props

[Destroyer]

Originally Posted by roffey

As you can tell I am getting ready to put my boat in the water for the first time. I was checking out the spare stuff like props. I found an extra prop in the engine compartment. It has stamped on it 14.5X17, the one currently on the boat has 15.5X17, is that possible? I thought the first number was the diamater and the second number the pitch. Is it possible I can use ether 14.5 or 15.5?

Yes, it's possible. Technically, as long as you can swing the prop safely (meaning it doesn't hit anything like your anti-ventilation plate) you can use any prop diameter. Now before I get a ton of corrections, remember I said technically.... the fact is there is much more to choosing the right prop for your boat than just diameter. But you can use just about any diameter you want as long as you don't over-rev or under-rev the engine.
The proper way is to find out what your engine's WOT (Wide Open Throtle) specs call for and then find a prop that matches those specs.

For example, lets say your engine manual says that WOT should equal 5600 rpm. So you start out with a 15p prop and you find that the rpms are 6000. You would then go to a 17p prop and see what that resulted in. The idea is to dial in, as closely as possible, to what your engine's specs say are ideal for you engine. Maybe the 17p was still a little over reved, but a 19p was way under-reved.... you could then increase the diameter of the prop from a 14 1/2 to a 15, but keep the same 17 pitch. See? Everything works together. There are other things to consider also, like rake, cupping, aluminum vs SS, etc., but for now just start out simple and find out which of the 2 props you have gets you closer to your proper WOT spec. In your case, since they are both the same pitch, the smaller diameter prop will give you higher revs than the larger diameter one.