Trying to get more speed

[edsjr01]

2001 Bennington 18'
2011 (I think) 60HP Mercury Big Foot

I know this thing will never be a speed demon but I really think it should go faster than it does. I have a friend who has a 24' pontoon with a 75hp 2 stroke and he walks away from me regardless of how loaded he is

Boat seems to sit very low in the back, it never really gets on plane....trimming has no effect at all

It doesn't have an underskin, seriously considering getting some aluminum and adding one. Also, I don't have much faith in the dealer who put the motor on so I'm not sure the height is set right.

I see what kind of RPM's that motor is supposed to turn, the tach shows 1k over that......pretty sure it can't be right because I would think it wouldnt have survived over revving for as long as its been on the boat

Does anyone have some advice as to where to begin?

 

[ahicks]

Just me, but I would just get it propped correctly (whatever that takes) and then just enjoy it. No experience to guide me, but I suspect skinning a boat that MIGHT crack 20mph when done is not real efficient when thinking bucks spent for bang received. That's me though...

 

[GA_Boater]

Welcome aboard, eds

Well just how fast does she go?

 

[edsjr01]

If I remember correctly it goes about a whopping 10 mph (I havent been on it since last summer).....its that bad. Motor runs good, no issues. It is set all the way to the bottom on the transom. Before I do anything with the prop I want to get another tach to verify the rpms

I do plan to take it out this weekend and will report back with actual speed.

 

[steelespike]

Often a longer pontoon will be faster than those that are shorter.Especialy a 18 compared to a 24.
Even if the 24 had the same motor. If you could give us your prop size(usually under the prop nut)lightly loaded rpm and gps speed.
I'm guessing your at about 18 or 20 mph.

I see 10 mph Is that gps? Pretty sure we can do better than that.

 

[edsjr01]

Often a longer pontoon will be faster than those that are shorter.Especialy a 18 compared to a 24.
Even if the 24 had the same motor. If you could give us your prop size(usually under the prop nut)lightly loaded rpm and gps speed.
I'm guessing your at about 18 or 20 mph.

Will do, I know I'm no where near 18-20 mph. Tach claims motor is spinning 6500 rpm, i've read online that it likes 5500-6000 which is what makes me question the accuracy of the tach.....just seems like it wouldnt live long over revving like that on a consistent basis

Just ran out and looked, prop is a 14x9

A little bit of reading on the net tells me I probably want to go to about a 14x12 which will decrease my rpm down to a level that will allow the motor to live a long life and give me better speed......am I on the right track?

One thing I did not disclose is my dad in his infinite wisdom told them to prop it to pull a tube......I have no use for that although I dearly love tubing that needs to be done behind a bass boat or ski boat IMO

 

[fhhuber]

Actually the engines can often survive high rpm low load... Its not good but your tach could be right. The way to check is with a strobe tach.

On the trailer, engine at normal cruise angle: (drive the trailer onto blocks for skeg clearance if needed)
Some pictures taken from the side with the camera height such that the anti-vent plate looks like just a line will help show if the height is correct or not. A grease pencil mark (rubs right off) on the pontoon that shows the at rest waterline helps a bit too.

 

[edsjr01]

Couldnt get images to upload, Hopefully this link will work. It the onedrive link at the bottom. Let me know if I screwed up the pictures

At rest waterline is the line of crap on the pontoons

 

[edsjr01]

Often a longer pontoon will be faster than those that are shorter.Especialy a 18 compared to a 24.
Even if the 24 had the same motor. If you could give us your prop size(usually under the prop nut)lightly loaded rpm and gps speed.
I'm guessing your at about 18 or 20 mph.

I see 10 mph Is that gps? Pretty sure we can do better than that.

yes, was with gps iphone app. Thats going from memory of last year

 

[edsjr01]

Ok....just got back from the boat dealer, not the same one who originally installed the motor. I think it needs to go up about 2 notches, it was installed in this location so it could be tilted up for transport without hitting the back cushion. Is it ok to shim the motor out off the transom? Do they make special shims for this purpose or can I just get some aluminum blocks?

