I have a 1987 230HP Mercruiser with Alpha One on a 22.5' Thompson boat. I bought the boat which came with an aluminum 19P prop. With the boat trimmed out, I was getting about 4000 RPM and 38MPH. I know the RPM range is between 4200 and 4600 RPM. I just recently tried a stainless steel 17P prop. With the boat trimmed out with that prop, I was getting 3950 RPM and 44 MPH. Also The hole shot was better. The engine has been tuned up, so I know the compression in all cylinders are good. The Engine purrs very smoothly. I liked the stainless prop but, I do not understand why the RPM's did not increase. Is there anything that would cause this? I borrowed this prop from the prop shop where I live. When I returned the prop and explained what my results were, another gentleman said if I liked the way the prop worked I should go woth it. It doesn't matter what the RPM is if it runs the way you want it too. I do not want to do any damage to engine. But if RPM is correct, shouldn't I be able to go even to a lower pitch which will give even more power?
Thanks for any help someone can give.
Thanks for any help someone can give.