Watt & Sea Hydro Generator Review

Reading Time: 12 minutes

‘Wattsson', a Watt & Sea 600 watt hydro generator, has become part of the Isbjorn (our Swan 48) family. He joins ‘R2-D2’, our autopilot, as simultaneously our most and least favourite pieces of gear on the boat.

We sail Isbjorn 10,000 miles a year, and Wattsson happily hums along, day and night, providing all of our electrical needs at sea and then some. However, it's taken a full year and nearly $10,000 to finally work out the kinks, but I still think he is worth it...to us. Here's why, and why he might not be worth it to you.

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Do You Need A Generator?
  22. Efficient Generator-Based Electrical Systems For Yachts
  23. Battery Bank Size and Generator Run Time, A Case Study
  24. Battery Options, Part 1—Lithium
  25. Battery Options, Part 2—Lead Acid
  26. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  27. Eight Steps to Get Ready For Lithium Batteries
  28. Why Lithium Battery Load Dumps Matter
  29. 8 Tips To Prevent Lithium Battery Load Dumps
  30. Building a Seamanlike Lithium Battery System
  31. Lithium Ion Batteries Explained
  32. 11 Steps To Better Lead Acid Battery Life
  33. How Hard Can We Charge Our Lead-Acid Batteries?
  34. How Lead Acid Batteries Get Wrecked and What To Do About It
  35. Equalizing Batteries, The Reality
  36. Renewable Power
  37. Wind Generators
  38. Solar Power
  39. Hydro Power
  40. Watt & Sea Hydro Generator Review
  41. Battery Monitors, Part 1—Which Type Is Right For You?
  42. Battery Monitors, Part 2—Recommended Unit
  43. Battery Monitors, Part 3—Calibration and Use
  44. Battery Containment—Part 1
  45. Q&A—Are Battery Desulphators a Good Idea?

Andy Schell is the co-founder of 59º North Sailing, which takes paying crew on offshore sailing passages around the Atlantic, Arctic, Caribbean and beyond. They are currently refitting the Farr 65 FALKEN as their new flagship, while they operate their Swan 59 ICEBEAR and Swan 48 ISBJORN in the meantime. Andy founded and hosts the ON THE WIND sailing podcast and recently launched the online seamanship platform The QUARTERDECK. Andy has sailed over 100,000 miles offshore, including 5 Atlantic crossings and an expedition to 80º North in Svalbard in 2018. Check them out at 59-north.com.

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For about half the cost of the Watt and Sea you can buy a Duo- Gen from Eclectic Energy in the UK. It produces 6-8 amps at 5-7 knots in water mode and is a useful wind generator at anchor


Hi Ted,

I sailed across the Atlantic on a Saga 43 fitted with a DuoGen – it worked so poorly that the owner replaced it with a W&S for the return voyage. A case of the classic trying to do two things well and ended up doing both things poorly. If you’ve had luck with yours that’s great. I’m only speaking from my own experience, and the DuoGen can’t hold a candle to the W&S, especially on output.

There are other options too. Ampair makes a towable generator for a few hundred bucks, and I may be missing some others. Yves Gelinas made his own homemade towable generator in the early 1980s when he sailed around the world solo on his engineless Alberg 30 ‘Jean-du-Sud.’


Ted Simper

Hi Andy

We have crossed the Pacific from Canada and made several trips from New Zealand to the Islands and Duogen has been very good. Less output than the WS but still sufficient to power everything in conjunction with our solar panels.


Hi Ted, happy to hear that, good on you!



Thanks for the honest review of the Wattsson,s real life capabilities and shortcomings. Many reviews fail to look at the full picture for a host of reasons.


Thanks Dave, appreciate the compliments!

Colin Speedie

Hi Andy

a very thorough and fair review of the Watt and Sea. Having used a couple (on a Boreal 47 and a 55) I’d add a few comments.

The standard bracket is the weak spot. The custom bracket Boreal fabricate is massive and works well, although the vertical pin needs to be lubricated to keep it quiet and easy to remove. If W & S have now come up with a custom bracket, then that has to be a good thing.

I’ve experienced that rumbling and vibration from the unit and put it down to bearings (worryingly), and I’ve heard complaints of the same from other users – there has to be some way to identify what the problem is and for W & S to cure it, as it is (in my view) too frequent an issue for comfort.

