Towed Water Generators: Are They Worth It?

Posted by Darrell Nicholson at 04:56PM - Comments: (8)

Cruising sailboats and local craft line the waterfront in Bergen, Norway.

The fact that two out of 10 cruising boats I saw docked here in Bergen, Norway, have towed water generators made me wonder whether the Scandinavians have had better luck with these devices than we have. My guess is that the units I saw on the sterns of two Swedish boats have had very little use over their lifetime. Most owners of towed water generators that I have spoken with, even those who take long passages when the generators would seem most useful, seem unenthusiastic about the devices.

It has been a long time since Practical Sailor tested towed water generators, and the number of choices remains extremely limited. (As I mentioned in the July 2013 editorial, the ocean cruising sailor is a small and fickle market.) The last towed water generator we reviewed was the Hamilton-Ferris towed water generator.

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, but it’s one more strike against them.

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.

We’ll continue our efforts to get a water-generator test going, but in the meantime, I’d like to hear from owners about their own experiences. I’m sure other readers would greatly appreciate the input.

Comments (8)

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 W | 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: CLYDE J | 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: Chris H | July 17, 2013 10:53 AM    Report this comment

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