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How to check and adjust propeller shaft alignment.

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Prop Shaft Alignment

  • By Perry Munson
  • Updated: June 8, 2011

sailboat propeller shaft alignment

Regarding John Gross’ question about how a shaft can be aligned with so many things being so wobbly: A shaft can’t be aligned if it’s wobbling around. You must first take the wobble out of it, then align the coupling flange on the transmission to the flange on the forward end of the shaft. Here’s one series of tricks that actually works if your boat is out of the water.

1. Loosen the hose clamps and remove the rubber boot from the front end of the shaft log.

2. Slide it and the packing gland ahead on the shaft.

3. Disconnect the two coupling halves connecting the shaft to the transmission by removing the four bolts holding them together. Slide the shaft back a bit, perhaps 1/2 inch.

4. Slip four pieces of carefully milled hardwood or square steel rod back a couple inches into the shaft log around the shaft, one each on the top and the bottom and one each on the sides. This centers the shaft in the shaft log and gets rid of the wiggle, assuming your cutless bearing was recently replaced. For instance, if the inner diameter of the shaft log is 1.5 inches and you have a 1.0 inch shaft, the square rods (whatever they’re made of) will have to measure 1/4 inch by 1/4 inch by whatever length is convenient. Now the shaft is stabilized.

5. Carefully wrap duct tape around the exposed rods so they stay in position on the shaft and keep it centered.

6. Slide the shaft forward (the rods will have to slip back and forth on the shaft or in and out of the shaft log a bit) until the shaft flange butts up against the transmission flange loosely.

7. Note the variations in the gap between the two halves. Slide the shaft back again 1/2 inch.

8. Using the adjustment nuts on your engine mounts, move the engine so it’ll take up the slack. Like this: If the coupling halves clicked together at the bottom but had a small gap at the top, the front of your engine probably has to go up some. This can also involve some port-starboard adjustment if there’s a sideways gap. Do whatever it takes. Any reputable engine mount offers the ability to make vertical and lateral adjustments.

9. Slide the shaft forward again so the two flanges click together loosely.

10. See how you did in adjusting the engine’s position so that the two flanges fit together snugly all the way around.

11. Check the gap using a feeler gauge. If the gap is more than 0.004 inch on any side, adjust the gap again.

12. Keep repeating Steps 6 through 10 until you get it right. The less gap the better. Ideally, the coupling halves should slide together easily and butt up to each other with no gap. This process of repetitive adjustments may take a few hours. If you get burned out, go home and come back. Having your most mechanically astute friend helping you will relieve the stress a lot.

13. When everything looks good, tighten down your engine-mount nuts, do a final check, then bolt the two flanges back together. Tighten all nuts a little, then go around again and do the final tightening. Check the set bolt that holds the coupler onto the shaft for tightness. Make sure it has a keeper wire around the coupling and through the hole in the square bolt head.

14. Finally, remove the rods centering the shaft in the shaft long, slide the boot and packing gland back so the boot is back to where it was, and cinch down both hose clamps. If you put the transmission in neutral and slowly rotate the prop shaft by turning the coupler around, you should see essentially little or no wiggle in the packing gland and the flexible boot behind it. If you start your engine and let it run at idle, everything will be jiggling and wiggling some as it’s supposed to. That’s why engines have a flexible boot between the packing gland and the shaft log and four flexible mounts. As the engine approaches operating speed, around 2500 to 3000 rpm, under load on the water, the jiggle should go away, and there should be no gross movements, only an engine and shaft humming away in a steady state. The transmission and cutlass bearing should now be able to enjoy extended lifetimes. If you plan to go cruising very far from home, this is a skill you should have. Doing an alignment requires great care and patience.

Perry Munson Baltika , Nor’Sea 27 Grosse Pointe, MI

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Ocean Navigator

Prop shaft alignment

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Nearly all marine engines are designed to be adjustable, to a point, relative to the propeller shaft by using adjustment or jacking nuts on their motor mounts. The adjustment should be thought of as no more than fine-tuning, the maximum range of vertical travel being limited to no more than an inch or two at the most, which is substantial when one considers that alignment is typically measured to just a few one-thousandths of an inch. Thus, the responsibility rests with the naval architect and boatbuilder to ensure that the design and execution of the engine installation guarantees near-perfect alignment with the shaft before the motor mounts are adjusted.

The other alignment There is another side to the alignment story; it involves the support and position of the propeller shaft relative to its bearings, the shaft log (the tube through which the shaft passes) and the engine. While engine alignment is, or is expected to be, well understood by most marine industry professionals, shaft alignment is, on the other hand, far more esoteric and well understood by far fewer in the industry. In my experience, precious few truly understand its importance and the consequences of misalignment, and fewer still understand the techniques and processes involved in making adjustments and corrections.

Contrary to popular belief, shaft misalignment rarely leads to vibration, as the bow or offset induced in a shaft by misaligned bearings is constant. Improper shaft alignment can lead to excessive shaft drag and a resultant increase in fuel consumption, as well as accelerated bearing and shaft wear.

A few years ago, I inspected a vessel while it was hauled out. When I came to the propeller, I made an unsuccessful attempt to rotate it in order to gauge the condition of the bearings and alignment. Regardless of how hard I tried, I was unable to rotate either shaft on this twin-screw 60-foot vessel. This is a clear indication of either severe shaft misalignment (as opposed to engine misalignment, which rarely imparts this sort of resistance) or, less commonly, swollen shaft bearings. While final alignment of an engine to its shaft should only be carried out once a vessel has been afloat for 24 hours, even when hauled out the shaft should turn without undue effort once adhesion between it and its bearings is broken.

How shaft bearings work In virtually all cases, propeller shafts are supported by one — and for longer shafts, sometimes as many as four — bearings, often referred to by their trade name, “cutless bearings.” Shaft bearings are pipe-like components, the outer shell of which is typically made of brass, or sometimes a fiberglass-like material (the latter is designed to be used on steel and aluminum vessels to avoid the corrosion potential caused by copper alloys), with an inner liner of grooved or fluted rubber. It comes as a surprise to many users that the sole source of lubrication and cooling is seawater; if water flow to the bearing is insufficient, or if it’s interrupted by marine growth or a line, net or other debris on the shaft, or if the shaft log water injection system is clogged, rapid bearing wear can ensue.

Shaft bearings may be found in and supported by struts — I- or V-shaped metal supports attached to the vessel’s hull, through which the shaft passes — and/or embedded within the shaft log in the keel or hull. When the vessel is built, the builder must make a concerted effort to ensure that bearings are properly located to support the shaft, while ensuring that they are also aligned with the theoretical shaft’s centerline, a line that is perpendicular with and begins at the center of the transmission output coupling, traveling aft through the bearings. The line must also be centered in and parallel with the bearings. If the builder is successful in ensuring this alignment, barring groundings or other damage, it should remain correct throughout the life of the vessel. While small adjustments may be made to the relationship between the engine and shaft by adjusting the location of the former, the shaft’s relationship to and alignment with the bearings should remain constant.

Analysis and adjustment In practice, it’s not uncommon to encounter shafts and bearings that are misaligned, and the greater the number of bearings, the greater the likelihood of misalignment. While shaft-to-bearing alignment can be challenging, aligning a shaft to several bearings, as well as the general location of the engine, can be daunting. As such, it’s easy to see how this process can go awry while the vessel is being built.

