cavitation problem

[georgiaboy]

I have a 16' Bass Tracker. I changed motors from a 1982 45hp Mercury to a 1987 Classic 50 Mercury. Each has the 5 adjustment holes for the motor angle. The problem is that set in the 4th hole with the 1982 and a 13 inch prop it did great but with the 1987 with a 14 inch prop it goes nuts after3500 rpm. The problem also arises that the boat takes the water better at high speed with the nose slightly elevated which the 4th hole gives me and I can't do that with the Classic 50. I am presently hunting for a tilt and trim unit. Any ideas about all this?

 

[steelespike]

Re: cavitation problem

As I understand it your problem is technically ventilation not cavitation.
If it runs normally in hole three then it is the right lower unit length.
Where is the anti vent plate in relation with the bottom of the boat?
Normal starting position is even with the bottom.
Does the motor have a series of holes to raise and lower the motor vertically?
Another possibility is your prop.If dinged up or a less efficient design it may ventilate easily.

 

[Texasmark]

Re: cavitation problem

Define "goes nuts".