Mariner 8hp prop

[Jack Blant]

Hi, I've posted about this before, but I have since done some testing.

I am trying to get the most out of a mariner 8hp on a 310 plywood floor sport dinghy, as part of a competition.

my top speed with the stock 9x7 aluminum prop is 23 MPH and it was revving out to 5700 RPM on the tachometer.

should I try a 9-1/4x9 aluminum prop or keep it the same?

Again, thanks!

 

[galamb]

23 mph is outstanding for that motor/boat combination but you are over the wot range for an 8 horse (4500-5500) ***if we are talking about an 8 horse 2 stroke, twin cylinder***

If you move up to the 9 1/4" x 9 pitch you will probably drop the rpms by about 450'ish, still above the mid-point of where you want to be but right in the range.

I don't believe you will pick up much speed, if any because the prop will be turning "slower" AND it will slip a little more (rate of slip tends to climb as the prop bites harder, all else being equal).

But at the end of the day this is JUST an 8 horse we are talking about here.