Traditionally, during construction or repairs, the process begins with a length of small-diameter yet stout string or wire, which is adhered to the center of the transmission output coupling. It is led aft through the shaft log toward the rudder, where it is anchored typically to a weighted object like a jack stand. Using this string or wire as a reference point, bearings (and, if present, struts) are positioned. When properly aligned, the bearings must remain centered on and parallel with the string or wire.

While this traditional approach is still used, more modern tools are now routinely employed; these include lasers and optical sights. Using a laser or sighting tool, an installer can position one or more bearings along the sight line with great accuracy. While this aspect of shaft alignment is critical, it’s the easy part. Setting the bearings in place permanently can be more challenging.  

Initially, the strut or bearing is “dry fit.” That is, it’s positioned roughly to determine what needs to be done to align it with the shaft. The process typically involves a technique known as “casting.” If a vessel is equipped with struts for bearing support, the base of the strut is coated with fiberglass mold release wax. It is then set into a mixture of thickened reinforced epoxy and positioned so that it remains centered on and parallel with the string, laser or optical sight or shaft line. The strut is “hung” from support fasteners, and wedges are used to adjust its height and orientation to the shaft centerline. Once the position is set, the epoxy is allowed to cure, after which — thanks to the wax — the strut is easily removed. Wax is removed from the strut and the epoxy surface, and the strut is then set in bedding compound, ensuring a watertight seal with the hull. In some cases, the bearing centerline may be below that of the shaft. In this instance, depending on the degree of misalignment involved, a recess may have to be made in the hull to accept the strut’s base, the strut may require modification or a new strut may need to be manufactured altogether.

A similar process is employed for bearings that reside within a shaft log and strut. The bearing itself is waxed and set in epoxy, and wedges are used to position it so that it remains parallel with and centered on the shaft line until the epoxy cures. All bearings should be a light press fit in the shaft log or strut. Ultimately, bearings are retained using set screws; a minimum of two must be used, and they should be installed at 60 degrees to each side of the bottom centerline, or at the 4 o’clock and 8 o’clock positions (alternately, they may be installed at the 3 and 9 o’clock positions, but not above the horizontal shaft centerline). Set screws must be harder than and galvanically noble to the bearing shell; indentations (not holes), which the set screws engage, should be drilled into the bearing shell using a drill bit with a tip angle that matches that of the set screw. A thread-locking compound should be used on set screw threads.

Ultimately, once the shaft-to-bearing alignment is complete, even a long and large-diameter shaft should — with the benefit of nothing more than light lubrication from soapy water — rotate with relative ease using one hand.

Before entrusting your vessel to anyone for shaft alignment analysis or adjustment, carefully scrutinize their knowledge and experience on this all too important yet frequently misunderstood subject. Don’t lead; simply ask, “How do you ensure the shaft is properly aligned to the bearings?”

Steve D’Antonio is an ABYC-certified master technician and owns Steve D’Antonio Marine Consulting.

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By Ocean Navigator

  • Propeller Basics 5
  • Propeller Sizing 3
  • Tip Clearance 3
  • Engine and Gearbox 3
  • Cathodic Protection 5
  • Vibration 6
  • Antifouling 3

To eliminate vibration from components that may be out of alignment, you must find the root cause, tracing through the likely sources – the shaft, the engine, the propeller, the shaft supports – and ruling out each component in turn.  As these parts are interconnected, if one component is worn out or not in alignment, it may exert extra stress on the other components.  Below are some issues of alignment that may help you eliminate vibration in your boat.

Transmission Output and Shaft Coupling Alignment

Bearings, shaft and couplings shall be aligned to a tolerance of no more than 0.004″ (0.102mm) measured between the parallel flange of the coupling with the coupling bolts loose.

Shaft Engine Alignment

Any imperfect alignment of the propeller mount, the mechanical seal and the engine / gearbox can create vibration, whip and noise. Those vibrations and the associated noise are then transmitted directly through to the hull of the vessel and thence throughout the boat.

Constant Velocity Joint

Do you have any constant velocity joint installed?  Consider SigmaDrive , a low maintenance, high torque, bearing free solution that stops noise and vibration.

Vibration from Engine Mounts

Check that the mounts are uniformly loaded, mount bolts are still securely fastened into the engine bed, that one mount has not collapsed, cracked, the rubber broken, a bracket broken or come loose and that they still have the required durometer hardness ~ have not become soft. This would cause the shaft to come out of alignment with the engine at the higher RPM, i.e. more thrust.

Vibration from Transmission / Gearbox

Is oil level ok? Are the clutch cones slipping?

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Shaft Alignment

  • By Vincent Daniello
  • Updated: September 15, 2009

sailboat propeller shaft alignment

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Advances in hulls, engines, propellers, and even acoustic materials have all made boats stronger, faster, and quieter. Today we’ve come to expect luxury-car comfort aboard 100,000-pound yachts traveling 30 knots. But the shafts, struts, and bearings that tie engines to props have changed little since the mid-1800s when the screw propeller eclipsed the paddle wheel, and quirks in this drive train often cause vibrations. Fortunately, a few specialists are employing sophisticated methods to find and eliminate vibrations from shaft and strut technology that far predate the Model T.

“Everyone wants their boat to run like a Lexus. They don’t want to feel a thing,” says Fred Zucker, president of Seaworthy Services in Palm Beach Gardens, Florida( www.oceanalloys.com ). “Unfortunately, the human body is particularly sensitive to the frequencies of vibrations typically found on yachts.” Zucker has been building yachts and chasing vibrations for over 35 years, back when a mechanic’s experience, intuition, and the soles of his feet helped track down annoying, repetitive thumps.

“We learned from trial and error what makes a boat shake,” Zucker says. “We’d take boats apart, fix something, put them back together, and go on a sea trial, but often we’d still get fooled.” Today Zucker relies on years of acquired knowledge, but uses sensitive accelerometers connected to computers to analyze the sources of onboard vibrations. “When something is thumping, we want to know how many times a minute-the vibration’s frequency-and how hard-its amplitude,” Zucker says. By determining the frequency, Zucker can match it to the offending equipment. A bent propeller, for instance, will vibrate at some multiple of shaft speed, depending on how many blades are damaged, whereas a bent propeller shaft taper is subtly different.

“You’ll see an abnormal propeller signature,” Zucker says, “But you’ll also get a thumping vibration at the frequency that the propeller shaft is turning.” Problems originating from an engine itself will usually show up at one half of engine rpm since, on four-stroke diesels, each cylinder fires on every other rotation of the engine. Misfiring generators, too, will vibrate at half their rpm, and other pumps and equipment can be tracked down similarly.

Zucker warns, though, that while measuring vibrations is an exact science, interpreting the results is still largely an art. “This is complex machinery moving in a dynamic environment,” he says. “You’ve got to understand the construction of the boat you’re working on as you’re taking these readings.”

Zucker says one common misdiagnosis is mistaking an exhaust issue-producing a vibration frequency that is some multiple of the number of cylinders times engine rpm-for a propeller problem-which vibrates at the rate the shaft is turning times the number of propeller blades. The close frequencies often compound either issue. “A vibration may start out as an exhaust problem at lower speeds and then become a propeller problem at higher speeds. Somewhere in between, if those two frequencies overlap, they may cause a much larger vibration than either the exhaust or the propeller would independently.”

