Table 1.1 ), so the hydrodynamic lift proportion would not be more than 20% of displacement, even if a hard chine demihull form is used. In this chapter we will discuss other design alternatives for high-speed vessels, including those targeted at speeds above Fr l  = 1.0.

  • Planing Hull
  • Wave-making Drag
  • Wave Piercer

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Yun, L., Bliault, A., Rong, H.Z. (2019). Other High-Speed Multihull Craft. In: High Speed Catamarans and Multihulls. Springer, New York, NY. https://doi.org/10.1007/978-1-4939-7891-5_10

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body plan and offset of catamaran

Discussion in ' Boat Design ' started by elaheh , May 20, 2012 .

elaheh

elaheh Junior Member

Hi I need offset and body plan of a catamaran with pax 150. it's a student project and really i don't know what should i do. my catamaran speed is 32 kn.  

gonzo

gonzo Senior Member

What are you a student of?  
I'm student of marine engineering at Tehran Polytechnic. actually I'm looking for a catamaran's body plan and offset and arrangement and ... I'll be so thankful if you help me through.  

Ad Hoc

Ad Hoc Naval Architect

what is the objective??....it seems odd to have a request for a lines of 150pax vessel. What is the relevance of the 150pax?....if you need a lines plan...you need a lines plan....if you need one for 150 pax AND 32knots...then you must design a hull suitable for such an SOR.  

daiquiri

daiquiri Engineering and Design

What I don't get is whether you have got an assignment to design a 150 pax catamaran, or an assignment to find lines plan of an existing catamaran...?  
I'm looking specifically for body plan and offset and arrangement of an 150 pax catamaran passenger ship which can have an operational speed of 32 knots. but I'm not sure that i can find the exact sample,so i asked you either you got any sample like this or not! I want an assignment to find lines plan of an existing catamaran  
What is the project. Certainly it has to be more than just finding a design.  
gonzo said: ↑ What is the project. Certainly it has to be more than just finding a design. Click to expand...

Mr Efficiency

Mr Efficiency Senior Member

What's wrong with you guys ? Haven't you got a set of plans lying around to hand over to Elaheh to save him the bother and cost ? No help at all.....  
elaheh said: ↑ hi we should take a catamaran offset and arrangement and mach it with our catamaran. .. Click to expand...

afshinzkh

afshinzkh New Member

guys let me take this straight , I have the same assignment as Elaheh , we just want a simple body plan for a catamaran and as long as i know i can modify any catamaran body plan to reach my own ship, so just a body plan of any kind of catamaran.... anyone????? pleeease????  
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afshinzkh said: ↑ ...so just a body plan of any kind of catamaran.... anyone????? pleeease???? Click to expand...

klowe34

Creating a body plans offset table

Cacciatore

Rebuild body-plan of 100 ft Sailboat

adt2

Anybody know of Kumarakom Houseboat plans?

Laranjo123

Body plan designing

Michaelp

Mini Speedboat - Anybody know where to get plans for the boat pictured?

schakel

Self steering for double wheels, can somebody help me out?

Owly

Control Stick anbody?

pironiero

Maybe somebody would be interested

Alexanov

SS Normandie body lines drawings, offset tables.

Hunterr

somebody feed my aluminum boat design to me

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Boat Design Net

catamaran body plan

MIKE WALLER 

Yacht design.

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WE SPECIALIZE IN BOAT PLANS FOR AMATEUR BUILDERS

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catamaran body plan

How To Create the Perfect Cruising Catamaran Layout

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More than ever before, sailing fans are gaining an interest in catamaran layouts and designs that define performance. Many others are also looking into either buying a cruising catamaran or designing and building one. While building a catamaran is no piece of cake, this article shows you how to create the perfect cruising catamaran layout. 

To create the perfect catamaran layout, carefully consider factors like a good hull design, optimal helm station placement, boat stability, and adequate load-carrying capacity. Excellent galley positioning, ease of handling, and spacious living and sleeping quarters are also crucial. 

The modern cruising catamaran is a far cry from the simple Polynesian double canoe of old. That’s because structural innovations and new composite materials have resulted in multihulls with impressive cruising abilities. Keep reading to learn more about exceptional catamaran layouts.  

The Changing Trends in Catamaran Designs

The early cruising catamaran designs resulted in boats that could sail much faster than traditional sailing boats. In addition, they could glide with ease in shallow waters and required less wind and crew. Unfortunately, these cruising cats were heavy, had small, cramped interiors, and boasted somewhat challenging handling abilities. 

Today’s cruising catamarans are different. They boast the utmost comfort, high speeds, and the safety of a well-designed cruising yacht. They are also more exciting, visually appealing, deliver the smoothest of rides, and sport more spacious interiors. 

Have a look at the below video showcasing the top ten cruising catamarans:

Features To Look Out for in Catamaran Design Layouts

Cruising catamaran designers understand what most sailors look for in a cruising vessel. They, therefore, design cruising multihulls that address these pertinent issues and more. Some of the features you might want to consider having in your dream boat include the following:

  • Responsive performance. Outstanding performance allows for pleasurable cruising and ensures your safety since you have more options during difficult weather.
  • Excellent load-carrying ability . This allows you to have an extended cruising vacation or ocean crossing.
  • Boat stability . Go for lightweight, robust construction, which results in a lot of buoyancy.
  • A low center of gravity for smooth rides and enhanced performance. Centering weight around a low center of gravity improves the overall sailing quality, reduces pitching movement and reduces the risk of capsizing .
  • Adequate bridgedeck clearance to reduce slamming and provide better performance in rough conditions. A high bridgedeck also means less noise and slapping action from the waves hitting the boat bottom, thus ensuring a quieter, smoother ride.
  • Comfortable sailing. To enjoy a quality life on board, you need comfort while at sea. Thus, elements like gentle movement, no creaks or groans, no bridgedeck slamming, and minimal pitching are essential for quality, peaceful and restful sleep.  

Now that you know what a cutting-edge catamaran features, let’s look at how to create the perfect cruising catamaran layout.  

Build a Larger-Sized Catamaran

The early catamarans ranged between 36-42 feet (10.9-12.8m). At the time, this appeared to be a good size in terms of safety and ease of handling. However, the boats were heavy, and the additional drag and displacement adversely affected their performance and windward ability. 

It’s now possible to make the new generation catamarans lighter, larger, and more spacious with excellent power-to-weight features. The current trend is larger-sized catamarans in the 45-50 feet (13.7- 15.2) range. Composite engineering and technologically advanced equipment such as furling systems, electric winches, and autopilot make it easier for a smaller crew to sail larger boats with confidence. And to do so without compromising safety or stability. 

Get the Best Catamaran Hull Design

A cruising catamaran’s performance depends on three main aspects; its length, the sail area, and the boat’s weight. Long boats are generally fast. A light boat with more sail area is also faster than a heavier boat with less sail area. In other words, you can make a multihull faster by making it longer, lighter, or adding more sail.

However, there are exceptions to this rule; a boat with too much sail area is more likely to capsize if there are brisk winds. Also, if the boat’s design makes it too light, it’ll be unable to handle much punishment, while a hull design that’s too slim would make the vessel incapable of carrying any significant loads. But that’s not all; if the boat is too long or too large, it’ll become grossly exorbitant. Narrow hull shape might also mean smaller cabins.

Nonetheless, these three factors alone are not enough to determine a cruising catamaran’s performance. While faster boats boast finer hulls, the wetted surface area tends to increase as fineness increases; thus, fine hulls end up becoming less fast in low wind speeds. Also, very wide hulls mean a reduction in actual performance.

The Prismatic Coefficient (Cp), a measure of how full the ends of the hull get, is the most essential design hull shape factor for any catamaran. A high Cp equals high speeds, although you can still use a lower Cp if you have fine hulls. Nevertheless, the key to a good Catamaran design is a higher Cp for fast sailing. 

To achieve a high Cp, there are several things you can do: 

  • Fit bulb bows . Unfortunately, the bulb bows tend to slam in a seaway when you do this.
  • Have an extensive planning aft section . However, this can increase the wetted surface area, WSA and lead to additional challenges. 
  • Flatten out the hull rocker and add a bustle aft. This helps to add displacement aft. 

catamaran body plan

Build Convertible Main Living Spaces

The open cockpit is now a thing of the past. Instead, pioneering designers for catamaran manufacturers like Nautitech, Gunboat, and Catana now replace traditional-style salons, cockpits, and cabins with spacious indoor and outdoor living spaces. The concept involves merging separate saloon and cockpit areas with duplicate lounge spaces and the use of hard-wearing composite materials. 

You can also design the cabin to suit your preferences. You may decide to add a cabin or remove one, add a bathroom, have the forward berth in the hull or on the wing deck.

  • The design enhancements boost usable space while opening up the living areas.
  • It reduces time and costs for interior maintenance and cleaning. 
  • Large windows bring in more light, increasing visibility. 
  • Luxurious, spacious, and airy owners’ cabins provide more comfortable living space. 

catamaran body plan

Bulkhead Helm Stations vs. Twin Stern Steering

Many catamaran owners have traditionally preferred bulkhead steering. This helm position remains popular, but twin stern steering positions come with more advantages since they provide greater sails visibility. The twin stern positions are also best suited for racing or day sailing since they often lack adequate protection for extended cruising. 

Exposed helms are not ideal for a long ocean passage. Go for a safe, secure, and well-protected helm station that provides good visibility and comfortable space for long watches. Again, it’s best to have all control lines at the helm to establish a static control station. Also, have all push-button-controlled winches, instruments, windlass, and autopilot prominently located inside the cockpit. 

  • Twin stern steering positions give you a better view of the sails
  • You get a better feel for overall sailing conditions.
  • Twin stern steering positions lack the necessary protection for extended cruising. 

catamaran body plan

Go for the Flybridge Design

The flybridge design is appealing because it offers excellent visibility, more comfort, and additional entertainment and lounging space for everyone on board. Unfortunately for smaller boats – those below 50 feet (15.24m), there is minimal protection from the elements. As such, you might want to consider adding enclosures to offer protection. The flybridge, thus the helm, remains cut off from the vessel, which makes communicating with the crew a challenge. 

  • It provides great visibility.
  • It offers comfortable spacing. 
  • It might be unsafe to move from the cockpit to the flybridge in bad weather.
  • It isn’t easy to communicate with the crew.

Daggerboards vs. Fixed Keels

Average cruising catamarans typically utilize fixed keels while high-performance cats have daggerboards . Fixed keels allow you to beach your catamaran easily, and your hull remains intact if a collision occurs. While you lose some angle when sailing upwind, you gain more interior space in the hulls that you can put to good use.

