Prop for Brand New Pontoon

[speedmerchant]

I have a brand new Legend Bayshore EXT Pontoon boat which is nearly 26'. It has a Mercury 90 fourstroke Command Thrust (2.38 gear ratio) on it. The operating rpm range on this engine is 5000-6000rpm. The dealer of course told me this prop is matched to the boat but we have all heard that before, and there is obvious performance issue with the engine operating WOT rpm. Here's the stats:

Prop: (didn't see a diameter but it has this number on it, 77344445) and 17P
Rpm at Max Throttle ? 4300
GPS Speed 24mph
No increase in speed from say 3800 to 4300 RPM

Obviously way outside the operating range here. Any suggestions on what prop to run. I'll be putting it on his desk when we figure out what it should be running so he can exchange it. My guess at this point is maybe something in a 13P?

Thanks in advance

 

[steelespike]

A 17 is too much prop. I think a 14" should be about right.
I found a test power command 90 on a 23.8 Crest 2450lbs. Inertia 14 prop 27 @ 5500.
While your 26 is longer and heavier the speeds are sometimes comparable from a short to a longer with the same motor.
20-24, 24-26. 60-90 hp.
We do need to keep in mind that pontoon speeds can vary widely for no apparent reason.