semi-clever non-cupped to cupped prop

I have heard that if one is going to switch from a 3 bladed non-cupped prop to a 3 bladed cupped prop, both of equal diameter, that it is recommended that the cupped prop be reduced in pitch. Example: 13" x 17" non-cupped prop replaced with a 13" x 15" cupped prop. Is this so? Also, what are the advantages and/or disadvantages of running a cupped prop vs. a non-cupped semi-clever?

Re: semi-clever non-cupped to cupped prop

A cup usually has the effect of increasing pitch by two. It depends on the prop and application. It is usually used in high power, high speed, low load applications (planing hulls). Generally a cupped prop will not ventilate as easily in turns. So if your engine is speeding up in moderate to sharp turns and losing speed, a cupped prop will reduce that. But it may not eliminate it entirely, especially if you are trimmed all the way out.
In my application, I have found that a cupped 19 pitch Michigan does not let my engine rev up to proper operating range, a regular 19 pitch Michigan does, and a 17 pitch cupped prop operates in the proper rpm but top speed is reduced slightly 1-2 mph. So I use the regular prop and trim in when turning.

Re: semi-clever non-cupped to cupped prop

Hey Frank, fancy meeting you here..lol

Thanks for the info...trying to find information as far as what prop to use on older Force engines is nearly impossible if one relies on prop manufactures.

Re: semi-clever non-cupped to cupped prop

I just dealt with that exact scenario. The stock non-cupped prop was replaced with a SS cupped prop. To get the same rpm I had to go from 17" pitch to 15". I tried the 17 cupped first and lost a bunch of rpm and some speed.

Re: semi-clever non-cupped to cupped prop

Thank you for the input flybuddy. Glad I kept the box and the receipt.

Re: semi-clever non-cupped to cupped prop

If you can trim all the way up without venting, the engine is too low, #1...Cupped props are more efficient in that they have less slip ratio.
Don't cut yourself short and just find a prop that fits the RPM range...
You're not gaining 2" of pitch, you're decreasing your slip..this also allows a higher X-demension and may allow the same pitch at a higher engine height(X-demension).
Another important consideration is Max RPM with a normal load...you don't say what model engine, but prop for the top of the range with your normal load for best engine life, performance and economy.