Daggerboards are essential in a performance cruising catamaran since they guarantee that the boat delivers good upwind sailing, including during difficult situations. During long passages, they allow you to point better upwind though the drawback is that they consume much interior space within the cruising catamaran’s hulls.

Since flying on foils ( hydrofoils ) isn’t that practical on cruising catamarans, designers of larger-sized boats have also come up with modified daggerboards. These daggerboards produce lift and prevent leeway, too, thereby improving performance significantly, as seen with the Catana 59’s curved daggerboards. These foil-like daggerboards lift the boat ever so slightly upon reaching higher speeds, making it feel less heavy and much faster. 

At the end of the day, calculating the performance of a boat sailing in a wide range of varying seas and winds might not be easy – despite a daggerboard or fixed keel configuration. This is because upwind speed depends not only on the sails’ quality but also windage and the height of the bridgedeck beyond the water.

  • The design innovations -curved daggerboards and hydrofoils- improve catamaran performance significantly.
  • Daggerboards enable you to access otherwise inaccessible anchorages.
  • Daggerboards take up hull space in the hulls of your vessel.

catamaran body plan

Galley Up vs. Galley Down

Galley layout are becoming more and more important as more people, including families, start sailing regularly. While at sea, your galley needs to be a safe place, well-ventilated, and functional. Everything should be well-thought-out for the sailor’s comfort, including handholds to make it safer to move around the boat. 

While the galley location can either be up the bridgedeck or down in the hull, galley up appears to be the most popular trend. This makes the galley the focal point of both the living space and entertainment areas.

If you have a family, this placement is ideal since you make your meals from the galley and get to spend most of your time here. Many cruising families and couples prefer this arrangement and find separating the galley down the hull unappealing. Besides, carrying hot food up and down the staircase is unsafe.

Still, galley down is ideal for charter boats since it offers a private cooking area and uses up hull space efficiently.  

  • Having the galley on the bridgedeck is ideal for families and cruising couples.
  • Placing the galley on a similar level with the serving area and cockpit is safer and less tiring.
  • There’s better ventilation on the bridgedeck, making for comfortable cooking. 
  • There’s less kitchen privacy galley up.
  • On smaller catamarans, this layout can impact the size of the saloon seating area significantly.

Production Catamaran vs. Custom

The choice of either a production catamaran or a custom design might seem pretty straightforward. Production catamarans from major brands come backed by proven designs, dependable construction, solid warranties, and many years of experience. The catamarans are easy to service, source for parts, and most – particularly the owner’s versions – hold on to their value, making them much easier to resell. 

On their part, custom boats are fantastic in that you can tailor them to your exact needs. However, they might be more challenging to maintain or service. That’s because of parts unavailability and lack of construction knowledge.

Choose Quality Construction Materials

The best quality materials to use on your catamaran are both light and robust. While carbon fiber is great, plywood, plywood/epoxy, and strip-cedar are excellent materials too. What’s more, they are also affordable, so you don’t have to get too hung up on cutting-edge building materials. What matters is build quality; thus, a well-built plywood catamaran boat can last as long as a boat made from more high-tech materials. 

Combining various materials also helps combat some of the issues that plague plywood boats in terms of resale value. At times, the design tends to make the boats appear pretty dated.  

  • Plywood and strip-cedar materials are affordable and provide excellent build quality. 
  • Plywood boats may have a lower resale value than those built with modern materials.

Consider Ease of Handling

An important factor in handling a cruising catamaran is deck layout. Most cruising catamarans sailed short-handed , so if your boat has one helm, all lines should run back here to allow for a static control station for the entire boat. 

The other essential element is visibility from the helm. The 360 degrees of visibility while maneuvering, docking, or underway is crucial to your boat’s safety, as well as life and property. As such, you should be able to view both bows, or at least the pulpits and sterns, while standing at the helm. If not, you may have challenges handling the boat due to blind spots.

catamaran body plan

Consider the Load Carrying Capacity

A well-designed catamaran is enjoyable to sail in all weather conditions. It’s also much easier to handle than a monohull because of its widely spaced twin engines. But when you immerse extra hull depth, the vessel gets sluggish and moves slower, maneuvering in tight spots or when docking becomes more challenging. Furthermore, the hull submersion reduces bridge deck clearance, leading to hull slamming. 

To allow for adequate load carrying capacity, you need a design that provides a generous displacement. This helps to ensure that you maintain reasonable bridge deck clearance even when fully loaded. It also allows you to avoid digging big holes in the water as you drag your transoms. 

Displacement refers to the amount of buoyancy designed into the hulls, which essentially means that your boat will cruise better if its weight is less than your designed displacement.

Note that an overloaded catamaran not only loses out on performance but eventually, on safety too. To counter this, choose a lightweight catamaran with hulls bearing cored construction and interiors made of lightweight materials.  

Remember, when you go cruising, you will need to carry fuel, extra water, supplies, equipment, and amenities, translating into thousands of extra pounds. Therefore, try and avoid the following design errors to ensure that your catamaran has an adequate load-carrying capacity:

  • Avoid putting in place too much accommodation space.
  • Avoid building a heavy boat ‐ use low-tech construction materials.
  • Avoid installing inboards in a small boat.
  • Lightly constructed catamarans perform faster and carry more weight.
  • Cored construction makes for a strong and stiff catamaran, thus enabling good performance.

Final Thoughts

A well-designed cruising catamaran is a joy to behold. Today’s modern technological advancements mean that you can buy or build a light but strong cruising catamaran. And as you can see from this article, there are many excellent cruising catamaran layouts that you can choose from. 

However, whichever layout you decide on needs to fit your sailing needs and purposes to ensure you remain comfortable and safe while at sea. Above all, ensure that you go for a vessel that you can handle with ease in all weather conditions.

Owner of CatamaranFreedom.com. A minimalist that has lived in a caravan in Sweden, 35ft Monohull in the Bahamas, and right now in his self-built Van. He just started the next adventure, to circumnavigate the world on a Catamaran!

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HOME / INDEX PAGE  

Definitions

Length overall (LOA)

Length of water line (lwl)

Length between perpendiculars (LFF)

Rated length

he hull of a yacht is a complex three-dimensional shape, which cannot be defined by any simple mathematical expression. Gross features of the hull can be described by dimensional quantities such as length, beam and draft, or non-dimensional ones like prismatic coefficient or slenderness (length/displacement) ratio. For an accurate definition of the hull the traditional lines drawing; is still a common tool, although most professional yacht designers now take advantage of the rapid developments in CAD introduced in Chapter 1.

In this chapter we start by defining a number of quantities, frequently referred to in yachting literature, describing the general features of the yacht. Thereafter, we will explain the principles of the traditional drawing and the tools required to produce it. We recommend a certain work plan for the accurate production of the drawings and, finally, we show briefly how the hull lines are generated in a modern CAD program.

The list of definitions below includes the basic geometrical quantities used in defining a yacht hull. Many more quantities are used in general ship hydrodynamics, but they arc not usually referred to in the yachting field. A complete list may be found in the International Towing Tank Conference (ITTC) Dictionary of Ship Hydrodynamics.

The maximum length of the hull from the forwardmost point on the stem to the extreme after end (see Fig 3.1). According to common practice, spars or fittings, like bowsprits, pulpits etc are not included and neither is the rudder.

The length of the designed waterline (often referred to as the DWL).

This length is not much used in yachting but is quite important for ships. The forward perpendicular (FP) is the forward end of the designed waterline, while the aft perpendicular (AP) is the centre of the rudder stock.

The single most important parameter in any rating rule. Usually L is obtained by considering the fullness of the bow and stern sections in a more or less complex way.

The maximum beam of the hull excluding fittings, like rubbing strakes.

catamaran body plan

Fig 3.1 Definitions of the main dimensions

Beam of waterline (bwl)

Displacement

The maximum beam at the designed waterline.

The maximum draft of the yacht when floating on the designed waterline. Tc is the draft of the hull without the keel (the 'canoe' body).

The vertical distance from the deepest point of the keel to the sheer line (see below). Dc is without the keel.

Could be either mass displacement (m) ie the mass of the yacht, or volume displacement (V or V), the volume of the immersed part of the yacht. mc, Vc and Vc are the corresponding notations without the keel.

Midship section For ships, this section is located midway between the fore and aft perpendiculars. For yachts it is more common to put it midway between the fore and aft ends of the waterline. The area of the midship section (submerged part) is denoted AM, with an index 'c' indicating that the keel is not included.

Maximum area section For yachts the maximum area section is usually located behind the midship section. Its area is denoted Ax (AXc).

Prismatic coefficient This is the ratio of the volume displacement and the maximum section (CP) area multiplied by the waterline length, ie CP = V/(AX • Lwl). This value is very much influenced by the keel and in most yacht applications only the canoe body is considered: CPc = Vc(AXc • Lwl). See Fig 3.2. The prismatic coefficient is representative of the fullness of the yacht. The

Copenhagen Ship Curves

Circumscribed cylinder volume = v = L^ Ay

Fig 3.2 The prismatic coefficient

Bateau Trie

BOX WL WL c

Circumscribed box volume =

Fig 3.3 The block coefficient

Block coefficient ( CB)

Centre of buoyancy (B)

Centre of gravity (G)

Freeboard fuller the ends, the larger the Cp. Its optimum value depends on the speed, as explained in Chapter 5.

Although quite important in general ship hydrodynamics this coefficient is not so commonly used in yacht design . The volume displacement is now divided by the volume of a circumscribed block (only the canoe body value is of any relevance) CBc = V J(Lwl • BWL • Tc). See Fig 3.3.

The centre of gravity of the displaced volume of water, its longitudinal and vertical positions are denoted by LCB and VCB respectively.

The centre of gravity of the yacht must be on the same vertical line as the centre of buoyancy. In drawings G is often marked with a special symbol created by a circle and a cross. This is used also for marking geometric centres of gravity. See. for instance, Figs 5.27 or 8.2.

The intersection between the deck and the topside. Traditionally, the projection of this line on the symmetry plane is concave, the 'sheer* is positive. Zero and negative sheer may be found on some extreme racing yachts and powerboats.

The vertical distance between the sheer line and the waterline.

Tumble home

When the maximum beam is below the sheer line the upper part of the topsides will bend inwards (see Fig 3.4). To some extent this reduces the weight at deck level, but it also reduces the righting moment of the

Fig 3.4 Definition of tumble home and flare

Plans Geometry

Tumble home crew on the windward rail. Further, the hull becomes more vulnerable to outer skin damage in harbours.

