Yes we are talking Apples and Oranges here.
Smaller boats are capable of producing Regenerative power at proportionate numbers to the size of their power plants. I run a 144V system and use less Amperage proportionately to a 48V or 72V system. I run an 18" prop and no transmission (thank god). I also have a 41' water line and might loose 1/2 knot do to my props dragging. But a boat with a fixed in water prop and an ICE will loose even more so I find the argument that "it slows the boat down" to regenerate power not to be in my case. At 8 knots I could care less about being a 1/2 knot slower. As for PV panels I wouldn't put the number of panels I would have to install for a 144V system on my boat however I will put panels on to remove the load off of the Propulsion bank going to the House bank. No generator is needed, the motors themselves are the generators however I have a genset on board to extend the run time to whatever I carry in fuel.
The Gunboats and a few other BIG (Tang) cats have used them and when installed properly work great. With the LiFePo4's I'll install in the future weight won't be an issue anymore and I'll hopefully gain 1 or 2 knots in speed. But heck I have a Condo on water so speed wasn't ever a factor anyway.
8O)
Steve in Solomons MD
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.
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