22' pontoon prop question.

[joegibbstruck]

I know it has probably been covered and recovered a million times, but there is allot of mixed reviews on the subject.

I recently bought a new to me pontoon boat, it's a 2002 22' fisher with a 2002 mercury 125 2 stroke and gear ratio of 2.07 and no lifting strakes or anything like that. Its relatively light, has poly sheeting decking plastic furniture etc... with me and 5 kids on board and trimmed all the way down it reaches max RPM of 5450 and a top speed of 17mph trimmed all the way down and if I start to trim up if will go to 19mph but loses traction really quick( way before the prop even gets close to the surface). It goes from 0-17/19mph in about 10 seconds right now and then bounces on the rev limiter the prop is a quick silver 77342a45(p15) 13.75" x 15p 3 blade aluminum. From all the calculators I have figured it has about 49% prop slip. Which I believe to be pretty high, I know pontoons will have more slip, but I would think closer to 25/30%

My questions are should I go with larger diameter and less pitch for more traction, or more pitch for speed? I know getting the slip lower should help in both cases, but I am trying to figure out which direction to go? I found someone local to me who has a new quicksilver aluminum prop 15" diameter and 17 pitch for $50 but I'm not a fan of wasting money on trial and error. And figured there should be enough knowledge to help me decide while spending the least amount of money lol.

Ultimately, if possible, I would like to be able to cruise around 25-27mph WOT and be able to pull a tube with 2 kids on it occasionally. It's mostly a fishing vessel for the family. Any and all help would be extremely appreciated.

 

[jlh3rd]

what is the diameter of your pontoons? Makes a big difference.

I have a 2006 , 24' pontoon, 25" diameter toons and a 2021 Mercury 115 hp CT, purchased new.
By myself I get 26 mph, 5800+ rpm @WOT. Both a Merc 4-14x14 and a 3-16x13 props give these numbers.
A merc. 3-16x12 prop gets me over 6000 rpm and about 24 mph but I used that prop to pull two tubes with 5 thin teenagers and 4 on board which kept my rpms around 5600+ and about 21+ mph. What I wanted.
When pulling a load, I wanted my motor's rpm in the upper range of the 5000-6000 rpm operating range. ( don't know yours).
Your boat is 2' shorter and 10 more horses. Your performance should be better than mine, unless your toons are smaller.
Have you checked, or do you understand correct prop/motor mounting height? That is critical with a pontoon. You said the boat was new to you, propping is simple in concept but can get expensive if guessing.
Is your prop damaged?
Ass-um-ing the prop is good, the motor is good, and not being there, the motor may be mounted too high. I'd check that first.
I switched from my higher pitched props to my 3-16x12 because my rpm was 5300-5400 when pulling teens and tubes. Too low for me.

there is a plastic "ring" that fits inside the gearcase in front of the prop on most mercs., including mine. It is to prevent ventilation from exhaust gases. They get broken, forgotten, missing, check yours.

 

[joegibbstruck]

what is the diameter of your pontoons? Makes a big difference.

I have a 2006 , 24' pontoon, 25" diameter toons and a 2021 Mercury 115 hp CT, purchased new.
By myself I get 26 mph, 5800+ rpm @WOT. Both a Merc 4-14x14 and a 3-16x13 props give these numbers.
A merc. 3-16x12 prop gets me over 6000 rpm and about 24 mph but I used that prop to pull two tubes with 5 thin teenagers and 4 on board which kept my rpms around 5600+ and about 21+ mph. What I wanted.
When pulling a load, I wanted my motor's rpm in the upper range of the 5000-6000 rpm operating range. ( don't know yours).
Your boat is 2' shorter and 10 more horses. Your performance should be better than mine, unless your toons are smaller.
Have you or do you understand correct prop/motor mounting height? That is critical with a pontoon. You said the boat was new to you, propping is simple in concept but can get expensive if guessing.
Is your prop damaged?
Ass-um-ing the prop is good, the motor is good, and not being there, the motor may be mounted too high. I'd check that first.
I switched from my higher pitched props to my 3-16x12 because my rpm was 5300-5400 when pulling teens and tubes. Too low for me.

there is a plastic "ring" that fits inside the gearcase in front of the prop on most mercs., including mine. It is to prevent ventilation from exhaust gases. They get broken, forgotten, missing, check yours.

