diy sailboat hydrogenerator

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Create Power While Under Sail

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Want to keep your sailboat's batteries charged without a generator or running the engine? A hydrogenerator might be the solution.

Modern hydrogenerators are lightweight and generate an impressive amount of battery charging power.

Sailors tend to use their engines far less than the average powerboater, and this creates an immediate problem of how to satisfy a boat's electrical needs. Lighting, electronics, refrigeration, and entertainment systems all require electricity to operate — all demands placed on the boat's battery bank. Solar panels, wind generators, and diesel generators have their place, but all have drawbacks.

I faced such a challenge many years ago on my first Atlantic crossing. We wondered how we were going to keep the batteries charged. By today's standards our electrical demands were modest, but we had no diesel generator. We calculated that we would need to run our main engine for two to three hours per day, a very inefficient and noisy way to charge the battery bank. Solar panels were rejected solely on cost, and there was no convenient place on the old ketch for a wind generator. Ultimately we settled for a "towed generator" — a small propeller at the end of a stiff line was trailed behind the boat, which turned a generator mounted on the back deck of the boat.

Watt and Sea's hydrogenerators are usually fastened on the transom. The lifting up and down is similar to a rudder blade's handling.

Modern iterations of the hydrogenerator are far more compact and easier to deploy. There are several manufacturers, but all use the same basic principle: they transform water flow energy into electricity using an alternator. Looking like a cross between a small outboard motor and a retractable rudder, modern systems are capable of putting out impressive amounts of power with minimum drag. In fact, all the boats in the last Vendée Globe race used hydrogenerators for producing all of their electrical energy needs. This made crucial weight savings by not requiring a heavy generator and the associated fuel tank.

Watt and Sea Hydrogenerator

In this video, you can watch one of the popular Watt and Sea units being towed behind a fairly modest sailboat. At 8 knots of boat speed in 14 knots of wind, the unit is putting out an impressive 16 amps of power. Price depends on which unit you choose, but expect to pay around $3,000 for a complete system.

• Watt and Sea
• Sail-Gen – Dedicated Water Generator
• Hydrogenerator Save Marine H240

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A marine surveyor and holder of RYA Yachtmaster Ocean certification, BoatUS Magazine contributing editor Mark Corke is one of our DIY gurus, creating easy-to-follow how-to articles and videos. Mark has built five boats himself (both power and sail), has been an experienced editor at several top boating magazines (including former associate editor of BoatUS Magazine), worked for the BBC, written four DIY books, skippered two round-the-world yachts, and holds the Guinness World Record for the fastest there-and-back crossing of the English Channel — in a kayak! He and his wife have a Grand Banks 32.

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Yachting Monthly

• Digital edition

Everything you need to know about hydrogenerators

• Sam Fortescue
• December 13, 2023

Design developments have made hydrogenerators the most efficient form of sustainable auxiliary energy for yachts. Sam Fortescue reviews the latest innovations

The potential of hydrogeneration has been well understood for decades, but it’s only over the past 15 years that the idea has started to become properly commercialised. In essence, it’s a very simple concept: the boat’s motion through the water turns an alternator which generates electricity to recharge the onboard batteries.

‘Every yachtsman owns a sophisticated wind energy machine in the form of the yacht itself,’ explains Peter Andersen of Eclectic Energy, which manufactures the Sail-Gen and Duogen hydrogeneration systems. ‘Hydrogeneration provides a simple way of converting a small part of the power harnessed by the yacht’s sails directly into electricity.’

Because water is a much denser medium than air, a small hydrogenerator fitted to the transom of a yacht can potentially produce a great deal more energy than if a larger wind turbine was fitted to it.

‘Kinetic energy increases proportionally to the cube of the velocity,’ adds Andersen. ‘That means producing 300 amp-hours per day or more is a realistic prospect while cruising at 7-8 knots with a hydrogenerator fitted. And it’s the reason why more and more boat owners are now opting for water generation, although it’s still not as popular as it should be.’

By contrast, a tradewind run with a wind turbine might yield just 80 amp-hours per day, because the apparent wind on a run is lighter. Good performance might see 40W output from 10 knots apparent. Similarly, solar panels only produce a fraction of their rated output for most of the day, so you’d need a large array to match the return of a modern hydrogenerator.

A blend of all three will, of course, give the best outcome for different conditions at anchor and under way – but on passage, it’s hard to beat the benefits of a good hydrogenerator.

Watt&Sea’s hydrogenerator is a flexible option

Speed v drag

The speed versus drag issue has always dogged hydrogeneration technology, mainly because hydrogenerators only put out meaningful energy once a boat reaches speeds of five knots or more. However, the increasing use of hydrogenerators on the international offshore racing circuit has started putting paid to most of those concerns, with all manufacturers now agreeing that the extra drag of the impeller in the water is negligible. It also becomes non-existent once the boat reaches hull speed.

The main issue for cruising sailors is the boat speed required to obtain meaningful energy from a hydrogenerator, which is mostly a question of the diameter and pitch of the impeller. Just as you need to ensure that an auxiliary propeller is matched to both the power of the engine and the speed of the hull, so the impeller on a hydrogenerator must be correctly sized for the speed of your boat under sail and desired power output.

The pitch also needs to be set to offer the optimum angle of attack for the boat’s likely range of speed through the water. That’s why leading manufacturers offer a choice of impeller, or at least an adjustable one.

Hydrogeneration is the most efficient form of sustainable auxiliary energy for yachts

The Watt&Sea is the most flexible in this respect. Its two models (300W and 600W maximum output) can be equipped with a 240mm diameter impeller or a 280mm unit. The difference in output is striking: at five knots boat speed, the smaller one produces 100W, while the larger one can manage 120W. Over the course of a day, that amounts to an extra 40 amp-hours on a 12V system.