Flare The opposite of tumble home. On the forebody in particular, the sections may bend outwards to reduce excessive pitching of the yacht and to keep it more dry when beating to windward.

Scale factor (a) This is not a geometrical parameter of the hull, but it is very important when designing a yacht. The scale factor is simply the ratio of a length (for instance the Lw,) at full scale to the corresponding length at model scale. Note that the ratio of corresponding areas (like the wetted area) is a2 and of corresponding volumes (like displacement) a3.

Lines drawing A complete lines drawing of the YD 40 is presented in Fig 3.5. The hull is shown in three views: the profile plan (top left), the body plan (top right) and half breadth plan (bottom). Note that the bow is to the right.

In principle, the hull can be defined by its intersection with two different families of planes, and these are usually taken as horizontal ones (waterlines) and vertical ones at right angles to the longitudinal axis of the hull (sections). While the number of waterlines is chosen rather arbitrarily, there are standard rules for the positioning of the sections. In yacht architecture the designed waterline is usually divided into ten equal parts and the corresponding sections are numbered from the forward perpendicular (section 0) backwards. At the ends, other equidistant sections, like # 11 and # 1 may be added, and to define rapid changes in the geometry, half or quarter sections may be introduced as well. In Fig 3.5 half sections are used throughout.

The profile is very important for the appearance of the yacht, showing the shapes of the bow and stern and the sheer line. When drawing the waterlines, displayed in the half breadth plan, it is most helpful if the lines end in a geometrically well defined way. Therefore a 'ghost" stem and a 'ghost' transom may be added. The ghost stem is the imagined sharp leading edge of the hull, which in practice often has a rounded stem, and the ghost transom is introduced because the real transom is often curved and inclined. If an imagined vertical transom is put near the real one at some convenient station, it will facilitate the fairing of the lines. The drawing of Fig 3.5 has been produced on a CAD system and no ghost stem is shown. However, a ghost transom is included.

In the body plan, the cross sections of the hull are displayed. Since the hull is usually symmetrical port and starboard, only one half needs to be shown, and this makes it possible to present the forebody to the right and the afterbody to the left. In this way mixing of the lines is avoided and the picture is clearer. Note that in the figure the half stations are drawn using thinner lines.

The above cuts through the hull are sufficient for defining the shape, but another two families of cuts are usually added, to aid in the visual perception of the body. Buttocks are introduced in the profile plan,

Buttock Lines Ship

* * ^ "i * 2 § 2 II II II II II II II ll II

showing vertical, longitudinal cuts through the hull at positions indicated in the half breadth plan. The diagonals in the lower part of the half breadth plan are also quite important. They are obtained by cutting the hull longitudinally in different inclined planes, as indicated in the body plan. The planes should be as much as possible at right angles to the surface of the hull, thus representing its longitudinal smoothness. In practice, the flow tends to follow the diagonals, at least approximately, so that they are representative of the hull shape as "seen' by the water. Special attention should be paid to the after end of the diagonals, where knuckles, not noticcd in the other cuts, may be found, particularly on lOR yachts from the 1970s and the 1980s. Almost certainly, such unevenncss increases the resistance and reduces the speed of the yacht.

The other line in the lower part of the half breadth plan is the curve of sectional areas, representing the longitudinal distribution of the submerged volume of the yacht. The value at each section is proportional to the submerged area of that section, while the total area under the curve represents the displacement (volume). A more detailed description of the construction of the curve of sectional areas will be given in Chapter 4.

In order to define exactly the shape of the hull a table of offsets is usually provided by the designer. This is to enable the builder to lay out the lines at full size and produce his templates. Offsets are always provided for the waterlines, but the same information may be given for diagonals and/or buttocks also. Note that all measurements are to the outside of the shell.

The drawing should be made on a special plastic film, available in different thicknesses. The film is robust and will not be damaged by

Photo 3.6 Tools (triangle, plastic film, straight edge, brush, pens, pencil, erasing shield and eraser)

Straight Plan Ribbon

Photo 3.7 Tr¿\nster of measures from body plan (top) to half breadth plan (bottom) using a paper ribbon

Model Boat Plans Free

erasing. Furthermore, it is unaffected by the humidity of the air. which may shrink ordinary paper.

Since the film is transparent the grid for the lines drawing is drawn on the back so that it will remain, even after erasing the hull lines on the front many times. Great care must be exercised when drawing the grid, making sure that the alignment and spacing are correct and that all angles arc cxactly 90°. In Fig 3.5 the grid is shown as thin horizontal and vertical lines, representing waterlines, buttocks and stations.

Black ink should be used when drawing the grid and preferably when finishing the hull lines also. However, when working on the lines a pencil and an eraser are needed. There are, in fact, special pencils and erasers for this type of work on plastic film. An erasing shield and a brush are also most useful (see Photo 3.6).

For creating the grid a long straight edge is required, together with a

Photo 3.8 Ducks and a spline used for drawing a water Iine

catamaran body plan

Photo 3.9 Templates used for drawing lines with large curvature

Ducks For Spline Geometry

large 90° set square. It is very convenient to have a bunch of paper ribbons, which can be used for transferring different measures from one plan to the other. For example, when drawing a waterline the offsets of this line may be marked on the ribbon directly from the body plan and moved to the half breadth plan (Photo 3.7).

To draw the hull lines it is necessary to have a set of splines and weights or ducks. Long, smooth arcs can be created when bending the splines and supporting them by the ducks at certain intervals. Photo 3.8 shows how these tools are used when drawing a waterline. The splines should be made of plastic, somewhat longer than the hull on the drawing, and with a cross-section of about 2.5 mm2. Many different types of ducks can be found, some of them home made. Preferably,

Buttocks Geometry

Photo 3.10 PI an i meter they should be made of lead, and the weight should be between 1.5 and 2.5 kg. To be able to support the spline, they should have a pointed nose, as shown in Photo 3.8.

The splines are needed when drawing the lines in the profile and half breadth plans. However, the lines of the body plan are usually too curved for the splines, so it is necessary to make use of a set of templates especially developed for this purpose. The most well known ones are the so called Copenhagen ship curves, the most frequently used of which are shown in Photo 3.9.

A very convenient instrument, well known in naval architecture, is the planimeter, used for measuring areas (see Photo 3.10). The pointer of the planimeter is moved around the area to be measured, and the change in the reading of the scale when returning to the point of departure gives the area enclosed by the path followed. Considering the difficulty in following exactly any given line the accuracy is surprisingly high, more than adequate for the present purposes. The need for measuring areas will be explained in the next chapter.

Since many calculations have to be carried out when preparing the drawings, and indeed in the whole design process, an electronic calculator is essential. A simple one would be sufficient in most cases, but a programmable calculator would simplify some of the calculations, particularly if a planimeter is not available. Most scientific calculators have programs for calculating areas with acceptable accuracy, and programs are available for most of the calculations described in the next chapter.

Designing the hull is a complex process, and many requirements have to be considered. One difficulty is that important parameters, such as the displacement cannot be determined until the lines have been fixed. This calls for an iterative method. Such a method is also required in the fairing of the lines. The problem is to make the lines in one projection correspond to smooth lines in the other two projections. For an inexperienced draftsman this problem is a serious one, and many trials may be needed to produce a smooth hull.

While the preferred sequence of operations may differ slightly between yacht designers the main steps should be taken in a certain order. In the following, we propose a work plan, which has been found effective in many cases. It should be pointed out that the plan does not take into account any restrictions from measurement rules.

Step 1: Fix the main dimensions These should be based on the general considerations discussed in Chapter 2, using information on other yachts of a similar size, designed for similar purposes. This way of working is classical in naval architecture, where the development proceeds relatively slowly by evolution of previous designs. It is therefore very important, after deciding on the size of the yacht, to find as much information as possible on other similar designs. Drawings of new yachts may be found in many of the leading yachting magazines from all over the world.

The dimensions to fix at this stage are: length overall, length of the waterline, maximum beam, draft, displacement, sail area, ballast ratio, prismatic, coefficient and longitudinal centre of buoyancy. One of the aims of this book is to help in the choice of these parameters and to enable the reader to evaluate older designs when trying to find the optimum for his own special demands.

Step 2: Draw the profile As pointed out above, this step takes much consideration, since the aesthetics of the yacht are, to a large extent, determined by tBfe pi^ffle-

Step 3: Draw the midship section The midship section can be drawn at this stage, or, alternatively, the maximum section if it is supposed to be much different. This may occur if the centre of buoyancy is far aft. The shape of the first section drawn is important, since it determines the character of the other sections.

Step 4: Check the displacement To find the hull displacement calculate (or measure) the submerged area of the section just drawn and multiply by the waterline length and the prismatic coefficient chosen for the hull. From the ballast ratio, the keel mass can be computed and the volume can be found, dividing by the density of the material (about 7200 kg/m3 for iron and 11300 kg/m- for lead). Assume that the rudder displacement is 10% of that of the keel and add all three volumes. If the displacement thus obtained is different from the prescribed one, return to step 3 and change accordingly.

The procedure described is for a fin-keel yacht. For a hull with an integrated keel, as on more traditional yachts, the prismatic coefficient usually includes both the keel and the rudder.

Step 5: Draw the designed waterline One point at or near the midship station is now known, together with the two end points from the profile, so now a first attempt can be made to draw the designed waterline.

Step 6: Draw stations 3, 7 and the transom The waterline breadth is now known, as well as the hull draft, and the sections should have a family

resemblance to the midship section. Often it is helpful to draw a ghost transom behind the hull.

Step 7: Draw new waterlines Two or three waterlines can now be drawn above and below the DWL. If the appearance is not satisfactory, go back to step 6 and change.

Steps 8 and 9: Add new sections and waterlines

Once this is done, sections I-9 should be completed as well as 7-10 waterlines. Constant adjustments, have to be made in order to create smooth lines in the body plan, as well as in the half breadth plan.

Step 10: Recheck the displacement and the longitudinal centre of buoyancy The curve of sec tional areas can now be constructed. Its area gives the displacement (excluding that of keel and rudder) and its centre of gravity corresponds to the longitudinal position of the centre of buoyancy. If not correct, adjustments have to be made from steps 5 or 6,

Step 11: Draw diagonals Inspect the smoothness, particularly near the stern. Adjust if necessary.

Step 12: Draw buttocks This is the final check on the smoothness. Usually only very minor corrections have to be made at this stage.

