Twin Johnson 150's 1995 prop size

[Agil]

I have a 1995 Wellcraft 23.8 open fisherman that I just bought. It has twin 1995 Johnson 150's 1995.

I want to know what would be the prop or pitch that I would need.

I am getting 4,100 rpm on these props at WOT. I know I should be at 5,500 to 6,000.

Can someone help me.

Thanks.

 

[HighTrim]

Re: Twin Johnson 150's 1995 prop size

The best propeller size for your boat and engine combination is based on the recommended operating range at WOT for your engine, which you will find in your operator's manual. This will be expressed in terms of a certain horsepower at a certain RPM.

The goal in prop selection is to determine what propeller style and size will maximize performance for your boat, while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum RPM where maximum horsepower is produced.

If your test results in your being able to ynder-rev the engine, you need to decrease the pitch of the propeller. Decreasing the pitch increment by 1" will result in approximately a 200 RPM gain.

Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM.

I think we may go for a ride though to the prop forum.

 

[walleyehed]

Re: Twin Johnson 150's 1995 prop size

Can you list what props you are running now??
This is one case where 200rpm per inch goes out the window because you are WELL below specs.

 

[jay_merrill]

Re: Twin Johnson 150's 1995 prop size

That value for WOT rpm seems odd to me for a 24 foot boat with 300 available horsepower. Has the boat been sitting in the water for some time? Any chance that the bottom is fouled with marine growth? Also, do you know that the rpm readings are accurate? Finally, what is the WOT speed of the boat as it is now?