Propeller nerds(experts).

[JOHNBOY]

Propeller nerds, sory experts. After 40 years of poor performance, prop wash vibrations and burnt tips, I've decided to make more space around the prop. She's a heavily built 10 ton long keel fast cruiser with the engine performance of a slug! The 16inch cut out will soon be 20. I can't make enough room for a folding P. Can,t afford a feathering. So! Fixed 2 or 3. What do you think? Drag V performance. Who wins?

 

[Twister_Ken]

Neither nerd nor ex-spurt I'm afraid, but if its a long keel and a rudder aperture, I'd say the waterflow is sufficiently disturbed around the back-end that a 3 blader isn't going to up drag by 50% compared to a 2, whereas it will contribute mightily to thrust when motoring.

 

[PaulJ]

I am told that a two bladed prop running in an aperture vibrates as it goes into and out of the "shadow" of the keel because both blades become "shaded" and exposed at the same time. This doesn't happen with a three bladed prop and therefore it runs more smoothly.

 

[JOHNBOY]

Cheers guy's I agree new 3 blade coming up .

ps Only 2 replies......pfffffff.