87 ICBM 29' prop blow out
 

I need help ! My 1987 29' ICBM with TRS drives with hydromotive nose cones continues to cavitate under acceleration. I have to ease into it very gradually, and it sometimes still does it at 4000 rpm. Presently running 4 blade bravo 1's, 24 pitch, have tried 26 but still does the same thing. I turn the 24's at 5150 rpm, when I can get there without blowing them out ! Has anyone else ever run into this ? Do I need to go back to 3 blades ? Nothing crazy on the power, approx. 425 hp, 454's. Any advice would be greatly appreciated.

TJR

hi todd did it do it befor the nose cones ..?????? my thinking is the nose cones might be causeing disterbed water to the props . if the 4 b are blowing out 3 b will be worse . robbie

Can't answer that as the nose cones were on it when I bought it and I have no way of contacting the original owner.

TJR

You might have a very high X dimension, set up for max speed only.

There are spacers that can lower the propshaft.

But better props are probably the answer. Find a dealer who will let you try lots of possibilities. More blades, not less, are usually the answer.

Be sure there are not problems upstream of the prop: no nicks in the outdrive, the cones are straight, no problems with the bottom of the boat. Clean water makes a difference. But that probably isn't your problem.

Todd,

I have had two ICBM's with TRS drives and Hydromotive nose cones, and haven't had any problems. My first one was a 1987 40' (12M) with 420's and I ran 3 blade mirages. My current one is a 1988 33' (10M) with over 600 hp and 4 blade hydromotives. The 33' jumps onto plane very easy even with the hydromotives. I know some people that have cavatation issues need to install diffuser rings on the back on the prop. I believe the Bravo 1's already have them installed.
The first thing I would do is make sure is that both your drives are all the way down, and together when taking off.
The second thing is make sure your transmissions are not slipping. That could be causing your problem also.

Hope this helps,

Good luck