Prop Question

[fishfool]

I have a Johnson v6 150hp sea pro with a 15 1/2 15 prop. Im pushing a 21'WA with a boat and motor weight of 2,891 lbs. It holds 113 gal of gas (i dont know the weight of the gas ). It's full throttle operating range is 4500 to 5500 . Now here is where i need help,when im running with a half a tank of fuel i can hit 5000 rpm's easy with a speed of about 40 mph,now with a full tank i have trouble getting to 5000 rpm's with a drop in speed,about 35mph using a gps......what prop should i try to gain back some speed and more ease of reaching 5000 rpms... thanks

 

[ob]

Re: Prop Question

First thing I would do is make sure that you have the engine mounted at its optimal height on transom.You can begin by noting where the anti-ventilation plate is in relation to the hull when trimmed level.You'd like to have it as high as possible without experiencing excessive ventilation on plane at around 2/3 throttle on plane, while executing tight turns.Too low will cause excessive exhaust back pressure and drag.Too high will cause prop ventilation and waterpump cavitation.There's a sweet spot.<br /><br />Dhadley is the resident pro at engine setups .He should be around shortly.

 

[Bass Runner]

Re: Prop Question

See if someone has a 15 1/2x13 they will let you try or some dealers will work with you as far as if it dosn't work bring it back and try another, it will bring your rpm up. The gas will weigh about 8lbs per gallon so you are hauling over 800lbs of fuel.