As an aside, anyone considering one for these units alongside a servo pendulum vane gear where the auxiliary rudder swings from side to side will have their work cut out to come up with a solution to stop the rudder and the W & S prop possibly meeting with disastrous results! They move around far more than I had expected. It is just possible to set up the Windpilot Pacific on a Boreal and the W & S to work at the same time – but it’s close. The vane gear can be angled slightly to make the necessary clearance without compromising the efficiency of the gear, but if a fix has to be made by altering the bracket of the W & S, then as you’ve identified, the work will need to be done to a very high standard indeed.

And I totally agree with your summation – a great thing to have on a long distance voyaging boat, but not for coastal cruising.
Best wishes


Hi Colin,

There’s two kinds of ‘rumbling’ I’ve experienced – the first, and less concerning, is when the batteries are fully topped up and the W&S is essentially ‘freewheeling.’ It’s an ominous noise, but according to everyone I’ve spoken to, unavoidable and not bad for the unit. So when we get to fully topped batteries, we either take up the W&S, or more likely, just run the watermaker a bunch to use the electricity! Problem solved.

The second was what I describe on our last day offshore en route to Horta. It was a terrible vibration, and the batteries were NOT fully topped up, so it was different. It was still putting out amps, but obviously something was wrong. I’m sending that one back to W&S, it’s still under warranty, so I’ll report back if I get an answer from them what it was all about.


Peter Passano

I bought a tow generator from Hamilton Ferris while in New Zealand in 1994. I sailed
SEA BEAR ( 39 ft steel cutter) singlehanded to Rio de Janiro, via Drake’s Passage, on my way to Maine. I only Started the engine once a week to be sure it would still run. The tow generator provided all the power I needed ( lights, radar, radio, no fridge) and I only towed it a few hours a day. Still have it and use it on passages. Simple and pretty inexpensive.


That’s great Peter! I’m envious of your small and simple boat – I miss our Arcturus a lot, especially when dealing with this expensive stuff! But alas, I need a bigger boat to run the business, and need a watermaker to keep the crew going, and subsequently need a way to make power! Good on you for keeping it simple!


We bought the 300W short leg version for our 31ft boat. The size of the propeller and unit is dependent on the boat one has. The 600W unit would have been nonsense for our boat since we never reach enough speed to use the upper 300W. The choice of propeller size and unit wattage should be made based on average passage speed. There are output curves on the W&S homepage.
We had to mount our unit eccentric on the starboard side to keep it away from the wind vane. Initially I regretted buying the short leg unit because the propeller sometimes breaks the surface on starboard tack. This turned out to be an advantage when we came into sea areas with much seaweed because the propeller rids itself of seaweed when breaking the surface (most of the time).
For anybody buying two units I’d recommend to buy two units with short legs and mount them on both sides of the transom. Mount them removable with a plug. If any unit fails the good one can be moved to the lee side. This would be the perfect solution for me that also leaves space for the windvane. The stress on the mounting will be considerably less for the short leg unit too. (I find the mounting on the picture still does not look very solid.)
The W&S-regulator doubles as a MPPT solar regulator. I bought 300W of portable solar panels that I use at anchor (en.sunware.solar/produkte/module_textil_tx). This is enough for our energy needs including refrigeration and watermaking. Portable panels are superior to fixed mounted ones since they can be moved around on deck and out of the shadows. This is even more important in the arctic where solar panels need to be angled towards the sun to be effective. Unlike almost everybody else we do not have a windgenerator and never missed it.
W&S have a good service and they are one of few French companies that deliver a comprehensible manual in languages other than French (most others seem to use google translate or worse).

In 14 month of fulltime cruising we never started the engine for charging and on our first Atlantic crossing we did not start the engine at all.

We also experienced the rumbling sound that Colin mentions. A technician from W&S replaced our generator unit witch solved the problem – for about 5 days. Thereafter we just left it. It does not impair energy production. The technician said he wanted our old unit to find out what causes the sound.

Never ever angle the pendulum rudder on your Windpilot!!! Peter from Windpilot told me this is a big mistake. Doing so produces to much stress on the mechanics and will damage the system (I did it and it broke my windvane). Windpilot produces different extensions for the mounting. Buy one that is long enough to keep the pendulum rudder vertical and away form the Hydrogenerator.


