>I agree!! There seems to be a dearth of logic. also boat shape, hull
>speed, and whether the prop is out in the open or tucked behind a
>deadwood affects prop selection. A faq or wiki would be helpful.
Hi,
I read recently that the boat/ship prop shape (remember they were the
very first propellers) was derived from a post hole auger. It wasn't
working well... until it broke off near the base. That became the
basis for the shape of future marine propellers. So much for science,
engineering, and efficiency modelling!
I've come across a 3 blade, 12" prop from a scuba propulsion unit
that has what my instinct says is a nearly "optimized" shape. It
looks more like a windplant propeller. It's thick near the hub and
gradually thinner out to the tips, also with (naturally) gradually
flattening pitch towards the tips. The cross section is like an
airplane wing. And a thin airplane wing like near the tips has
maximum lift to drag ratio, like a glider wing.
Unfortunately it's plastic, and the hub wouldn't fit an outboard
anyway. I'm going to cast the blades in zinc-aluminum, with a new
'more typical' hub... for the outboard with the U-joints 90 degree
bend at the foot, that I haven't got around to making yet. I'll cast
it first since it should be a relatively short term project.
(notwithstanding that I've never cast any metal before except an
ingot of aluminum into a muffin tim a couple of days ago.) Then I'll
try to find an outboard to compare it to a 'regular' prop.
Cheers,
Craig
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