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Remembering the towed generator

Jan 1, 2003

Your special section on alternative power sources in a recent issue (Issue No. 84) was, as usual, well done. However, I feel that this section would have benefited significantly by the inclusion of an article on the often-overlooked towed generator. Although they are far less common on voyaging yachts than either solar panels or wind generators, I believe that they can provide real benefits and should not be neglected as an alternative source of electrical power.

I have been interested in alternative power sources for voyaging yachts since 1965 when I sailed from the Caribbean to Australia on a Piver-designed trimaran, Cygnus-A. On this voyage, our only source of electrical power was a single 6-volt automobile battery. Since we had no means for recharging it, we would take it ashore to recharge it at each port and then use it to power only the compass light during the next leg.

While in Puerto Rico, we fitted a solar panel consisting of rejected solar cells from the Telestar satellite program, courtesy of friends at Bell Labs. I suspect that this was the first use of a solar panel on a voyaging sailboat. I also suspect that, at the time, the value of this three-square-foot panel probably was several times the value of the 35-foot boat on which it was installed. The maximum output of the panel, as I recall, was less than an amp, but it was our only onboard means for battery charging. The biggest problem was in sealing the panel against seawater intrusion.

By today's standards, our instrumentation, communications, and navigation seem practically prehistoric. For navigation, we used a surplus Navy compass and bubble sextant (without bubble), as well as a mechanical VDO Sumlog and a portable shortwave receiver for time signals. We had neither radio transmitter nor fathometer, and the running lights were kerosene.

After a 25-year hiatus, my wife and I have spent the past two years sailing in the Caribbean. During the first year's voyage, our only alternative power source was a single 75-watt rigid solar panel. For the second voyage, I installed a Hamilton Ferris towed generator. This unit is quite small and light, and it installed easily to a bracket on the taffrail. The same generator could be fitted with a wind propeller and suspended in the rigging while in port, although I never did this.

I towed the generator only during ocean passages when the autopilot, running lights, and instruments more than doubled our daily power consumption by adding approximately 100 amp-hours per day. Because of the tremendous density difference between water and air, a tiny seven-inch water propeller is able to extract as much power at five knots as can a wind prop several feet in diameter at 15 or 20 knots of wind speed. I found that I was charging at approximately five amps at a five-knot boat speed, and that the output increased rapidly to more than seven amps at six knots. The combined output of the solar panel and the water generator was sufficient, on most passages, to supply all of our electrical needs, including continuous use of the autopilot, refrigeration, running lights, and instruments; generous use of the HF transmitter and computer; and modest use of the PUR-35 water-maker.

Probably the greatest drawback with the towed generator is the launch and recovery of the long towline that attaches the water propeller to the generator. Practice is required to launch the propeller without getting hockles in the line. To recover the line and propeller, the rotation of the prop must first be stopped. I did this by using a split funnel that I sent down the line to cover the propeller. Except in large seas, the boat had to be luffed up or otherwise slowed to remove tension from the line to allow the funnel to be dragged down the line. Once the line stopped rotating, it and the propeller could be hauled aboard quite easily, even in rough conditions. Although I have heard of fish striking the propellers of towed generators I did not experience this problem. On several occasions, the prop did get fouled with Sargasso weed, and I had to recover the prop to clear it. The effect of propeller drag on boat speed was imperceptible. I am certain that the drag it added was less than the drag we saved by use of our Max Prop.

Based on our experience, I would urge voyagers looking for an alternative power source not to overlook towed water generators. Not only do they have the ability to quietly and reliably provide power under normal sailing conditions, they also may be better able to survive a dismasting, knock-down, or other catastrophic event that could place even greater significance on the need for alternative power.

In spite of my near-addiction to onboard HF e-mail and reliance on GPS, I would gladly trade all of today's modern conveniences in return for the uncrowded anchorages and islands without airports that we experienced in the Pacific in 1965.

Sidney H. Shaw has more than 45,000 ocean miles and lives in Falls Church, Va. He and his wife Rebecca currently own a Hallberg-Rassy 352, Dovka.