Hi Enno,

Good point about the 300W unit for slower boats that would never get the added 300W out of it anyway. I’m still not sure it’s worth the expense, but if you’ve had luck with it, that’s excellent. I have no comment on the wind pilot, as I have no experience with that particular gear.

I also have similar good things to say about W&S and their manuals and service, for the most part.


I have purchased a 300 watt unit for my boat and have been thinking about the mounting requirements. My understanding of the situation is that the center of the propeller should be a minimum of 12″ below the waterline. More precisely, wouldn’t that be the dynamic waterline? The waterline when our boat is sailing at 5 knots or greater?

If that is the case, it makes little difference how high your transom is from the water at the dock because when sailing it will be very near the water.


Hi Caleb,

Yes, get the unit as low in the water as you can. You make a good point about the sailing waterline, but there’s a few caveats. 1). We have ours mounted centerline – when we’re going hard to windward, and heeling 20-30º, it’s barely in the water. Yes, the waterline down on the low side stretches aft, but centerline it’s still high, and remember, the W&S will be angled AWAY, the same amount the boat is heeled. 2). In light airs going downwind, and with any swell, the prop often comes out of the water completely as the stern rises under a wave. No harm, but you’re losing some precious amps! 3). Finally, we had ours mounted such that it sits the requisite 12″ underwater even at the dock – that’ll only help when the boat digs in when she starts sailing.


Marc Dacey

Andy, I have puzzled over these issues for some time. Our solution (to date) was to go for a larger bank: six L-16 6 VDC in series-parallel for a total of 1575 Ah capacity, of which I consider one-third conservatively useable. And it’s right under the mast, which is nice, beneath rebuilt saloon steps.

We have four 135 W solar panels, a 300 W wind generator and will sport a pair of 90-110 A alternators. The idea, like yours, is to make amps while we can and “go quiet” electrically where we can’t. If I’m motoring anyway, I’ll take the output happily, but, like you and Mia, that’s not the goal, nor would we have a diesel genset to that end. Our windvane installation, as has been pointed out, likely precludes this generator, but it’s an excellent review that made me at least think about it for a minute!


Good on your Marc! Probably not worth the expense or maintenance in your case, you sound like you’ve already figured it out.

Bill Attwood

Hi Marc
Can you point me to a web address for your batteries. I assume from the description of your house bank that the individual 6 volt batteries are 525 Ah each. I’d be interested to follow up on size and weight.
Thanks in advance,
Bill Attwood

Marc Dacey

I can give you the blog post I made on the topic, which features the spec sheets:

They are sold by Crown primarily for electric forklifts and sweepers, but also are popular with the off-grid crowd. They aren’t easy to source; not rare, but you have to be specific as the 430 Ah ones are far more common. They weigh about 125 pounds each: I shifted them as detailed here: https://alchemy2009.blogspot.ca/2016/07/getting-lead-in-part-2.html

I was in contact with an off-grid homesteader named “Handy Bob”, who was kind enough to give me a lot of good advice on the care and feeding of lead-acid batteries of this capacity: https://handybobsolar.wordpress.com/

Certainly, my successful baptism into off-the-dock electrics has been greatly enhanced by the experience of off-grid renewable tech and installation/monitoring techniques. For sailors going this route, those sorts of resources are invaluable.

Bill Attwood

Hi Marc
Many thanks, and I look forward to following up your tip about off-grid homesteaders.
Yours aye

Greg Beron

You didn’t mention any performance penalty. There must be some drag associated with that unit.


Hi Greg,
Good point. I’ve never bothered to test it. I don’t notice any drop in performance at all, which is in line with what W&S promotes, and what others have said. The racing version has hydraulically adjustable pitch on the propellor blades to optimize output v. drag, but not the cruising version. And anyway, it hardly matters even if it’s costing us half a knot (which I KNOW it’s not). The power it produces is well worth whatever very minor penalty there is in boatspeed.

Marc Dacey

We gained half a know with our Gori folder on our sloop and our feathering Variprop on our cutter. I would give some or all of that back to never have a generator or to “need” to run the engine for charging over propulsion. But that’s me. Everything’s a trade-off and most people can jog faster than the average cruiser in average conditions can sail…over a mile course, at least!