Finding the cause, or causes, of vibrations is only half the battle. While many specialists employ equipment and techniques similar to Zucker’s, Seaworthy Services actually does the work necessary to mitigate the shakes. “There are some very smart people doing [vibration analysis],” Zucker says. “But we sea trial the boats and see the computer diagnosis, and then we take the nuts and bolts apart and actually see the problem, and either prove or disprove what the computer is saying.” Zucker enjoys the instant gratification, and he also learns nuances from each repair that aid him in future, tricky diagnoses.

As mentioned, misaligned propeller shaft bearings are responsible for many vibration issues. Zucker says about half of the boats he works on for vibration mitigation have at least one misaligned or misplaced strut or shaft log. The shaft log is the tube that allows the shaft to penetrate the hull, with the stuffing box or shaft seal at one end, and typically a bronze and rubber shaft bearing within. Fortunately, resolving these alignment issues has gone high-tech, too.

“The first step, and the key to getting it right, is to make sure the yard blocks the boat just like it sits in the water,” Zucker says. The age-old method relied on strings or wires suspended tightly across the boat, with measurements taken from these wires to key points. Today technicians use laser equipment developed for land surveying, which shoots beams of light at precisionadjustable horizontal and vertical angles. “We use multiple laser systems and set up numerous targets before the boat is hauled,” Zucker says. “Then we make sure we hit those targets again as the boat is blocked.” The goal is to prevent misshaping or twisting the hull by supporting it exactly as the water does. Engines, too, are targeted, so they remain in the precise position they’ll take when the boat is relaunched.

sailboat propeller shaft alignment

With the boat sitting on land just as it floats, and with the propeller shaft removed, Zucker shoots a laser from the propeller’s normal position, up through each strut and the shaft log, off a mirror placed on the transmission’s shaft coupling that bounces it back toward the propeller. “Each laser is set up on four-plane micrometers,” Zucker says. “We can adjust them up and down, side to side, or tilt them, measurable in thousandths of an inch.” Inserts in each strut ensure the laser finds both the strut’s center and angular alignment to within thousandths of an inch, and a target on the forward-facing surface of the insert indicates how far off center the reflected laser beam is. “When that laser beam shoots up to a mirror on the transmission’s coupling and straight back into itself, we know we’re dead-on,” Zucker says.

Rather than moving each strut, Zucker looks for at least two points that are aligned within tolerances, and moves other components to match, reducing the job cost. Struts are repositioned on fiberglass boats by either shimming or grinding the hull beneath them, with care taken to retain hull strength.

As the shaft bearings are aligned, the engine is also brought into precise alignment with the shaft. “Even experienced yacht people think that if you get the two faces of the propeller shaft coupling exactly parallel, the engine is aligned, but you’ve got a huge amount of weight, seven or eight feet of shaft and a heavy coupling, hanging out there unsupported once it leaves that last bearing,” Zucker warns. “All too frequently we find that the front end of the engine is about a quarter- to a half-inch low. The back is a bit low, too, because the engine had been aligned to a drooping shaft.” Zucker’s technicians prevent this with the same laser system, raising or lowering each of the four corners of an engine until the transmission’s output shaft is exactly parallel to and centered with the propeller shaft. A laser reflected off the coupling verifies the angle, and shooting it into a precisely centered target ensures vertical and horizontal alignment.

Zucker has further streamlined his system with high-resolution cameras viewing the laser targets and broadcasting to monitors in the engineroom and at the laser. “Rather than having one guy outside the boat telling someone inside the boat which way to move the engine, one or two guys working entirely within the engineroom can align an engine very quickly,” Zucker says. “When we slide the shaft up, we check that the coupling surfaces are parallel with a feeler gauge, but we’re usually within one or two thousandths. You can’t machine a shaft and coupling with the kind of accuracy we’re getting.”

Even with everything precisely aligned, some boats still vibrate. “Sometimes struts themselves will move. It’s a resonant frequency response to the shaft spinning through the strut. If you go a little faster or a little slower, it usually goes away, but a minor nick in a propeller blade may excite that strut and cause a noticeable vibration,” Zucker explains. “Like a tuning fork, there will be some frequency that every single-leg strut will vibrate at. Hopefully it is not at cruise rpm.” To avoid this, yacht designers try to design struts with resonant frequencies outside the normal range of propeller shaft rpms, though they’re not always successful.

Zucker and other vibration experts tell of innumerable variations and dozens of oddball circumstances that cause hard-to-find vibrations. In the past, yacht owners often just accepted them as too expensive or troublesome to find. But thanks to technology, today every boat can ride like a Lexus.

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Running gear alignment.

By Steve D'Antonio , Nov 4, 2010

Tips on adjusting the engine, bearings, and shaft for maximum efficiency

Laser alignment assures the correct location and articulation of a shaft bearing.

Many consider running-gear alignment to be a black art. At a yard I once managed, I clearly recall watching a contractor, who specialized in this work, take a decidedly seat-of-the-pants approach to “calculating” shaft weight and the associated sag or droop.

When it comes to ensuring that an inboard propeller shaft and its supporting bearings are properly installed and aligned, there might be some art, but there’s no magic. The practices and procedures are straightforward, and if you take care to ensure accuracy and precision, the results should be predictable.

There are essentially two types of alignment. The first is positioning the engine relative to the shaft. The second is more difficult: adjusting the shaft bearings and/or their supports.

Engine Alignment Engines and motor mounts are designed to accommodate some adjustment. Most mounts employ jacking screws that allow for a narrow-range change of elevation. Side-to-side adjustment is often facilitated by the mount’s elliptical-base fastener holes—again, with a limited range.

In this type of adjustment the engine is moved relative to the position of the shaft, because the shaft’s position is assumed to be nonadjustable. Unless the installation includes a thrust bearing of some sort, all the thrust created by the propeller is transmitted to the vessel’s hull via the motor mounts. The boat is pushed through the water by virtue of the mounts and their associated hardware. Keep this in mind as you select and install components.

Because you should tighten all fasteners with a torque wrench, avoid thin fender washers that are easily distorted when you install mounts. Likewise, through-bolts, locking nuts, and machine screws should be favored in place of self-tapping lag screws. Because of the pressure and leverage imparted on motor mounts, installers and those performing adjustments should avoid maximum extension of the mount’s adjustment screw thread, which could cause cyclical loading-induced failure. If more of the mount’s adjustment screw threads are visible under the engine support bracket than on top of it, a shim should be installed beneath the mount’s foot plate to close the gap. Ideally, when adjustments are complete, the engine bracket should rest somewhere in the middle of the adjustment stud. Shim material should be rugged, incompressible, and resistant to splitting or fracturing. Steel or aluminum plate works well; prefab FRP such as GPO or G10 is also suitable. Avoid high-density polyethylene, including King Starboard and other non-reinforced plastics.

Coarse adjustment of this motor mount was performed with a composite shim.

The face of the transmission output coupling and the face of the propeller shaft coupling must be parallel, or made parallel, to within no more than 0.004″, or 0.1mm (rules of thumb for this calculation vary; the stated figure is from a shaft manufacturer). Inspect the faces for damage, scoring, corrosion, dents, and distortion of any sort. Any irregularities will make it difficult, if not impossible, to measure for alignment analysis.

What’s often not well understood about alignment is the requirement that the theoretical centerline of the shaft to be centered on the transmission output coupling.

