T-Pain Is On A Boat: [Electric Boats] Re: First impression of an electric sailboat

Tuesday, August 25, 2009

[Electric Boats] Re: First impression of an electric sailboat

Keith,

I agree that most people would not recommend replacing a 55hp diesel with a 3.5kw electric drive, but this drive seems to fit the owner's needs fairly well. This is truly only a harbor drive, for navigating around the crowded So Cal harbors. The system was set up when the boat was on a mooring, so it doesn't have a shore power charger installed, rather the installed solar panels have provided virtually all of the recharging that the system has done to date.

I hear that the 200w regen was sustained, the boat was sailing at 6kts. Add this to the 400w of solar and the boat can generate 600w for hours, 5 hours of sailing should replace 3KWh. Stronger sailing conditions would increase the prop driven charging, so the 6kt estimate is fairly conservative. James knows that the regen circuits in available controllers are not optimized for sailing, he wants to put together a system that he thinks can regen more than double his previous systems. Of course, seeing is believing. I'm sure that he'll post the results of his developments on his site as they become available.

I am very aware of the limitations of electric drives, I've personally converted 3 cars to electric, which have much more difficult design parameters to reach. I've gone 60 miles in an hour on a single charge and driven over 90mph (different battery packs). By comparison, these small auxiliary sail drives seem pretty straight forward.

As far as hull speed goes, it takes more than 18kts true to get my Cheoy Lee above 6kts under sail, and more than 90% of my motoring over the last 7 years has been at 5kts and below. I've read that increasing your boat speed 1 to 1.5kts doubles your power consumption. If 5kts is 4kw, then 3.5 to 4kts would be 2kw, 2.5kts would be around 1kw. This sounds about right for sailboats around 10,000lbs displacement, is that close to your observations with your boat?

All drives are compromises; electric, diesel, gasoline, outboard, etc. It is up to the owner to determine the best fit to meet their needs.

Fair winds,
Eric

--- In electricboats@yahoogroups.com, "aweekdaysailor" <aweekdaysailor@...> wrote:
>
> Eric,
>
> glad you enjoyed the ride...but why was the boat only going 3.5 knots? That boat has a hullspeed of what, 8knots? That setup sounds grossly under-powered to me. How would it have handled a headwind? I have nearly the same on my 10K lb displacement and it is barely adequate. Driving that hull to 3.5kts probably only used 1KW. Driving it at a reasonable speed (say 5) will take ~4KW - depleting a 200AH bank in < 1 hour.
>
> Peak regen numbers are also useless - unless it can sustain something in that range it barely covers your house load.
>
> Your boat can _probably_ use the mars (heavier than mine I bet) - but carefully consider what sailing a boat with 1 gallon of fuel (your battery equivalent) is like. I got reminded again on Sunday sailing upwind against 30kt winds and 4' chop...after about 3 hours was starting to miss the smell of diesel...
>
> -Keith
>
>