The smaller impeller has a maximum boat speed of 11 knots, which will be enough for most cruising monohulls. Only sporty catamarans would need to consider the smaller 200mm impeller with its 13-knot top speed. Faster than that and you’d need to look at a race model with a variable pitch.

Charging performance

Apart from price, the factors differentiating the various brands on the market are their charging performance and mounting system.

Eclectic Energy is the only manufacturer whose generators rectify the current on board to produce a DC output that can be wired directly to the batteries. This has the benefit of simplicity, but requires beefier cables running all the way from the generator to the batteries.

The Duo Gen hydrogenerator from Eclectic Energy

Watt&Sea’s hydrogenerator puts out a three-phase, low-amperage alternating current that runs through a DC converter. The converter monitors the battery voltage to determine whether it is in the higher power absorption phase or the lighter float phase of charging. After that, an electromagnetic brake stops the impeller if it’s spinning too fast and becoming dangerous.

Swi-Tec’s charge controller funnels all the power from the generator into the batteries until they reach a predetermined voltage. At this point, the MPPT (Maximum Power Point Tracking) algorithm reduces the charge to nearly nothing, a buzzer sounds to alert the skipper and the impeller brakes itself automatically. It can then be changed to ‘freewheel’, allowing the propeller to rotate freely.

The Remoran is perhaps the most ambitious of all, with a charge controller that can automatically detect the system voltage and then apply a ‘smart charging algorithm’. It also interacts with a smartphone app via Bluetooth, allowing you to keep a close eye on its performance and power output.

A Sail Gen hydrogenerator mounted on a yacht’s transom

Mounting systems

While Watt&Sea supplies a pod-based system that can be permanently fitted under the hull, a removable transom fitting is still the most popular choice, allowing the unit to be removed and stowed when not in use. Alignment, though, will have a significant impact on a hydrogenerator’s performance, with the best results coming from a clean, clear flow of water. Manufacturers therefore recommend an offset mounting outside a direct line with the rudder.

There is a balance to be struck, however, as heeling can make one tack more productive than the other. On twin-rudder boats, a central mount works well.

Swi-Tec and Watt&Sea both offer an optional pivoting mount for fitting to a raked stern, while the Remoran has in-built pivoting as standard, using a spring-loaded knob to tab between different settings and offering a rake of up to 40 degrees. Watt&Sea also offers different leg lengths to suit different installations, while the Remoran Wave 3 has a telescopic leg that can be adjusted by over 30cm.

Watt&Sea unit with an optional pivot mounting for attaching to a raked stern

The Seagen and Duo-Gen take a very different approach to mounting, with a flexible yoke providing a single point of attachment. The alternator is attached at this end, while the impeller is at the end of a 1.6m tube which can be fastened out of the water in a vertical position when not in use. ‘It means the units are not rigidly attached to the yacht but are free to pivot,’ explains Eclectic Energy’s Peter Andersen. ‘This de-couples the impeller from the hull movement, reducing stress on the mounting.’

Main propeller regeneration

While a standalone transom-mounted unit is the most common type of hydrogenerator technology, there is another approach – using your main propeller to ‘regenerate’ electricity whilst under sail.

Oceanvolt’s HighPower ServoProp

Fully electric propulsion from the likes of Oceanvolt and Bell Marine has long had this capability built in, as do systems from Torqeedo and ePropulsion. But parallel hybrid systems are also available, where an electric motor is installed alongside the engine to both generate electricity and drive the boat electrically. Lynch Motors in Devon has been supplying its permanent magnet DC motors to the Vendée Globe boats for years, purely as a re-generator, and now produces the flexible Red Snapper motor for cruising yachts.

The only problem with a regeneration system is that the pitch required for the propeller to drive the boat efficiently through the water may not always be the same as the pitch for optimum regeneration. ‘The lift surface on a propeller is on the wrong side for efficient extraction of energy from the water,’ explains Eclectic Energy’s Andersen.

Manufacturers have tackled this in different ways. Oceanvolt has developed its ServoProp for saildrives, which electronically adjusts its pitch depending on speed and function. The latest incarnation allows total 360-degree blade mobility and faces forwards, which increases efficiency, albeit at greater risk of collision damage. At six knots, it produces an astounding 1kW of power.

Bruntons has another solution with the cleverly engineered Autoprop, which automatically pitches up to match the boat speed. Its Ecostar version of the prop can generate 200W at five knots and up to 1kW at 10 knots when connected to an electric motor.

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hydro-generator

Discussion in ' DIY Marinizing ' started by HuwFernie , Jan 8, 2012 .

HuwFernie New Member

Anyone ever tried to make a generator to mount behind a sailing boat? There is one made by Watt and Sea http://www.wattandsea.com/en which started me thinking about re-wiring and re-propellering an electric trolling motor but I'm getting stuck at figuring out how much power I'd be generating. I've also thought about building one from scratch which sounds like an interesting challenge. We have a 24v battery bank of 320Ah and run our boat at around 10 - 15 Amps with most stuff on; so the 500w from the commercial option looks good. I'd like to give this a go out of interest but I'm out of my depth with the motor choice. Any help would be appreciated. Huw  

gonzo Senior Member

There isn't much to change on a trolling motor with permanent magnets. The propeller would ideally have a high pitch to be more efficient. You need to decide what your usual cruising speed is and select the pitch accordingly.  

pistnbroke I try

I am sure this has been on before ...you need to make up a metal prop and get twisting with it over the side of a power boat going at your normal cruise speed. Your problem is you will need a series regulator to control the output to 14.4v which will generate heat and probably be an own design though a solar panel regulator would also be suitable .  