Shaft Alignment Yard personnel often ask, “How difficult should it be turn a shaft and prop when the vessel is blocked?” I know a shaft that’s too tight when I encounter one, but that’s not a helpful answer to others making a determination whose results could lead to costly repairs.

Here’s a rough rule of thumb that I go by: provided the vessel is properly supported, and the bearings are lubricated with diluted dishwashing detergent, even large shafts—say 2.5″ (63.5mm) in diameter, 18′ (5.5m) long, and supported by three bearings—should move with no more effort than an adult can impart with one hand. That’s subjective to be sure. Recently, I was able to lift my entire body weight off the ground in an attempt to turn a 3″-diameter (76mm) by 18′-long two-bearing shaft installation. Clearly it was too tight, and the bearings and shaft likely needed realignment.

Shaft alignment is typically thought of as nonadjustable. As mentioned earlier, that’s not strictly true. When the shaft supports, strut, or keel/shaftlog-mounted cutless bearings are installed, their position should be carefully chosen to ensure that they are parallel and share the same theoretical shaft centerline . If the bearings are not aligned with each other, if they are not parallel, or if they deviate from the shaft centerline, the shaft and/or bearings will be distorted during installation. The classic pinched bearing is an indication of that, as is the shaft that’s exceptionally difficult to turn from the propeller end. The distortion induces a range of maladies, including excessive bearing and shaft wear, vibration, increased drag, and diminished fuel efficiency and performance.

If the bearings are not properly aligned with the shaft at the time of initial construction or installation, then they or their supports, the struts, shaftlog- or keel-mounted bearing(s), must be repositioned. While this wouldn’t strictly fall under the definition of “adjustable,” modifying the position of these bearings becomes the only means of resolving the misalignment. So, shaft alignment is adjustable, but not easily.

I’ve supervised many shaft and support realignments. While there are several methods, my preference is to begin by assessing the misalignment with a laser alignment tool. The full procedure is beyond the scope of this article, but in short: by placing a laser in the aftmost cutless bearing, with the shaft out, and pointing it toward the engine, you can determine, with purpose-made targets, if the aftmost bearing and any intermediate bearings are properly aligned. The laser pinpoint should land in the middle of the transmission output coupling as well as the targets placed in any intermediate bearings, confirming that the theoretical shaft centerline is aligned with the output coupling centerline.

Engine alignment also can be confirmed by installing the laser in the coupling shaft bore and shining it aft to targets placed in the bearings. A final engine alignment must still be confirmed by coupling clearance measurement after the vessel has been launched and running gear components have settled.

Yards that routinely confirm or adjust shaft alignment typically make or have made a series of targets and jigs to support and aim lasers through and onto a variety of bearing and coupling sizes and types.

Bearing Relocation If a bearing is out of alignment, from either a centerline or parallel point of view, it must be adjusted. If the bearing is strut-mounted, the strut must be removed and a base wedge of cast epoxy or fabricated FRP installed to relocate the bearing. Again, repositioning is confirmed with a laser and target. The strut must be held firmly in place, with the laser on target, until the epoxy cures. Afterward, the waxed strut is removed, cleaned, and bedded and fastened in place. If the bearing is mounted in a keel or shaftlog, the process can be more challenging; however, casting in the realigned position remains the order of the day. In some cases, a section of shaft can be used to align both ends of a keel- or shaftlog-mounted bearing during the casting process.

This strut was shimmed to reposition the bearing.

A final variable to consider is shaft sag. The shaft section that lies between the forwardmost bearing (in a multiple-bearing installation) and the coupling will droop or sag under its own weight and the weight of the coupling. If the droop is not corrected before the shaft and transmission couplings are aligned, then a bow, or curve, will be built into the finished assembly.

If you’re skeptical of just how much a shaft can droop, allow the length of shaft from the bearing to the transmission, with the coupling installed, to hang off a sturdy workbench or table. Then measure the difference between the distance from the floor to the shaft at the table and the floor to the shaft as it enters the coupling. The result is the droop.

Sag can be factored out by aligning the centerline of the transmission output coupling with a laser shot from the cutless bearing. If a laser shaft alignment has not been carried out, and if the shaft has not been removed, the droop can be negated by calculating the weight of the unsupported shaft (shaft weight data is available from all shaft manufacturers; one example is http://www.wbmetals.com/faqs.asp#Tip11 ), dividing that by 2 (because one end of the shaft is supported), adding the weight of the coupling, and then lifting, or “neutralizing,” the weight using an industrial hanging scale or compression scale under the shaft.

Applying a calculated lift can offset shaft sag while aligning running gear.

For example, 4′ (1.2m) of 2″ (51mm) shaft weighs 42 lbs (19 kg), divided by 2 is 21 lbs (9.5 kg), plus the weight of the coupling—which we’ll say is 22 lbs (10 kg)—equals 43 lbs (19.5 kg). Lifting 43 lbs at the coupling end of the shaft will negate the effect of the droop. In practice, the droop is negligible for small-diameter shafts and for shafts whose unsupported overhang is comparatively short, making the above procedures unnecessary. For long spans and heavy shafts/couplings, those steps are worth the effort.

Roughly one-third of the new vessels I encounter suffer from some form of shaft misalignment—either misaligned bearings or shaft droop. The next time someone mentions checking alignment, take a moment to discuss exactly what’s meant and what’s involved in ensuring alignment is right in every respect.

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Prop shaft alignment

  • Thread starter J. Mark
  • Start date Apr 14, 2009

Petty Officer 1st Class

  • Apr 14, 2009

Working on rebuilding a true inboard. I have read the prop shaft alignment guide from Borg Warner and they are very specific and the tolerances are .003 of parallel between the output shaft and the prop shaft couplers. To align, the engine has to be moved at all 4 corners. The motor mounts allow up and down adjustment via a sandwiched nut arrangement . . . but the motor mounts also use a locking shim to keep the lower nut from turning once it is set. Am I correct in assuming I need to bend these flat to set the alignment and once I am done bend them back to lock the lower nuts in place? The specs call for the final adjustment to be done with the boat in the water. To turn the nuts I need to lift weight off of the engine and I don't see how to do that with the boat in the water. Are these specs overly rigid? I don't imagine boat manufacturers put every boat in the water for final adjustment, but if I need to, I will. If you have reinstalled an inboard set up I'd like to know how you did it and your thoughts on the process. Thanks  

Ned L

Re: Prop shaft alignment I have done a number of inboard installations. Yes, .003" is the maximum recommended allowance (closer is better). Can you be farther off than this(?), sure, but it will result in more vibration and more bearing wear in both the cutlass bearing in the strut and in the reverse gear. How much more (?), depends on how far out of alignment it is, a bit out & it may not cause an issue for as long as you own the boat, to far out & you might be replacing parts every couple of years. I'm not familiar with the 'locking shimes' you are describing, but by your description I'd say you are right on. As for lifting the engine to make the adjustment, that is not necessary. Unless there is a problem you should be able to turn the bottom nuts quite easilly with a wrench without lifting the engine. When you are done with the alighnment there should be pretty much even weight on all four bottom nuts (equal difficulty to turn), and then you tighten the top nuts. You didn't say how large the boat is, which will affect the need to re-allign after launching. The smaller the boat the less the issue. If the boat is blocked up well you should not have a problem. At the very least I would recommend pulling the flange bolts a day or so after launching and checking the allignment (chances are pretty goo it will be fine).  

