prop size

[B_C_Rosehill]

I have a 90 hp Mercury motor. The standard aluminum prop is 12.75x21. I bought a new stainless prop that is 13.25x21. Will my engine pull this prop. It turns about 5500 rpm's with the aluminum prop.If it will only drops a couple hundred rpm's I wouldn't mind.

[adam7456]

Switching to a stainless steel prop of same diameter would have the same effect on the RMS as going up in pitch by. That means the RPMs will be reduced by 150 to 200 RMPs. Increasing the diameter will also reduce the RPMs but I'm not sure how by how much. What is the max RPMs for your motor?

[B_C_Rosehill]

It is rated for 5500 rpm's. Would raising the motor one hole help any?

[adam7456]

There are several more factors that will come into play. Do you have adjustable tilt and trim so you can trim the motor while running? What type of load are you carrying? Just yourself or a couple of people with full fishing gear? How heavy is the boat itself?

Just for a reference, I have a 1998 90hp Force motor, which was built by Mercury, on my 19.5ft fish and ski with the boat weighing at just over 2,000lbs. I have a 12.5 x 23 pitch prop which if I'm on the boat by myself with no gear is still just a little more prop than the boat can handle. Loading up a friend and all our fishing equipment that was way too much prop. My max RPMs are 5200 but with the 23 pitch prop the boat is lugging and gets 4800 to 4900 RPMs.

If your boat is smaller and lighter you might be able get away with using that prop. But if you plan on hauling a lot of people or gear with it I think you will have problems getting up on plane even if you have adjustable tilt and trim.

[TEE]

NOT TRUE! I did the same thing and all the prop "gurus" told me I'd need to move down to a 19...wrong. I went with a 13x21 Quicksilver and couldn't be happier. 5400 RPM's @WOT and 43 with two people:)

[B_C_Rosehill]

my boat is an aluminum PT 185 Tracker. motor is 2004 model