Fourwinns 16ft Prop Recommendation

[resolute]

Could use some help regarding my recently purchased used boat

1.) performance issue - boat bogs down at higher throttles and barely gets up to plane with 2 people in it. Basically you punch it and the engine boss down and you just push water. Have been going through the entire engine correcting issues as found without success. When it gets to plane it tops out about 22 mph. a little slow

2.) Current Prop - Michigan 13 3/4 - 21 pitch stainless 3 blade

3.) Prop dia -13 3/4 prop pitch 21

4.) unfortunately tac not working. Its clearly low and well below the recommended 4200-4600 needed for max HP.

5.) drivetrain info - 3.0L Mercury Marine, Alpha 1, 1987, 130 (supposedly, probably a little tired)

6.) boat - 1987 fourwinns freedom 160, 16ft, 1900 or so I believe.

 

[junior1113]

Re: Fourwinns 16ft Prop Recommendation

first thikng i would do is a compression test and get a tach. 21' sounds about right for a 16' boat with that motor. or take a shot and get a 19" . wot rpms is the most important thing in choosing a propeller.

 

[resolute]

Re: Fourwinns 16ft Prop Recommendation

Compression is at 110-120 PSI accross all four cylinders. Originally 2 and 3 were low, about 80. A buddy and I replaced the head gasket which I had hoped was the only compression problem. The gasket had a clear failure between the bores. The bores weren't exactly stellar but I'm trying to use the jedi mind trick into making it not be rings/bores causing the poor performance.

Which get me wondering about the prop

 

[hwsiii]

Re: Fourwinns 16ft Prop Recommendation

Resolute, if you have a 1:98:1 gear ratio, please check this, I show you should be running an 18" pitch prop and that should bring your RPM up close to maximum RPM, if you motor is running fine. I show your boat at 2,100 pounds and with 2 people, gas and gear about 2,700 pounds. With an 18" pitch you should be doing about 35 MPH with the right geometry prop. If Dale or Ken will chime in they can tell you which prop to buy. Here are my numbers.

Prop Pitch

H

 

[resolute]

Re: Fourwinns 16ft Prop Recommendation

Great thank you for all the good info!

I wouldn't say its running all that well yet but tach and fine tuning are the next steps

 

[MikDee]

Re: Fourwinns 16ft Prop Recommendation

Make sure your spark advance is working in the distributor.