Towed Water Generators: Are They Worth It?

Posted by Darrell Nicholson at 04:56PM - Comments: (14)

Jonathan Neeves
Jonathan Neeves

The Watt and Sea hydrogenerator for cruising is based on a design developed for around-the-world racers.

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. 

This towed water generator seemed to have a homemade impeller (stowed vertically, next to the anchor).

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 boat’s 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.

This Duogen windgen/water generator was on a Hallberg-Rassy 43 docked in Stavanger, Norway.

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 ship’s 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.

Comments (14)

When we bought Antara (1998), we had a pole mounted Four Winds generator installed on a quarter. We also had a Hamilton Ferris wind and towed generator (vintage about 1990). When used at anchor, it was supported in the fore triangle. At sea, it was used as a towed unit. In the latter mode it produced 6 - 8 amps with a boat speed of 6 - 7 knots. Drag was not noticeable. When used as a windmill, it produced a similar output. The two windmills produced similar amount nets of power (swept areas identical) In the tropics (tradewinds) they pretty much provided all the power we needed, including running a freezer, refrigerator, fluorescent lights and brief comm. use.

Both manufacturers have been courteous and helpful.

Negatives: Four winds slightly noisier, but not objectionable. H - F as a windmill was easy to put up (I tied a loop in the end of the tail-line around a tip of the blade and the mounting bar, and pulled it off the blade when the mill was in place). Getting the mill down was done with great care as one has to reach the end of the support bar (behind the rotating prop) with one hand while managing the halyard with the other. This has been done many times without injury. The H - F blade is made from Sitka spruce and needs to be treated with care. Also, the windmill components are inconvenient to store.

Posted by: | June 17, 2019 9:02 AM    Report this comment

My wife and I used an Ampair towed generator in a 5 year circumstances navigation. It gave us 6 amps at 6 knots. A slight reduction in speed but who cares when you are having fun.
Ted Nobbs

Posted by: TedNobbs | September 3, 2017 5:13 PM    Report this comment

I have an Ampair 100 towed watergenerator. Still with the original prop. I gave it a shorter line so I can use it in Dutch coastal waters without loosing it. This means it sometimes jumps out of the waves, but that is only when we sail downwind with windforces of 6 and up. I have an old Nicholson 43, as soon as we come near hull speed the little bit of drag of "Flipper" is not noticeable. I love the towed generator as it means I don't have to use the old noisy Perkins engine for power. I'd like to save that machine for maneuvering in harbours etc. Having said that, I recently increased my solar panels to 230 WattP and this meant we could sail the whole Fastnet (5 days 11 hours) without use of engine or "Flipper" and at arrival still had 50% power left in our AGM 220Ah battery. The cool-box switched off at night.

Posted by: GerardJonker | August 28, 2017 2:35 AM    Report this comment

We have used DuoGen for our ARC Atlantic crossing. Over 3-4 knots of boat speed it generates decent power, at around 6-7 knots over 8 Amps.
We bought it instead of installing a genset and it worked fine.
It works as a wind generator too though it tends to hunt too much, not staying in the wind.

We would recommend it to cruisers doing long passages.

Posted by: Aussie | August 24, 2017 7:33 PM    Report this comment

For water generators that flip down from the transom to be used by around the world racers, is a big stamp of approval that the drag is worth the power.

They do have much larger boats and sail plans that make the drag from the generator comparatively tiny. Such boats also have solar power. It would be interesting to know if world racers use the underwater generator only when solar is not plentiful, all the time, or as a last resort?

Posted by: Dan C | August 24, 2017 10:29 AM    Report this comment

I've done 3 transatlantic crossings and one long coastal trip with Watt & Sea hydrogenerators and have been impressed with their output. These passages have all been on Outremers, a rather quick performance cruising cat. Two of the boats had the racing version and 2 had the standard. At our cruising speed of 8-10 knots we are getting an easy 20A and when we are flying at 11-16 knots, we get 40A. There is a bit of noise in the hull where the generator is attached but that is partly of function of the light build on these boats. We have broken props too, usually on sargasso weed. And when we are racing the boat, we do lift the generator so we don't sacrifice that .5 (max) knot. They are a big investment but if you are cruising on a quick boat its a very productive source of energy.

