Help With My 115 Hp Mercury Please

[macmichael]

We have a 22 foot Bass Tracker all aluminum pontoon. We traded in our 60 hp  Mercury big foot for a 115  4 stroke  Merk. Shouldn't it go faster than 18 or 20 mph? The prop is a 14/11 stainless steel. Any help or ideas would certainly be of help.  Thanks

[Kevin22]

Maybe. I only get 35mph with a 115 merc on a 17' ranger bass with 2 people. A heck of a lot less weight than a 22' 'toon. Alone, with the tanks almost empty, livewells empty, and no gear I can get up to 40-42 GPS speed. 

[RoLo]

The hull design on pontoon boats is a mixed bag, which range from semi-planing to full displacement hulls.

I'm not familiar with your hull, but if it's a displacement hull than it'll have a terminal speed.

Adding horsepower to a displacement hull will add response and acceleration but may not much to the top speed.

 

Roger

[Crappiebasser]

I have a 22' Premier pontoon with a 75 Yamaha that runs 25. How many RPM are you turning at WOT?

[macmichael]

I have a 22' Premier pontoon with a 75 Yamaha that runs 25. How many RPM are you turning at WOT

around 6000

[Crappiebasser]

I would try a 15p to take the top end down to around 5200 and give you more thrust. See if you can borrow one to try before you buy it though.

[J Francho]

Are you saying you have a 14 inch, 11 pitch prop?

That sounds way too shallow, even for a pontoon. You need to do a prop slip calculation, do a google search, and report the numbers. My guess, you need something more like a 20 or 22 pitch prop. My 115 ELPTO pushes my 1400 lb. bass boat to over 50. I think I have a 23P Lazer on it.

[Kevin22]

I used the prop selector tool to throw in some #'s and it came back with stainless 15p 13.25 for a 22ft 'toon and 2011 merc 115 4stroke. Didn't know your year model, just tossed in a newer motor. 

 

you can do it yourself here http://www.mercurymarine.com/propellers/prop-selector/#

[Kevin22]

Are you saying you have a 14 inch, 11 pitch prop?

That sounds way too shallow, even for a pontoon. You need to do a prop slip calculation, do a google search, and report the numbers. My guess, you need something more like a 20 or 22 pitch prop. My 115 ELPTO pushes my 1400 lb. bass boat to over 50. I think I have a 23P Lazer on it.

 

 

You might want to check out the prop selector too. I put in your motor and 1400# bass boat and it gave me 62mph with a 29P

 

Not saying real world results would be even close, but I think you should be able to get well over 50. Like I said, I can 42 with an alum boat and the same motor.. and I'm pitched for acceleration and not speed. 

[J Francho]

Real world props don't have a lab finish and lack the typical "Oneida prop mods."

[J Francho]

Here's the link to a full explanation of how to determine the right prop, and what's going on with your current setup.

http://www.go-fast.com/Prop_Slip_Calculator.htm

Prop selectors are marketing tools, and they assume zero slip. Therefore, it's not very useful to dialing in to the right prop.

Also, while a 29P prop may sound like it will be fast, using bad math, it would be terrible. My boat would probably never plane. Also there's the issue of additional weight from people and gear, that isn't considered. Measuring prop slip does factor that into the equation, along with the resistance specific to the hull design. Add in three or four blade prop to that.

My 1280 lb. Bullet will go 78 with a 26 Trophy. I tried a 28 cupped Trophy Plus. It was a bear to get on plane, but was quickly approaching 80 with plenty of RPMs before redlining my 2.5 Pro Max. If I used a prop selector to judge potential speed, I'd be disappointed, since without slip, that prop should have gotten me well into the 90s. I'll keep my sub 3 second hole shot, and planing at 16 mph with my current setup. I think when I checked, slip was around 14%. It's all a trade off. Go to steep, too much slip, bad hole shot. Too shallow, never get on plane.

For the OP, I think he needs a much steeper pitch, but without capturing numbers and plugging them into a calculator it's hard to say what to recommend. So much is trial and error. You might teach out to other similar toon owners to see what they're running.

[Way2slow]

I sure hope the OP has enough since the realize there's no way on gods green earth that his pontoon should be running 50mph with that motor. I put a 300hp motor on a friends 25' fiberglass deck boat and it would only run 62, and that's a lot faster hull than a pontoons. Somebody needs to learn more about hull designs.

If there is not doubt the prop is good and not damaged, there is no need to change it. 6,000rpm is a good number, that way if he has a few extra bodies on the boat, it's not going to load it down too much. That probably won't be true if he goes up another prop size and seriously doubt he would see any more than 1 or 2 mph in speed, if he sees any.

[J Francho]

An 11 pitch prop, though? Lol. I'd think he should get up to mid 20s with a steeper prop. 18 is unacceptable. I've seen toons with 25 hp motors get those numbers.

