prop diameter question

[superwooter]

here's a link to the props i'm looking at for my 1978 merc 70 hp on a 16' trihull from 1979...

http://boatpropellers.iboats.com/Me...andard&**********=954848833&*******=119113279

i'm considering the top two on the list. from what i've read, the diameter doesn't really matter unless you have a clearance issue (prop too big and hits the fin when it tries to spin). other than this, is there anything else i should consider regarding diameter? i'm sure this has been asked in the past but i couldn't find it on the first couple pages of a search of the forum for the word "diameter".
thanks,

superwooter

 

[jdub2]

Re: prop diameter question

I'd do an internet search regarding the effect of prop diameter. In my opinion, I would think a prop of the same pitch, but larger diameter would make a difference, since it would be "moving" a larger volume of water. If you're talking 1/4", maybe not so much, but an inch larger or smaller diameter would make me wonder.

 

[superwooter]

Re: prop diameter question

everything i've read says that the diameter would only be an issue if it is too large to clear the fin on the lower unit. i just installed my new prop which is approximately half an inch larger in diameter than my old prop and i have no issues.

 

[usskydvr]

Re: prop diameter question

As long as it fits, don't worry. The prop manufacturers take a lot of things into consideration when designing their props. Pitch, (which may be variable across the blade or fixed), rake, cup, bow lifting, stern lifting, etc to get the best design for the specific application. They determine the diameter for the design.