Folding prop/ generating electricity?

[onavegador]

Hi all,

Instead of experimenting with the folding prop or bying a expensive feathering prop I would invest in a towing generator. Wher are some models available what can be mounted direct on the hull, but I do not speak about the very, very expensive wattandsea but of a model for about 1400 USD, so less expensive than a feathering prop but also a little (yes a little) less effective than the wattandsea.
Good luck
James

[sengland]

Originally Posted by Bmorgan562

Can you have the best of both “worlds”? I was just thinking about how you could benefit from a folding prop to reduce drag but also generate electricity? Seems to me it’s one or the other?

Hydro generators are the only way to go.
https://www.sailmagazine.com/diy/kno...dro-generators

[Cadence]

Originally Posted by Bmorgan562

Can you have the best of both “worlds”? I was just thinking about how you could benefit from a folding prop to reduce drag but also generate electricity? Seems to me it’s one or the other?

It is folly!

[jmschmidt]

You just can fool physics. Or, there is no free lunch. Every watt, BTU, F/P of torque or whatever standard of energy production you choose to call it that that a spinning prop extracts from the water or air is extracting the exact same amount of energy from your sails while underway. Wind generators only provide non-deductive power when you are at anchor, your generator is aligned with the wind and it is blowing at a velocity above the minimum that your wind generator needs to produce. Using a wind generator under sail or power only creates drag on your sails or engine.

[Jim Cate]

Originally Posted by jmschmidt

You just can fool physics. Or, there is no free lunch. Every watt, BTU, F/P of torque or whatever standard of energy production you choose to call it that that a spinning prop extracts from the water or air is extracting the exact same amount of energy from your sails while underway. Wind generators only provide non-deductive power when you are at anchor, your generator is aligned with the wind and it is blowing at a velocity above the minimum that your wind generator needs to produce. Using a wind generator under sail or power only creates drag on your sails or engine.

A wind generator does not detract from boat speed when sailing downwind. In that case, it's drag vector is forward.

There is no such situation for hydro generators... they always detract from boat speed. The amount varies depending on point of sail, how near hull speed one is sailing and the design of the generator.

IME, wind generators don't add much to the equation when sailing downwind in normal cruising conditions, for the apparent wind is too low. Hydro generators shine in that situation, supplying power 24/7 at a small cost in speed.

I miss the towed generator I had on our previous yacht.

Jim

[Mike Banks]

I think there is a special prop for those systems, it alters the pitch from drive to regenerate automatically--but it has to be one or the other.

[Madehn]

all of this to generate power for the 10% of the time the boat is on passage and sailing -most are on passage for less than that 10%- for the added complexity just not worth it. cheaper to add a wind generator that works 24/7 WHEN there is wind-- better yet wind and solar combo-- the spinning prop thing always comes up but reality tends to kick the idea to the curb jmho-- your results may vary and opinions are free

[Jim Cate]

Don’t know if you ever saw the one we had on “Sundowner”...

sure did, Sandy! I remember the short wire leader and the set of foils that kept it down. IIRC when we saw it the track record was pretty short, so I'm glad to hear that it worked out well for you.

We're not doing many long passages these days, but if that were to change I'd be thinking about a new version... and the short wire "tow rope" would be a leading idea! If nothing else it would eliminate the Gordian knots that sometimes erupted in our ~50 foot 1/2 " double braid tow line and hopefully avoid the acrobatic leaps that our prop and shaft would describe when the speed exceeded ~7 kts.

Good memories of good times, mate!

Jim

[nuku34]

Hi Jim and Ann,
Re towing genny: Correction, the tow rope was not wire, it was a super stiff braided synthetic 10mm diameter rope that I found in a place that made commercial fishing gear, nets, trawels, etc. here in Nelson.

I put a lot of miles on that unit and it performed flawlessly. I did lose the prop/hydrofoil assembly coming down the OZ coast on the way to Tassie. The rope to shaft connection failed due to lack of maintenance on my part. Crafted a new unit in Eden while waiting out the super bad weather that trashed the Sydney-Hobart fleet that year, 1998?

The basic idea of that whole unit came from Volker, Rondi’s German partner before me who died in a home-made gyro-copter crash in 1987. He was a brilliant innovator and I just refined his ideas. He also came up with the idea of putting the long narrow solar panels between the masts and cap shrouds on Sundowner.
Cheers,
Sandy