Boat props

[SteveT]

I have a dilemma I have a 1976 Sea Ray 20 foot I/O 888 Mercruiser 302 Ford and I am trying to figure out the right prop I want to get back to full throttle rpm of 4200 and boat speed of 41 mph I currently run a 15 1/2 x 18 prop what do I need to do ?

 

[NorCal Boater]

The first thing you should do is find a reputable, experienced prop shop in your area. They should be able to help. You don't say what the current WOT rpms and speed are but from what you are asking it looks to me like you may be "over-propped. In other words, your prop may have too much pitch and possibly the diameter is a bit too large. However, I am not familiar with the gear ratio of that engine/outdrive package. Also prop pitch is usually in odd number i.e. 15", 17" 19" but not always.

Look for a place in your area that sells and repairs props and they will be your best bet to get on the right track.
Shawn

 

[Lazy Daze]

Definitely need more information to be helpful. BUT... are you saying that you have personally run that boat and achieved 4,200RPM and 41mph? What has been done to the boat since then and what prop were you using at that time? Their website has been flaky, lately, but there is a Prop Matrix on SR's website that lists original prop size and gear ratios - that would be a good starting point. You could also contact SR to ask them. Shawn's recommendation is a good one, as well.