96 Force rpm spike on turns

[1973Chieftain]

I just got my boat in the water last week, and noticed that if I made a very hard turn at WOT the engine would spike 500-600 rpms along with the corresponding off sound. Currently the cavitaion plate is 2" above the keel. I was thinking perhaps the prop was coming out of the water but when I had someone else drove and I hung off the back it looked like the prop was still in the water. Any ideas? Is it mounted too high? I tried tilting it down all the way and had no problems. Thanks for the opinions!!

 

[Frank Acampora]

Re: 96 Force rpm spike on turns

You are experiencing ventilation. It is typical for engines mounted high on the transom for performance to have this happen in turns. Because of the engine height and the angle of the engine and boat during a sharp turn, at high speeds the prop will suck in surface air.

Typically, with a set-up like this, you trim all the way in during sharp turns and trim back out for best performance after the turn is finished. If it is severely objectionable, you can try lowering the engine in one hole increments until it is to your liking. However, you will be trading-off some top speed.

 

[1973Chieftain]

Re: 96 Force rpm spike on turns

Thanks Frank! I really appreciate the response! I build a new transom for the boat and converted it to a long shaft... looks like I must have build the transom slightly too tall! Ill play around with the trim a bit then perhaps cut the transom down a bit.

 

[riptorn]

Re: 96 Force rpm spike on turns

I don't see a problem, you just had it trimmed too high or you have too much weight in the front.
What boat are you referring to?

 

[1973Chieftain]

Re: 96 Force rpm spike on turns

I don't see a problem, you just had it trimmed too high or you have too much weight in the front.
What boat are you referring to?

Its a1965 Starcraft 15' aluminum runabout. It could have been tilted a bit high, I adjusted it so I could top out.... ill try it lower next time I take her out.