yamaha 150 drive slipping

[dougtrellis]

I wonder if anyone can assist me. I have a Roballo 2320 Sports boat with two ageing 150 Yamahas which have been rebuilt and serviced a few times. The engines are working fine but I have a problem under power as follows.

Taking both engines to 3000 rpm no problem
Starboard engine seems to free rev to 6000
As boat "planes" to horizontal revs on starboard emgines slowly come back to match port engine.

This seems to indicate some sort of drive slippage which goes when the boat load decreases, however I get no slippage or overrevving when driving the boat with the starboard engine alone.

[boats.net]

Check the props, scratch a line across the hub of prop and the thrust washer then run boat if the line is misaligned after running then the prop is slipping on hub and the prop needs to be rehubbed. Has anything been changed or added to boat hull in front of outboard that could cause cavitation, like a transducer or a sea****?

[dougtrellis]

Nothing has been added and bottom of the boat is clear of anything that may cause cavitation.

I think it is the prop hub fortunately here in Qatar
I have recently found someone who can do this.

Cheeers for the useful advice will check it out.