Engine slips at full throttle

[mtiernan]

I have a 15 hp Mariner outboard on a 10 ft tru-line sports cat. The boat is rated for up to 15 hp and 700lbs. It is a center console boat with a tri-hull. I am 220lbs. When I first go at full throttle the engine seems to slip occationally for approx 1 minute. Not sure what this slipping is but does not sound good? Eventually the boat reaches plane and the boat goes at approx 20 mph if no head wind or waves, add any rough stuff and the boat seems to never get back to plane. Also when my wife joins me (approx 150lbs) the boat never reaches plane. I have added fins and this seems to help when I am alone but with a little more weight it never reaches plane. The outboard is a long shaft 23" and the center measurement on transom to keel is 18". The fin on cavitation plate is approx 3 inches below keel. Also my water intake is on the underside the cavitation plate.

Would raising it up 2-3 inches help? I am thinking about buying a mini jack plate.

 

[sschefer]

Re: Engine slips at full throttle

I have a 15 hp Mariner outboard on a 10 ft tru-line sports cat. The boat is rated for up to 15 hp and 700lbs. It is a center console boat with a tri-hull. I am 220lbs. When I first go at full throttle the engine seems to slip occationally for approx 1 minute. Not sure what this slipping is but does not sound good? Eventually the boat reaches plane and the boat goes at approx 20 mph if no head wind or waves, add any rough stuff and the boat seems to never get back to plane. Also when my wife joins me (approx 150lbs) the boat never reaches plane. I have added fins and this seems to help when I am alone but with a little more weight it never reaches plane. The outboard is a long shaft 23" and the center measurement on transom to keel is 18". The fin on cavitation plate is approx 3 inches below keel. Also my water intake is on the underside the cavitation plate.

Would raising it up 2-3 inches help? I am thinking about buying a mini jack plate.

The underside of the cavitation plate on the motor should be even with the bottom of the keel. You can set this up with a straight board. I think you may actually have a 20" motor. The 25's are rare and usually setup for sailboats. If its a clamp on motor you can just make an extension to raise the motor. A jack plate would cost you nearly as much as converting the engine to a 15" shaft or 20" if it really is a 25. But, yes, it could be a solution to your problem.

 

[mtiernan]

Re: Engine slips at full throttle

Thanks for the quick reply. TRhe jack plate costs $90. IS that the same as converting the long shaft to the short shaft?

 

[sschefer]

Re: Engine slips at full throttle

Thanks for the quick reply. TRhe jack plate costs $90. IS that the same as converting the long shaft to the short shaft?

No, that's much less. Go with the JackPlate you found it should do the trick.