Fine tuning performance

[DMontana]

Hey All,

Sorry this may be a long post but want to make sure I provide all info.
Bought a 2017 20' Avalon pontoon with a Suzuki DF60AV this spring. From what I understand is this motor has "High Energy Rotation" to push bigger boats, and essentially has the same Lower Unit as the 140hp motor.
When I got the boat, the motor was mounted all the way down on the transom which looked too low to me, so I raised it one hole. It also came with a 14"x11" prop.
My top speed at wot was 17 mph (gps) with 2 people and full tank of fuel (25 gal +/-), however, the motor was maxing at 5200 rpm's which isn't even in the 5300-6300 range. I bought a 14"x9" prop to hopefully gain some rpm's. Now, wot is 15 (gps) with same load and rpm's at wot are now 6200. Maybe this is the best I can get, but looking at the test data on Suzuki's website, this motor with "similar" boats is getting anywhere from 19-23 mph.
Since at wot, my cavitation/ventilation plate is still just below the water. Thinking about raising motor one more hole to see if that will give me a few more mph. I know it's a pontoon, not a speed boat, but I would like to make sure I'm getting the most out of boat I can get. Any suggestions?

 

[Scott Danforth]

since your RPM's went up significantly and you lost speed, my guess is you are now venilating the prop.

only way to get the most out of the boat is a hydraulic jack plate to change the height of the motor with varying loads.

 

[jlh3rd]

Is that boat a tri-toon?...
A 2 inch pitch change should have upped rpm's to about 5600-5700 +/- , not a 1000 rpm increase, so something isn't right.
If you're ventilating, raising the motor will not help, it'll make it worse. Actually, you might need to lower it. You kinda made the mistake of making multiple changes at one time so it's hard to figure out what caused a 1000 rpm change.
People " misrepresent" their results on internet forums. Mine's "bigger" , right?
There is nothing magical about bigger gear cases. Mercury has their "big foot" "Command Thrust" lower units. They can enhance performance , allowing a bigger selection of props but nothing amazing...sorry...
As a rough comparison, the 60hp Merc. on my twin tube , 24' pontoon gave me a little over 20 mph on an early spring, chilly, air and water temp., by myself. 24' vs 20', so if you do not have a tri-toon, you should see better performance. My tubes are 25" diameter, that makes a difference also.

 

[DMontana]

Is that boat a tri-toon?...
A 2 inch pitch change should have upped rpm's to about 5600-5700 +/- , not a 1000 rpm increase, so something isn't right.
If you're ventilating, raising the motor will not help, it'll make it worse. Actually, you might need to lower it. You kinda made the mistake of making multiple changes at one time so it's hard to figure out what caused a 1000 rpm change.
People " misrepresent" their results on internet forums. Mine's "bigger" , right?
There is nothing magical about bigger gear cases. Mercury has their "big foot" "Command Thrust" lower units. They can enhance performance , allowing a bigger selection of props but nothing amazing...sorry...
As a rough comparison, the 60hp Merc. on my twin tube , 24' pontoon gave me a little over 20 mph on an early spring, chilly, air and water temp., by myself. 24' vs 20', so if you do not have a tri-toon, you should see better performance. My tubes are 25" diameter, that makes a difference also.

Actually I did not "make multiple changes at one time". I test drove the boat as is when I bought it, the motor looked to be too low in the water. I raised it one hole after I bought it, but before I changed the prop. It still wasn't even in the proper RPM range. THEN, I switched props. That at least got the motor in the range.
You say I'm ventilating, wouldn't I hear that if I were?
This is not a tritoon, and I know I'm not gonna break any speed records. Just trying to get all I can out of what I've got, that's all. I guess all I can do is experiment.
Talked to a prop shop and they recommended trying to raise it one more hole and trying the 14x11 prop again. Have nothing to lose giving it a shot.
The bigger gear case allows a larger diameter prop to be used to push heavier boats, per Suzuki's website.
Also the test data I was referring to was actual data from Suzuki not random people online. I know people tend to bend the truth in online forums, and I know every boat, even similar sizes are different in many ways.

 

[jlh3rd]

some mis-communication.
I don't know if you're ventilating, I said if. Someone else said you were.
Sorry, I mis-read. The 14x9 got you in the upper rpm range. That may be it for you.
Sure, raise the motor, see what you get. Raise it, run the 14x9. Then run the 14x11.
I understand bigger cases and what they "do". My 60 was a big foot, my 115 is a CT. They're Merc's equivalent to Suzuki high efficiency.
Anyway, as stated, my 60 pushed my 24' toon to just past 20. Add my girlfriend and 19+ I'd get. You're at 15, I would think you'd be closer if not over since you are 4' shorter.
So raising is your last option it seems.
My toon is an '06 Lowe, maybe a 20', 2017 avalon is heavier.
Again, my toon diameters are 25".

 

[DMontana]

some mis-communication.
I don't know if you're ventilating, I said if. Someone else said you were.
Sorry, I mis-read. The 14x9 got you in the upper rpm range. That may be it for you.
Sure, raise the motor, see what you get. Raise it, run the 14x9. Then run the 14x11.
I understand bigger cases and what they "do". My 60 was a big foot, my 115 is a CT. They're Merc's equivalent to Suzuki high efficiency.
Anyway, as stated, my 60 pushed my 24' toon to just past 20. Add my girlfriend and 19+ I'd get. You're at 15, I would think you'd be closer if not over since you are 4' shorter.
So raising is your last option it seems.
My toon is an '06 Lowe, maybe a 20', 2017 avalon is heavier.
Again, my toon diameters are 25".

No worries.
Took it out today, just me and it touched 18 briefly. That was with a full tank of fuel but kept the Bimini down. I am having second thoughts about raising the motor anymore. Today once I was at wot, I trimmed up one " push" at a time until it did ventilate. It wasn't very many presses to get there.
The only other thought was to maybe try a 10" pitch prop, or just leave well enough alone and enjoy it.

 

[jlh3rd]

yeah, I can relate and have a story, but just briefly.....I learned that 1.5 inches can make all the difference in the world concerning ventilating.
Initially with my new motor, I couldn't trim up without ventilating. Luckily the motor had one more lower bolt hole , about 1.5 inches, to go. That worked.....so, there's that.
Pontoons in general do have tougher issues with propping and motor height because of the toons , motor pod over a planing hull. Different wake dynamics.

 

[cyclops222]

And a captain who does not order people into correctly placed groups to keep it level. I am a no fun captain.

 

[DMontana]

And a captain who does not order people into correctly placed groups to keep it level. I am a no fun captain.

Yes! I have to keep telling my wife not to sit on the same side as me when we are under way.