Thanks Eric, that makes the regen problem even worse! With slip figures that high I'm not surprised that regen rarely seems to deliver anything worthwhile at normal sailing speeds in practice.
My system won't regen (although the controller is capable) because the prop folds (as a weed-clearance measure). I have worked out some prop parameters with some others for a small (20ft) sailing boat project and we concluded that the optimum prop size for regen was around 20% bigger in diameter than the optimum for propulsion, assuming a fixed ratio drive between the prop and motor. I looked at doing this with a partially folding prop, with high aspect ratio blades. The idea was for the prop to be partially folded (via a rod down the centre of the hollow shaft) when used for propulsion, then allowed to swing out to its full diameter for use when generating. I think it would work OK, but we didn't pursue it as it looked a bit complex to engineer.
Jeremy
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Hi Jeremy,
>
> When you're dealing with displacement auxiliary sailboats, even the good propellers run at slip rates above 35%. If you look at the propeller calculators from most of the propeller manufacturers, the typical figures for displacement sailboats are around 50-55% slip. Here's the figures that came from my boat, before and after:
> "Doing the calcs, the old prop showed 39% slip at 3kts and 58% slip at 5.5kts. The new prop calcs to 27% slip at 3kts and 37% slip at 6kts. Better, but not 6 times better."
>
> I know that for lightweight canal shells like yours, the numbers are radically different, but I'm a little fuzzy about what kind of regen scenarios that you would get while using your boat.
>
> Variable pitch will make a more effective hydro-generator as proven by "the amazingly expensive french hydrogenerators (more than $7000 US each) that have been discussed on this board more than once this year."
> http://www.velux5oceans.com/#/ocean-sprint-4-news/brad-hydro-power-sustainability/1902
> The variable pitch props are computer controlled to maximize the charge while minimizing drag. I get the impression that they have an algorithym that optimizes the tradeoff for different speeds. They have the advantage of sailig at much higher speeds than most of our boats and they are only looking to supply house loads.
>
> I agree that larger diameter props are more efficient in both directions (propulsion and regen), but we're all limited in the size of prop that we can pratically fit under our boats.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
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