Changed to 17p with negative results

[tedder]

I was running a 19p alum prop on my 17.5ft alum smokercraft with a Mariner 115 2 stroke. I picked up a 17p as a spare hoping to improve hole shot and the result was totally negative. Prop slips and takes forever to get the boat moving.

I guess the 19p was the best pitch for hole shot and if I want another "spare" prop I should move up to a 20 or 21 and look for more top end speed? more top end speed would be nice!

I'm looking at the Vortex prop

 

[Silvertip]

Re: Changed to 17p with negative results

You can't just slap props on the motor and hope for the best. Put the 19P back on the boat and make some wide open throttle runs with what you consider and average load. Note the engine RPM at wide open throttle and optimum trim. If the engine is not able to reach the top end of the manufacturers wide open throttle rpm you need to decrease pitch. If it revs higher than recommended you increase pitch. As a general rule, and assuming the props are identical in design and from the same manufacturer you should see a 150 - 200 rpm change (up or down) with each inch of pitch change. Just going for top speed is not a valid test of a prop if the engine is lugging at that speed. It's a good way to kill it. Of course changing props is also NOT a good way to optimize performance if the engine is in need of a tune up or simply down on power due to age. The 17P prop that you said slips may indeed have a spun hub.