New Motor Performance Issue

[mofn]

I upgraded my motor from a old 85 h.p. Force (Which I really liked) to a Johnson 175. We went out yesterday for the first time, the shop warned us even before we went out it needs a lower pitch on the prop.
Now has a: 14 1/2 x 19 SS
Going to: 14? x 17 Alum, with hub kit?

Boat Info:
Older 24' Harris
Converted into a tri-toon.
Outside toons older 19" style
3rd...28" 15 feet long w/ motor pod on the rear (length due to trailer issue).
Motor is even w/ the two outside toons
It is skinned

Yesterday using GPS off my phone which I believe was off a few MPH, I only got 25 mph @ 4000 rpm @ WOT. I expected better!
Prior to this on glass one a.m. I got 21 mph.
After adding 3rd toon it dropped...16 mph max!
Yesterday, no cavitation issues.
Heard no slipping.
Looked down, I could see the fins just above the prop.
I played w/ the trim, but no noticeable increase... about 1.5 to 2 mph. You could tell I was moving it, but it then just maxed out.

I wanted mid-30's. Will the new pitch make up this difference? Any and all thoughts welcomed.

[teecro]

You need to drop more than 2" of pitch... My 150 Yamaha is turning a 14.5" x 15P prop on a lift-straked 24 foot tri and I'm mid to upper 30's...

[JLester273]

So your third toon is 9 inches bigger than the outside toons... That seems like a lot of drag in the water. I can't imagine it lifts that much out of the water.

Just seems like most middle toons are 1-2 inches bigger than the outside ones.

[ron nh]

Also 28" middle tube and 19" outer tubes? Who knows what that's gonna do, Could be a ton of drag from that center toon. Of course I've never seen that before so just spit balling on some physics.

[mofn]

JLester: I agree on the drag, I thought about it before I did it. I thought by going big on the power brute force would get it up?
The two outside toons at 25 mph the ends are completely out of the water I can see the drain nut.

Ron: Same as above, I agree I may be in a physics area? As it sits at anchor, more than 1/2 the outside toons are above the waterline. My drag is only 15 feet, again I thought brute force would work.
I can feel and hear it brake suction but how far I'm coming up out of the water is unknown. I have only had 1 day to play around w/ it? Strakes may be an answer? Will have to play around w/ it some more and see what I get?

[ron nh]

Sorry for the repetitive answer, I guess we were typing at the same time.

[JLester273]

Will be interesting to see if you get it figured out... Seems like it would be rough to get it out of the water. Brute force may be getting you where you are but that is a lot of extra weight on that one toon so I doubt your getting full advantage of the lift.

I actually have a 1988 Harris and have the 19 inch toons too. I have thought of a center toon. Dreaming really. I think a 20 or 21 inch would work but I have read most manufactures go with a couple inches difference for the center toon is all. But what do I know I am still learning.

Did anyone make a 20 inch toon. That would be a cool find ....heck another 19 would be cool someday.

[mofn]

Jlester

Do not let my issue slow you down!!!! I wish I had put it on years before.
We have the same boat, and I'm sure you have had some fin-less brown's moments like I have had. Not one since the 3rd toon:
raised me up 5-6 inches
Steering SO MUCH better
Due to being up higher less noise from water slapping up underneath.
Go big on a toon, I'm over 3000 lbs. capacity now, no more low rider! (3rd added 1256)

I'd rather be slow, than not have it.

[JLester273]

interesting. I'm doing a toon up restore soon. So after that all is done I'll see what Is going on. I figure if I replace the toons later I have a brand new boat LOL

I'm getting 18-19 MPH out of mine now with 8 people on-board with my 75 HP. Plenty fast enough for me. I may eventually go with bigger toons but then I will have redone everything but the cross members. LOL

[ron nh]

[quote="mofn"]Jlester

Do not let my issue slow you down!!!! I wish I had put it on years before.
We have the same boat, and I'm sure you have had some fin-less brown's moments like I have had. Not one since the 3rd toon:
raised me up 5-6 inches
Steering SO MUCH better
Due to being up higher less noise from water slapping up underneath.
Go big on a toon, I'm over 3000 lbs. capacity now, no more low rider! (3rd added 1256)

I'd rather be slow, than not have it.[/quote]
Hell yeah, If you get that dialed in it'll turn like a deep vee. Well worth the gamble and the effort.

[rockhound]

4000 rpms???

should be more like 5300 rpms should it not. you need way less prop

[Bamaman]

Your much larger center toon may be dragging too much to go any faster. It also may be too heavy keeping you from performing better.

The lifting strakes are the secret to improved speed and efficiency. They get the nosecones out of the water and fool a pontoon's displacement hull into performing like a planing hull.

Without strakes, a tritoon's only benefit is the abilty to handle more people and more weight on the deck. With strakes, it's speed, efficiency and improved handling vs. an two toon boat.

When you start improvising with additional toons, etc., often speed will go backwards. These things are a balancing act. Sometimes mods work and sometimes they don't.

[H8Monday]

If it were me, I'd be getting my hands on a 14 pitch prop to try. You'll see an increase in RPM, which will let your motor get up in the power band a little. You'll get a better hole shot, and your boat will feel snappier. Keep us informed on your progress with your setup.