Aquasport Mechanicals - things that need a wrench, screwdriver or multimeter > Props

Prop recommendation 170 70hp

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Sal LI,NY 170:
I'm looking to see what you guys are running on 170 ospreys with 70hp w strokes.  I just put a 70hp 3 cyl evinrude on mine that came with a 13/19 3 blade aluminum prop.  Not getting up on plane or up in rpms like it should.  Local guy says I need a 13.5/15 prop. 

What are you guys running on yours and what kind of mph and rpm are you getting?

will4570:
Hey Sal,
I just put a 70hp Yamaha 4-stroke on a 1978 170 and made a couple runs.  I'm still messing with the prop configuration but will try to get back to this thread as I have updates.  A few things that may give you some direction in the mean time:
WOT for that engine is spec'd at 6300rpm tops.  The Coast Guard rating on the hull says 1235 lbs max.  I loaded up the boat with jugs of water, a couple coolers full of water, kettlebells, etc to bring the total with motor, fuel, persons, etc to 1500 lbs and took her out a couple weeks ago on a very calm day.  Trying to get a 'worse' case for the torque I need from the prop to get on plane.  Obviously, it took a bit longer to get planed out than with a more appropriate load but still did fairly well.  On plane, was able to rev the motor beyond the Yamaha rating still by a smidge.  Tack topped out at 6500rpm.  This test all with an aluminum 13 5/8 x 13 pitch.
This would indicate that I can go up in prop pitch which will hurt my hole shot but keep the WOT below max.  I'm trying to locate a 15 pitch to try.

Sal LI,NY 170:
Well I replaced the prop with a 13.5/15 3 blade prop and the boat now does 25mph @4800 rpm. Cruises at 20mph @4000. 

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