[Kevin22]

Just to be sure, this is GPS speed and not speedometer speed right? My ranger says 28MPH on the speedometer when I'm running 42 GPS

[Way2slow]

Ok, I was thinking it was a 14 pitch.  Still though, If the motor is not hitting the rev limiter and holding the rpm at 6,000, then that still all the prop he can run.  If it was mine, I would try to find someone with something like a 14/15 pitch I could try and see if it will turn it.  Not knowing who or how someone set it up, but he could be rev limiting.  As for those big number props though, it will never turn one, the pontoon is not going to turn anywhere near the prop a regular boat or bass boat turns.

[J Francho]

I agree, that's where the conversation turned - big prop = more slip, not more speed, which was the point I must not have made so well.

[Kevin22]

It will turn a 20 pitch prop, but he'll be one of those guys you see at the boat ramp that take off at full throttle going about 6mph and then turn around 50' out and full throttle back to the ramp cussing all the way. 

 

I asked a buddy who has a 22' tritoon with a 150 4 stroke. He said he is getting 37mph at 5700rpm with a 15p. So, I would try something in the 14-15P like the prop selector said... 

 

I just did a quick google search and it appears 13-15P is what you want for a 22-23' pontoon. So, coupled with what my buddy said and what the prop selector said and I would try the 15P first and then drop down to 14P if need be. 

[RoLo]

I believe the majority of pontoon boats are displacement hulls, or semi-planing at best

(the Tritoon is an exception, which is a planing hull). Water is very heavy (8.3 lb/gal) and can only be moved so fast.

Changing the horsepower or propeller on a displacement hull doesn't make nearly as much difference to top speed

as it does to a planing hull (which rides on 'top' of the water). There are pontoon boats on nearly every lake we fish,

and most of them brush along about 15 to 25 mph.

 

Roger

[jhoffman]

I just repowered my boat too, my motor is a rebuilt 40, it came with a 12 pitch prop. I was at 6k in rpms with more to go, so I plugged it into mercs prop selector all the info I had and it recommended a 14 pitch which will be here soon.

 

Smaller pitch usually = better hole shot

Larger pitch usually = top speed

 

But you need to adjust for what the motor is telling you to do. If youre hitting 4000 rpm at WOT you have too big of a prop or too big of a pitch, 6500 at WOT and your WAY to small.

[jhoffman]

Do you guys really like to turn your motors at 6000rpm or more at wot? Thats crazy

[macmichael]

I sure hope the OP has enough since the realize there's no way on gods green earth that his pontoon should be running 50mph with that motor. I put a 300hp motor on a friends 25' fiberglass deck boat and it would only run 62, and that's a lot faster hull than a pontoons. Somebody needs to learn more about hull designs.

If there is not doubt the prop is good and not damaged, there is no need to change it. 6,000rpm is a good number, that way if he has a few extra bodies on the boat, it's not going to load it down too much. That probably won't be true if he goes up another prop size and seriously doubt he would see any more than 1 or 2 mph in speed, if he sees any.

Of course I do. I just think it should run at least in the low to mid 20's. Thanks for all the ideas and suggestions fellas. I  in contact with the store I bought it from and he is thinking may a different prop. I think I might contact Mercury directly.

[RoLo]

Of course I do. I just think it should run at least in the low to mid 20's. Thanks for all the ideas and suggestions fellas. I  in contact with the store I bought it from and he is thinking may a different prop. I think I might contact Mercury directly.

 

I would expect Mercury to reiterate much of the same: that it's really not about HP, RPMs or Props.

It's not feasible to discuss displacement hulls and planing hulls in the same context.

Mercury will ask if you notice any difference in throttle response; and any difference in acceleration,

but I'd be surprised if they demonstrated much interest in terminal speed. 

 

Roger

[J Francho]

Jhoffman, I run around 6750 at WOT. Mine is not a stock motor, though.

[Kevin22]

Do you guys really like to turn your motors at 6000rpm or more at wot? Thats crazy

 

My merc manual says 5700-6000. I top out at 5800 WOT trimmed out. I'll check in the morning but I don't remember what pitch the prop is. I just know we used the selector and it gave us 3 options. The middle of the 3 ran the best with 3 people so that is what we chose. I do remember it could be upped one pitch and with one person gain close to 5mph but with 3 people it sucked, and I almost never fish alone so it made sense to choose the middle one. I suggest the OP do the same. I was lucky enough to have a local dealer with a stock of used merc props. He let us try the different options as long as we committed to buying a new prop through him. Which we did, and it was well worth it. 

[Way2slow]

6750 is actually fairly low rpm for a 2.5. I run 6,500 - 6,800 on my modified 3.0 OMC,s. On a properly built two stroke, the main thing high RPM does is shorten ring life. For instance, that 2.5 Merc 225 turning 6,000 rpm, rings may last 1,000 hours. Same motor ported and modified to 300 hp, turning 9,500 rpm, ring life is approx 100 hours..

I can take a carbureted Johnson/Evinrude 3.0, 200 hp the factory rates at 6,000 rpm and using all the same factory rods, crank, pistons, etc, port and modify it so it's making apprx 350 hp and turning 8,000 rpm. Now for a light boat like a Bullet, it will fly. A heavy boat like my Javelin, it won't work, I have to be more conservative on the porting and limit the RPM to about 6,500 - 6,800 and 325 hp.