Computer aided design of hulls

As mentioned in Chapter 1, most CAD programs use master curves for generating the hull surface. Each curve is defined by a number of points, called vertices. Photo 3.11 shows, in a plan view, the grid of master curves used for generating the YD-40 hull. One of the transverse curves has been selected in Photo 3.12 and it can be seen how the smooth hull surface is generated inside the curve, which is shown as piece-wise linear between the vertices.

Photo 3.11 Grid of master curves used for the YD-40 (the vertical line to the right marks the origin of the coordinate system)

Photo 3.12 A section with vertices (crosses), master curve (between the crosses), hull surface and cuwature (outermost line)

Bateau Trie

The task of the designer is to specify the vertices in such a way that the desired hull shape is created.There are different ways of achieving this. Some programs start from a long cylindrical body or a box, while others start from a flat rectangular patch, defined by an orthogonal grid. These original shapes are then distorted by moving the vertices around, and it is relatively easy to produce a yacht-like body. However, it takes experience and experimentation to obtain a shape that satisfies criteria set up beforehand. In practice, designers very seldom start from scratch, but work from earlier designs, which already have a desirable shape and a known grid of master curves surrounding it. Since most new designs are evolutions of previous ones this approach is very natural.

A problem encountered when the first CAD programs for yachts appeared was that the scale on the screen was too small, and the resolution too low to enable the designer to create fair lines. Small bumps on the surface could not be detected 011 the screen, and it sometimes happened that the bumps were noticed only after the start of the hull construction . Therefore the CAD program developers introduced plots of the curvature of lines on the hull. Such a plot is shown.in Photo 3.12. The curvature of the line, which essentially corresponds to a section, is almost constant, except at the ends where it goes to zero.

Photo 3.13 illustrates the sensitivity of the curvature to small changes of the surface. The sheer line is shown in a plan view. In the top photo (the real design) the curvature is smooth and relatively constant along the hull. In the bottom photo one vertex point has been moved 10 mm at full scale perpendicular to the surface. The resulting change in the sheer line is so small that it cannot be detected by eye, but the curvature exhibits a considerable bump and some smaller fluctuations, showing that the line is not smooth. By looking at the curvature, lines may thus be generated that look fair even at full scale.

Photo 3.13 Sheer line with vertices and curvature. (top) Real design. (bottom) One vertex point moved 10 mm

catamaran body plan

Photo 3,14 Perspective view A great advantage of most CAD programs is that the hull may be of the YD-40 shown in perspective. As pointed out in Chapter 1 it is important to study the sheer line in particular from different angles, since the impression of the hull contour in reality is also influenced by the beam distribution, which is not visible if only the profile view is studied. Fig 3.14 shows the YD-40 in perspective, and a good impression can be obtained of the shape. "

By using a CAD program a fair hull can be produced rapidly and different requirements may be satisfied without too much work, such as a given prismatic coefficient or longitudinal centre of buoyancy. Meeting such requirements accurately in a manual process is extremely time consuming, so it is understandable that CAD techniques are always used nowadays by professional designers. However, due to the considerable cost of a CAD system, most amateur designers will still have to use the manual approach described above.

