Pitch perfect

[75Qwest]

I have purchased a new Pontoon. 22ft and 2200lbs. I have a 2024 Suzuki 75hp. I started with a 4 blade 13.75x15 pitch prop
It ran at 5300 rpms, didn't get wot MPH. Switched to a 14x13 black max. It ran at 5600 @ 21 mph. It would blow out at 21mph. I was able to maintain that speed with 4 passengers and pulling a tube. I just couldn't turn at all. I switched to a 4blade spitfire 13.8 x 13. Also added a fin to the motor. I can do 19mph all day @ 5800 rpms. Thats a 30% prop slip. The motor is mounted all the way down. The 3 blade was on 20% when it wasn't blowing out. My question is should I be happy with this or try something different.

 

[FunInDuhSun]

Welcome to iboats! Lots of knowledge here.
Have you tried to adjust the trim? Sounds like the motor needs to trim down/in.

 

[75Qwest]

Welcome to iboats! Lots of knowledge here.
Have you tried to adjust the trim? Sounds like the motor needs to trim down/in.

Any adjustment to the trim causes blow out. I have to keep the trim all the way down. The cavitation is a known problem with the boat manufacturer. The manufacturers suggested fix is a 4 blade prop and a hydrofoil on the motor. I'm just trying to decide if I want to try a 13.4 x 15 spitefire or keep the 13. The first 15 pitch the marina put on was a Evinrude prop. I'm guessing with smaller diameter on the spitefire I might be at 5600 rpms. I'm guessing 23 mph with 30% slip.

 

[Scott Danforth]

Lower the motor if your getting blow out.

Pontoons really need a jack plate in addition to trim

 

[jlh3rd]

I have a 24', twin tube (25") , '06 pontoon. It came with an '05 Merc 60hp Big Foot, factory setup. I'd get almost 21 mph on a early spring cool day, cold water, by myself. It would blow out in sharp turns so trimming the motor down would stop it , then trim back up for going straight. I put a 4 blade on it which seemed to help. This was years ago and before I learned about "propping" and proper motor height.....and quirky pontoon operating characteristics.
I know more now which helped with my re-power a few years ago.
You said the motor is all the way down, motor height is more critical with pontoons and if trimming down doesn't help in turns, you're kinda stuck. A jack plate .....or a re-power with a longer shaft motor....are really the only solutions.
But, as stated, a 4 blade may help. I would prop for maximum rpm limit at WOT, or a little higher with just you on board so when loaded down the rpm won't drop too low.
Max rpm @WOT and motor health are my main concern.....speed, slip, etc., are secondary and may be unadjustable.
Propping can get expensive , especially when guessing, even if just looking for max rpm@WOT.
What is the operating WOT rpm range of your motor ? That's the primary focus.
You might just be where you need to be since you can't lower the motor. My guess is if you lower the pitch, which will increase rpm, the speed is gonna drop...that has been my experience and can show my results.....my mercs WOT rpm range is 5000-6000.

 

[75Qwest]

I have a 24', twin tube (25") , '06 pontoon. It came with an '05 Merc 60hp Big Foot, factory setup. I'd get almost 21 mph on a early spring cool day, cold water, by myself. It would blow out in sharp turns so trimming the motor down would stop it , then trim back up for going straight. I put a 4 blade on it which seemed to help. This was years ago and before I learned about "propping" and proper motor height.....and quirky pontoon operating characteristics.
I know more now which helped with my re-power a few years ago.
You said the motor is all the way down, motor height is more critical with pontoons and if trimming down doesn't help in turns, you're kinda stuck. A jack plate .....or a re-power with a longer shaft motor....are really the only solutions.
But, as stated, a 4 blade may help. I would prop for maximum rpm limit at WOT, or a little higher with just you on board so when loaded down the rpm won't drop too low.
Max rpm @WOT and motor health are my main concern.....speed, slip, etc., are secondary and may be unadjustable.
Propping can get expensive , especially when guessing, even if just looking for max rpm@WOT.
What is the operating WOT rpm range of your motor ? That's the primary focus.
You might just be where you need to be since you can't lower the motor. My guess is if you lower the pitch, which will increase rpm, the speed is gonna drop...that has been my experience and can show my results.....my mercs WOT rpm range is 5000-6000.

Is it possible that my motor is too low.

 

[75Qwest]

My RPM range is 5000-6000. 19mph is with the bimini open and 6 adults on board. Maybe I'm right where I need to be for now. I never ran it with just myself and the bimini closed.

 

[jlh3rd]

ventilation is more probable the higher the motor is, not lower. Pontoon boats seem to be more susceptible to ventilation especially when turning.
When I re-powered my toon, it would blow out with very little up trim and on turns. Luckily, I had one more lower bolt holes left so lowering the motor the extra 11/2" made all the difference in the world, thankfully as I'd just spent $11,500 for the new motor.
Propping gets expensive. Initially the dealer put a merc 4-14x14 prop on. By myself, I got 5800rpm @wot, 25-26 mph. But loaded down pulling teens on 2 tubes had me at 5300 rpm. I went to a merc. 3-16x12 . I got over 6000rpm @wot and 22-23 mph. But loaded down I'd see 56-5700 rpms , 20 mph. I propped for torque and load....what I wanted.
Point is, I found no magic prop. I propped for the higher rpm range which cost me speed.
also, I got essentially the same performance #'s with the 4-14x14, a 3-16x13, both mercs...and a Solas 3-15.5x13. So there's that.
Running the 16x13 as I messed up the 16x12.
just talking twin tube older toons. I can't speak for tri-toons or the newer designs.