CDK retired engineer

You will get approx. 80% of the nominal power of the trolling motor, so if it draws 20 Amps as a motor, it produces 16 Amps as a generator. That power can be used for instruments, lights etc. but for proper battery charging you need a higher output voltage. That means a voltage converter/ charge controller that will skim another 25% from the generator output. So in the example you get 12 Amps.  

Thanks for the info. For charging, is voltage not proportional to rpm so spinning the motor faster = higher voltage? most of the graphs I have seen show a linear relationship (but I'm only looking through google). And from CDK's numbers 25A at the motor would give 20A as a generator and put 15A into the batteries. So at 24v 25A I'm looking for a saltwater, 600w, permanent magnet DC motor. For the charge controller I have seen this: http://www.mdpub.com/555Controller/ which I think will work. I'll have a look and see if there are any suitable trolling motors out there.  

i force or bison in the UK are a good buy ..I dont follow CDKs logic if its a 24v 86lb motor it draws 50A ..so to my mind thats the max the windings will handle continuously ..remember of course a 12v battery will need a regualted 14.4v and a 24 v battery 28.8v.. Whatever your charging system you will not get more than 25 A into a 100AH battery and only for a short time as it will drop fast to 15 A and then on down  

FAST FRED Senior Member

To see the effect on sailing , turn the existing motor to thrust forward and operate it at full throttle while underway. That is the drag creation you will need to live with. No free lunch. FF  

Thanks Fred, I'm not too worried about drag at the moment, I'm more concerned with having to run a generator/engine for charging and not being able to sleep!  

philSweet Senior Member

Yes HuwF, lots of folks have tried. The info above is all basically true, but folks are trying hard not to rain on your parade. As a practical device, it has absolutely no chance of replacing any generator. Turbines and propellers are different animals. Yes, they both have one moving part with one degree of freedom, so how hard can it be? The trouble comes from the fluid, not the machinery. If you insist on thinking of it as a prop in reverse, you won't ever get a handle on it, but perhaps this analogy will help- If the prop is moving the boat at 3 knots, the water jet created by the prop is probably three times this. So that is the speed you would have to tow at to get that sort of power. (Except that doesn't work either, it's actually somewhat worse than this if you are measuring power in/out of the batts). A solar panel is much easier to live with. I can cruise a 38'er on two panels and a 30amp controller feeding three WalMart batteries. (and no drag) Fast Fred's comment about drag was probably intended to discourage you a bit. Mathematically, there isn't any natural relationship between the thrust made and the drag caused by the two cases. It depends on engineering, the drag could be nearly anything. Drag of turbines is usually a secondary issue for turbines. You won't find much info on it. A design for best power/drag will be different than a high nominal efficiency design. I have yet to see a report of any trolling motor producing 2% of its rated amperage behind a smallish sailboat.(peak,yes- average over time,no) I think some of the 20knot Vendee boats used a custom generator to manage the autohelm power draw. Or was it the ORMA boats? Really fast boats. Some practial considerations. Propulsion benefits from the slowed wake behind a boat. Obviously, generation would suffer if towed in the wake. The slipstream a prop creates effectively straightens out the inflow condition seen by the prop. The heave of the boat has less effect than you would expect. On a generator, the situation is reversed, any heave or inflow irregularity is magnified. Just watch any air generator on a pole on the transom of a sailboat. They don't work very well when the boat is underway in a breeze, which is real annoying to people (they also don't work very well when underway and there isn't a breeze ) There's a bunch of info at the electric boat forums. Yahoo Groups has one.  

Thanks Phil, I like the brutal honesty! The Watt and Sea web page I linked in my first post is the consumer model of the Vendee used towing generator you mention. It was this that got me thinking in the first place: I've heard reports that it works, but it does cost about $4000! So for something that looks like a laser dinghy rudder with a trolling motor bolted to the end, a new propeller and a little bit of electronics in the boat I figured I could build something for say $400 It's only an idea, and it doesn't look like I'll get enough time to try before this trip. I still find it an interesting idea to play with though. We are looking at a solar option, but it does need a pretty big investment and also a lot of deckspace. Thanks for the idea about Yahoo groups, I'll look into it. Cheers, Huw  

"I'm more concerned with having to run a generator/engine for charging and not being able to sleep!" The really interesting question is can we have a water generator that works in the current , as we are anchored? The only attempt I know if was a gent that took 100ft of canvas 4 inches wide sewed it in a loop and installed (wired) hinged 4x4 thin plywood flaps to it. An auto verticle front spindle clamped on the aft deck with the bearings and a steel wheel. The canvas was dropped over the open wheel,flaps out, and in 1/2 K or so the flaps would open dragging away from the boat , and hinge closed on the return. In a 2K current one could not stop the wheel with foot pressure , so good power was being made. Tho 2K in an anchorage might not be common. Sadly his budget did not include bucks for a better generator than bike units ,so the concept was not perfected. Something low cost and simple might work if refined a bit. GO FOR IT! FF  

GTom New Member

Sorry for reviving an old thread but I haven't seen any recent info on hydro generators. Costs of the commercial models is still far from realistic, asking the price of 4 tons of diesel for a device with a complexity of a 250$ trolling outboard. Anyone actually tried to use a ~500W trolling motor (ebay, 2-300$) for power generation? I understand that they are probably not PM motors, but AFAIK that can be dealt with. Any suggestions for propeller design for a typical 3-7kts boat speed? CDK said: ↑ You will get approx. 80% of the nominal power of the trolling motor, so if it draws 20 Amps as a motor, it produces 16 Amps as a generator. That power can be used for instruments, lights etc. but for proper battery charging you need a higher output voltage. That means a voltage converter/ charge controller that will skim another 25% from the generator output. So in the example you get 12 Amps. Click to expand...

srimes Senior Member

If it's a PM motor with simple resistive speed control then it would generate power whenever it's forced to spin faster than it's powered speed. Then it just comes down to fitting the right prop. Maybe I'll dig my motor out from under the porch and see if I can spin it with a drill and produce power.  

srimes said: ↑ If it's a PM motor with simple resistive speed control then it would generate power whenever it's forced to spin faster than it's powered speed. Then it just comes down to fitting the right prop. Maybe I'll dig my motor out from under the porch and see if I can spin it with a drill and produce power. Click to expand...

