Thread:

Wierd issue at full throttle only. Cavatating the prop? or just wrong pitch

I recently installed a nicely built 350 chevy into my 1984 Bayliner 18ft boat with a Volvo Penta 280 outdrive and i ran into a wierd problem. Boat pulls great up to 4000rpm, as soon as i open the secondaries and go full throttle it revs instantly to the rev limiter (5800) and the boat slows down. Next i tried to roll slowly into the throttle and it did the same thing, seems as if the prop just spins in the water without pushing the boat anytime i go full throttle. If i hold it at 4000rpm the problem is not there, already going 45mph at 4000rpm, and if i roll into the throttle it still does it. Seems like the boat looses speed and it comes off plane and the rear sinks down when this happens.

Am i cavatating the prop? wrong pitch? I'm lost and i'm so new to boats i have absolutely no idea where to start. Boat hauls ass, is very snappy, and runs great, all the way up to the point i go full throttle. Engine will make a HONEST 375 to 400 hp. Am i overpowering the outdrive? Or is this more of a propeller issue? If it is a prop issue how do i pick the correct one?


Any help would be very much appreciated!

I have been told by many people not to go full throttle at less than 15/20mph so i have never tried to do that. I was also told by a friend i might of spun the hub in the prop, or maybe a clutch tower problem? How can i diagnose the problem so i can pinpoint it and fix it?

Originally Posted by Dominic

I have been told by many people not to go full throttle at less than 15/20mph so i have never tried to do that. I was also told by a friend i might of spun the hub in the prop, or maybe a clutch tower problem? How can i diagnose the problem so i can pinpoint it and fix it?

Borrow a prop.

Originally Posted by "Flat" foot'n

X2
3 blade aluminum is pretty weak with that power. Probably need a 3-4 blade stainless 24 pitch.

would try a prop the clutch will hold at high rpms it would be more of a problem at low speed pull the prop you can see if it was slipping there will be grooves where it rides on the thrust washers

Thank's for all the info!! I will pull the prop and check the hub and washers. I was also concerned about the clutch tower, but it does not feel like the clutches are slipping and like i said it never gets power put to it untill im already moving a decent speed. What's the difference between stainless and aluminum props? and what's the difference between 3 and 4 blades?

OK, found a huge problem,

The hub in the prop is slipping, and it's all torn up. Time to buy a new prop and hub. What would you all reccomend? Stainless? Aluminum?