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Readers' Questions

How to figure the width to height to length of a yacht?
To figure out the width, height, and length of a yacht, you typically need to refer to the yacht's specifications provided by the manufacturer, yacht designer, or owner. These specifications should include the appropriate measurements. Consult the yacht's specifications: Look for the official documentation or technical information provided for the yacht. This documentation usually includes the length, width, and height of the yacht, referred to as LOA (Length Overall), Beam, and Draft, respectively. The specifications are usually available in brochures, user manuals, or on the official website of the yacht manufacturer. Seek professional advice: If you cannot find the specifications yourself or need more specific information, consider reaching out to yacht brokers, yacht builders, naval architects, or other professionals in the yachting industry. They have extensive knowledge and can guide you with accurate measurements or provide information by using the yacht's model or brand. Measure the yacht yourself: If you have physical access to the yacht and cannot find the specifications through other means, you can measure it directly. However, this method is less accurate and should only be used as a last resort. Use a measuring tape or other appropriate tools to measure the overall length, width or beam, and height. Ensure to measure from fixed reference points for consistency and accuracy. Remember that yachts come in various sizes, designs, and layouts. The width or beam, for example, may be different at different points along the vessel's length due to design variations. It is essential to refer to the official specifications or seek professional advice for the most precise and reliable measurements.
Can you use geometry on boats?
Yes, geometry can be applied to various aspects of boats, particularly in the design and construction phase. Here are a few examples: Hull Design: Geometry is crucial in designing the shape and dimensions of a boat's hull. The angles, curves, and mathematical calculations are used to ensure stability, hydrodynamics, and buoyancy. Stability Analysis: Geometry is used to determine the center of buoyancy, center of gravity, and metacenter of a vessel. These calculations are essential for assessing a boat's stability, both at rest and in motion. Navigation and Bearings: Geometric concepts such as angles, triangles, and trigonometry are used to calculate headings, course corrections, and bearings while navigating a boat. Sail Measurement and Adjustments: Sailboats utilize various geometric principles to determine sail sizes, aspect ratios, and shapes. The geometry of sail adjustments, such as tightening or loosening the sail, can affect the boat's speed and performance. Nautical Charts: Geometry plays a vital role in nautical charting, which involves representing the Earth's curved surface on a flat chart. Projections, grid systems, and coordinate systems are employed to accurately depict and navigate waterways. These are just a few examples of how geometry can be applied to boats. Overall, geometry is critical in ensuring boat design, navigation, and performance, making it an important aspect of the boating industry.
How to find ship displacement from submerged area?
To find the ship displacement from submerged area, you can follow these steps: Determine the underwater or submerged area of the ship. This can be done by calculating the area of the ship's hull that is below the waterline when it is fully submerged. Convert the area into a volume by multiplying it by the ship's beam (width) or mean draft (depth). Multiply the volume by the density of the water. The density of water varies slightly depending on temperature and salinity, but a typical value is around 1,000 kilograms per cubic meter. The result of this calculation will be the ship's displacement. It represents the weight of the water displaced by the ship when it is fully submerged. Note: This method assumes that the ship's hull has a constant shape below the waterline. In reality, the shape may vary, especially towards the ends of the ship.
How to draw a simple ship?
To draw a simple ship, follow these step-by-step instructions: Start by drawing a horizontal line slightly curved at the ends to create the ship's hull. Add a smaller curved line above the hull to outline the ship's deck. At the front of the ship, draw a triangular shape for the bow. On top of the deck, draw a small rectangular structure or cabin. Add a flagpole at the back of the deck by drawing a long, thin rectangle. Draw a small rectangle or square at the top of the flagpole for the flag. Next, add a slightly curved line near the waterline for the keel of the ship. On both sides of the hull, draw a series of diagonal lines to create the ship's planking. To indicate windows or portholes, draw small oval or circular shapes along the cabin. Add a couple of mast poles on the deck. To do this, draw two vertical lines with a horizontal line connecting them at the top. On top of the mast poles, add triangular or rectangular shapes for the sails. Finally, erase any unnecessary guidelines, and you can add more details like waves or seagulls to complete your simple ship drawing. Remember, this is just one way to draw a simple ship. Feel free to modify the design or add additional elements to make it your own!
How to draw a pin keeldrawing tutorialtop keel?
To draw a pin keel, follow these steps: Begin by drawing a slightly curved horizontal line. This line will serve as the water surface. Next, draw a long vertical line that will represent the keel. The keel should start at the bottom of the water surface line and extend downward. At the bottom of the vertical line, draw a slightly curved horizontal line. This line will represent the lower part of the keel. On the left side of the keel, draw a diagonal line extending outward. This line will represent the forward part of the keel. Repeat the previous step on the right side of the keel, drawing a diagonal line to represent the aft part. Connect the ends of the diagonal lines with a curved line, forming the bottom part of the keel. Add additional detail to the keel by drawing a small horizontal line near the top. This line represents the top part of the keel. Finally, erase any unnecessary lines and add shading to give the keel more depth and dimension. Remember to take your time and practice as much as needed to improve your drawing skills.
How do you draw a ship?
Drawing a ship can be a fun and creative process. Here's a step-by-step guide on how to draw a ship: Start by drawing a long, slightly curved horizontal line in the center of your paper. This line will serve as the ship's waterline. From one end of the waterline, draw a slanted rectangle shape, slightly wider at the bottom than the top. This will be the ship's hull. At the other end of the waterline, draw a smaller rectangle shape, slightly tilted upward. This will be the ship's bow. Connect the bow and the hull with two diagonal lines, creating the ship's front structure. Add a large, slightly curved rectangle shape at the top of the hull. This will be the main deck of the ship. Draw a smaller rectangle shape above the main deck to represent the ship's superstructure. Sketch two parallel, slanted lines on the front of the ship's superstructure to create the pilot house. On the main deck, draw a few rectangular shapes to indicate windows or portholes. Add details like railing, stairs, and lifeboats on the sides and top of the ship as desired. Extend the hull below the waterline using a curved line to give the ship depth. For the finishing touches, you can draw some waves around the ship, seagulls in the sky, or a flag on top. Remember to be creative and modify the design as you like. Don't worry if your drawing doesn't turn out perfect at first; practice makes perfect!
What hull curves do yachts fallow is it x squared?
The hull curves of yachts can vary depending on the design and purpose of the yacht. While some yacht hulls may follow a curve that resembles the function of x squared, others may follow different curves such as parabolic curves, ellipses, catenary curves, or other mathematical shapes. The specific curvature of a yacht's hull is determined by factors such as the desired speed, stability, maneuverability, and hydrodynamic efficiency of the vessel. It is typically designed by naval architects and engineers who consider various factors including the size and weight distribution of the yacht, the intended use (e.g., racing, cruising, etc.), and materials used in construction. In summary, while some yachts may have hull curves similar to x squared, there is no universal standard hull curve for all yachts. The hull design depends on various factors and can incorporate different mathematical curves to achieve specific performance characteristics.
How to calculate the curvature of a boat?
To calculate the curvature of a boat, you would need to determine the radius of its curvature. The curvature refers to the degree of how much the boat's hull curves or bends. Gather the measurements: You will need the length and width measurements of the boat. These measurements can be obtained from the boat's specifications or by physically measuring it. Determine the midpoint: Locate the midpoint of the boat's length. This can be done by dividing the boat's length measurement by 2. Measure the rise: Starting from the midpoint, measure the distance between the bottom of the boat's hull and a straight line connecting the bow and stern (i.e., the rise). Measure the run: Measure the distance between the midpoint and the bottom of the boat's hull at the bow and stern. Calculate the radius of curvature: The radius of curvature can be calculated using the following formula: Radius = (run^2 + rise^2) / (8 x rise). The curvature: The curvature is calculated as the reciprocal of the radius of curvature. It's important to note that this calculation assumes a boat's hull shape can be represented by a simple section of a circle. More complex hull shapes, such as those with multiple curves or irregular shapes, may require different mathematical models or numerical methods to accurately determine curvature.
How to measure the curveture of a boat hull?
There are several methods to measure the curvature of a boat hull. Here are three common techniques: Profiling: This method involves taking measurements at specific points along the hull's surface to understand the curvature. You can use a flexible measuring tape or string to measure the distance from the hull to a straight reference line at different points along the boat's length. These measurements can then be plotted on a graph to depict the curvature of the hull. Reflection Method: For this technique, you need a laser level and a measuring tape. Firstly, position the laser level at a fixed distance from the boat hull and horizontally direct the laser beam towards the hull. The laser beam will be reflected back from the hull surface. Measure the distance from the laser level to the hull at different points along the boat's surface. These measurements can be used to calculate the curvature of the hull. 3D Scanning: Utilizing modern technology, you can use a 3D scanner to create a digital model of the boat hull. The scanner emits laser beams or projects structured light patterns onto the hull, capturing its shape in detail. The resulting 3D model can then be used to measure the curvature of the hull accurately. It is important to note that measuring the curvature of a boat hull may require specific tools and expertise. Hence, it is advised to consult with industry professionals or specialists for accurate measurements.
How to draw a yacht keel?
To draw a yacht keel, you can follow these steps: Start by drawing a horizontal line on your paper. This line will serve as the waterline. From the center point of the waterline, draw two vertical lines going downward to create the main part of the keel. These lines should taper towards the bottom. At the bottom of the keel, draw a horizontal line connecting the two vertical lines. This will form the bottom edge of the keel. Now, draw a diagonal line on each side of the keel, starting from the top and curving slightly outward. These lines will form the shape of the keel as it narrows towards the top. Connect the ends of the diagonal lines at the top with a smooth curve to create the rounded shape of the keel. Next, draw horizontal lines across the keel to represent the different sections or layers. These lines can be evenly spaced or closer together at the top and gradually getting wider towards the bottom. Add details such as ribbing or reinforcements by drawing diagonal lines across the keel, intersecting the horizontal lines. To give the keel a more realistic look, you can shade the bottom part and add some shadow where it meets the waterline. Finally, you can add additional details such as a bulbous bow or a fin at the bottom of the keel based on the specific design of the yacht you are drawing. Remember to sketch lightly at first and gradually darken your lines as you refine the shape. And don't forget to have fun and experiment with different styles and variations to make your drawing unique!
How to draw a boat into transverse stations?
Drawing a boat into transverse stations can be done by following these steps: Start by selecting a suitable scale for the drawing. This will depend on the size of the boat you want to draw and the size of the paper or canvas you are using. Begin by drawing a horizontal line across the paper, representing the waterline. Next, draw vertical lines representing the transverse stations at regular intervals along the waterline. These lines should be evenly spaced and represent the cross-sections of the boat at different points along its length. Use reference drawings or images of the boat to guide your drawing. Start by drawing the outline of the boat's hull within each station. Pay attention to the curvature and tapering of the hull as it moves towards the bow and stern. After drawing the outline, add any additional details such as deck lines, windows, hatches, and other features of the boat. Use shading techniques to add depth and dimension to the drawing. Pay attention to the light source and add shadows accordingly to create a realistic representation of the boat. Finally, go over your drawing and make any necessary adjustments or corrections to ensure accuracy.
What is nonprismatic hull?
A nonprismatic hull is a type of hull shape in naval architecture that does not conform to the standard prismatic shape of traditional sailing vessels. Nonprismatic hulls are designed to increase performance in certain areas such as speed and efficiency, as well as to reduce drag and enhance maneuverability. Nonprismatic hulls are also often used as part of a wave piercing design to cut through wave crests, thus reducing the size of the wake behind the ship.
How to design a schooner hull?
Research the history of schooner hulls and their design features. This will help you understand the shipbuilding principles and methods used in their construction. Consider the type of schooner you want to design. Is it a racing vessel or a cruising boat? This will help you determine the size, weight and other characteristics of the hull. Consider the type of material you will use for the schooner. Traditionally, schooner hulls have been made of wood or fiberglass, but there are other materials that can be used as well. You need to choose a material that meets your needs and budget. Work with an experienced maritime designer or drafter to create a 3D model of the schooner hull. This will help you visualize the hull and make sure it meets your specifications. Have a qualified shipwright or boat builder construct your schooner. Ensure that the schooner is tested and certified by a naval architect before you take it out on the water.
How to draw hull lines plan from boat existing images in reverse engineering?
Take a picture of the boat's existing lines plan. Import the image into a vector graphic program such as Inkscape, Adobe Illustrator, or Corel Draw. Trace the contours of the boat's hull using the Pen Tool or other trace tool in the program. Adjust the lines to make sure they accurately represent the boat's shape and contours. Once the lines plan is complete, use a ruler to draw perpendicular lines from the boat's existing lines plan as a reference for the hull. Use the curved line tool to refine the shape of the hull and make sure everything is in proportion and accurate. Double-check to make sure the hull lines plan is correct, and save the file for future reference.
What does half a sideways figure eight mean on a ship drawing?
Half a sideways figure eight on a ship drawing typically denotes the ship's waterline—the line where the ship sits in the water.
How to work out the shape and profile of a yatch datum line?
Establish the design criteria and parameters of the yacht. This should include the length, width, height and any other characteristics relevant to the design of the yacht. Define the design goals and objectives of the yacht, including the purpose and function of the yacht, how it will be used, and what type of sailing or other activities will take place on it. Choose an appropriate hull shape and size for the yacht based on the design criteria, goals and objectives. Create a 3D computer model of the yacht design, incorporating the appropriate hull shape and size. Use the model to define a datum line for the yacht, which will help to accurately measure the craft's performance and characteristics. The datum line should run from the center of the waterline around the hull to the transom. Using the 3D model, define the profile of the yacht by “lofting” the curves of the hull and the deck. Refine the design by adjusting the curves of the hull and deck to ensure that the yacht's performance characteristics are maximized. Use the computer model to run “virtual wind tunnel” tests on the design, to ensure that its performance characteristics are optimized.
How to draw a boat on water?
Start by sketching the basic shape of the boat. Start with a long, rectangular shape to form the hull of the boat. Add a slight curve to the top of the boat to give it an authentic boat shape. Draw a smaller rectangular shape for the cabin of the boat. Sketch two triangular shapes on the left and right side of the cabin for the sails. Draw a series of small circles along the bottom of the boat to create the waterline. Now add the details to your boat: windows, doors, life preservers, etc. Finally, draw some small waves around the boat to create the illusion of the boat sailing on water.
What are fair lines and sheer lines of a yacht?
Fair lines are the contours of the yacht's hull. Sheer lines are the long, gradual arch of the deck, starting at the bow and extending to the stern.
How to draw a hardshine boat hull quickly?
To draw a hardshine boat hull quickly, you can follow these steps: Start by drawing a horizontal line to represent the waterline. This line will serve as the base for the boat hull. Sketch a rough outline of the boat hull shape above the waterline. Keep in mind that hardshine boat hulls are typically streamlined and have a sharp, angular shape. Add a slightly curved line below the waterline to depict the bottom part of the hull. The curve should be gentle and gradually merge into the horizontal waterline. Extend two diagonal lines downward from the front end of the boat hull to create the bow. The bow should be pointed and sharp to cut through the water efficiently. Add a small transom at the rear end of the boat hull. The transom is usually flat or slightly curved upward. Sketch two straight lines from the bow to the stern to represent the deck of the boat. Draw a horizontal line across the middle section of the hull to indicate a separation or border between the upper and lower parts. Add details to the hull, such as chines (angled lines along the sides of the hull) and spray rails (small fins or ridges). These elements contribute to the boat's stability and improve its performance in the water. Shade the lower portion of the hull with a darker tone to emphasize the hardshine effect. Use quick and light strokes to achieve a glossy appearance. Finally, erase any unnecessary guidelines and refine the drawing as needed. Remember, practicing and experimenting with different techniques will help you improve your drawing skills and speed over time.
How to measure a ships hull shape from inside?
One way to measure a ship's hull shape from inside is by using 3D laser scanning. This technique uses lasers to take precise measurements of a ship's inner hull shape. The lasers scan around the interior of the ship and create a 3D image of the ship's shape. This data can then be used to create a precise and accurate measure of the ship's hull shape.
How to lay out a lines drawing for displacement hulls?
Start by drawing the waterline at the mid-point of the vessel. Draw the bow from the top of the waterline to the nose of the vessel. Draw the stern from the bottom of the waterline to the end of the vessel. Draw in all of the chines of the vessel, the curved lines along the bottom of the sides of the boat, at the waterline. Draw in any other details such as the upturned bow, the tail, or any other details that the vessel may have. Draw the sheer line and the sheer forward, running along the top of the vessel and curving inwards and downwards in the center. Add in any additional lines needed to complete the displacement hull. Use a protractor to make sure all of the angles are correct. Use a ruler to draw the exact lines and make sure the lines are the correct length.

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Catamaran Construction – Hulls, Laminates, and Composites

  • Post author By BJ Porter
  • Post date October 15, 2020
  • 3 Comments on Catamaran Construction – Hulls, Laminates, and Composites

catamaran body plan

It’s a given that catamarans are more sensitive to weight and loading than monohulls. Catamaran builders strive to build the lightest boats they can without sacrificing strength and stiffness, and have adapted new building techniques and materials to meet this target. Cutting weight allows more passengers and gear without sacrificing performance.

And the marketing materials reflect it–they load every review and website with polysyllabic technical jargon describing the design and production choices each builder made to deliver the best boat they can.

catamaran body plan

But when you’re reading a brochure and you come across phrases like “ hand laid bidirectional GRP ” or “ vacuumed bagged e-glass with vinylester resin over a Divinycell core ” do you know what that really means?

All modern production catamarans are made with “FRP” construction (for Fiber Reinforced Polymer). Composites aren’t new–it’s just using materials together to strengthen the whole assembly. Straw was added to bricks centuries ago, and steel reinforced concrete is a staple of construction over the last century. For boats, it’s the use of stranded fibers and cured resins which make FRP different.