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As bonus, the alternator can be used with a wind turbine when anchored. Of course then you have noise 24/7/365 , if the wind is blowing.  

a hydrogen gas fueled triple engine

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Power Sources for Life Off the Grid

• By David Schmidt
• January 25, 2022

One of the strangest things that I have to regularly explain to nonsailing friends is why ­engines are often run offshore to generate onboard DC ­electricity. While savvy friends understand that charging needs to happen if one is going to rely on their batteries, those less technologically inclined are sometimes stumped. And rightly so. If sailing is so green, they ask, why do sailors emit CO2 to keep their nav lights on? 

Contemporary sailors, though, have their choice of several alternatives to producing electricity without starting up their diesel engine, starting with solar panels and progressing to hydrogenerators and wind generators. While plenty has been written about solar panels, this ­technology depends on the sun, which is dormant during nighttime hours, and sometimes during the day too, especially on my home Pacific “Northwet” ­waters, as we like to call them. 

By comparison, hydrogenerators and wind generators are also highly effective, sometimes for entire 24-hour ­cycles, and can often satisfy all of a vessel’s DC-power needs. Alternatively, these generators can serve as part of a multipronged energy-producing system aboard yachts with significant DC-power needs to run heating and air conditioning, powered winches, refrigeration and the like. Here, then, is a look at how wind and water generators work, the benefits they provide, and some practical considerations for owners interested in greening up their onboard-power production.

Working with Water

As their moniker implies, ­hydrogenerators are electromechanical machines that ­harness the energy of moving water. Hydrogenerators typically capture this energy as ­alternating current, convert it to direct current, and then send it to a battery for use later. While ­hydroelectric dams are an ­everyday form of ­hydrogeneration ashore, ­marine-facing systems ­typically come in different sizes, and with varying charging capabilities, but most employ an underwater turbine consisting of a propeller or impeller that’s part of an assembly that hangs from a yacht’s transom or is fitted to its undercarriage, directly abaft the keel. 

“In essence, a hydrogenerator consists of an impeller ­designed to extract kinetic ­energy from the water, and an alternator to convert the rotary motion produced to electricity,” Peter Anderson says. He is Eclectic Energy’s managing director. Eclectic’s line of hydrogenerators employs a dive plane beneath the impeller, which allows the system to “fly” through the water at a controlled depth, similar to how a hydrofoil allows a boat to rise above the water at a ­desired height. This approach differs from other designs that resemble an outboard motor. 

“The amount of ­kinetic energy available in a fluid stream—air or water—varies as the cube of its velocity,” Anderson says. “For a water generator, this means even a modest increase in boatspeed produces a substantial increase in power output. Equally, at lower speeds, the amount of energy available falls rapidly, as do outputs.”

Because of the direct ­correlation between a vessel’s speed over water and a hydrogenerator’s ability to produce power, the size of its propeller or impeller matters greatly. Spec the system with too small a prop, and it won’t ­generate much juice; spec too large a spinner, and it will create ­excessive drag and could possibly break if a vessel’s speed surpasses certain thresholds. Because of this, most hydrogenerators come—or can be ordered—with different size impellers. 

With a properly sized system, hydrogenerator-induced drag is minimal, Anderson says. It could cost a 30-footer that’s making 6 knots roughly a 10th (or 1/5 of a knot) of boatspeed; this likely drops to an invisible metric for a 50-footer in similar airs.

Sabrina Huet, communication and sales manager at Watt&Sea , another hydrogenerator manufacturer, echoes this: “Our cruising hydrogenerators produce energy from boatspeeds of 2 or 3 knots up to 20 to 25 knots,” in the case of racing yachts. “It all depends on the propeller size. We offer four propellers with different diameters to accommodate different sailing speeds. The aim is to minimize the drag effect while optimizing the output. To put it in a nutshell: We suggest a bigger diameter for slower boats, and a smaller ­diameter for faster boats.”

As mentioned, as a boat moves through the water, ­hydrogenerators initially ­capture the energy from the spinning propeller as AC power, which is converted to DC. “Most modern generators use alternators,” Anderson says. “AC power is rectified to DC within the housing.” ­Watt&Sea’s systems work in a similar manner. 

As with other technologies described in this article, batteries are sold separately. A sailor can use any kind of battery, they would just have to check if a particular battery or battery bank requires any specific voltages, Huet says. If a battery or bank has needs that are different from Watt&Sea’s factory settings, those parameters can be changed easily, thanks to the system’s integrated mobile application. 

That said, it’s ­important to confirm that a yacht’s ­batteries are in good shape before connecting them to a hydrogenerator. “A ­minimum of 300 amp-hours at 12 volts is ­recommended,” Anderson ­advises. Most cruising yachts have at least 400 amp-hours of battery capacity, with 200 amp-hours that are usable. Batteries should not be routinely discharged below 50 percent, he notes, so it’s sensible to increase battery capacity if space and budget allow.

Both Eclectic Energy and Watt&Sea employ smart ­technology to ensure that their systems don’t create overcharging issues. “A charge ­regulator normally forms part of the ­installation,” ­Anderson says. “This terminates the charge once the batteries are full, which prevents possible damage through ­overcharging.” Once the battery or bank is topped up, the regulator then connects the generator to a power resistor in order to dump additional electrical energy.

