I have exactly the same boat/engine and a 16*11 2 blade Flexofold and it works well. You really don't need a 3 blade as the 2 blade will do every thing you want. Mine will achieve 7.5 knots at 3100 and cruise a 5.5knots at 2000. Never any problem keeping up in adverse conditions or stopping/reversing. Note that the factory fit is a 16*13 2 blade, but I don't know how this works as I fitted the folder from new.
While that is the correct size (worked out by Darglow) for the Flexofold another brand may not be the same size. So if you are buying another brand then take the recommendation of the supplier. 16" would be the correct diameter, but the pitch may vary depending on the shape and efficiency of the blades. The above speeds/revs ar what you should be looking for.
