Re: force prop interchange
There are a number of degrees of cup, but for simplicity, cupping is a slight bending of the trailing edge of the prop. This "cup" results in the prop "holding" or "biting" the water better. The effect is less ventilation/cavitation, especially in turns. Because of this cup, the prop has the same load on the engine as an uncupped prop about 2 pitches higher. However, a cupped prop can usually be run with a little more up trim and the boat may perform a little better.
Thus: With the same brand and model prop---When you install a cupped prop you will usually choose a pitch 2 inches lower to keep engine RPM about the same. NOW: If you are running a plain aluminum prop and go to a stainless cupped prop, you may be able to keep the same pitch. This is because on Force engines, Stainless props run about 200-400 RPM faster than equivalent aluminum. Thus: A cupped stainless in the same pitch as the plain aluminum will usually run about the same RPM with a slight increase in speed.
Just be aware: Installing a cupped prop with less pitch on your Force engine MAY result in a reduced top speed. It really depends upon what the current RPM is and how well the engine can swing the cupped prop. My recommendation is to at all costs try to borrow one and test before buying