Hydrogenerators can make great use of trade-wind conditions, however too much of anything becomes a negative. “Our hydrogenerators can withstand difficult conditions, but it’s essential to lift up a generator when approaching rough conditions, and to secure it with a rope or even ­belowdecks,” Huet says. “It’s also important to think about the lifting and lowering system, such as a hoist, to make the handling easier in both rough and calm seas.” 

“Prudence would suggest water generators be raised out of the water and possibly stowed,” Anderson says of preparing for heavy weather. “However, many owners report operating their Eclectic generators in storm conditions without problems.”

As with all systems, ­installation is an important consideration. 

Watt&Sea recommends hiring professional ­installers. Eclectic Energy, however, is more geared toward do-it-yourselfers. “Our generators are supplied with standard mounting hardware and installation instructions,” Anderson says. “Many owners do install these systems themselves.”

One concern for sailors—especially those who voyage in log- and debris-strewn ­waters such as the Pacific Northwest—is an encounter with an ­unidentified floating object, which could damage the impeller or propeller, or even the entire assembly. Much like during storm conditions, sailors are advised to retract their hydrogenerators based on ­localized conditions.   

The amount of power that a hydrogenerator can produce is an important and ­subjective question. Much hinges on how fast a boat is sailing (or ­motoring), the size of a hydrogenerator system, and the size of its impeller/­propeller. Because of this, Anderson and Huet advise customers to check manufacturer websites for more information about specific models and impeller/­propeller sizes. 

While the drawbacks to ­using a hydrogenerator—aside from turnkey costs, minimal drag, and attention to debris in the water—are minimal for sailors frequently on the move, the upsides are substantial, ­especially if you don’t care for the sound of a diesel engine or generator. “Water generation is the only renewable technology capable of matching the power consumption of a typical cruising yacht on passage,” Anderson says. “This removes the need for daily engine or genset runs to charge up the batteries.”

Counting on Breeze

The concept behind wind generators is equally ­simple, and most manufacturers ­rely on a turbine with blades that are exposed to airflow, which makes them spin. If this sounds to you a lot like an ­inverted (or dry) water generator, you’re spot-on—with a few ­exceptions. 

First, hydrogenerators are under the water’s surface, while wind generators are fitted on deck atop poles or on struts mounted on a mast. ­Second, wind generators are typically larger, employing longer blades, with greater cord widths than would be found on hydrogenerators. Third, since hydrogenerators depend on boatspeed to produce power, their performance is typically more consistent and not affected by small puffs and lulls of the wind. Lastly, the two types of generators typically produce different types of electricity.

 “All of our wind turbines produce DC Power,” says Dan Kruger, president of RDK Products . His company manufacturers wind turbines under the brand name Nature Power Products. “It starts out as high voltage, but through our controller, the system will step down the voltage to correctly charge your 12-volt batteries.”

Nature Power ­Products come with a generator, three carbon-fiber blades, and a charge controller. Customers need to supply their own mounting pole, and ­Kruger notes that most of his ­customers purchase theirs from fence stores. 

As with hydrogenerators, wind generators are ­available in different ­sizes, with ­different ­energy-­producing ­capabilities. Nature ­Power offers 400-, 500- and 2,000-watt systems. ­Kruger says: “These are designed to run most of your smaller ­electronics, televisions, GPS, fans and lights. They aren’t ­designed to power air conditioners unless you build a fairly substantial hybrid system that also includes a battery bank and solar energy.”

As with hydrogenerators, wind generators are compatible with a range of battery technology, including lithium and absorbed glass mat batteries. “A typical marine-grade deep-cycle 12-volt battery is fine for a basic wind-turbine system,” Kruger says. “Many sailors will have a bank of batteries. We also ­manufacture 24- and 48-volt ­wind-turbine systems for larger, more ­complex installations.” 

Determining the right-size wind generator for your sailboat starts with calculating your vessel’s power needs. “There’s no minimum-size ­vessel for a wind turbine to make sense,” Kruger says. “But if you’re getting into larger vessels, such as a Swan 88, you would definitely want to be looking at the Nature Power 2,000-watt system.”

Nature Power Products protect their connected battery or battery banks from overcharging by entering a “float” mode when the system’s controller senses that the storage ­reservoirs are topped off. 

As with windmills, wind generators are most ­effective in a good, steady breeze. The working range for Nature Power’s 400-watt system is 6 to 24 knots of wind, with 24 knots being the optimal windspeed. Kruger says that the goal is to expose the wind generator to steady, laminar flow, not ricocheting gusts. “The higher you mount the wind turbine, the cleaner the wind will be and the more efficiently your system will operate.” 

Too much breeze, he says, can be problematic. “The ­only time you would want to take down the unit is if you feel the storm might jeopardize the actual physical installation,” Kruger says, ­explaining that Nature Power Products are designed to withstand ­serious wind without sustaining ­damage to the turbine, its circuitry, or the connected battery or battery banks. The systems accomplish this by employing its float mode when windspeeds crest certain thresholds. “The system’s ­actual ‘survival’ windspeed is 96 knots,” Kruger says. 

While installing a wind ­generator isn’t a plug-and-play operation, the systems are relatively lightweight and generally require somewhat basic wiring schemes, making them DIY-friendly. Maintenance is also a typically easygoing affair. Kruger suggests ­replacing a system’s turbine blades ­every few years and installing the system’s controller in a dry place near the battery or bank. 

As with all technologies, wind generators have their downsides. Breeze can be an inconsistent actor, and ­air-density changes ­depend on atmospheric pressure and temperature, both of which can complicate a system’s ­daily output. Also, some generators are loud, making the owner unpopular, say, in a crowded anchorage. And while they are capable of ­impressive ­power generation while ­anchored in the trades, downwind runs—typical of trade-wind ­passages—reduce the apparent wind, ­rendering ­generators less productive. Lastly, ­depending on their ­installation, a wind ­generator can possibly interfere with running rigging and sails, or depending on their size, they might cast shadows on a ­vessel’s solar panels. 