The term “FRP” doesn’t get into the technical detail of which fibers and which plastics, and how they’re put together to build your hull. There’s a wide variety of fiber types which can be stranded, woven, chopped or sprayed in a varied of patterns then combined with several types of resins to make hulls with different characteristics.

Some FRP techniques produce lighter, stronger shapes, while others are quicker to build and less expensive to produce. The choice of technique is a function of many factors, from the number of hulls and parts to be built, the type of parts, the budget for the project, and many design specific requirements for weight and strength.

1. FRP Basics

The principle behind all FRP construction is the same – you lay our fibers in the shape you need, then saturate them with resin, removing all the air and voids you can. Resin is left to cure, then the piece is ready to finish and use.

catamaran body plan

The reality is more complex, since building a boat isn’t like making a flat board or a simple door. You’ve got a complex shape with a designed set of curves to build. “Tooling” is the set of shapes to make the boat parts; molds to cover with fiberglass to get the right shapes.

That’s what makes FRP so effective – you can make almost anything out of it. But to do so requires a lot of choices about what you need for the project at hand.

There isn’t a “best” all around material or technique choice for all jobs, and sometimes a lower cost technique or easier to work with material may be the better solution to the problem.

A. Fiber types

Fiber choices in the last few decades have expanded past the glass fibers used in the first mass produced boats in the 1960s. FRP construction wasn’t new even then, they built the first composite boats using modern fiberglass in the 1940s.

The major fibers used in marine construction fall into three categories – glass, aramids, and carbon. The primary differences are in the strength to weight ratios of the fibers, durability, elasticity, and cost. Some construction may use blends of fiber types to combine performance characteristics.

Glass – the most common material still, because of its low cost and versatility. The most common variety used in GRP (Glass Reinforced Polymer) is “E-glass” which refers to its strand size and mineral content. Other grades have different and sometimes better mechanical properties, but may be more expensive and less appropriate for boat building use. Fiber sizes run 10 to 25 microns for E-glass, though other grades may be smaller.

catamaran body plan

Brands like Leopard, Lagoon, and most higher production volume builders use E-glass.

Aramids – this includes brand names like Kevlar, Technora and Twaron. They have higher tensile strength than E-glass, and resistant abrasion and punctures. Kevlar is a common choice for bullet proof body armor, and can built a tough, lightweight hull. The materials can be difficult to work with, as it is very tough to cut the cloth. It is often blended with carbon fiber or other materials – Catana is known for using Twaron blends in hull construction.

catamaran body plan

Carbon – the ultimate in lightweight, strong construction material. Carbon fiber is the most expensive fiber, and is available in a variety of weights, grades and strengths. Fibers are smaller than glass – down to 5 Micron.

The lightest, most expensive hulls are made from carbon, but a catamaran builder may use carbon in places other than the hull to add strength and stiffness. Carbon boards, rudders, and reinforcing structures can enhance performance without driving the price of the boat beyond reach. Carbon is the fiber of choice for many custom builds, racing cats, and Gunboat.

B. Mats, Strands, Roving, Direction, and Weights

Fibers are woven into matting and cloth for construction. Depending on the application, different weights of cloth and cloth patterns and weaves may be more appropriate for the job.

Cloth weight refers to the weight per square yard (or meter) of the cloth. A square yard of nine ounce cloth weighs nine ounces. The heavier the cloth, the stronger it is in a laminate.

Fibers carry loads along their length, so cloth weaves have directionality to their strength. Most builders use several layers of cloth with different orientations to give good universal strength to hulls. Specific FRP applications with strict load-path requirements may have more unidirectional fiber layering – for example, a chainplate manufactured from carbon fiber may use unidirectional fiber.

Cloth – fiberglass cloth is commonly used on outer layers of composites. Cloth may have unidirectional or bidirectional strength. Bidirectional cloths have maximum load strengths in two perpendicular directions. Variations on weaves like a modified twill allow a more flexible cloth for better shaping around complex molds.

Mat – is omnidirectional strands of fiber compressed into a cloth. This is often held together with a resin soluble glue, which makes mat great at conforming to mold shapes without folding and bunching as it collapses when wetted. Because the strands do not align, fiber strength is the same in all directions.

catamaran body plan

Woven Roving – a heavier cloth made from larger bundles of strands. Woven roving allows for quicker buildup of material and strand weight.

Most FRP layups include multiple layers of different cloth and mat. Finished layers may be finer cloth over courser cloth, over woven roving and mat.

Three primary resins are in common use in marine construction – polyester , vinylester , and epoxy . All resins have materials safety concerns and require care in their use and handling.

Polyester is the least expensive and requires breathing protection because of the VOC emission (Volatile Organic Compounds…nasty, smelly fumes). It doesn’t have good bonding/gluing capability, and should only be used with glass fibers for structural building. Some polyester resins are referred to as “isophthalic” resins.

Vinylester is chemically similar to a hybrid of polyester and epoxy, and performs best with fiberglass. It shouldn’t be used in high strength applications with carbon or aramid fibers. It has some adhesive qualities which polyester lacks, it shrinks less during curing, and has better impact resistance.

The added strength of vinylester coupled with increased water resistance makes it an attractive option for many catamaran builders. It costs less than epoxy, but still has better performance than polyester.

Epoxy is the most expensive, but is three times the strength of the others. It offers the best adhesion and the only resin for building structural elements with carbon and aramid. It resists water intrusion better than the other resins, resists blisters, emits no VOCs, and shrinks less. The major drawback is it is more brittle if it takes an impact.

While epoxy is “the best” in terms of strength and ease of building, there are many applications where other resins are appropriate. Budget is a big driver – a boat made from E-Glass doesn’t need epoxy resin, and considerable cost savings to meet a construction price target may drive the choice.

They can build quality boats from all material combinations, but price and performance will drive materials choices to keep some boats more affordable.

2. Cored Construction

What’s the best way to make fiberglass strong? To a point, you can make it thicker. As it gets thicker, it gets heavier. A hollow shape can take more compressive load than a solid one of the same weight, and the same principle applies to fiberglass construction.

Consider an I-Beam used in building construction. It has the same strength (or more) as a solid rectangular beam of similar mass. The compressive load on the beam is supported by the outside edges of the material, the metal in the middle doesn’t contribute much to the strength. So we can remove metal to get the “I” shape while still keeping those sides rigid, making a lighter girder with less material.

The same principle applies to cored construction with fiberglass. Making a sandwich of two layers of fiberglass with a light core between them allows for the greater strength with weight savings.

There are drawbacks – the biggest risk is damage which breaks the skin, which can let water into the core. Earlier cored construction used materials prone to saturation and rot if they got wet. Some builders opt to do cored construction above the waterline and solid below to minimize some of these risks.

But the advantages in weight savings and increased stiffness offset the drawbacks, and there may be a few other side effects like sound and temperature insulation. Like resins and fibers, core materials offer distinct advantages, disadvantages and price points.

Most builders have adopted a hybrid approach, building solid hulls below the waterline, and cored hulls and decks above. This gives a balance of weight and safety.

A. Balsa Core

Balsa is light and inexpensive. The first cored construction used balsa, but it has the disadvantage of being wood. As a natural material, if it gets wet it can rot and break down. Builders use “end grain” balsa – shorter cross cut sections – to prevent wicking of water if there is an intrusion.

catamaran body plan

B. Foam Core

Closed cell foam cores give good strength to weight savings while minimizing water intrusion. If you get water in the core, it won’t spread very far. Divinycell is a popular PVC foam core, though there are several choices with different densities and compressive strengths.

catamaran body plan

Some foam cores are not suitable for heat treatment, but infused or vacuum bagged boats like the Outremer and PDQ do well with it.

C. Honeycomb

Honeycomb cores are often the most expensive, but also give some of the best strength to weight ratios. Honeycombed cells made from resin cured aramid papers are some of the best, but also among the most costly. They offer good stiffness, but can be hard to shape. Aluminum and other resin-infused papers are other core materials builders can choose from.

3. Construction and Resin

When building a hull, there are optimal ratios of fiber to resin saturation for target strength and weight. Too little resin and you may not have enough strength (or worse, voids and gaps), and too much, and you’re just adding weight without adding strength. Resins are also a significant material cost in building the boat, so over application not only increases weight but adds cost.

catamaran body plan

There are many ways to assemble the cores, fibers and resins to build a finished laminate hull – we’re addressing the most common in boat building. Each approach has strengths and limitations, and an impact on the bottom-line cost to build the boat. Any voids or air pockets in the laminate can be disastrous; these techniques have been developed to increase saturation and reduce the risk of voids.

A. Hand Layup / Open Molding

As the name implies, this is the application of resin by hand to cloth as it’s laid into a mold. Wetting is done with a brush, and the laminate is rolled out to remove any air pockets and voids. This is the simplest way to lay up fiberglass, but also the least precise and consistent and will use the most resin.

Skilled craftsmen have built some of the finest vessels in the world this way. Though it’s more popular with monohulls, which are less sensitive to weight, many catamarans built with hand layups on open molds are still out cruising and performing well.

B. Spraying

Using chopped-strand fiber mixed with resin, a “chopper gun” can spray the mixture into a mold to lay down the composite. A consistent thickness can be difficult, but this is a low cost construction technique which makes a very resin-rich laminate. Using sprayed fibers gives lower strength in all directions compared to meticulously laid down mat and bi-directional cloth. But it is a quick technique popular with mass produced, smaller boats.

It is an excellent technique for parts with complex geometry where weight is not an issue, but you will not see it often in catamaran construction. It’s heavy with resin without any resultant increase in strength.

C. Vacuum Bagging (Wet layup)

When an open molded component has been laid up and wetted with resin, vacuum bagging takes the process a step further. After the wetting is complete, air tight plastic bagging is secured around the wetted area, and the air is pumped out of the bag. The vacuum pulls excess resin out and collapses air pockets.

catamaran body plan

The goal is to get thorough wetting and produce as strong a laminate as possible without excess resin. Knysa and Leopard are two builders that use vacuum bagging on their hulls to reduce weight.

D. Resin Infusion

For resin infusion the cloth, matting and core is laid in place dry, then sealed in an air-tight bag. A vacuum pump attaches to one side of the bag, and on the other a feed for resin. The vacuum sucks the air out of the dry cloth stack, then pulls the resin through the stack, infusing and wetting it.

Resin infusion, when done right, gives the lightest, strongest laminates with no voids and the minimum resin weight for maximum strength. SCRIMP is a variant of the resin infusion process used by some builders, including TPI which build many early Lagoon cats.

