Re: prop for 75 HP Optimax
Rsimmons -- if you haven't guessed, prop selection is a real crap shoot. Charts and calculations get you close to what you need but rarely hit perfectly on the first attempt. The main reason is that everyone loads their boat differently, drives it differently, uses it differently, the engines are in different states of tune, hulls are in varying degrees of clean, and the props they select may come from different manufacturers, different models, and be made of different materials. In that regard a 19P prop from Mercury for example can be any one of a number of different "Models" each of having different performance parameters. Complicate things by comparing that prop to one from Apollo, Turning Point, Michigan, etc and you have a totally different set of parameters. In other words 19P (or any other pitch) props from several manufacturers may not and rarely do perform identically. We are providing you with a starting point. If you selected a 19P Merc prop and found it to be not correct for your application and decided to try a 17P from someone else, you may be very surprised to drastically "overshoot" your target or in some cases may see little to no improvement or even degraded performance. So unless you have deep pockets and can spend large sums of money on props, do your research well. Look for test reports on your boat, your motor, and study the test conditions very closely to make sure they match yours or are at least reasonably close. Start with the exact prop used in that test. Any other prop would likely produce very different results. Or, work with a prop shop that has a try before you buy program. A good prop shop may also be able to recommend a prop as would your Merc dealers. If the first thing they do is head for the prop calculator, be wary because their "estimate" is no better than what you were offered here. Experience and tests are the best source of data.