My plan of attack is to get the motor the correct height first so that the trim actually has an effect on the boat
Verify tach is correct
re-prop according to what the motor is spinning

Just got off the phone with Mercury.....I'm beyond mad. There is no way on earth that motor is turning 6500 rpm. The rev limiter shuts down 2 cylinders at 6225 and shuts down all cylinders at 6300.

 

[steelespike]

​What is the diameter of the tubes?

 

[edsjr01]

​What is the diameter of the tubes?

The pontoons? 23" it looks like

 

[ahicks]

Some tachs are SUPPOSED to be set to the correct number of cylinders (2,3,4,6?) by the tech installing it. If set incorrectly, tach readings are completely out to lunch. If you suspect incorrect readings, that's where I'd check first. See if it needs to be/can be set, and if so, verify it's been set correctly for your engine.

Another idea, rather than trying to shim the engine at the right height, so it doesn't interfere with the upholstery, you might look into shimming the upholstery?

 

[edsjr01]

Mercury said it should be on setting #6 or #12. I haven't taken a look at the tach yet but I did borrow a tach / dwell meter from a buddy so I should be able to find out exactly what it's turning.

This boat originally had a Johnson 50hp 2 stroke. I'll bet the idiots didn't change the setting on the tach. Fact is it's not possible for 6500 rpm to be correct

 

[ondarvr]

You don't need any blocks to raise the motor, just unbolt, raise it up, put the bolts back in.

 

[edsjr01]

Motor was set in current position to keep it from hitting back deck cushion when tilted for trailerimg. My thought was to shim it out from transom and up to be able to tilt it for trailerimg. Now my thought is if I shim out from the transom it will actually add to the problem. In all reality the keel is above the lowest part of the trailer so it is protected and even after raising the motor it can still tilt a considerable amount so I think it's really a non issue.

 

[Jeep Man]

I can probably give you solid info on what you should have. I have a 60 hp Merc with 18' pontoons.My boat is a 20', but the design has the rear deck protruding over the rear of the toons, so it's listed as a 20' even though the toons are 18'.
The prop you should have is a 14x11 for a 3 blade and a 14x10 for a 4 blade. Whether it's a 3 blade or 4, you will not see a noticeable difference in speed. I tried a 14x9 and WOT was 6200 with a decrease in speed. The motor should be a Bigfoot model which has heavier gears and a different gear ratio. A Bigfoot will usually have a wider blade for more push, consequently lower gear ratio. Ether way, the engine should be one hole from being all the way down. Being too high will result in prop ventilation when turning. Being too low on a pontoon boat has little effect unless your dealing with big motors, i.e. 250 hp.
Underskinning will help. I picked up about just under 2 mph by doing it. I get about 18 mph top end. Longer toons will do a little better. If you are only 10 mph, you likely have the wrong prop and probably too much weight at the rear. As it sits at the dock, the rear of your toons should be about 50% below the surface.

 

[edsjr01]

Ok next problem.....picked up plugs yesterday. Got NGK 6 heat range. Pull old plug out today it's a champion 8 heat range. Went back to the dealer and sure enough an older generation had that plug. Anyone know which is the better plug to run in this motor? It appears my motor has some leftover parts in it (build date Jan 2011). Obviously Mercury made the change for a reason.

 

[Reel Kahuna]

You don't need any blocks to raise the motor, just unbolt, raise it up, put the bolts back in.

...Says "Hercules" :lol: . I'd use a Cherry picker, chain-fall, or come-along to raise it...but that's just me with the wife watching.

 

[edsjr01]

...Says "Hercules" :lol: . I'd use a Cherry picker, chain-fall, or come-along to raise it...but that's just me with the wife watching.

Obviously