Pontoon Issues...

[winterfunguy]

I just purchased a new to me 1994 28 foot Manitou limited toon with a 90hp Evinrude also a 1994. My engine revs to 4900 and cavitates frequently over 3000 rpm...is this where the engine should be running? The engine is all the way down on the transom plate so i'm thinking the prop may be due for replacement due to its age and the possibility of it being stressed/washed out. I also have tremendous water spray from between the logs and the engine, that shoots up and onto the sunpad!! I am new to toons but don't think this spray is normal. The keel in front of the engine appears to be in good condition bit also seems to be causing the rediculous spray. I am able to get 23 MPH on GPS and the logs plow all the time and show no signs of lifting the front of them at all, even at WOT. Any help or advice would be appreciated greatly...

 

[Jeep Man]

Re: Pontoon Issues...

You may have a spun prop and/or prop ventilation. Check to see if your prop is deep enough. As to the spray, you can seal your floor but you would be better off underskinning your deck. At 23 mph, your toons should be up a bit at the front. If not, adjust the weight by moving a body or two towards the rear. Also check for water in your pontoons.

 

[winterfunguy]

Re: Pontoon Issues...

Just curious how underskinning or sealing the floor would help with the spray? I understand it will waterproof the floor but i'm looking for a solution to the spray shooting up 4 ft behind the boat...

 

[reddogg]

Re: Pontoon Issues...

It almost sounds to me like your motor may be mounted to high or you have it trimed up to high.

red

 

[USM89]

Re: Pontoon Issues...

I agree with reddogg sounds like you are not getting enough bite with prop. On the trailer with motor trimmed down where is foot, or in the water trimmed down where is water on shaft?

 

[winterfunguy]

Re: Pontoon Issues...

With the engine trimmed all the way down, the anticavitation plate is about 4" below surface...the engine has electric trim and is trimmed all the way down. My brother is a big time off shore guy and his oppinion is that the prop has washed and no longer has any "grip" on the water...does that sound legit? There was whale tail on the engine that I just removed and the cavitation/ventilation seems to have gotten worse

 

[lncoop]

Re: Pontoon Issues...

Okay, a few things. First, not to put too fine a point on it, but I think you mean ventilation, not cavitation. Ventilation occurs when the prop fails to bite because it's surrounded by air and is likely the reason the PO was using a hydrofoil. Cavitation is something entirely different and is actually pretty rare. By "stressed/washed out" prop I suspect you mean spun hub, which is possible, but I'm doubtful since you're getting 23 mph out of her, which is pretty good for a 28 footer with a 90, especially given her age. I agree that the symptoms possibly indicate not enough motor in the water. You could test that theory by ordering everyone to the back of the barge when under way, which of course would push the foot lower into the water. If that resulted in a vast improvement you'd likely have your diagnosis. The solution would be a different kettle of fish since you've said the motor is already at its lowest point. Also, I'm curious. What do you mean exactly when you say your engine revs to 4900? Are you saying that's how high you've gotten the RPMs, or that's the specified max? In either case, it sounds low to me. There's a lot going on here and it sounds like you'd benefit from a visit to a shop that has experience with pontoon boats. Good luck.

 

[Silvertip]

Re: Pontoon Issues...

If the prop had a spun hub, was ventilating, or simply blowing out, the engine rpm would easily surpass 4900 rpm so I'm suspecting you are mistaken about what is actually happening. At 23 MPH on that size boat none of those symptoms would be likely. If it was, you would see a very sudden decrease in speed the instant the symptom appeared. engines on pontoons operate in very turbulent water passing between the pontoons so with bigger engines a certain amount of spray is normal. You might however ensure there is nothing hanging down too far under the deck or motor pod.

 

[Bamaman1]

Re: Pontoon Issues...

My 24' pontoon has a 20" Yamaha 115 hp 2 stroke off a bass boat. When 3-4 people get in the front seats, the front end sinks and the rear end raises--and I get a little cavitation.

My motor really needs to be lowered a little. Unfortunately, it's trial and error as an inch or two can make the difference between running good and a prop blow out. The best way to lower the engine is by an adjustable jack plate. I just move everyone to the back--and keep on running my boat as it has been since 1985.

I would suggest you switching props to start--a couple of inches of pitch below what you've currently got. You're already close to redline. See Iboats.com for available props--starting around $100 for aluminum. If you're still having blowout problems after changing the prop, you might need to adjust on the motor mount--to get the engine lower.

 

[winterfunguy]

Re: Pontoon Issues...

By 4900 rpm im talking about WOT with the prop biting the water correctly...I want to know if this is where my engine should be operating before I reprop, That just seems low but it might be right??? by a washed prop I am refering to the prop naturally loosing its cup and proper shape from flexing for 12 years. My propshop said for $12 they will inspect and recup my current prop!

 

[lncoop]

Re: Pontoon Issues...

Okay, so you're maxing out at 4900 RPMs but you're not sure if that's the top. There should be a plate somewhere on the motor that specifies the RPM band. If you can't find it you should easily be able to get the info from the manufacturer. In any case, I doubt whether recupping or even repropping will solve your problem. Ideally the back should sit a little lower than the front and the toons shouldn't be plowing that much water, and you're correct that water shouldn't be spraying up onto the sundeck. Turbulence around the motor pod is normal, but not that much. The PO clearly had the same issue, that's why he or she slapped on the foil. If it's feasible you really need to test your barge with a back heavy load and see what happens. If the problem is abated or eliminated then you'll know you need to devise a way to lower the motor.

 

[winterfunguy]

Re: Pontoon Issues...

I will try and get a load of people this weekend and see what happens. I was unable to find this plate when I was trying to find the plug gap...I will call Evinrude and see what they say on the rpm's.

 

[rickdb1boat]

Re: Pontoon Issues...

The range for that engine is 4500-5500 RPM's. Even though you are in that range, it's best to prop it toward the maximum 5500.

 

[winterfunguy]

Re: Pontoon Issues...

Thanks a bunch Rick, I have found 1 other post that said 5000 but didn't specify a range of acceptability. Thanks for answering my #1 question.

 

[Silver Eagle]

Re: Pontoon Issues...

If the boat is just sitting in the water not running, how far should the top of the prop be from the water line. ?

 

[winterfunguy]

Re: Pontoon Issues...

Got the cavitation issue fixed today, I removed the whale tail planing aids and installed a sport SE model that extends back over the prop instead of out to the sides...problem gone! And my spray is being caused by 2 broken welds for the transom lift strakes...they are flexing and spraying water straight up no big deal for now.

 

[5150abf]

Re: Pontoon Issues...

I would get the welds fixxed pretty soon, they will hold for awhile but eventually you will fatigue the aluminum and it will break, just keep and eye on it and look for any cracks.