Mercruiser 4.3L pushes 2400# runabout only 36mph max

[Scott06]

I sent the new 21p back because I wasn't reaching the rpms I wanted. It had a 14 1/4in diameter. I don't really want to go lower than that pitch because the theoretical speed a 19p is supposed to create wouldn't fix the issue im trying to solve (I want to try and get the boat in the high 40's.) Im thinking about dropping the extra money on a name brand enertia 21p that has a 13.6in diameter to see if that helps not only raise rpm but also gets me a little faster than the 21p turning point express I had on it. What are your guys thoughts?

id bet the enertia would have lower rpms than the turning point due to better bite and less slip. if you are only swinging an aluminum 21 “ to 4100 rpm, assuming the tach is accurate, you need more power or go down in pitch. You will only get more speed out of a higher pitch prop if the engine make enough power to swing it.

 

[Scott Danforth]

I sent the new 21p back because I wasn't reaching the rpms I wanted. It had a 14 1/4in diameter. I don't really want to go lower than that pitch because the theoretical speed a 19p is supposed to create wouldn't fix the issue im trying to solve (I want to try and get the boat in the high 40's.) Im thinking about dropping the extra money on a name brand enertia 21p that has a 13.6in diameter to see if that helps not only raise rpm but also gets me a little faster than the 21p turning point express I had on it. What are your guys thoughts?

Prop diameter has so little to do with the prop performance compared to the pitch. I would drop down to a 19P