Re: Prop shaft alignment Thanks Ned, it is a 19 foot Marlin Ski boat. I know I need to be close and intend to be dead nut on if possible. My front motor mounts have sliding pins (as do the rears) that are frozen in place. I'll pull them off and get them freed up before I try and align things. When I got the boat the alignment was so bad that the bottom of the shaft log was eaten away. Hopefully I can do better than the PO!  

  • Apr 15, 2009

Re: Prop shaft alignment I'll post an update in my restore thread when I get it done. http://forums.iboats.com/showthread.php?t=292744  

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Shaft Alignment

  • Thread starter MikeHoncho
  • Start date Apr 4, 2023
  • Forums for All Owners
  • Engines and Propulsion

MikeHoncho

I have experiences a bad "rattle" after hitting a log with my '78 Hunter 30 with a Brunton Autoprop. A little bit a vibration but much more noticeable "rattle" sound. It sounds like a hose is vibrating against the hull. I removed my Autoprop and installed my fixed 3 blade that was previously on the boat before the Autoprop with no issues. Put it on and took it for a spin and the sound was much worse and continuous. I could make the sound stop at different RPMS. I sent the Autoprop in for service and was thinking I had a bent shaft due to the fixed blade having the same issue. Today I dove on it and had my son run it in gear (no prop on) and did not see any noticeable bent symptom while the shaft was spinning but I did notice the shaft was very, very close to the bottom of the hole were it comes out of the hull. I do not doubt it was actually contacting it. I could pull the shaft down while the shaft was spinning and a cloudy material came out as it the shaft was contacting the hull. Inside of the boat with it idling and out of gear I could get the rattle to come at a lot lower volume and could get it to stop by grabbing onto the shaft. I believe the shaft is contacting the hull. Last year I installed new motor mounts and aligned the engine to the shaft with the shaft being supported by the cutlass bearing/strut and the packing gland. I D/C'ed the shaft today and it stays put and clearances seem ok with the feeler gauge but could be a little better laterally. For my question (s).......my research seems to result in aligning the engine to the shaft as it sits but it appears the shaft is resting on the hull and I think with a out of balance prop, probably aligning the engine a little lower with the mounts, it is now hitting. Is there another technique I should be using other than described? Is this a packing gland/nut issue? It does drip as it is suppose to and nothing extravagant. It is a total pain to get to were it is located. My thought is to just adjust the motor mounts up a couple turns each to raise the elevation of the engine and, in doing so, the shaft but then how do I align it later being that then the shaft will sit lower when disconnected? Thanks everybody.....  

SycloneDriver

SycloneDriver

I remember reading an article years ago that stated a lifting force equal half of the weight of the should be applied to the coupler. In other words connect a pulley above the coupler and hang a weight equal to half the weight of the prop shaft so that the lifting force is applied the coupler. I'm sure someone else can describe it more clearly than I.  

RoyS

Aligning a prop shaft is a very tedious process and it is seldom explained well. As you have noted, it is possible to get seemingly correct feeler gauge values at the motor coupling faces even while the shaft is not correctly aligned with the stern tube. You mentioned that you hit a log. It is possible that the strut has been shifted out of place or deformed in some way. What you should do now is haul the boat and place it on stands. This job can take a few days. With the engine in neutral rotate the prop shaft while looking in the stern tube to detect any visible wobble of the shaft in the tube. That would indicate a bent shaft. While rotating the shaft in neutral feel for resistance that may indicate binding in the cutlass bearing. Compare to neighboring boats. Examine the strut carefully for damage. Check for a tight fastening. Next, do as you said, disconnect the coupling, and raise the motor while aligning the coupling faces. With the coupling aligned, you must have two conditions for a happy future: 1) shaft is centered in the stern tube. 2) No binding in the cutlass bearing. One final alignment check, using your feeler gauges rotate the shaft and recheck to be sure there is no bent shaft or misalignment between the coupler face and the shaft. Some people readjust the alignment after placing the boat in the water but I never have. If your strut is bent, it can be straightened by a prop shop. Re-bedding the strut after removal while trying to achieve proper alignment is another can of worms. Let's hope you do not have to go there.  

Helpful

I’m confident the strut is fine. I checked with he shaft while it was in the water (scuba), so I’m right where you mentioned with alignment: If I alight the engine to the shaft, it remains not center in the tube but properly aligned with the engine.  

I guess I need to align he shaft in the tube first but how do you do it that? If I use the engine to lift it off then that eliminates the ability to align the shaft with the engine.  

You have to do as you said and raise the engine. The shaft coupling half seems to stay centered on the transmission half even with the coupling bolts removed as long as the faces are touching each other. There must be a hub in there, but I never really looked. Keep checking for binding in the cutlass as you raise the motor. Assuming the shaft and strut are not deformed or displaced, the only adjustable features are the motor mounts. As I said, a tedious project.  

NYSail

If this started after you hit the log, I would think your problem is not the alignment.... Sure you might be able to compensate for a problem by changing the alignment but is this really fixing it? If it were me I would pull the boat remove the shaft and send it to a prop shop to have them make sure it is true..... they can straighten it if its slightly off. Also, you said you can move the shaft down while it was spinning? The shaft should not be able to be moved at all other than a rotation. The cutlass bearing is there to hold the shaft in place aligned with the coupling / trans. Speaking of, did you check the trans to see if there is any play there?? Sounds like something broke somewhere...... Good Luck! Greg  

MikeHoncho said: I guess I need to align he shaft in the tube first but how do you do it that? If I use the engine to lift it off then that eliminates the ability to align the shaft with the engine. Click to expand

dmax

dlochner said: You do this by suspending the forward end of the shaft so that the shaft is centered in the shaft log and the weight is evenly distributed between the strut and whatever is holding up the forward end of the shaft. Click to expand
dmax said: When I aligned my prop shaft (1" shaft in 1 1/2" log), I disconnected the coupler and used a couple of 1/4" drill bits to raise and hold the shaft in the center of the log - like in this diagram. I also made a tool with 1/4" rod that allowed me to measure all around the shaft to make sure the there was 1/4" clearance all around. Like everyone says, it's a pain in the butt. View attachment 214353 Click to expand
NYSail said: If this started after you hit the log, I would think your problem is not the alignment.... Sure you might be able to compensate for a problem by changing the alignment but is this really fixing it? If it were me I would pull the boat remove the shaft and send it to a prop shop to have them make sure it is true..... they can straighten it if its slightly off. Also, you said you can move the shaft down while it was spinning? The shaft should not be able to be moved at all other than a rotation. The cutlass bearing is there to hold the shaft in place aligned with the coupling / trans. Speaking of, did you check the trans to see if there is any play there?? Sounds like something broke somewhere...... Good Luck! Greg Click to expand
RoyS said: You have to do as you said and raise the engine. The shaft coupling half seems to stay centered on the transmission half even with the coupling bolts removed as long as the faces are touching each other. There must be a hub in there, but I never really looked. Keep checking for binding in the cutlass as you raise the motor. Assuming the shaft and strut are not deformed or displaced, the only adjustable features are the motor mounts. As I said, a tedious project. Click to expand

