Prop size and pitch?

I recently purchased my first boat. It is a 18' tri-hull 1976 Sea Sprite. The boat was garaged and well taken care of, but when the owner became too old he donated it to a church, who wanted nothing to do with it, so they sold it for $200. It has a Mercruiser sterndrive rated at 165 HP. It is a complete boat with service records from out of state, at several marine mechanics shops. The problem is it has no prop on it. Having a good friend with a metal scrap yard, we were able to find a old aluminum boat and engine with a prop on it, and placed this prop on this stern drive just to start up the engine and idle it to test out the water pump and such. Here's the problem, I cant find what prop size and pitch I should be running, and want to order in a prop asap to go to the lake. Understand I'm in New Mexico, a desert, and there are few lakes, and fewer marinas or boat mechanics. I can install a prop myself if it can find the correct one I need. The lake is over 100 miles away, but it doesn't have a marina or boat mechanic. Any help is greatly appreciated.

Ayuh,.... Ya need the prop pitch that will allow yer motor to run 'bout 4600 rpms, at Wot, average load, average conditions, trimmed out, 'n Runnin',....

Middle of available pitches is 'bout 17" or 19", as most available props are 'tween 15", 'n 23" for our drives,...

So I guess I'd start with a 17", 'n even if to small, it'll make a great backup prop,....

Thanks for that pitch suggestion. Ill order it today, one more question. What size of prop should I order?? Mine is chewed up to the point that I really cant tell what size it is. Thanks

Ayuh,.... Ya shop props by Pitch,.... 'n blade design,...


Diameter is a function of blade design, not really part of the choices ya choose,....

Smaller pitches, bigger blades, larger diameters,....

Taller pitches, Various blade designs, 'n diameters follow those designs,....