Can someone explain how does number of propeller blades and blade angle affect performance of boat motors?
kabosu coin
Go to the top of this page and click on parts, props, tutorial. If you want an engineering evaluation, consult the www.
1. Fewer the blades higher the efficiency but higher vibration and a decrease in usable thrust...all else identical.
2. Prop thrust is the blade pushing against the water and is what pushes the boat, similar to a screw's threads pushing against the medium as it makes it's way through it. However screws usually operate in a solid whereas props don't.
3.Pushing heavy loads at slow speeds (for a given engine) means large diameter and shallow pitch...like gears of a truck transmission, in low gear engine revs a lot but speed is slow. Light loads and fast hulls make for small diameter props (engine dependent) with high pitched (usually highly variable across the surface of the blade to maximize performance at different speeds), laid back blades from the root (rake for bow lift at speed) with the tail of the blade bent in (cupping for better grip at high transom angles....which work with rake to get the hull up and out of the water.....at speed, not talking about a Sunday afternoon cruise type operation). Some really fast boats have the tail end of the prop chopped and cupped, called Cleaver props used in things like ocean racing.
4. Props are screws and they screw through the water at some angle (usually variable pitch across the blade with the blade rated for the average pitch). Since you aren't dealing with a solid there is a slip factor. Usually the factor has to do with the design of the prop and type of load its trying to push.
That's a few tidbits I picked up over the years for starters.
