I did a search for towed generators on google. There are a number of articles about installations that have an alternator attached to the shaft. The people who tried it seemed to have very good experiences with little percived loss of speed. Here's one that actually tried to measure the difference between using the alternator and not.
http://www.sailnet.
They found no measurable difference in speed under the ad-hoc conditions they tested it in. What I got from the reading however was that this was most useful for people that go on longer voyages and have a large ratio of sailing days. A weekender might be better off with solar or wind.
I think that some controllers have circuitry to enable useful generation at lower rpms. It has something to do with letting the magnetic field collapse I think. Because electric boats already have sophisticated control systems they might be able to better use these techniques.
It should also be noted that a wind generator will also produce drag and slow the boat down. What a wind generator can do is allow you to go straight upwind;-)
--- In electricboats@
>
> chris, dave, myles.
> cris you mention 200 watts per hour and being nirvana and 100 wats per hour as being acceptable. There is no free lunch so what drag sacrifice would be acceptable to you. e.g.1/4 to 1/2 knot?
>
> I have to agree with Myles. Originally i thought that only racers would be interested in feathering or folding propellers. The around the world cruisers i have talked with(The company has a booth at the Annapolis boat show every year)quickly sorted that out for me. Cruisers have even more interest in low drag. A 1 knot difference can add an extra day or two to a week long passage. It makes sense if they can average say 5 kt then a 1 kt drag will add 20% more time to the passage.
> But is there a break even point for watts vs speed? and what about the comfort and convience factor. Many cruisers enforce very strict power conservation rules while making a passage. how much is it worth to relax those rules?
> larry
>
> --- In electricboats@
> >
> > Chris, I'm not sure but I believe your the first to mention the word cruising with electric propulsion. Â Cruising longer distances are my intentions also, so on 2 to 20 day passages I should be sailing, not motoring. Â I'm happy to see another glass half full.. Â Dave K
> >
> > --- On Tue, 3/9/10, Chris Baker <chris@> wrote:
> >
> > From: Chris Baker <chris@>
> > Subject: Re: [Electric Boats] propellers
> > To: electricboats@
> > Date: Tuesday, March 9, 2010, 6:19 PM
> >
> >
> > For me the enticing thing about regen is to have a reliable source of power when cruising. Â And even though 200 watts doesn't sound like much, when coastal sailing, and being at sea for 24 for 48 hours at a stretch, the potential is enormous compared to what I'm used to.
> > From the sun, even though I have nominally 500 watts of solar power, the reality is that I rarely see more than 200 watts flowing into the batteries, and its mostly commonly around 100 to 150 watts. Â And because this is only available for just part of the day, it doesn't amount to much each day. Â Considering overcast, shading of panels, sun angles and bird shit, I can count on around 500 watt hours of energy each day.
> > On the other hand, if I could get 200 watts every hour I'm sailing - well, holy smoke - that would be fantastic. Â In only three hours I'd get what I normally get in an average day. Â And over 24 hours I'd get 4800 watt-hours of power. Â Nirvana!
> > In truth, I'd be happy to get 100 watts of continuous power. Â Strangely enough, the biggest load for me is the house load, not the engine. Â And especially when sailing - cos then I have not only the usual fridge, lights, laptop, phone charging (and you know the list...) but also the navigation load of chart plotter, depth sounder, wind instrument, nav lights, auto pilot and so on. Â At those times the load is probably averages around 50 to 100 watts. Â So If I could get 100 watts of regen that would cover my house load, and at times even have something to spare for the engine batteries.
> >
> > Cheers
> > Chris
> >
> > On 09/03/2010, at 10:56 AM, Myles Twete wrote:
> >
>
> >
> >
> >
> >
> >
> > Regen is an interesting recurring
> > topic on this forum.And there are various ways to look
> > at it---find the way that suits your needs and go with it.Just be sure to respect the laws
> > of physics and known applicable equations and curves.As mentioned by Chris, the return
> > is not great and if the regen is to be had while under sail (rather than
> > anchored in current), there’s a penalty to be paid: Speed of boat in
> > water.Where the regen tradeoff is not
> > worthwhile for sailing is if you need to keep the speed up to reach the
> > destination by a certain tide or time and if you will have power available at
> > your destination anyway. If it costs 1knot on your speed to capture a
> > mere 200watts of electricity, while it requires a doubing of power for the boat
> > to increase speed by 1knot, the cost of regen can be steep if the primary need is
> > to cover distance quickly and you expect good wind the entire way.Where it would certainly be
> > worthwhile is if you’re sailing and really don’t need the speed,
> > but could or will need the electricity later.And there’s a million other
> > circumstances between these that could swing either way. Be conservative
> > and have backup plans---having regen can be part of that backup plan. But
> > you might best add a wind generator instead. Â Of course the no-brainer
> > free-energy case is where you expect to be anchoring in a high current zone----but
> > how often do you really want to do that?  -Myles  Â
> >
>
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