Features December 2017 Issue

Towing Generator Field Report

A real-world assessment of water generators for cruising.

For free power when under sail on ocean passages, towing generators are hard to beat. In the early 1980s I purchased a first generation towing generator from Hamilton Ferris. At six knots the output was five amps providing all the electricity I needed on passage. During 15 years and 100,000 miles of use I only needed to replace brushes and bearings twice.

Hamilton Ferris water gen
The author's Hamilton Ferris water gen survived thousands of sea miles.

Our current boat, a Hallberg-Rassy 46, came with a 24-volt house electrical system, and shortly after launching I contacted Hamilton Ferris to purchase a 24-volt towing generator. He replied that he’d had few requests for a 24-volt model and didn’t plan on developing one. Currently Hamilton Ferris is working on an updated 12-volt model from their WP 200 which they plan to release this summer.

Watt & Sea's water generator
Watt & Sea's water generator.

Several years ago I discovered the Aquair 100, made in the UK and distributed in the U.S. by Marine Warehouse in Miami. They offer 12, 24, and 48 volt units and the price is surprisingly reasonable: $1,495 plus $270 for a regulator. The kit consists of a generator in a stainless circular frame, 30 meters of very sturdy towline, and a towed turbine. The only other cost for me was a $50 for a Hella Marine waterproof plug that I mounted inside a cowl vent on the transom. The installation of the stainless circular frame is a simple lashing – no drilling holes in the deck required. I find that lashing the generator to the pushpit/stern pulpit with Spectra cord allows enough movement plus the convenience of taking only taking a minute to untie and stow.

When deploying the turbine for the first time I suggest keeping boat speed under three knots so you have an idea of how quickly the line feeds out. I’ve found faking the towline back and forth on the deck and standing clear when tossing the turbine in the water works well. Once deployed, there is a very slight hum, barely audible below decks. I haven’t been able to detect any drop in boat speed after deployment and sharks or fish attacking to turbine have never been a problem. The output depends on how deeply discharged the vessels batteries are, but we generally see around 5 amps with 6 knots of boat speed.

A Delrin connector attaches the tow rope to the generator and is designed to break if the turbine snags the bottom or a large object and although we’ve caught Sargasso weed and abandoned nets we’ve never had the connector break. I’ve found that slowing the boat down by luffing up slightly makes pulling in the turbine easier. For a better grip, I wear the heavy rubber gloves that I use for handling the anchor chain. While pulling the turbine in at speeds of over 5-6 kts, the rope sometimes gets kinks in it. To remove the kinks, just unshackle the turbine and trail the rope astern for a minutes allowing it to unwind.

Spare parts are listed on Marine Warehouse’s website, www.marinewarehouse.net and I’ve ordered but not yet needed a spare turbine, shaft seal and bearings.

Both Hamilton Ferris and Aquair offer wind conversion kits to turn their towing generators into wind generators but after reading the Practical Sailor February 15, 2003 test report, you may find a dedicated wind generator more user friendly.

Another more powerful option are the Watt&Sea Hydrogenerators, utilized by many French racing boats. The power output is staggering: 10 amps at 5 knots for the 300 which costs $3,290 and 40 amps at 9 knots for the 600 which runs $4,690. Bainbridge International is US distributor and Hydrovane, located in Vancouver is Canadian distributor and has developed a very clever bracket ($450) allowing Hydrovane owners to attach a Watt&Sea directly to their windvane.

Amanda and John Neale spend seven months at sea sailing 10,000 miles a year while leading sailing training expeditions. The have more than 500,000 sea miles combined experience. When not at sea, they enjoy winter kayaking from their island home at Roche Harbor, eight miles east of Victoria, B.C. Their website is: www.mahina.com.

Comments (10)

A timely update on the Watt & Sea. One of the 2018 Transpac boats lost it's rudder and used their Watt & Sea as an emergency rudder to get back to California. More info is in today's Latitude 38.

Posted by: Bear Boat | July 17, 2019 2:31 PM    Report this comment

Did the author do any research before publishing this article?

Marine warehouse does not work with ampair as can be seen in the email below.....

Hi Paul,
Unfortunately we are currently out of stock on the items requested and we are no longer working with Ampair. Your order has been canceled. My apologies for any inconvenience. I am sorry that it didn't work out with this order but hope that you keep us in mind for future marine needs. Please find attached a copy of our introduction. Please let me know if I can be of further assistance.