Marc Dacey

I agree on most of Andys article. However the crucial point is for sure the bracket – I also figured out that the hinges are too weak for the loads which are act on the watt and sea – especially when sailing upwind in big waves. I also replaced my bracket in Cape Town by a carbon fiber one and replaced the hinges with stainless ones. Done so far about 20 K miles offshore with this power plant and I am completely satisfied so far. I using it on a Luffe 45 you can find some pictures under http://www.lifgun.com

Klaus Matzka

I have just realized that there is a new version called pod 600 that is to be installed below the hull, aft of the keel. As I have a large opening transom on my Beneteau Oceanis 48 I am thinking about the pros and cons of such a solution.

I like the „out of the way“ feature of such a setup, it has a shorter shaft and thus less force on it, is always under water, less in danger of debris behind the keel. But it needs additional holes in the hull, is not easily reachable for maintainance, always on or blocked (with increased drag?) by an off-switch/relay.

Any experience or suggestions on this type of solution?

Thanks and best regards,

Klaus Matzka

BTW, here‘s the link to the Watt and Sea website showing the pod 600:

John Harries

Hi Klaus,

I don’t have any experience with these generators so this is speculation, but speculation based on a lot of offshore miles.

That said, given the reliability problems with these generators I would not consider this option because of the difficulty of service, which you, quite rightly, highlight.

As to alternatives, I think I would consider a small generator instead, perhaps something like this: http://fischerpanda.com/fischer-panda-dc-agtpm5000/

An advantage being that it could also be used at anchor.


Hi John,

thank you for your feedback! I tend to agree that it is potentially a not so reliable solution.

On the other hand I am quite satisfied with my decision NOT not to have a combustion engine generator on board. Another piece that burns fossil fuel, is noisy and needs engine service regularly.

Nearly 600 Wp of solar at the davits work well in tandem with 1,100 Ah of service batteries, so far for all situations except when running multi-day on auto-pilot + watermaker like we did for the Atlantic crossing. This type of energy need is what I am looking to solve with a Watt & Sea hydro generator.

So I will keep investigating how to best fix the 600 watt long shaft version to my boats transom.

Eric Klem

Hi Klaus,

I have no personal experience with the Watt&Sea but I did want to share a general thought on energy production. One of the things that happened with early off-grid solar systems is that people focused too much on the worst case situation and ended up with huge arrays that were far larger ($ and carbon footprint) than needed for the vast majority of the time. Many of these systems were replacing generators and and it turns out to be not a bad idea to size for the vast majority of the time and either lessen loads occasionally or turn that generator on.

If you are doing what Andy does where he makes a living by sailing tons of miles, then I think a combination of solar, wind and hydro that covers nearly all needs is an excellent idea. However, if you are someone who mostly coastal cruises and every 5 years does an offshore passage over 4 days where your solar doesn’t keep up, I would argue you should at least consider using the main engine occasionally. While the engines’ efficiency is very low at this sort of task, your overall system efficiency is likely higher over the course of owning the boat thanks to not carrying the other generation sources around all the time when not needed. You can also do things to boost the efficiency such as trying to match charging time to slow sailing periods when a little speed boost wouldn’t be bad and also trying to only run the engine when the batteries are low so you can get full alternator output and let the solar top it up (assuming lead acid batteries). The drawbacks of going this way is that you do burn a bit of extra fuel which you hopefully have the capacity for and you lose some redundancy.

I have no idea what your particular usage profile is but just wanted to throw this into the conversation as people can become fixated on covering 100% of needs without using the main engine as opposed to using it to charge maybe 5 times a year. With our 140W tilting panel and MPPT controller, we almost never have to start the engine just for the purpose of charging and when we do, I don’t sweat the maybe 3 hours a year we do it.


John Harries

Hi Klause and Eric,

Funny, I was just in the car thinking about your situation and was ready to comment as soon as I got back to the office with exactly the same recommendation as Eric made: run the main engine and don’t worry about it.

That said, Eric has done a better job of explaining the reasoning than I would have, although I do have some thoughts on the same vein here:

One added suggestion: You may want to make sure you have a good alternator and a regulator that’s programmed well. See these posts:

There two upgrades will cost a fraction of what a Watt and Sea will and will, for most usage profiles, be far more useful.


