New prop

[trekmc]

I have a 22 foot sun tracker pontoon. I had a 16 x13 black max aluminum prop. I changed the prop out ( broke the end of blade off) I replaced it with an same size prop but an extra cup version. With 2 people on boat I hit 27mph on smooth lake. Which is about what I got before. Might be a tad slower. However, my WOT dropped from around 5800 to 5200 rpms. Seems like an awful lot to drop. I just got it back from the shop and wondered if maybe the messed up throttle limits. TIA

 

[jimmbo]

Welcome to iboats

"Same size" doesn't mean Identical, so there is no reason to expect Identical results compared to the original Prop. You said "extra cup version". What brand and model is the replacement Prop?
Cupping can add a bit of pitch, and/or rake, depending on where the cup is on the blade. Cupping can also improve a Prop's 'Grip' on the water, and can reduce Slippage, which might account for the drop in Rpm.
What do you mean by "messed up throttle limits"?
I will assume the prop was damaged by an Impact. Did you check that the Prop Shaft hadn't been bent?

 

[Scott Danforth]

Pontoons don't follow the same rules as other boats.

You have a brick you are trying to push thru the water (displacement hull). Yes, adding cup will simply decrease RPM and add load without increasing speed.

To go faster, you need a whole lot more power, a 3rd toon log and lifting strakes.

Plenty of people went from 50hp to 90 or 115 only to increase noise and fuel burn

 

[QBhoy]

I think a prop with cup added, will usually drop a few rpm on hulls that can’t take advantage of it fully. You didn’t say what engine you have, but I’d assume at low 5000’s you are only just in the rpm range and the mention of running with only 2 on board, you’ll be lugging that engine with any more load or people on board. Generally most engines like to and run at their best when propped near the top of the rpm. Especially modern 4 strokes, should that apply to you.

 

[04fxdwgi25]

LOL... Look up the Big Block Mercruiser powered toon on you tune. Dang thing skips along at around 60 mph.

But I would never ride in that thing. Stability does not seem to be it's strong point.