Regards - Jonathan B.

Marine Warehouse

Posted by: biggles72 | July 14, 2019 5:33 PM    Report this comment

I have a aquair100 that needs a new regulator. Marine warehouse has them on the website, but have not been able to provide them for over a year. I've found no one else that stock parts.

Don't recommend buying as you can't find spare parts. Mine has been sitting now for years and is not usable,

Posted by: biggles72 | July 14, 2019 5:26 PM    Report this comment

What options work in what order are highly dependent on the particular situation you are in. For us, there was not enough room for enough solar to provide a guaranteed 200AHr/day every day. A wind generator doesn't work very well sailing downwind. So the best choice for us after dismissing running the engine with our 160A alternator was a Watt & Sea hydrogenerator.
Yes there was added drag but as a percentage of the total drag of a 10t semi-displacement boat it was minimal.

Posted by: Bear Boat | July 14, 2019 10:59 AM    Report this comment

As an electrical engineer (who specializes in renewable energy design) and sailor, the hierarchy of alternative power for a sailboat should be: solar #1, wind generation #2, towing generators a distant #3, fuel cells #4. This assumes all four are viable options for your boat. Solar works regardless of whether the boat is moving or not and is the simplest by a wide margin.

Posted by: Joseph | July 10, 2019 8:53 AM    Report this comment

I know of several cruisers that have had a different arrangement for power. A generator is located at the aft end of the engine. A belt is connected to a wheel attached to the prop shaft. By allowing the prop to turn, sufficient charging is provided.
In New England, contact Merri-Mar Marine in Newburyport, MA for an installation.

Posted by: SteveLee | July 9, 2019 9:07 PM    Report this comment

I know of several cruisers that have had a different arrangement for power. A generator is located at the aft end of the engine. A belt is connected to a wheel attached to the prop shaft. By allowing the prop to turn, sufficient charging is provided.
In New England, contact Merri-Mar Marine in Newburyport, MA for an installation.

Posted by: SteveLee | July 9, 2019 9:07 PM    Report this comment

Simple hydrodynamics says these generators--or anything else you tow through the water--create drag. This may or may not be an issue for a cruising boat. Racing boats have to weigh that drag against things like the weight of fuel to run a generator or the main engine for charging, etc. Solar panels are also a real option for either cruising or racing.

The bottom line? There is no such thing as "free" power. There are various options, each with associated costs in performance, equipment.

The effort required by the racing boat to retrieve the towed unit? That's a measure of the pure drag it added.

Posted by: CalypsoNick | July 9, 2019 5:10 PM    Report this comment

Simple hydrodynamics says these generators--or anything else you tow through the water--create drag. This may or may not be an issue for a cruising boat. Racing boats have to weigh that drag against things like the weight of fuel to run a generator or the main engine for charging, etc. Solar panels are also a real option for either cruising or racing.

The bottom line? There is no such thing as "free" power. There are various options, each with associated costs in performance, equipment.

The effort required by the racing boat to retrieve the towed unit? That's a measure of the pure drag it added.

Posted by: CalypsoNick | July 9, 2019 5:10 PM    Report this comment

Used a W&S Cruising 600 hydrogenerator for the Pacific Cup 2018 race and couldn't be happier with the expericence. There were several boats in the race that used the W&S. We ran a frig, autopilot, Iridium Go!, laptop, 2 chart plotters, 5 instruments, AIS transponder, occasional radar use, and lots of personal electronics off of USB outlets. We averaged a steady state draw of about 7-8A for 24 hrs a day. The W&S provided more power than we consumed so the 400AHr Odyssey house bank was maintained at near 100% for the entire 13 days of race from SF to Hawaii and the 20 day return back to California.

There are a couple of practical use issues that came up during our race, but overall device was fantastic. For what we were doing, I would have added the shorting relay so that we could have left the device in the water rather than raising it and lowering it as we ended up doing.

Our unscientific experience is we really didn't see any drag as we were sailing at our above hull speed for the 2200nm of the race. But the forces generated by the force of the propeller on the long lever arm of the W&S were significant. We had to heave to to raise and lower the unit and even then with a 4:1 block system it was difficult to get the unit into the down position to get the locking pin in place.

Posted by: Bear Boat | July 9, 2019 2:57 PM    Report this comment

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