"The size should be stamped on
"The size should be stamped on the hub of the prop.
Something like: '14x17' or '14in.-17p', or something to that effect. The first number shown is the diameter of the prop, the second number is the pitch.
If it's an Alpha 1 sterndrive, the 14x17 is probably going to be pretty close to the size you need.
The gear ratio in the stern drive, the weight of the boat, the shape of the hull, and the power of the engine are all factors that determine the right prop for the boat. Also, alot depends on how you use the boat and what kind of performance you're looking for.
If you want high top end speed or want to keep the revs down while cruising to save a little gas, and acceleration isn't a big concern, go with the steeper pitch, 14x19 or 14x21 maybe. Going to a harder material (stainless steel instead of aluminum) or adding more blades will have the same effect. Don't over-do it, or it'll never get on plane.
If you want acceleration, like pulling a tube or skier, go with a less aggressive pitch, 14x15.
The final upcheck for the right prop is where the WOT engine RPMs peak out. You'll have to check you're service manual out for that, my book doesn't have your engine in it.
Shooting from the hip I'd guess your WOT should be somewhere around 4800rpm."