Some builds don't have the shaft in the shaft log in perfect center but I agree it should not touch and moving it slightly may do the trick as a temporary fix. However, in raising the engine you may now put uneven pressure on the strut / cutlass bearing causing another issue.... it all works together. Thats why when people change the strut it takes a lot of patients and know-how to set it in perfect alignment all the way through the tunnel and to the trans. Good Luck! Greg  

NYSail said: Some builds don't have the shaft in the shaft log in perfect center but I agree it should not touch and moving it slightly may do the trick as a temporary fix. However, in raising the engine you may now put uneven pressure on the strut / cutlass bearing causing another issue.... it all works together. Thats why when people change the strut it takes a lot of patients and know-how to set it in perfect alignment all the way through the tunnel and to the trans. Good Luck! Greg Click to expand

capta

It is quite possible you have done some damage to your transmission and/or engine mounts as well. These sorts of incidents can cause a cascade of damage. You stated that you are sure the strut is OK, but how can you tell underwater when we are speaking of hundredths of an inch? Just a few days back, I saw a picture of a boat sunk in her slip. The caption said the owner straightened his bent shaft by hammering it straight on concrete. I suggest you haul the boat and check things out carefully. I don't think I've ever seen a fixed position stuffing box. They are all mounted on a flexible hose or tube, so do not let the position of the shaft in the stuffing box be a big factor. The guiding factors are the shaft taper end, strut alignment, the cutlass, and to the center of the engine output shaft. When repairing running gear damage we use a piece of yarn from the rudder (or something from the ground up) where the shaft center would hit, to the center of the engine output shaft, then make all the parts line up with the thread, starting with the strut, then cutlass bearing. Next we would do an alignment. After a few days in the water we would realign the engine after the boat has changed back into her "in water" shape. In a perfect world, if you couldn't hear your engine running, you wouldn't have any vibration or noise from the running gear.  

Got down to the boat and the mounts are maxed out so I had to scrub the day and fab up thicker shims. I’ll get back to it next week.  

Tally Ho

I'm claiming SUCCESS. I moved the engine up about 5/16 and symptoms are all gone along with it is shifting without clunking everytime. I think the shaft has been sitting on the tunnel since the day I bought it. The mounts were maxed out so I fab'ed up 3/4" aluminum shims and with adjusting the existing shims I raised the engine 1/2" and brought it down about a 1/4" to give some adjustability on the mounts. This resulted in about a 5/16 difference between the shaft coupler's existing location and the engine coupler. I took a woodworking bar clamp and raised the shaft coupling to meet up with the coupler then aligned the engine to the shaft down to about 3/1000ths. While doing so I also drilled out three of mount lag screw holes (in the aluminum angle that sits on top of the stringer to accept 1/2' lags since the 3/8ths didn't snug down. Took it for a spin and no more "Clunking" through RPMs and it appears to be working well. I did have a very minimal vibration that I didn't recall having before but it was minimal and not RPM related. I did have a tough time getting the packing gland set up proplerly though. It seems to be dripping from between the gland nut and the locking nut and not so much from the shaft. I threaded the gland nut all the way off and found some bronze "glitter" seeping out. I think this was trapped in the tunnel from before. I motored around for a hour or so working through different RPMS and making hard turns and could not replicate the symptoms I had prior. I'm thinking this will get me by until I need to pull it and then i will probably replace the packing gland, associated hose and possibly the tunnel.  

Always good when a plan comes together! Greg  

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Quaycraft Model Boats & Fittings

QuayCraft

Installing the Propshafts

  • Post published: 08/07/2023
  • Post category: Modelling tips

The propeller tube should be the first thing to fit into the model, and using the plans / instructions it’s time to get the ruler out and start marking up the hull.

It is wise double check that any such markings are correct otherwise things may not function correctly when installed, as the old saying goes “measure twice, cut once”.

The good thing with a quality GRP hull is that they normally come with markings on them when the propshafts and rudders would go, and this is a great start, however I would still recommend checking all your measurements.

If twin screws are fitted, then equally spaced from the centre-line unless otherwise stated in the instructions. If you fail to do this then the model will still operate but you run the risk of encountering some odd sailing characteristics.

Cutting hull

When making holes through plastic hulls it is wise to cover the area around the hole with masking tape to prevent any accidental damage to the surface while drilling/cutting. The rudder tube hole can usually be drilled to the exact size but it is always a good idea to start with a smaller pilot hole first. The propeller tube, usually being at an angle to the hull bottom, will need an elliptical hole. The obvious way to make this is to drill a hole to match the tube in the middle of the desired opening then use a round file to get the desired shape. The aim should be for a snug fit without any suggestion of the hull being deformed when the tube is at the correct angle.

Long unsupported tube lengths can be prone to vibration which destroys motor/propeller shaft alignment and creates noise, wear and a loss in performance. A simple half bulkhead, or even just a block of wood glued between the tube and hull would prevent such problems.

Fixing the propeller tube into the hull can be done at this stage, again read the instructions and see it makes sense for your model. Suitable adhesives ought to be specified but you may have to make your own choice. Epoxy types will bond well to metal tubes and GRP (Glass Reinforced Plastic) or wooden hulls.

Motor Mounting It is vital that the motors are secured firmly into the model and correctly aligned with the propeller shaft. There are many ways to install the motor, but a typical one is using a mounting bracket which is secured by screws to a wooden block fitted to the bottom of the hull. The block is shaped so that the motor and propeller tubes will be aligned. To ensure that this is so a rigid connector, (usually a close fitting tube of the same length as the intended coupling), is slipped over these two shafts.

Couplings The coupling between motor and propeller shafts comes in many forms and sizes. No one type is inherently better than the others and all can be badly installed to cause no end of problems.

By far and away the most common type of couplings are those using a ‘Universal’ type of joint. The central part is plastic with brass inserts fitted to the ends which make the connection with the shafts. A grub screw usually connects the coupling to the motor shaft whilst the propeller shaft can be plain and secured with a grub screw or threaded and must have a matching threaded insert. It is vital that these inserts are the correct size and type for the motor and propeller shafts. Incorrect inserts will result in vibration and almost certainly fail at the most inopportune moment!

Now the question you have wanted to raise: if the coupling can accommodate misalignment, why go through all the trouble to get the motor shafts as near perfectly in line in the first place? Well, these couplings can only accept a limited amount of angular displacement before they start to protest, usually no more than 10-15 degrees. Rotation is possible at larger angles but significant power loss will occur and the couplings have even been known to show their displeasure by disassembling!

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Marine Insight

How Sighting, Boring and Alignment of Ship’s Propeller Shaft Is Done?

It is seemingly easy to visualise a ship from the design drawings. And it is equally tough to turn the drawings into steel in a shipyard. That too, with the same precision as it was designed and drawn on paper, which brings us to one of the most relatable examples of this aspect.

The main engine of a ship is coupled to the propeller by means of a shaft. The translational motion of the pistons induces a rotatory motion on the crankshaft, which is in turn, coupled to the propulsion shaft. The shaft then passes through the stern tube. At the aft end of the shaft, and outside the stern tube, is coupled, the propeller . The arrangement is shown in Figure 1.

propeller shaft

The centreline of the crankshaft must be along the centreline of the propulsion shaft, and the propeller. If that fails, the propeller will wobble about its position during running condition. Even few millimetres of wobbling can result in development of high stresses in the shafting arrangement, leading to structural failure. Not only that, the rupture of propulsion shaft can also lead to a major accident on ship.