Otherwise, wind generators can be a great source of green energy, and are ­commonly bundled with other green ­solutions to create ample ­onboard power.

David Schmidt is CW ’s ­electronics editor and frequently reports on other types of gear.

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Hydrogenerators – on test

If you’re planning to go long-distance cruising you’ll most likely be looking to fit one or more forms of power generation to avoid running your propulsion engine.

Thanks to modern alternator designs that offer increased power at lower rpm, hydro-generators are becoming a worthwhile investment for yachtsmen who regularly sail long passages. Yes, they do create a slight drag on the yacht under way, but only around 0.25kt or so, which is unlikely to worry most long-distance cruisers.

How do they work?

A hydro-generator has an impeller (reverse prop) that rotates when towed behind a yacht. That rotation is applied to an alternator, which produces AC power that is rectified to produce a DC charge for your batteries, in a similar way to a shore-powered battery charger.

Early models towed an impeller on a long line behind the boat, which was attached to an alternator on board. But their trailing impellers were often bitten off by large fish and they frequently tangled up when fouled or if not retrieved correctly. Current devices have an impeller attached to a submersible leg – not unlike an outboard motor.

Modern, brushless alternators with magnets have reduced turning resistance and increased efficiency, enabling them to produce more power at lower revs. A hydro-generator is an effective way to provide constant electrical charge over a long distance. On a 40ft yacht one of these can produce around 200Ah of charge every 24 hours at 6kt, which is enough to run most electrical items on board.

They also require little maintenance, other than weed clearance and periodic checking of the electrical connections.

Swi-Tec Hydrocharger

First this HG produced a high current flow, although not stable as it fluctuated considerably between readings. Hence the charge levels in our results table are derived from a mean between lowest and highest reading for each speed. The control box is liable to overheating, as the fan appears to be prone to failure. Our test team felt the box was more complicated than necessary.

• Verdict 6/10

Watt & Sea

We tried the 600W model with the mid-range impeller as that was more compatible with the others on test. Although not as powerful as the Save Marine and Swi-TEC HGs at the lowest and highest speeds, at a typical cruising speed of between 5-6kt the output is strong and, importantly, stable.

We liked the ease of installation and straightforward operation, including the simple ‘plug-and-play’ charge controller.

• Verdict 7/10

The SailGen is easy to mount and, having the heavy alternator at the boat end, is light and easy to deploy and lift. The dive plane idea works well and, though its real-time output is less than others, being always kept at the correct depth means its charge level is far more consistent.

• Verdict 8/10

The output is a bit lower than SailGen’s, which itself is middle of the range in comparison with all the others, but having the 2-in-1 option of a wind generator could be a real bonus for those planning to make long passages then coastal cruise in windy areas such as the Trades.

Save Marine

We liked the lightness and ease of deployment of the Save device, especially the arm that kept the lines tidy and secure. We also thought the turbine design to be innovative, quiet and very efficient. Finally, we loved the idea of the remote monitoring on a smart device, especially as the charge controller is fully automatic so there are no switches to be flicked or audible alarms to listen out for.

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Hydrogenerator

Hydro generator.

The hydro generation or “creating energy while sailing” function is an automatic feature in all Oceanvolt motors. 

This feature is activated by pushing the button on the Oceanvolt displays for 5 seconds. The display will automatically switch to regeneration mode showing the current generated power, RPM and time until the batteries are fully charged. 

With a normal folding propeller the motor kicks the blades out and centrifugal force combined with the motor controller keep the blades open. The motor controllers tune the system actively at 10 Hz which prevents the blades from closing (too much braking would close the propellers). This is continuous monitoring, the system will adjust the propeller RPM depending on the boat speed. 

The system shuts itself down when the battery is fully charged or if boat speed is too low for efficient hydro generation.

OCEANVOLT SERVOPROP

The patented Oceanvolt ServoProp variable pitch sail drive combines a high efficiency sail drive with the most powerful hydro generator on the market. The unique feature of the ServoProp is the possibility to turn the propeller blades more than 180 degrees. The software controlled variable pitch sail drive adjusts the pitch of the propeller blades automatically so that the power generation and power output are optimal. Combined with uniquely designed blades it delivers optimal efficiency in both forward, reverse and hydro generation. And with the blades set to the neutral sailing position, the propeller creates extremely low drag similar to the drag of a feathering propeller. The benefits of ServoProp include an estimated +30% increase in forward propulsion, +100% in reverse and +300% increase in hydro generation effect.

A normal fixed propeller (that by nature does not have the blades ideally shaped for regeneration) generates less than half the power of ServoProp at a given boat speed. ServoProp is capable of generating more than 1 kW at 6-8 knots. The power generated can be used to power both the propulsion system as well as all the electronics on board without the need to have a separate generator. With this in mind we can definitely start talking about the possibility of a totally self-sufficient cruiser!

The ServoProp is suitable as a propulsion motor for monohulls up to 50 ft & multihulls up to 60 ft. It can also be used as a hydro generator in boats up to 100 ft.

Videos of hydro generation

power created by hydro generation

Oceanvolt systems are optimised for either 2 or 3 blade Flexofold folding propellers & Gori propellers.  Other folding propellers can also be used but they provide 30-50% less propulsion and regeneration power. 

The highest regeneration power is gained with fixed blade & adjustable pitch propellers and also with dedicated systems for hydro generator use, because they allow using a higher pitch/dimension propeller.

