[Jeff Barnett]

Hi folks,
Took the boat out yesterday and noticed top speed seemed down, boat would only rev to about 4200 rpm, at about 40 mph. it would get on plane, and as I would trim it out I would feel it get faster and smoother, then at a certain point if I kept trimming up, I would hear and sort of feel a mechanical growling vibration, if I would lower the drive a bit it would go away, raise it back, noise comes back. last time I took the boat out, I got a rope caught in the props, did not seem like a big deal at the time, it stalled the engine, I just had to unwrap it. now I'm wondering if this caused some damage to the outdrive gimbal bearing thing..
Help

[ShabahZ280]

I believe what you're feeling when you trim it up too much is what's called "Cavitation". It's when too much air is getting in with the prop. If it goes away when you drop the drive back down, that's most likely what it is. I have the same thing when I'm trimmed up too high. I don't think your rope incident is what's causing it.

Here's an article on wikipedia. Cavitation

[boatman]

I concur with Chris. If I trim up too much I get alot of vibration and noise once I draw in some air. I rapped a rope around my wave runner impeller once, but after I cut it free everything ran OK. Not sure about you only getting 4200 RPM's.

[Z275]

Jeff, what you may want to check is the rake angle of each blade on your prop. Make sure the rope didn't bend one of the blades in or out. That could explain some vibration and a noticable loss of performance.

[moondance100]

Jeff, my last boat had the same symptoms and it turned out to be a gimbal bearing....not a huge deal...about $400 on an alpha 1...I'm sure a B3 would be a touch more...

[Jeff Barnett]

I think I may have figured out the lack of top speed.. Perhaps it's because it's the first time I took the boat out with the Bimini Top on, and it was up, I was impressed that it did not fly off, however now I am thinking, that thing is like a sail, it had to cause at least 15mph top speed loss, don't you think?.

[moondance100]

hmmm....I kinda doubt it would be that much...but I sure could be wrong.....I guess take the bimini down and we'll see! I hope you are right, keep us posted!