Boats don’t normally operate well at wide open throttle. You only do so for testing.

If this Captain was the one who ordinarily operated this boat, I’d be a little weary. No one would quickly throw the motor in WOT. That would be huge back pressure. However, it should operate normally and the engine should make its max rated rpm, at WOT. That’s why you run that test occasionally, but you would test every couple hundred rpm along the way too.

It seems there must have been a transmission problem, if they rebuilt it. Get the exact invoice/details of what that means. Was it all clutch plates, thrust bearings, etc, or just a repair. Needing a new aquadrive is very unusual, but they are a very nice set up.

Do maintenance records suggest good care?

 

Prop may need to be re-pitched. I'd consult with PYI. Engine should be able to reach max design RPM at WOT.

Was this a brand new Aqua drive install, or a new replacement. Was shaft length adjusted, new soft engine mounts etc. installed.

Trans rebuild would need details. Rebuilding the trans without replacing the clutch plate etc. never makes sense to me

 

Thanks so much for your insights
The broker was driving at the time.
The transmission had a full rebuild including damper plate and clutch plates.
The aquadrive was a new replacement. Shaft length was not adjusted and engine mounts were not changed. I guess I’m not suprised by the vibration at WOT but only that it seems so odd that there is something that is still causing the slipping.
The PO is unwilling to continue on what could be a wild goose chase, which to be fair I would be too. I’m just trying to get more clarity on whether this is a red flag. Hoping to hear back from PYI. Cheers

 

Is your surveyor saying it’s slipping? Does rpm change? Sounds like an agreed upon symptom caused the current owner to have a rebuild, for which the symptom didn’t go away.

 

Would there be extra bubbles seen at the surface if the prop were ventilating or cavitating? It seems to me there would be. Maybe a GoPro on a stick would be able to show what is going on.

 

This is beyond me, and interesting. Tkx.

 

If a prop is turning, at speed faster than that which can be converted to forward speed, it will cause cavitation.

 

There are only a few possibilities. Drive train slipping, or prop cavitating. The drive train seems to have been given proper attention, so probably the prop. If its the prop it could be dirty. Barnacles and such destroying the flow at speed. But the more likely answer is it simply has a bit too much pitch. It can take a bit of trial and error to get the pitch correct. Someone in the past may have said "good enough".

 

If it was normal cavitation at excessive throttle, why would the seller have agreed to rebuild the transmission. Seems like there is more to what’s going on.

 

Probably because he doesn't know what the problem is. The rebuild didn't fix it, and it was the most expensive option he could have chosen. But what do I know? We are all just arm chair qtr backing.