Sharrow prop on a trolling motor?

[Neil McCauley]

I'm surprised MinnKota or another company hasn't experimented with this yet. The steel/aluminum props for gas motors are incredibly expensive because they're custom machined based on the engine/transmission, but a plastic prop for a trolling motor with known thrust numbers seems like it would be very easy to make. Anyone heard of this being done?



Toroidal propeller - Wikipedia

 

[Susky River Rat]

It wouldn’t be weedles and one hard hit I’d say it’s done. If you go with metal that’s to expensive for the beating those TM takes.

[Bankc]

I've seen people make 3D printed ones.  But again, it's the same problem.  Sure the thrust and motor is the same, but the weight and drag will be different.  So, they won't provide much benefit without a custom fit.  From what I've seen the numbers a pretty much the same as a similar size and pitch normal 3 blade prop. 

Also, trolling motors usually don't need maximum speed or maximum efficiency.  The way most people use them, they're constantly speeding up and slowing down and changing direction.  So any benefits aren't huge.  Weedlessness is pretty important, however, and I don't know how well these would perform in weeds. 

 

Plus, I believe the design is patented.  So I doubt any other company could make them for trolling motors without a license. 

 

And for applications like a kayak, where trolling motor speed actually is important, you'll do better with a RC plane prop, because it's thinner and only has two blades, so it has a lot less drag.  You'll lose torque, but you don't need torque with a lightweight kayak.  Or better yet, go with a motor that was actually designed for speed (like a Torqeedo), as most trolling motors are actually designed to move slowly on purpose. 

 

Props are one of those things where there isn't a once size fits all scenario.  It's all a balance of give and take.  You add one thing, and you have to take away from something else.  The only advantage of the Sharrow prop over a normal 3 blade prop is it reduces tip vorticies, because the tip folds back into the prop.  Now if you're pushing a system to it's extreme and are near the limits on every other aspect of your system, then something like tip vorticies can be a big deal.  But if you're no where near the limitations of your entire system now, then something like a Sharrow prop would be a big waste of money on such a tiny fraction of gain. 

 

[airshot]

They are designed for speed, not much to gain at trolling motor speed. Actually low speed efficiency is altogether different from high speed efficiency as far as a prop goes.