prop

[searover]

Hi, guys anyone know the calc to obtain correct prop, going from a 3 blade to a 4 blade. as have a 5.6 boat with a 115 4 stroke max 6000 revs, at the moment i have a 14x21 3 blade. and i want to get the revs down as i can rev over max with this prop cheers guys...

[Razorbill RIBs]

Originally Posted by searover

Hi, guys anyone know the calc to obtain correct prop, going from a 3 blade to a 4 blade. as have a 5.6 boat with a 115 4 stroke max 6000 revs, at the moment i have a 14x21 3 blade. and i want to get the revs down as i can rev over max with this prop cheers guys...

Poss not the answer you are looking for, but on recommendation from here i spoke to the very helpful lady at 'Steel Developments' for advice (do a search on here)....who came up trumps!

Dan

[martini]

It's all guesswork really but if you're going from a 3 to a 4 blade then sticking with 21" should bring your revs down by 200-300. The increase in surface area usually has a similar effect to increasing the pitch by 2".