1999 18 ft Searay Outboard - Wrong Prop

[bmac1482]

I have bought a 1999 18 foot Searay with a Mercury 125 outboard, a standard configuration put together by Searay. Searay calls for a 48-77348 prop (12.75x21). The 1999 Mercury 125 outboard, model #1125412WD specs out WOT of 4750 to 5250 RPM. Currently the stats are, maximum RPM is 6000, 40 mph. At 5250 RPM, 35 mph. The weight of the boat, ready to go is about 2900 lbs.<br />The question is, what prop should I be using. I believe that I need to be using a larger diameter and maybe a little less pitch, but I can't find anything on the effect of the diameter on the RPM. The boat is used for a lot of water skiing, so deep water starts with 200 lbs guys is normal. Any suggestions would be appreciated. I am also amazed that Searay would spec that prop for this boat/motor combination, with the resulting high RPM's. Thanks for the help.

 

[JB]

Re: 1999 18 ft Searay Outboard - Wrong Prop

Howdy, SeaRay.<br /><br />I agree that you are underpropped and should be using a 23" prop.<br /><br />I guess they specified the prop for hole shot and skiing.<br /><br />Good luck.

 

[bmac1482]

Re: 1999 18 ft Searay Outboard - Wrong Prop

Going to a 23" pitch is only going to reduce the RPM's 200 to 300. I think I need to go to a 13.5 inch diameter prop, but I don't know what effect that will have on the RPM's. If you leave the pitch and just up the diameter on an engine, what impact does it have on the RPM's?

 

[bmac1482]

Re: 1999 18 ft Searay Outboard - Wrong Prop

Does anyone know if you leave the pitch and just up the diameter on an outboard engine prop, what impact does it have on the RPM's?