Propeller help needed

[timothylee]

I have a 1985 SeaSwirl, Sierra, bowrider, 3.8 V-6, the propeller that came on the boat when I got it is 15" pitch, I can't run full throttle because the RPM is way into the red at around 5600, the owners manual says full throttle the RPM should be 4200 to 4600. Props are expensive to play around with and I'm not real sure what I should try, I have read that a 2" pitch increase will drop the RPM 300 to 400 RPM so I'm thinking I should try 21" or 22". Does this sound reasonable?

 

[SeaDooSam]

This sounds like a reasonable bet. You definitely want to go up in pitch. Is there a prop shop near you that may have some expertise or let you try a few out?

 

[alldodge]

Agree, try the 21. If you can find a local prop repair place many allow testing. You buy the prop and can exchange until you find the right one

 

[jimmbo]

Do you know what gear ratio you have? It should be on the outdrive near the upper gears

 

[timothylee]

None of this I understand but the book says this
Gear Ratio Overall 1.77:1
Upper 21:20
Lower 14:26

 

[jimmbo]

Based on the gearing and what I assume is a 17 - 18 ft boat, a prop in the 21 - 23 range would be the right one to allow the engine to run in the proper rpm range.
OMC stringer drive?

 

[timothylee]

Nailed it Jimmbo! 18' boat with OMC stringer drive.