Changing prop, wondering results

[EJ3]

I have a 60hp Merc, 2-stroke, on a 15' CC. Currently I have a Michigan aluminum prop, 10.5x13. I have found a Rapture SS prop, 13.25x15, that I am considering buying. They are both from the same manufacturer. I am wondering what the difference in diameter, pitch and material will do to my rpm's. Currently at WOT I am at 5400 of the recomended 5500 rpm's.

Just as a note, I am playing with the height of the motor right now as well. The previous owner had it up way too high. They were using the lowest hole. I currently have it in the middle and intend to lower it all the way (5 holes total to choose from.) The boat gets on a plane but leans, and the lean gets better with every hole down I go. Lowing the motor has also raised the rear end of the boat out of the water more when underway. I mention this as I think the boat is pushing the water a little more than it will be once I lower the motor down more, decreasing resitance against the hull. But again this is just my guess!

But back to the original topic, what will this prop probably do for me?

 

[steelespike]

Re: Changing prop, wondering results

The 15 will lower your rpm too much, About 400 rpm.
Generally ,assuming your not having venting problems, lowering the motor will reduce speed.Most that fine tune their setup run right at the edge of the ventilation point.If your having trouble with leaning you may have a hull problem check that the bottom is not deformed perhaps a hollow near the transom called a hook.You may need to trim up more.Sometimes leaning could be caused by a motor that is too deep in the water.
Sometimes leaning is caused by prop torque.Leaning to port.Does it lean through most of the speed range or just as it planes and reaches speed?

 

[EJ3]

Re: Changing prop, wondering results

It will lean to the right, starboard I think is the right term.

 

[steelespike]

Re: Changing prop, wondering results

Leaning to the right,starboard, is abnormal.If a boat leans it is usually to port from the prop torque.Thus the normal driving position on the starboard side.
A center console is the exception.Does the boat float level at rest?
Is the bow difficult to get up at wide open throttle?At speed the front 2/3 to
a half of the boat should be out of the water.