FWIW we went from an 18x12 Martec folder to a Campbell 17x11 without issues, smoother operation and good (much better) backing as well. The adjustment Norm is suggesting seems standard when switching to Campbell Sailor props.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)