24" toons, I also thought the motor may be too high, but it sits as low as it will go on the transom and it is the factory mounted motor for the boat. operating range is 4750-5250 and 5450rpm is the rev limiter, the aluminum prop has small knicks on the end of a couple of blades, but I don't think it would be enough to hurt the performance this much. Which is why I'm thinking the 15p is too much pitch, your 3-blade prop is a 2" less pitch and 2" larger diameter than mine Which would give you a larger amount of traction than what I have I'm at I don't know what your gear ratio is... but I plug a 2.0 like mine then you have ~25% slip vs my 49% There is also not a plastic ring Infront of the prop on my motor. I'm guessing I need to go larger diameter and less pitch, which would theoretically bring my slip down and hopefully my speed up a bit.

 

[jlh3rd]

ok...
so, yep, your over the rpm limit@WOT..So you go up an inch on pitch.
general rules: 1inch +/- pitch, decreases/increases rpm by 200 rpm +/-.
1" diameter +/-, decreases/increases rpm by 100 +/-..

 

[joegibbstruck]

How long does it take yours to get to operating range at WOT I feel like mine gets there extremely fast it gets out of the hole and almost instantly is at the operating range.

I just got home and double checked, I have 26” pontoons and the cavitation/ventilation plate is about 8” below the water line so I dont think the motor is to high either.

 

[jlh3rd]

The stationary water line isn't the correct reference.
Generally, the plate should be at or slightly below the bottom of the pontoon's motor pod. Like it is for a Vhull, at or slightly below the center of the "V". This is a starting point.
When underway at speed, the plate should be at /and/slightly below the flowing water....that's what I've learned/ been told.
Curious what make/model pontoon?
Unfortunately, my opinion, based on the repower/propping scenario I encountered, my motor had to be lowered to the last position to correct my ventilation issue. And the 1 1/2" lower made the difference. So if your vent. plate is above your motor pod bottom that might be a problem.

My motor warms up quick, I guess....Never really paid much attention.
By the time I leave my slip and exit the marina, it's up to temp.

 

[joegibbstruck]

Vent plate is well below the motor pod, The boat is an 02 fisher 22 dlx or something like that and the motor is an 02 mercury 125 2+2

 

[jimmbo]

If you are hitting the Rev Limiter, you definitely need more Pitch. If you are experiencing loss of Bite, as you trim up, your engine might be too high for the Prop you are running. A Prop with more Cup might be be better suited as they tend to grip the water better. Getting pic over the Transom while under way, would show if the Engine is too high or not high enough. I have Pics where the Anti-ventilation Plate was clearly visible while under way. Granted my Boat, had the AV Plate about 4 inches higher than the bottom of the Boat, and a 12 inch Setback.

 

[jlh3rd]

thanks for the pic.
I always fix what is wrong (car,boat, etc.) regardless of whether I think it is the problem or not.....so....
That prop is chewed up and needs replacing regardless. Maybe you could redress (file) it. I'm not there. Also, just maybe the hub is "spinning".
Like I said, your rpms are too high even under load so you need : higher pitch or bigger diameter or a 4 blade.....or a combination of those factors.
The motor definitely appears low enough but the actual test is when underway. Is the plate on or slightly below the water level.
4 blade props supposedly help out with ventilation issues....supposedly...
Yep, a cupped prop can help.

But now you're getting into the rabbit hole of "propping". Do you have access where you can borrow props? If not, it gets expensive unless you guess right the first time.

My gearcase is a 2:38/1 ratio.

 

[jlh3rd]

roughly what calculations #'s say from prop selectors and internet opinions:
3-13.75x16
3-14x16
3-15x15
3-16x14
4-14x15, 4-14x16
4-15x14
4-16x13
I'm illustrating how #'s work. Technically, these props would theoretically produce the same results.....emphasis theoretically.
not saying props exist in those exact sizes.
I can't tell you what exact prop to get, I'm not running the same exact boat.
and different prop manufacturers may have the same size prop but give different results.
My prop hubs have to fit my gearcase diameter, there's that

If I was in your shoes:
I'd try a 4-14x16....and hope I guessed right.

these are results from 3 props:

 

[joegibbstruck]

Yea I have a habit of fixing things that are not broken lol, the prop is getting replaced no matter what, I’m just trying find the most cost effective way to do it and get the correct results. The hub is definitely not spinning, I checked that first. When under way the bottom of the v transom is about 2” in the water and flush with the water when sitting still.

I can find a few different size props on marketplace for $50-75 so I guess I’ll start there and one I find what I’m looking for then I’ll spend the money on a good stainless one.