Re: [electricboats] Elco vs ePropulsion

Any suggested size pitch for a 24v ?

 Thx 

On Wednesday, November 2, 2022, 07:29:34 AM PDT, cpcanoesailor via groups.io <cpcanoesailor=yahoo.ca@groups.io> wrote:

Has anybody tried or know how to pick a model airplane prop for electric outboard?

I first did some boat speed and electrical power measurements using the stock prop that came with the motor, to get a performance baseline.

I read an article that said prop efficiency increases with diameter, so I determined how large a prop could I reasonably use with my motor, based on submerged depth, length of the skeg, etc.

I also estimated the pitch of the stock prop. Then I translated that pitch value to the larger prop size to get the pitch number for a similar speed performance (but now more efficient).

That gave me an idea of which pitch numbers to look for in the larger sized airplane props. In my case, I thought I wanted about twice the pitch of the stock prop, since the motor was hitting its RPM limit but drawing only half the rated current.

That actually worked out well for me - the motor with the larger, higher pitched prop now draws rated current at max RPM. And power measurements indicate that for a given speed, the new prop takes noticeably less electrical power than the stock prop did.

One downside to slim airplane props is they slip a lot more than standard marine props. This is only a problem if you're pushing your boat into a strong wind, or trying to tow a heavy load with lots of drag. For me, on a sailboat, it's not a serious issue. But I do keep the stock prop and a wrench in the bilge...