E. Pre-preg

Using pre-preg (for “Pre Impregnated”) cloth for your laminating gets rid of the resin bucket. They manufacture cloth with a partially catalyzed resin pressed into it, then it’s chilled or frozen to stop the curing process. There is no need for seperately mixed resins, and there’s no worry your resin might “go off” and harden before you’re done wetting the cloth. Instead, the cloth is assembled, vacuumed, then heated to kick off the curing process.

There are both advantages and disadvantages to using pre-preg for your laminate work. The big disadvantage is the cost; it is most expensive material to use. You also need to chill and store the cloth until you need it, though some can be at room temperature for a couple of weeks without kicking off. And you need an oven which requires some clever tricks if you’re building a forty or fifty foot boat.

But the strength to weight ratio will always be perfect. High tech honeycomb cores are best suited to pre-preg lamination, and without racing against resin cure times, you can ensure perfect cloth placement and precise layout in the build process.

The primary use for pre-preg in boating is high performance race boats. With catamarans, pre-preg may be used high load parts, like Gunboat does for foils and rudders.

4. Industry Examples

Across the catamaran building industry you’ll find almost all the above techniques and materials used, though some are less common. You aren’t likely to find chopped strand sprayed layups in ocean going cats, and hand layups can lead to heavier hulls than weight sensitive catamaran designers prefer. Most manufacturers have moved to vacuum bagging or resin infusion, with a few of the highest end boats using pre-preg for key components.

Built by Robertson & Caine in South Africa, the hull material is vacuum bagged, end-grain balsa-cored E-glass with polyester.

Hand laid, bagged vinylester over an Airex foam core in the hulls.

Earlier Prout catamarans like the Snowgoose 34 featured hand laid solid FRP hulls and decks. Over time they switched to foam or balsa cores for decks and above the waterline.

Older PDQ boats were made from vacuum bagged vinylester – solid below the waterline and cored with CoreCell foam above the waterline and in decks. Newer PDQ models switched to epoxy resin.

All glass is vacuum bagged. Below the waterline is solid E-glass and vinylester. The rest is unidirectional, bidirectional, and triaxial cloths over a Nida-Core polypropylene honeycomb core with isophthalic and vinylester resins.

The Gemini cats are built with a solid hand layup of woven roving and fiberglass mat and polyester resin. Decks are cored with end grain balsa. The Gemini 3200 introduced vinylester resin into the layup to prevent blistering.

Older Lagoons were SCRIMP infused vinylester with and end grain balsa core above the waterline and in the decks.

Newer Lagoon catamarans use polyester and vinylester resins, also infused with balsa cores above the waterline and solid below.

With a carbon fiber inner skin, Catana also uses Twaron aramid fibers in the sandwiched hull over a foam core.

Fontaine Pajot

Primary hull construction is resin-infused vinylester with a balsa cored hull and deck.

Beneath the waterline, Outremer uses a single layer, solid vinylester laminate for safety. The hulls and deck are vinylester with a Divinycell foam core. They stiffen certain components with carbon for rigidity and durability.

Gunboat hulls are epoxy infused carbon fiber with a Nomex honeycomb core. They build dagger boards and other high load components with pre-preg carbon.

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BJ Porter

By BJ Porter

Owner of Hallberg Rassy 53; world explorer.

3 replies on “Catamaran Construction – Hulls, Laminates, and Composites”

Excelent. Thank you for this I learned allot. Johan

Very straight forward information. Thankyou for doing this.

Damn…What an Amazingly Informative Article. *Cheers*

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Catamarans and Trimarans

Catamaran and Trimaran Boat Plans make it a reality to build your own catamaran or trimaran. Multi-hulled sailing vessels are a special class of boat. A very different mind set is required when thinking about sailing a multi hull, let alone getting your head around building one.

There are some unique challenges building a multi-hull sail boat, the extra beam added by each hull for instance can create storage issues while under construction. Hartley boat plans make the build process straight forward for even amateur builders. However with all things considered, building a multi can be an amazing journey.

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The technical information page is a collection of documents (mostly in pdf format) on the materials and systems used in schionning catamarans. including data sheets, engineering information, strength comparisons of each core material and informative articles from jeff outling the design of certain system such as engine choices and main sheet systems., detailed engineering data for your research, we understand that getting your head around the process of building your own boat, or having one built, can take a little while. to gain a greater understanding of the materials used in our designs, the below data sheets have been supplied by atl composites, and contain all of the technical data you could need regarding the composites we use. in addition are articles or documents written by jeff about certain systems used on our designs and why., all technical information and data sheets on west system/duflex/durakore provided courtesy of atl composites. for more information please see the atl composites website here., documents library.

Information Sheet – CE CERTIFICATION PROCESS

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Kit materials' contents, so if you order a schionning kit, what exactly is going to arrive see an overview of the materials you will receive, and what each is used for during the build process. fibreglass cloth or tapes microspheres, microballoons or microfibers take a closer look and you can answer these questions., our schionning kits are a no nonsense, common-sense approach to building a boat. we offer great service, fast delivery and access to anything you could need for your boat straight from the supplier to your door. our construction plans and kits are sold with 100% professional boatbuilder support via phone and email, any time you're unsure or just need a second opinion, we're here..

catamaran body plan

Our kits contain all of your basic materials to build your boat to a faired shell stage, ready for painting and fit-out. We have sail-away costing estimates available for all of our standard designs, and this will give you an accurate idea of the overall cost of your project. This costing varies depending on your level of finish, as you can imagine different options vary greatly in price.

Below is a quick glance at what your Schionning Kit will include and what each item is primarily used for, we hope this is helpful and if you should require more detailed information please don’t hesitate to contact our office.

What do I actually receive?

Superlight Balsa - End-Grain Balsa - Foam - Paper Honeycomb - Western Red Cedar - SDI - End-Grain Balsa - 150kg per cubic metre Paper Honeycomb - 50kg per cubic metre Superlight Balsa - 94kg per cubic metre Western Red Cedar - 360-380kg per cubic metre - Foam

DUFLEX PRE-LAMINATED PANELS

DuFlex pre-laminated panels are the main and most important material used in our kits, predominantly in the flat panel designs, however they are used in Strip-planked designs also, though to a lesser extent. These panels are 2400mm x 1200mm and are CNC routed to speed up build time on our Wildernes X Series, as well as some of our power designs. For internal furniture, a paper honeycomb core is used instead of the end-grain balsa wood core that is used for main structural areas. The use of this is purely to save weight in the shell and therefore produce a faster, more responsive catamaran.

Schionning Catamaran Kit Materials contain Kinetix Laminating Resin & Hardener Kinetix Laminating resin is used on all of our designs and is used for laminating the strip-planked areas, so round-bilge designs will use it more often whereas our flat panel designs not as much.

KINETIX LAMINATING RESIN & HARDENER

Resin Choices for Catamaran Kit Building by Schionning Designs SDI - We choose ATL Composite's resin systems for their superior quality, reliability and value for money. West System Epoxy Resins

WEST SYSTEM EPOXY RESINS

Fibreglass Tapes (Double Bias) These double bias fibreglass tape rolls are used for the joining of panels in our flat panel designs, or in round-bilge designs to a lesser extent. Anywhere that DuFlex panels need to be joined, tapes will be used. The smaller rolls come in different widths for ease of use and to save time on cutting larger rolls of cloth.

FIBREGLASS TAPES (DOUBLE BIAS)

Schionning Designs Catamaran Kit Materials Carbon Fibre Cloth Carbon fibre is used on a number of our designs and can be incorporated into any design to save on weight and increase the performance capabilities. Carbon comes in unidrectional and double bias, however is much more expensive than standard fibreglass (as one might expect). It is very similar to work with, however the resin choice may change when using carbon.

CARBON FIBRE CLOTH

Schionning Designs Catamaran Design Kit Materials Fibreglass Cloth Fibreglass cloth is the strength and stiffness that holds your boat together, this is used in most areas for strength and is used in a variety of techniques depending on the area or job that is being performed. Fibreglass is one of the most widely used materials for low weight and high strength properties.

FIBREGLASS CLOTH

The kit process, building your own boat can be a daunting prospect, however to demonstrate each step in the kit assembly process, we've created this guide for you to study. as you can see our kits are the ultimate in building efficiency and have been streamlined over 30+ years to ensure that you're on the water faster and with less effort., how does it all go together.

Schionning Designs Catamaran Kit Build Process - Step 1 The first step to building your dream catamaran begins with a strongback - this is a square frame used to position the temporary frames that will be used to form the hull shape. This frame will be set up and must be square and accurate, a string or laser level can be used to achieve this.

The first step to building your dream catamaran begins with a strongback – this is a square frame used to position the temporary frames that will be used to form the hull shape. This frame will be set up and must be square and accurate, a string or laser level can be used to achieve this.

Step 2 pre-cut frame panels are erected along the strongback in sequence - catamaran building step 2 SDI

The forebeam is now installed along with the striker attachment fitting, as shown above. The bridgedeck is installed shortly after and taped onto the bulkheads with webs installed, this now completes what is a quite stiff and strong platform to work on.

Step 8 catamaran kit building - forward webs and dash will be fitted - SDI

Now that the bridgedeck is in place, the forward webs and dash will be fitted. At this stage, all furniture and internal work begins, with the main panels left off for ease of access when working.

Catamaran Kit Building Processs by Schionning Designs SDI -Step 9 The internal furniture is now installed, if you chose Kit Option 2, this furniture will be pre-cut to your previously decided upon layout. If you chose to receive blank panels, this is the period in which your internal living areas are to be built. This construction uses paper-honeycomb Duflex panels, as these are superior in weight when used non-structurally. Cabin soles, engines and daggerboard cases are also now installed.

Material Choices

Schionning material choices, solutions that work best for catamarans & why, our designs are based on cored composite construction techniques using west system epoxy resin and knitted fabrics. but given the range of today's composite technologies, which solution works best for catamarans and why written by jeff schionning, selecting the correct materials, resin choices.

Resin Choices for Catamaran Kit Building by Schionning Designs SDI - We choose ATL Composite's resin systems for their superior quality, reliability and value for money.

It also fully protects the boat against water absorption and it can not develop the dreaded Osmosis.

We choose ATL Composite’s resin systems for their superior quality, reliability and value for money.

Having worked closely with the ATL Composites team and their products for many years, we know we can stand by their material solutions, and rely on great service should something unexpected happen.

Colan brand cloths for their quality and low resin absorption - Schionning Designs SDI - We prefer Colan brand cloths for their quality and low resin absorption, custom made for Schionning Marine at six (6) stitches per square inch for easy wet-out and rounding corners.

