Cavitaition?

[mark.p]

New boat,still trying to work out the kinks. Last time I took it out, (1990 20' Bayliner Capri Cuddy, 4.3 Merc, Alpha 1), power trim doesn't work yet, still troubleshooting that, we trimmed to about even with the bottom of the hull, 90 degree's from the transom, as we were at full speed occasionally the engine would rev up and the boat would slow down. I've heard the term prop blow out, what does that mean? Today we put it out and trimmed all the way down, we were skiing anyways, so we didn't need top end, still happened a few times. Engine revs up occasionally with loss of speed. Right when it happens we throttle back down, and works fine. We were out for 6 hours, I think it happened maybe 4 times. By the way for this boat I have a 21Pitch 13.5" prop, front of the bow has to be up in the air 8 -10 feet for the first 5 or 6 seconds. I want to go to maybe an 18Pitch for water sports, but what about a whale tail hydrofoil thingy? Any thoughts? I know cuddy's aren't really known for performance, but seems like it could do a little better job getting on plane.

 

[Don S]

Re: Cavitaition?

When you are trimmed to high, the rpms go up and the speed goes down. That is normal. If that happens, trim it down a little, if it's smooth water and the boat is porposing, then trim it down a little bit more till it stops. Now, you are at optimum trim.
IF you trim down and the speed drops and the rpm drops, then you are trimmed to low. Trim it up till you get best operation.
You should start with the drive trimmed all the way down or almost down to get the bow down as soon as possible, then as speed picks up, start trimming up.
Practice, Practice, Practice.
It soon becomes natural, with or without a gauge or trim limit.
If you think you still may have a prop problem, try posting your question over in the prop forum. That's what it there for.