The regeneration feature is extremely suitable for catamarans because twin motors means double the energy generation.  Catamarans are also faster, which means that regeneration power capture is higher.

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Towed Water Generators: Are They Worth It?

Jonathan Neeves

A few years ago, I noticed that 2 of the 10 cruising boats I saw docked in Bergen, Norway, had towed water generators, making me wonder whether the Scandinavians have had better luck with these devices than we have. In the October 2017 issue of Practical Sailor, offshore gurus John Neal and Amanda Swan Neal of Mahina Tiare Expeditions share their experience with these systems.

It has been a long time since Practical Sailor tested towed water generators, and the number of choices remains extremely limited. The last towed water generator we reviewed was the Hamilton-Ferris towed water generator . And the last long-term test was of the Aqua4Aeroben made by LVM in the United Kingdom.

The units I saw in Bergen looked like they were the Aquair 100 made by the British manufacturer Ampair. In our article on Choosing a Wind Generator , we mention Ampair, and we describe its wind generator in greater detail our marine wind generator test (available only to subscribers). We have not yet had a chance to test the Aquair 100, but it operates in a similar way to the Hamilton Ferris unit. Both tow a small impeller that looks-and this is one of the problems-like a big fishing lure with propeller blades. As the impeller spins, it turns the generator fixed to the boats stern. Old-timers may remember how much the fish seemed to like those pricey impellers for the Walker Knot Log , even though they were painted black.

One thing I noticed in Bergen was that one of the towed water generators had what looked to be a homemade impeller, and it is quite probable that the original one was lost. This is one of several problems with towed water generators; they get tangled, fouled in weed, snagged, and lost-sometimes eaten by big fish or sharks. I suppose one reason there might be more of these units here in the north country is the waters don’t have as many surface-feeding pelagic species as we have in warmer climates.

Towing isn’t the only option, though. While I was in South Africa a few years ago, I spoke with the local representative for Duogen to try to arrange a test of this product, a combination wind and water generator. At the time, the company was fairly early in the product development, and I was not impressed with the fabrication. One thing I did like was the apparent ease (the key word is apparent, because I did not try this at sea) with which the Duogen deployed: It is suspended over the stern like an electric outboard. In its water-gen mode, it looked very similar to the Watt & Sea hydrogenerators that Practical Sailor contributor Dan Dickison examined during the Velux 5 Ocean Race. These are now available in a cruising version , but they are expensive units, and again we have not tested them.

All of these products have another problem in that they add drag underway. Some owners report speed losses of a quarter- to a half-knot. This isn’t a big deal if they can help keep the ships systems running on a long passage of the kind that John and Amanda routinely tackle on their offshore training sails aboard their Hallberg Rassy 46, Mahina Tiare III .

Call me a skeptic, but when I look at the prices for hydrogenerators and consider how much time they will actually be delivering power to the boat, I think there are much better ways to spend my money. If an efficient and convenient dual-purpose generator comes on the market, I may change my tune. But right now, I think solar, then wind still reign in the world of ship-board alternative energy.

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Hydrogeneration: The Importance of Hydro Electric Power and How It Works

Hydrogeneration, which harnesses natural resources to generate electricity for optimal sailing experiences, is driving the future of boating. The technology prolongs the battery life of electric outboards and is more energy-efficient and eco-friendly than conventional charging methods. Hydro generation could well be an important milestone in achieving completely self-sufficient cruising.

In this post, I will guide you through everything you need to know about hydrogeneration.

Table of Content:

• How does hydrogeneration work
• What can hydrogeneration do for you

The strength of hydro electric power

Why hydrogeneration is important for you.

• Hydrogeneration: the bigger picture

How does hydrogeneration work?

Hydrogeneration enables a boat’s electric motor to charge its own battery while the boat is sailing or towing. During hydro generation, water, instead of electricity, passively spins the propeller on the motor in either a forward or reverse motion, which generates electricity through electromagnetic induction. This electricity is storage in the battery bank, which is then used to power sailing systems and electrical appliances, such as microwaves, on boats.

What can hydrogeneration do for you?

Travel further and more sustainably with a hydrogeneration-enabled electric outboard, such as motors from ePropulsion’s Spirit Evo and Navy Evo series, which are the industry’s first known hydrogeneration-powered electric outboards.

The Spirit Evo , the first electric outboard to feature hydrogeneration, is one of the brand’s lightest outboard motors and also their best-selling since 2015. The Spirit 1.0 Evo is a portable 3HP electric outboard that was designed for dinghies, tenders, and sailboats. It comes in a remote version, the Spirit 1.0 Evo Remote, that allows remote steering.

ePropulsion’s Navy Evo , which the brand considers the backbone of ePropulsion electric outboard motors, is available in two power levels, 3kW and 6kW. Also featuring hydrogeneration, the Navy Series provides efficient and clean power for aluminium fishing boats, dinghies, daysailer and cruising sailboats, and can operate in both salt and freshwater.

The most compact of the brand’s motors, ePropulsion pod drives are great for sailboats and small watercrafts. Offered in three models – 1kW, 3kW, and 6kW – the hydro generation-powered pod drives are a silent, eco-friendly alternative to internal combustion outboards.

Check out what Captain Rick Moore says about ePropulsion outboards in his hydrogeneration test (starting from 7:48):

With the power of renewable resources, ePropulsion motors, for example, generate different levels of wattage depending on the boat’s towing speed and the drive system models. When it reaches a speed of 10 knots, the 3HP Spirit 1.0 Evo can generate 330W; the 6HP Navy 3.0 Evo, 660W; and the 9.9HP Navy 6.0 Evo, 1,010W. Stored electricity generated while the boat is sailing can be used to power electrical appliances, such as microwave ovens.