Hi Eric, John,

great thoughts to work with, thanks a lot!

On my sailing profile, I plan to cross the Atlantic two more times before I hope to start a long term voyage that might include crossing the South Pacific, all during the next few years. Becoming a live aboard is what I am working on. 😉

So far I have used the main engine to top up the batteries when solar has not been sufficient or loads have been high like with autopilot and watermaker loads over sustained periods of time. For that reason I have installed a Sterling AB1280 regulator that keeps the amps coming from the alternator and offers a 3-phase charging cycle on the batteries end of things. (https://sterling-power.com/collections/alternator-to-battery-chargers/products/alternator-to-battery-chargers-up-to-130a). I know some people think that this product is not a good idea for a few reasons. On the other hand I know of a trusted 30-year-in-business service technician that has personally installed and serviced dozens (or even hundreds) of those setups without experiencing or knowing of a single failure/issue.

Burning fuel for charging purposes adds up on the fuel consumption side quite fast and leaves less reserve capacity fuel for motoring if weather conditions ask for. My next leg will be from Caribbean via Azores back to Europe where having full fuel tanks might increase options navigating the weather situations. In my opinion this increases safety. Would you agree?

I looked into the costs of installing a larger alternator with programmable regulator and it is not far off the cost of installing a Watt & Sea hydro gen (total about EUR 4,000). The currently installed alternator on my Yanmar 75hp engine has only about 1000 hours of usage, most of it in low load situations and without the Sterling regulator setup. Should be good for another 1000+ hours without touching the system, I would guess.

All that said led me to the conclusion that going with a hydro gen installation seems to be a great solution as it increases safety, one by adding redundancy and two by increasing the range I can go by fuel if weather conditions ask for. Increased self sufficiency and ability to drive a large fridge/freezer are additional soft/convenience factors.


Andy, how are you “lashing” the unit in the down position? I share your concerns and dislike for the rather small, point-loading pin, but haven’t arrived at an effective alternative to keep the unit firmly seated in the v-notch over time without placing the pin.


Hi Jonathan,

I’ll try to dig up a photo, as I think it’s impossible to describe here. But in short, it worked great – once lashed down when the boat is stopped, it doesn’t come undone at all. I’m going to make it simpler next season too, this was sort of temporary to see if it worked or not, but it most definitely does.


John Harries

Hi Andy,

If you send me the photo I will add it to the post.

Bill Bourlet

I installed the larger Watt and Sea unit in Vancouver before we left. On the way down the coast to San Diego I honestly thought it wasn’t working. We had it checked by a professional in San Diego and they assured me it was working fine. We changed the prop to the larger one that would be better at lower speeds. They showed me the chart where it says 5 knots and up for good charge. Below that little power. Sail faster they said. Down the coast to Puerto Vallarta we did get some power output now that I knew how to check it. Flashing lights under the unit in the rear compartment. Impossible to see but I could get a video of it. It was working. We left for the big passage to Tahiti. As usual 2 hours on the engine in the evening to get 95% + charge. I later discovered that and hour in the morning and an hour at 6.00pm did a better job of charging. In the year I passed over the Equator we had a low wind year. We had reckoned on 23 days to the Marqueses. It took us 27. No mater. We enjoyed the sail even though it was a bit slow. We mostly made 3 to 4 knots bursting up to 6 + during the Squalls which fortunately were not too often. Scary as they were!
I have an Island Packet 40 foot. The only sail we did manage 6 knots average was from Hawaii to Vancouver when we had frequent storms and relatively high winds. Very uncomfortable. We are a power hungry boat. Auto Pilot. Older fridge that doesn’t have the insulation that modern ones have. SSB radio that we operated for at least an hour every night, very power hungry to broadcast. Lights. Multiple computers and phones Many batteries to re-charge. etc.
Would I install the Watt and Sea again? Yes, probably as when it does work its great. It’s a love hate thing. It is vulnerable to damage in harbour and around other boats. You have to get it set down properly before heading out to sea. Trying to pull it down against the water flow when going forward is very hard. The French system of lowering it is poor. It really needs a bolt to hold it in place when fully down. Would two devices work better on the same boat. Not really. You need a faster boat.

S V Music.

John Harries

Hi Bill,

Thanks for a great field report, always the best information. Really highlights the difference we so often see between claims and reality.