Engine mounted too high?

[BirdChaser]

I just installed a CMC PT-130 power lift unit beteen my 16ft alum bass boat & the Merc 25. The engine is now elevated a bit (intentionally). The cavitation plate is about 2 inches abouve the bottom of the transom. This is within recommended height per CMC. <br /><br />The engine is making a howling sound (from the prop) while on plane. Water pressure seems good and RPMs are within range as long as I don't go to WOT. I plan on adding some prop pitch and cup to bring the RPMs back down at WOT, but what about the loud engine noise? It's obviusly not getting enough water to the prop. Will this hurt anything as long as the water pressure is good & RPMs stay at or below 5500?

 

[Kenny Bush]

Re: Engine mounted too high?

Birdchaser, It sounds like you are slightly to high on the motor. Most I have seen are about 2" or more from the Keel to the cavitation plate. When your running on plane, your cavitation plate should be right on top of the plane of water. If not your prop will make an air pocket whirlpool affect. You must find a balance of running the motor as shallow as possible without creating a cavitation condition. Hopefully others on the board will offer help. Especially those Bay guys with scooters and jackplates.

 

[BirdChaser]

Re: Engine mounted too high?

Thanks for the input. I would still like a bit more feedback on any damage this might cause to the motor. I'm sure there's a bunch of guys out there with this experience using jackplates.

 

[Mufasa]

Re: Engine mounted too high?

So long as the water pressure holds you will not hurt the motor. I suspect you also have noticed a change in propeller torque steer. More prop pitch with extra cupping should help it sounds like the propeller is just about to break loose and ventalate. How much water pressure do you have at that hieght at WOT?

 

[BirdChaser]

Re: Engine mounted too high?

Water pressure stays pretty steady at 13 to 15psi.

 

[FlyBoyMark]

Re: Engine mounted too high?

If your looking for more performance speed wise, the sound is normal. What you do need to do is start running a cupped prop if your going to run the top part of the prop actually out of the water at speed. You CAN run the top of the prop out of the water, you jus' gotta have a cupped prop. Part of the sound you hear is the exhaust because its so near the surface now.