As you can see above, it is very easy to visualize such an arrangement on paper or in a computerized drawing. But consider this. Suppose, during construction of the ship, the shaft was not positioned exactly along the crankshaft centreline. Given the fact that the shafts are long enough, up to more than 7 to 10 meters in average ships, the offset of the shaft centreline at the aft end would end up in order of centimetres. And that is not a design failure, but a failure in the production method.

So how do ship builders ensure the alignment of shafts exactly as per the design? In order to ensure that, builders follow a method called Boring and Sighting of the stern tube, which is described in the points below:

1. Sighting and Boring of a ship’s stern tube is done to establish practically the centreline of shafting, as accurately as per the design.

2. The stern tube consists of two bearings. One bearing at its forward end (called the forward bush bearing) and the other at its aft end (called the aft bush bearing). It is through the aperture of these bearings that the propulsion shaft passes. The clearings between the bearings and the shaft are very minute, and hence the shaft centre line is to be correctly established in line with the centres of the bearings. By maintaining this, it is ensured that the shaft centreline matches the centreline of the bearings, and the crankshaft. Again, the bearings are fitted within bosses (discussed in detail later). Follow Figure 2 to understand the arrangement of bosses in a stern tube.

stern tube

3. The stern frame of the ship is the aft most structure of the hull and it is forged separately, and then attached to the remaining hull structure. The stern frame also houses the stern tube. The stern tube, in turn, houses the aft bearing. So the shipyard orders the manufacturer of the aft bush bearing with a machining allowance on the internal diameter. Why? Well, machining allowance means, if the required internal diameter of the bearing was 0.5 meter, the manufacture will order for an internal diameter with 0.49 meter. When the ship builder passes the shaft through the bearing, it is then, that he will machine the internal diameter to 0.5 meter, so as to match the design value.

4. Now, how do these bearings fit within the stern tube? The stern bearings are fitted within hollow steel cylinders within the stern tube, called bosses. Therefore, the shaft is housed within the bearings, which are housed within bosses, which again, are housed within the stern tube, as shown in Figure 2. So the aft boss houses the aft bearing and the forward boss houses the forward bearing. In order to be able to match the centreline of the bearing with the bosses with that of the bearings, the bosses are ordered with a machining allowance for their internal diameter (just for the same reason why the bearings have machining allowance in their internal diameter.)

5. The stern frame is welded to the hull structure and the stern bosses are welded to the stern tube.

6. Now arises a problem. Because of multiple welds on the hull structure and also because of the cutting allowances considered for each steel plate on the hull, the geometric centreline of the aft and forward bosses will not match the required centreline as specified in the design drawing.

7. A telescope is placed at the required height which matches the height of the design centreline. Multiple targets are placed at the aft and forward ends of the aft boss, forward and aft end of the forward boss, and along the centreline of the engine output flange.

8. The arrangement is then viewed through the telescope, and the position of the targets are aligned accordingly unless and until all the centrelines of all the targets appear to be in one line through the telescope.

9. The centres of the forward and aft boss are then marked. These centres should now match the centrelines of the forward and aft bush bearings respectively. So according to the obtained centres of the bosses, the internal diameter of the bush bearings are machined to the required internal diameter so as to be able to house the propulsion shaft. (This is why, the shipyard always orders the bearings with a machining allowance on the internal diameter.)

10. Care is taken regarding the achievement of correct internal diameter of the bush bearings (If the internal diameter is too large, the shaft will wobble within it, and the centrelines will not match. If the internal diameter is too less, it will not be able to house the shaft within the bearing) This is why, the internal diameter is measured precisely by a micro-meter after machining the internal diameter.

11. As a matter of fact, the forward and aft bush bearings are ordered with 5 mm machining allowance on their outside diameters. The outer diameter of these bearings are machined so that there will be an interference of about 0.01 to 0.02 mm between the internal diameter of the bosses and external diameter of the bearings.

12. This allows the bearings, to be pressed into the bosses of the stern tube, with an interference fit. Figure 3 shows the arrangement after the bearings are fitted within the bosses.

ship shaft arrangement

13. Once the centreline is achieved, the propulsion shaft is fed into the bearings, for installation.

Advanced technologies of boring and sighting also use laser technologies to ensure better precision than the above explained method. Boring and sighting is also used to line up the centreline of the rudder spindle with the steering gear equipment.

However, even though the shafting system is aligned such precisely during the building process in the shipyard, the shaft may still deflect from its original alignment due to the bending of the hull girder. Different bending scenarios occur, depending upon the loading conditions and the sea states the ship is sailing in. Therefore, the change in shaft alignment may occur due to bending of the propeller shaft, during this process.

Therefore, it is important for designers, to consider the effect of hogging and sagging of the hull girder on the change in alignment of the shafting system. To give a slight peek in the designing process of this aspect, let us understand that the underlying principle is yet very simple, and follows the Euler’s beam bending theory. In the design of the shaft for a ship, designers estimate the torsional, bending and shearing loads on the shaft, and thereby, the critical points of bending are found out. Accordingly, the position of the bush bearings (aft bearing and forward bearing) are decided so as to ensure that the deflection in the shaft is as low as possible in the worst loading conditions.

Classification societies, being related with the development of structural safety rules for ships on a proactive basis, have been involved in developing rules considering this effect. They have also researched various types of ship for this aspect, and documented the obtained statistics for future reference by ship designers, builders and dry dock personnel.

It is also very important and necessary to carry out regular checks for bearing clearances between the bush bearings and the propulsion shaft. Due to prolonged use in various loading conditions, the inner linings of the bearings tend to wear out, thereby increasing the clearances between the shaft and bearing metal. This may also lead to wobbling of the shaft.

During tests for checking the shaft alignment and deflection, the observations should be noted at lightship condition (in which case the shaft deflection will be minimum, and will exhibit the inherent deflection in the shaft), and in the fully loaded draft condition (wherein, the deflection will be maximum owing to the additional deflection due to the bending of the hull girder itself).

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can you please make an animation regarding about this please. would appreciate it. ! thanks!

This is a good rundown of some shipyard processes but there are even more advanced methods than dicussed. Most large ships are aligned using strain gauges and only use optical or lasers for very rough alignments. Find out.more at http://www.lamalotech.com

I want to join merchant navy

Hi plese send for me proseuder of main shaft alignment with laser in big ship best regard for you

Hi, thanks for the nice article. I have a small doubt. While aligning the shafts, what is the permissible gap and sag at the couplings? Or after the shafts are coupled, what is the permissible slope of the shaft at the coupling?

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IMAGES

  1. How Sighting, Boring and Alignment of Ship's Propeller Shaft Is Done?

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  2. Marine Propeller Shafting and Shafting Alignment

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  3. Marine Propeller Shafting and Shafting Alignment

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  4. Tackle the propeller shaft

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  5. Ship shafting alignment procedure

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  6. SigmaDrive

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VIDEO

  1. Servicing A Feathering Sailboat Propeller #sailboat #sail

  2. 💪🏼Let’s do these in PROPSPEED! #boat #catamaran #propeller #repair

  3. Engineering New Boat Parts To Fix Our Bad Vibrations & Fitting Flexible Shaft Couplings

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COMMENTS

  1. How to check and adjust propeller shaft alignment

    The alignment you will be checking is the space between the propeller shaft coupler and the output coupler from either the transmission or the v-drive. 1) Locate and identify the propeller shaft coupler. On inboards, it's easy to see at the end of the transmission and on a wakeboat, has 4 bolts connecting it to the propeller shaft coupler.