Posted by: claudia | August 24, 2017 9:53 AM    Report this comment

My experience with an ampair towed generator was that I had to extend the rope and add some shaft anodes to the shaft to increase weight and stop it jumping out of the water. After that it was nearly faultless for 10000 miles producing 4-6 amps 24/7 running fridge lights and autopilot. The shaft shown in the photo above is not home made. The blades can be replaced or changed for different sizes to suit speed. So to sum up imo they are great for ocean passages and on my yacht 36ft there was no noticable reduction in speed, though there must have been a slight reduction. I don't use it for coastal sailing.

Posted by: janiguentim | August 1, 2015 5:17 AM    Report this comment

I installed a Duogen on my nicholson 31 before heading across the pacific. I LOVED the water generator and found the wind gen ok. The water gen didn't seem to slow me down much at all and at any speed over 3 knots I got significant amperage out of it. I thought the quality was also quite good. The only negative I think is that it's one more hunk of equipment hanging off the stern, so it does detract from the boat's looks.

Posted by: Grant R | April 15, 2014 11:49 PM    Report this comment

Well, I do 98% of my sailing during the day. I do like to use the autopilot on trips and a few 30 watt solar panels (read:no moving parts)providing almost 8 amps has provided enough power for that and any lights (LED)used at night. I'll be adding a wind generator, to supplement the photovoltaic when I add refrigeration. Since I had real good lock with an Ampair on a previous boat, Ill consider one of that brand. I found no annoying noise from it, but will be willing to change brands based on output and decibel ratings from future testing.. As far as inverters go... I'd rather keep the electrical system free of fairly inefficient energy conversion. Regarding water's just another thing to srore on the boat when not in use. Not for me.

Posted by: Ed White | December 4, 2013 8:21 PM    Report this comment

I just returned from a trip from Connecticut to Horta (Azores) onboard a friend's Freedom 40. We installed an Aquair 100 towed generator for the trip. We would deploy the propeller and 100' tow line when sailing. We took the line in while motoring figuring it was more efficient to use the engine alternator for battery charging rather than burn more fuel for the tow generator. According to the manual, the unit has a modest output of about 2 amps at 4 knots, increasing to about 6 amps at 8 knots. The manual also lists drag estimates. We found when sailing in light air, the unit would cut our speed by about 1/2 knot. In wind above 12 - 15 knots, it made little difference since we had wind power to spare. The generator helped extend the interval between running the engine for battery charging and allowed us to keep the DC refrigerator going but could not meet the power demands of the boat. We also had an 80-Watt PV panel but its mounting was sub-optimal and frequent partial shading reduced its output significantly. I am not a fan of small wind turbines on sailboats. I consider them potentially dangerous and find the noise objectionable.

Posted by: Alan S | July 17, 2013 9:07 PM    Report this comment

A towed generator differs from a wind generator in that it always creates drag that reduces the speed of the boat. A wind generator creates drag, but the direction of that drag and its effect on boat speed vary with the relative wind direction. On a beat the wind generator drag will slow the boat. On a run the drag should actually add to boat speed. On a beam reach the wind generator may just contribute to leeway.

Posted by: C Jenkins | July 17, 2013 1:26 PM    Report this comment

What about the "outdrive" style of water generators mounted to the transom, as seen on virtually all of the last Vendee Globe boats? What's the concensus on those? Wind rules when at anchor, but underway (particularly on a run) H2O gens should definitely outperform wind.

Posted by: oscark | July 17, 2013 12:37 PM    Report this comment

I sense that you feel the towed generators slow the boat more than a wind gen would. Seems to me that if each generator puts out the same amount of power that the drag should be roughly equivalent. The power has to come from somewhere. I can't prove this but it we generally always come back to the fact that there's no such thing as a "free lunch". Perpetual motion anyone?

Posted by: BillR | July 17, 2013 11:17 AM    Report this comment

I have often wondered whether one of these could be deployed on a moored boat in a strong tidal area. I usually winter in Fernandina Beach FL and there must be a 3knot current through there. Someplace like St Mary's GA. I bet it was close to 5 knots. Seems like a big impeller just hanging off the back of the boat would give you a lot of power.

Posted by: squarpeg | July 17, 2013 10:53 AM    Report this comment

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