Too much slip...

[Mach1ForMe]

I have a 1989 Freedom Mach1 with 350 mag and Alpha 1. Currently running a Michigan 21p aluminum prop and im calculating about 38% slip. WOT is 5700 rpm and im hittin 47mph on gps. I believe my prop is disfunctional cuz im guessing this boat should be in the mid to high 50's on gps. Any help would be great. Thank you

 

[86 century]

Re: Too much slip...

The prop gurus are gana need to know the weight of the boat,gear ration in the drive and the numbers off of the prop would help.

I have found when the slip comes out that high most of the time its the tachometer or how you are getting your speed is off.

 

[jestor68]

Re: Too much slip...

What is your WOT rpm range(it's shown in your owners manual)?

5700 is a bit too high. What kind of boat is a Freedom Mach1?

You need to get your WOT rpm down to about 4800, if you expect your engine to survive the season. Running it at 5700 rpm is going to kill it fast.

Expect 150-200 rpm drop for each inch of pitch increase. Since most props come in 2 inch increments, expect 300-400 rpm going from a 21 to a 23. If your running 5700, that's still may not be enough.

In my testing, Solas or Mercury props worked best(in aluminum).

 

[steelespike]

Re: Too much slip...

The prop gurus are gana need to know the weight of the boat,gear ration in the drive and the numbers off of the prop would help.

I have found when the slip comes out that high most of the time its the tachometer or how you are getting your speed is off.

I have to agree I also suspect the tach , especially with 38% slip.Your speed is by gps so should be accurate.
What is your gear ratio?

 

[Mach1ForMe]

Re: Too much slip...

I have to agree I also suspect the tach , especially with 38% slip.Your speed is by gps so should be accurate.
What is your gear ratio?

The boat weighs 4,025 lbs unloaded. Gear ratio is 1.5. Im thinking the tach is off as well. I know speed is accurate by gps. The boat is very slow out of the whole and just doesnt seem to max out on the top end. But i do hear the 4 barrell carb open up when maxing it out at WOT. Everybody i boat with keeps telling me that my boat should be in the mid to high 50's top end. What do you guys think?

 

[rte592]

Re: Too much slip...

What are the other numbers on the Michigan 21p
Maybe too small a DIA with lots of pitch == dont work either.
Bent fin causing cavitation?
What does the prop look like color wise (even black color or paint missing in spots)