  2. Prop Shaft Alignment

    You must first take the wobble out of it, then align the coupling flange on the transmission to the flange on the forward end of the shaft. Here's one series of tricks that actually works if your boat is out of the water. 1. Loosen the hose clamps and remove the rubber boot from the front end of the shaft log. 2.

  3. Prop shaft alignment

    Prop shaft alignment. Nearly all marine engines are designed to be adjustable, to a point, relative to the propeller shaft by using adjustment or jacking nuts on their motor mounts. The adjustment should be thought of as no more than fine-tuning, the maximum range of vertical travel being limited to no more than an inch or two at the most ...

  4. All about Propeller Shaft Alignment

    General Boat Parts. Split Hub Shaft Couplings; Groco Raw Water Strainers; ... Split Hub Propeller Shaft Coupling Kit (ZF 800 80 85 A/IV, ZF 220PL, 280A/IV, 286A/IV, 301, MG506 5061 507) ... Home » Tony's Tips » Articles » All about Propeller Shaft Alignment.

  5. Aligning sailboat propshaft w flexible shaft coupling between motor and

    So doing a propeller shaft alignment, or at least check is the best answer. This is normally done using feeler gauges in between the faces of your drive coupling faces. This has some limitations but is much better than a lot of others that dont check theirs.

  6. The Ins and Outs of Engine and Shaft Alignment Part I

    Engine and propeller shaft alignment are among the most critical aspects of propulsion system installation, reliability and maintenance. Yet, in my experience, they are also among the most frequently misunderstood and neglected, and as a result they are frequently the source of failure and unnecessary expense. ... Palm Beach International Boat ...

  7. prop shaft alignment

    162. Catalina 36MKII Waukegan, IL. May 29, 2014. #1. Over the winter I pulled the transmission and installed a new damper plate. While at it I replaced the bellows on the PYI dripless shaft seal. This spring I notice I have wobble in the prop shaft. So I checked alignment and it is out more than the recommended .003 at the coupling.

  8. prop shaft alignment

    prop shaft alignment" at 50 hrs and then again every 600 hrs or one year. I. have had the boat for three years and other than filters and oil have not. done anything else. I figured *IF* the prop shaft was mis aligned I would. soon know it by vibration. There are no vibrations. In fact the drive line. runs really smoothly at all engine speeds.

  9. Prop shaft alignment

    We recently purchased a 1990 Hunter 30 while she sat in the water and when we got her on the hard, we noticed the shaft strut was bent to the starboard, I plan on removing the strut and gettng it to a local machine shop for repairs and in the meantime I'm planning the re-install and can't see...

  10. vibration and alignmentAlignment

    Shaft Engine Alignment. Any imperfect alignment of the propeller mount, the mechanical seal and the engine / gearbox can create vibration, whip and noise. Those vibrations and the associated noise are then transmitted directly through to the hull of the vessel and thence throughout the boat. Constant Velocity Joint

  11. Shaft Alignment

    As the shaft bearings are aligned, the engine is also brought into precise alignment with the shaft. "Even experienced yacht people think that if you get the two faces of the propeller shaft coupling exactly parallel, the engine is aligned, but you've got a huge amount of weight, seven or eight feet of shaft and a heavy coupling, hanging out there unsupported once it leaves that last ...

  12. Running Gear Alignment

    Applying a calculated lift can offset shaft sag while aligning running gear. For example, 4′ (1.2m) of 2″ (51mm) shaft weighs 42 lbs (19 kg), divided by 2 is 21 lbs (9.5 kg), plus the weight of the coupling—which we'll say is 22 lbs (10 kg)—equals 43 lbs (19.5 kg). Lifting 43 lbs at the coupling end of the shaft will negate the effect ...

  13. PROP SHAFT ALIGNMENT & ENGINE ROOM UPDATE PART 2

    WOULD LIKE TO GET ON BOARD BRUPEG?If you want to see all of Brupeg's episodes and behind the scenes bonus content, help make the channel & boat great plus ph...

  14. The Ins and Outs of Shaft Alignment Part II

    The maximum tolerance for shaft wear is just one thousandth of an inch. The shaft shown here has been condemned as a result of excessive wear, caused by gross misalignment. In last month's column I reviewed the importance of, and techniques for, ensuring proper engine alignment. That is, the alignment between the engine and the propeller shaft.

  15. Prop shaft alignment

    Apr 14, 2009. #1. Working on rebuilding a true inboard. I have read the prop shaft alignment guide from Borg Warner and they are very specific and the tolerances are .003 of parallel between the output shaft and the prop shaft couplers. To align, the engine has to be moved at all 4 corners. The motor mounts allow up and down adjustment via a ...

  16. Prop shaft alignment: on the hard or in water?

    Re: Prop shaft alignment: on the hard or in water? Definitely better in water where boat/engine operate. Should actually be floating for 24 hours or longer before aligning, so Boat can take it's floating shape based on keel hanging rather than boat sitting on it and impact of rigging load.

  17. Shaft Alignment

    That is, the alignment between the engine and the propeller shaft. Nearly all marine engines are designed to be adjustable, to a point, relative to the propeller shaft, using adjustment or jacking nuts on their motor mounts. The adjustment should be thought of as no more than fine tuning, the maximum range of vertical travel being limited to no ...

  18. Shaft Alignment

    Apr 5, 2023. #3. Aligning a prop shaft is a very tedious process and it is seldom explained well. As you have noted, it is possible to get seemingly correct feeler gauge values at the motor coupling faces even while the shaft is not correctly aligned with the stern tube. You mentioned that you hit a log.

  19. PDF Propulsion Shafting Alignment

    The ABS shaft alignment program, combined with alignment optimization software, is capable of analyzing complex propulsion installations and, when used as design tool, may provide an optimal solution to the alignment problem. We welcome your feedback. Comments or suggestions can be sent electronically to

  20. Installing the Propshafts

    Installing the Propshafts. 08/07/2023. Modelling tips. The propeller tube should be the first thing to fit into the model, and using the plans / instructions it's time to get the ruler out and start marking up the hull. It is wise double check that any such markings are correct otherwise things may not function correctly when installed, as ...

  21. How Sighting, Boring and Alignment of Ship's Propeller Shaft Is Done?

    1. Sighting and Boring of a ship's stern tube is done to establish practically the centreline of shafting, as accurately as per the design. 2. The stern tube consists of two bearings. One bearing at its forward end (called the forward bush bearing) and the other at its aft end (called the aft bush bearing).

  22. PDF PRACTICES Shaft Couplings

    a nd construction, propeller shaft couplings are the sole mechanical tie in the drivetrain between the propeller shaft and the transmission and engine. To fulfill their essential role in a boat's propulsion system, they must be prop­ erly selected and installed. The design of a coupling is simple. It's a wide, flat flange mounted on the

  23. Alignment of propeller shaft to engine

    Boat: IP445. Posts: 35. Re: Alignment of propeller shaft to engine. The proper way to align a shaft is not a feeler gauge. Mount a dial indicator to one shaft and set the clock on the other, with no bolts. Rotate one shaft 360. Then put the bolts in and rotate 360 again. Need less than a thou both times.