Having a hydrogeneration-enabled outboard extends the runtime of your motor, which means you get to travel further and more sustainably. Take ePropulsion electric motors as an example. It takes only 4.8 hours to charge the brand’s 1,276Wh large integrated lithium battery to 90 percent while sailing at 16km/h. You could even extend the runtime by replacing the integrated battery with one of ePropulsion’s E-Series batteries . Sailing at the same speed, the 2,048-Wh E40 battery takes 7.6 hours to reach 90 percent capacity, while the 8,960-Wh E175 battery takes 33.3 hours.

How to activate hydrogeneration

Enabling hydrogeneration on your ePropulsion outboard motor is easy. Hydro generation on ePropulsion motors can be activated when the outboard is in a neutral position and the boat is sailing at 4 knots or faster. ePropulsion’s hydrogeneration system will shut itself down when the battery is charged to almost 90 percent, or if the boat is too slow for hydrogeneration.

Stay up to speed on the hydrogenation process with the tiller, which features an indicator that will flash when the battery is being charged with hydrogeneration. When hydrogenation is enabled, the indicator light will turn on. However, on ePropulsion outboards, hydrogeneration can only be activated when used in conjunction with batteries from the brand, which, for safety, can only be charged to a maximum of 90 percent.

To ensure steady charging from hydrogeneration, use an anticavitation plate to ensure a constant flow of water spinning the propeller on the motor.

By harnessing the power of natural resources to generate electricity, hydro generation is one of the industry’s most eco-friendly and forward-thinking sailing solutions. A longer battery life means spending more time on the water doing what you love, without worrying about “wasting” precious power from your generator on electrical appliances, and overspending on fuel.

In the long run, hydrogeneration helps you save money. Charging batteries is simply less efficient and economical: you use almost as much fuel to charge the batteries on your boat as you would motoring, and running your engine just to charge batteries could reduce its lifespan as it is not designed to operate below its rated level. A five-hour trip on a motorboat could cost you more than US$300 worth of gas; even a slower pontoon boat could set you back around US$3,000 a year in gas if you take a five-hour trip once a week.

Hydrogeneration: The bigger picture

Water replenishes naturally and is virtually infinite, whereas the burning of fossil fuels to generate electricity has been linked to consequences such as rising global temperatures — on land and at sea — and extreme weather.

Changing precipitation patterns and sea-level rise negatively impact marine ecosystems, while ocean warming is often the cause of coral bleaching and the loss of breeding grounds. If you care about the wellbeing of oceans, rivers and lakes and are looking for a way to help slow the process of climate change, consider making mindful and informed lifestyle choices.

One way is by reducing our carbon footprint when boating, which does not necessarily mean giving up our passion for sailing and sacrificing comfort. With their efficient, durable and fuss-free electric outboards, brands such as ePropulsion offer eco-friendly alternatives. Harnessing the power of nature to generate electricity, their hydrogeneration-powered motors also minimize the consumption of fossil fuels and help you reduce costs in the long haul. 

Our world is changing, and it is up to us to ride the waves of change — starting with hydrogeneration.

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Cruising 300 Hydrogenerator

CRUISING 300 Hydrogenerator

Cruising 300.

• Technical specifications sheet
• Output Curves

An input of energy up to 300W (24 Amp in 12 V), for more comfort in the respect of the environment !

The CRUISING 300 is usually recommended to boats measuring up to 35 feet :

Available in two lengths in order to optimize the immersion of the propeller depending on the place choosen for the fitting.

Ideal on boats sailing generally from 4 to 6 knots, and consuming around 8 Amps (12 V installation)

Delivered in standard with the 240 mm diameter propeller (output 8 Amps at 5,2 knots), it will produce even more with the 280 mm propeller (8 Amps at 4,5 knots)

Mobile application : converter equipped with a Bluetooth chip allowing the reading of charge data, various technical informations, as well as the adjustment of voltages if necessary (Lithium battery)

Available in 2 versions :

• short (Ref. PK-610-300)
• long (Ref. PK-970-300)

Packs characteristics :

Technical characteristics

Dimensions and weight

Output power curves

Watt Speed in knots

The propeller supplied in standard with the CRUISING 300 hydrogenerator pack is the 240 mm model which allows to produce 8 Amps at 5 knots .

It is the more “universal” model guaranteeing the energy self-sufficiency on most boats with a negligible drag. To produce at slowest speed, the 280 mm diameter is more efficient.

To produce at higher speed to minimize the drag effect, the 200 mm diameter is available as well as the 200 mm with manual variable pitch to be used on applications like MINI 6.50.

General Questions

How to choose the right power : 300W hydrogenerator is designed for boats under 35 feet, and 600W is ideal over 35 feet sailing boats. It also mainly depends on the equipment you have on board !

How to choose the right lenght for my boat : First define the location for your installation onto the transom.

You have to respect 3 rules to choose the ideal location :

• The hydrogenerator should not be in the rudder blade axis to avoid water perturbations. 10 or 20 cm aside from this axis will be fine.
• The leg must be vertical in the lowered position for the production to be optimized : the propeller axis must be horizontal, aligned with the water flow.
• the recommended depth between the surface and the propeller axis is 300 mm(12 inches), even when the boat heels.

Taking in account those 3 points, the 610 mm or 970 mm leg will be chosen.

Watt&Sea recommends servicing every 2 years or every 10 000 miles. It should be noted that, regularly, you can :

• remove the propeller and clean the conical fitting
• check all the cables, to be sure it’s not cut , spoilt or pinched (what could damage the energy output, and generate some noise)
• check the good condition of the plugs (corrosion can damage/stop the power passage and the energy production)

Mechanical installation

Eletrical installation.

Accessories

Removable mounting kit for transom

Universal support for all kind of transoms

Cruising hydrogenerators range.

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Cruising 600