This is called regen.
In short - it does not work in the real world.
About 100W may be sometimes produced, at cost of 200W - 1000W in drag.
100W is too little to bother with.
(It works very little, very poorly, for many reasons. Most companies who
advertised it closed, and very few solutions are sold any more.
Like towed generators - its just not worth it.
Large PV panels produce much more energy, and are much less bothersome,
and much cheaper.)
(Tehnically - it can work. But sailboat props are very inefficient for
this, there is too much drag, and thus the real power produced is very
very small).
A regen solution would work ok IF, for example you could
-use a very large 3 m diameter prop designed and built for regen
-use no transmission
-use a special generator built for this
Efficiency has to do with area cubed, iirc, and speed to the third or
fourth power. Thats why tidal stuff needs big props and fast currents.
Transmissions eat too much power in parasitic drag.
Generators dont work well at low rpm.
A towed generator might produce 1 kWhr over 24 hours in ideal
conditions, maybe 1 day in 10.
Thats 100W for 10 hours, at best, delivered to battery.
Costing about 0.5 knots in speed.
A 300W solar panel will produce about 6 hours at 50% nominal, on 70% of
days, or about 0.950 kWhr.
And over 1kWhr every day in sunny areas of the world. The UK counts as
sunny, btw- during half the year.
All averages for normal typical 10-12 m sailboat, 6-7 knots max speed,
small prop.
For the types discussed here, no-one advocates using these in 24 m long
6M$ sundeers from Dashew.
On 31/12/2013 05:40, Christopher wrote:
> Pretty useful thing for sail boats though, using an existing electric
> motor to be able to charge batteries while under sail.
>
> I have a Farrier F-31 (see www.fleetwing.com.au) which I only motor in
> and out of dock or on the rare occasion when there is no wind here in
> Tasmania. I much prefer to sail. This trimaran has different
> characteristics to a monohull (greater range of speed and less
> tolerance of weight). This sort of battery charging configuration
> would especially suit a monohull where batteries could provide very
> useful ballast down low in the boat, and where speed has a lesser range.
>
> I have not been able to find any posts on this topic yet, can anyone help?
>
> Cheers,
>
> Chris Wilson
> Abels Bay, Tasmania
--
-hanermo (cnc designs)
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