Re: Any propeller recommadations for a 2004 Mercury 40hp and a Boston Whaler?
Either prop will work. What I'm saying is that engine typically gets fitted with a 13P prop. Since your boat is only a 13 footer you might be able to run a 15p. The thing you need to consider is wide open throttle rpm. I believe that is 5500 rpm for your motor. On your boat, a 13P may not have enough pitch which means the engine might over rev at wide open throttle. A 15P in that case would be necessary to bring the rpm down. So you see -- it's not a cut and dry situation. If you normally have a two people and lots of gear in the boat, then the 13P would perform better but you would need to keep an eye on the tach (if you have one) to avoid over rev. If you run with a light load, then the 15P might be the best choice but performance would not be as good with a heavy load. Talk to a Whaler dealer and see what they recommend but if I had to take a swag, having no reference, I'd try the 13P. Props for that size engine are not a budget buster so if the 13P is not quite right, about $75 gets you another prop.
