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.

 

[Scott06]

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.

I might try a different 4 blade than the spitfire. On my 21 ft bow rider I got a ton of slip with the spitfire. It was pretty disappointing compared to the sales schtick.

would also verify motor is low enough doesnt sound like it is - do you have a pic of the motor trimmed all the way down

 

[75Qwest]

 

[75Qwest]

Im thinking about trying a 14 x 13 Hustler 4 blade by turning point or maybe a Michigan wheel vortex 13 7/8 x 13 pitch

 

[Scott06]

View attachment 404938

The cowling looks great... Where does the cav plate sit in relation to the water when at speed and the engine pod bottom when fully trimmed in

 

[Scott06]

Im thinking about trying a 14 x 13 Hustler 4 blade by turning point or maybe a Michigan wheel vortex 13 7/8 x 13 pitch

you hear hit and miss things about TP (at least from the dock chair experts here...) I have had decent luck with the Vortex 4 blades on my previous boat. they are a good value and for me were a great way to cut my teeth prop selecting with out breaking the bank.

The vortex doesnt have a ton of bite and may blow out easy since you are already having that issue. I have tried both a 4 blade vortex and a Spitfire on my boat, based on that I dont think the vortex would do anything better than the spitfire.

I think first verify your motor height. if indeed this is a known issue with this manufacturer you are going to want something that is made to run up by the surface and has cup and grip like a revolution 4 or maybe enertia. both are a different buy in level than AL props... you might be best to try and find a prop shop who will let you try before you buy and can guide you. You hear good things about BBlades, Prop Gods, and Prop MD in MN. I have used Prop MD for repair

I got best top speed on my boat with a revolution 4, which is also a little bit of a special case, very azz heavy and throws a pretty big wake for a typical 21 ft lake bowrider. I can fully trim up with the revolution 4 with out blowing out which lifts the hull out more. I got 4 mph better than with a Vensura which has smaller blade area and 1 mph better than Enertia 3 blade. Vensura had the best holeshot because it slipped more so engine spun up to its power band more. Overall the Rev 4 was best total performance, but I just have enough power to swing it out of the hole, it grips that much

 

[cyclops222]

Calculate / call the prop manufacturer for the PROP SLIP of any prop you are interested in. Before buying anything.
Sadly pontoons also need 2 different props to run at their best power and speed.

 

[jlh3rd]

Just a fyi. I learned , the expensive way, years ago that mercury CT motors have a bigger gear case than "regular" merc motors. That's why I have a TP 4-14x13 on my shelf.
Do Suzuki's work like that? just double check.

 

[75Qwest]

My gear case is 4.25 so normal for a 75 HP. However Suzuki runs a 2.59 gear ratio. So I can spin a larger diameter and pitch than most 75hp.