This may not seem important but when working with a material for an extended period of time, the small things make all the difference.

CORES Which One to Use?

Superlight Balsa - End-Grain Balsa - Foam - Paper Honeycomb - Western Red Cedar - SDI - End-Grain Balsa - 150kg per cubic metre Paper Honeycomb - 50kg per cubic metre Superlight Balsa - 94kg per cubic metre Western Red Cedar - 360-380kg per cubic metre - Foam

  • End-Grain Balsa – 150kg per cubic metre
  • Superlight Balsa – 94kg per cubic metre
  • Western Red Cedar – 360-380kg per cubic metre
  • Foam – 80kg per cubic metre

BALSA END GRAIN (150 kg/cubic metre)

Balsa  has very good values and we can produce a shell using a very light laminate. It will be very stiff and very resilient to fatigue.

It has exceptional qualities including very high compression strength, extremely good sheer capabilities and fantastic sheer stiffness.

Compressive strength is the resistance to collapsing when pressure is applied perpendicular to the surface as when pushing directly onto the material with the point of your finger. Balsa is far stronger than Foam (80kg/cubic metre) in compression.

Balsa is also very strong in shear. This is when the core sample is held flat between your hands, one hand slid one way and the other slid the opposite way, when the core tears through the middle the core has failed in sheer. The amount of stretch you feel before the core shears is shear stiffness. To compensate for sheer weakness the core is made thicker. So 13mm Balsa may be equal in sheer to 19mm Foam.

(80 to 200 kg/m³)

There are many boats sailing that are built from foam as it’s mechanical properties are good for boat building.

  • Initially one would expect this cat shell to be lighter as it is ½ the weight of Balsa. We do have to compensate for its weaknesses and will then add to the reinforcement the reinforcement on the outside to spread that compression load over more core and need a triaxial type weave to compensate for the veneer content that runs fore and aft on the Durakore.
  • Secondly, we need to increase the Core thickness to compensate for the shear value, usually neutralizing the weight advantage.
  • We only use structural foam core that is closed-cell and cross-linked.

The end result using foam core amounts to a very similar total boat weight. Professional builders can achieve a good result but usually use vacuum bagging and very good molds to achieve this.

Secondary Issues

Balsa can absorb water. It needs extreme neglect to rot (very unusual). Water soaks along the end grain quickly. It travels very slowly across the grain. We use balsa under the waterline especially because of it’s high compression strength for beaching etc. any core type must be sealed. Damage to all cores results in the same sort of repair. Notice a damp spot remaining when drying out to anti-foul… simply grind back the surface glass exposing the core, dry it out and re-glass – it’s that easy.

Timber cores are cheaper than Foam in most cases.

A light, high tech cat returns a far better (often 2 – 3 times) re-sale than lower tech materials. Often saving $10,000 on materials initially, loses $200,000 on re-sale – a serious reality.

Our boats can be built using Balsa, Foam or Western Red Cedar. Combine strength, stiffness, lightness and cost, with ease of use – it just makes good sense!

IMAGES

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VIDEO

  1. On the way #catamarans #travel

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  5. Are Performance "Cruising" Catamarans Safe?

  6. RC boat Catamaran Zenoah V2 twin (66 mph)

COMMENTS

  1. Catamaran Hull Design

    If you have fine hulls you can use a lower Cp. Most monohulls have a Cp of 0.55- 0.57. And that is about right for displacement speeds. However the key to Catamaran design is you need a higher Cp if you want to sail fast. So a multihull should be at least 0.61 and a heavy displacement multihull a bit higher still.

  2. PDF Chapter 10 Other High-Speed Multihull Craft

    Fig. 10.1 (a) Planing catamaran model C body plan; (b) TPC model D body plan 426 10 Other High-Speed Multihull Craft. ... Fig. 10.2 Offshore racing catamaran Fig. 10.3 Body plan of conventional planing monohull model B 10.2 Planing Catamaran and Tunnel Planing Catamaran 427. and, consequently, the impact load on the hulls and to improve the ...

  3. Catamaran Design Formulas

    T c = 0.57. Here we put B TR = 1.9 to minimize boat resistance (for her size) and get the draft calculation for a canoe body T c (Figure 1). Midship coefficient - C m. C m = A m / T c (x) B WL. We need to estimate a few coefficients of the canoe body. where A m is the maximum cross section area of the hull (Figure 3).

  4. body plan and offset of catamaran

    elaheh Junior Member. I'm looking specifically for body plan and offset and arrangement of an 150 pax catamaran passenger ship which can have an operational speed of 32 knots. but I'm not sure that i can find the exact sample,so i asked you either you got any sample like this or not!

  5. DIY Cruising Catamaran: Complete Building Guide

    If you were to build a 40-foot (12.1-meter) catamaran, your cost of materials would range between 20-30% of the total cost. Therefore, for $300,000 total, the boat's materials would range between $60,000 and $90,000. The hull tends to range between 15-35% of the total build.

  6. Catamaran 3-D body plan view MAXSURF. The calculation of the

    Download scientific diagram | Catamaran 3-D body plan view MAXSURF. The calculation of the construction of fiberglass boats can referred to the FRP vessel regulations Indonesia Classification ...

  7. Plans For Catamarans And Monohulls

    YACHT DESIGN. We provide stock boat plans for both monohull and multihull sailing vessels, including sailing skiffs and sharpies. Our designs mainly feature timber construction, in plywood or cedar strip plank composite construction, using the W.E.S.T. system (wood epoxy saturation technique). Our designs are intended mainly as cruising boats ...

  8. How To Create the Perfect Cruising Catamaran Layout

    A cruising catamaran's performance depends on three main aspects; its length, the sail area, and the boat's weight. Long boats are generally fast. A light boat with more sail area is also faster than a heavier boat with less sail area. In other words, you can make a multihull faster by making it longer, lighter, or adding more sail.

  9. Catamaran Model 5b Demihull Body Plan

    Download scientific diagram | Catamaran Model 5b Demihull Body Plan from publication: Evaluation of a CFD Program AEGIR (trademark) for Bare Hull Resistance and Seakeeping Prediction Capability ...

  10. Catamaran Stock Plans

    The DESIGNER'S book TRIMARAN and CATAMARAN CONSTRUCTION is part of the plans (over 21') and covers all phases of construction. Plans are leased to build ONE boat, NO time limit. Tri-Star designs are proven designs, sailing the seven seas since 1964. Free consultation is provided to the original non-professional builder till he or she is sailing ...

  11. Body plans of catamaran design

    2.3+ billion citations. Download scientific diagram | Body plans of catamaran design from publication: Experimental Study of the Probability Distributions on the Seakeeping Performance of Monohull ...

  12. PDF Course Objectives Chapter 2 2. Hull Form and Geometry

    catamarans, planing vessels, hydrofoil, hovercraft, SWATH, and submarines . 4. Learn Archimedes' Principle in qualitative and mathematical form . 5. Calculate problems using Archimedes' Principle . 6. Read, interpret, and relate the Body Plan, Half-Breadth Plan, and Sheer Plan and identify the lines for each plan . 7.

  13. Bruce Roberts, CATAMARAN boat plans, CATAMARAN boat building

    Fast cruising ALUMINUM CATAMARAN . BOAT PLANS & FULL SIZE PATTERNS - Package Includes latest sail boat plans, SAILBOAT building plan updates & revisions, PLUS direct contact with the designer. This CATAMARAN was designed for personal use or charter work and the accommodation was laid out with that in mind.

  14. PDF Selecting Monohull, Catamaran and Trimaran as

    of catamaran, in particular, are rather poor in oblique waves. This is attributed to the configuration of Body plan of * Corresponding author: Richard B Luhulima, PhD student, research fields: naval architect and shipbuilding engineering and renewable energy. E-mail: [email protected] catamaran when heeling aside due to rolling motion,

  15. Bruce Roberts, CATAMARAN boat plans, CATAMARAN boat building

    The new CATAMARAN 465. CATAMARAN MS 65. SEE MORE. POWER CAT VERSION. FIBERGLASS PLANS & FULL SIZE PATTERNS FOR ALUMINUM STEEL or FIBERGLASS CONSTRUCTION. The CATAMARAN 65 MS was designed for personal use or charter work or as a people carrier and the accommodation was laid out with that in mind.

  16. Geometry

    In the body plan, the cross sections of the hull are displayed. Since the hull is usually symmetrical port and starboard, only one half needs to be shown, and this makes it possible to present the forebody to the right and the afterbody to the left. ... Catamaran Design Guide - Catamarans Guide; LOD and LOA - Cruising Sailboats Reference; Hull ...

  17. Catamaran Construction

    All modern production catamarans are made with "FRP" construction (for Fiber Reinforced Polymer). Composites aren't new-it's just using materials together to strengthen the whole assembly. Straw was added to bricks centuries ago, and steel reinforced concrete is a staple of construction over the last century.

  18. PDF Skoota 24 By Woods Designs www.sailingcatamarans

    Conclusion. The Skoota 24 offers: stability, low wake, the ability to maintain high speeds in rough conditions, superb directional stability, a self-draining cockpit, fully buoyant hulls for safety, fuel-efficiency, lots of interior space, low speed maneuverability and the security of twin engines. A clear winner by anyone's standards.

  19. Catamaran and Trimaran Boat Plans

    However with all things considered, building a multi can be an amazing journey. Fast Twin Catermaran. $ 30.00 - $ 45.00 (USD) Lively 28 Cruising Trimaran. $ 170.00 - $ 185.00 (USD) Lively 35 Cruising Trimaran. $ 355.00 - $ 370.00 (USD) Catamaran & Trimaran Boat Plans from Hartley Boats make it a reality to build your own multihull at home.

  20. Our Catamaran Build Kits

    The use of this is purely to save weight in the shell and therefore produce a faster, more responsive catamaran. KINETIX LAMINATING RESIN & HARDENER. Kinetix Laminating resin is used on all of our designs and is used for laminating the strip-planked areas, so round-bilge designs will use it more often whereas our flat panel designs not as much. ...

  21. The TUD catamaran body plan.

    Download scientific diagram | The TUD catamaran body plan. from publication: Computation of wave-induced motions and loads on catamaran hulls with forward speed | Wave-induced motions and global ...

  22. PART 2 Creating Hull Form from LinesPLan using Maxsurf ship ...

    Join Dr. Patrick Couser, MAXSURF Product Manager, for this 2-part series and hear how you can quickly produce models of existing vessels for hydrostatic and ...