25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

[jimmybuffington]

Have a 2001 25' Voyager with an 04 150HP Johnson. The boat cavitates badly at half to full throttle and drives the nose downward with the boat uncontrollable, the prop is pitted badly too. At a loss as to what the problem is, I appreciate any help anyone has to offer. Thanks

 

[The Rooster]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

Welcome to the forum, "Jimmy". A little more information might help. Have you had this barge for a while, or just purchased ? Twin tube or triple tube ? When you say it cavitates / ventilates at 1/2 to full throttle, do you notice rpm's increase, but you loose speed and the nose drops ? If that's the case, may be a spun bushing in the hub of the prop !!!

 

[jimmybuffington]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

Welcome to the forum, "Jimmy". A little more information might help. Have you had this barge for a while, or just purchased ? Twin tube or triple tube ? When you say it cavitates / ventilates at 1/2 to full throttle, do you notice rpm's increase, but you loose speed and the nose drops ? If that's the case, may be a spun bushing in the hub of the prop !!!

The rpm gauge fluctuates wildly. The pontoon is a Twin tube and was purchased used a few months ago. Thank you

 

[Lawnmedic]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

I would start by having the Prop hub checked. If the prop is in real bad condition (pitting/damage) replace it.

 

[lncoop]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

The pitted prop could very easily be the result of cavitation, and if the boat is porpoising I'm betting it's something other than a spun hub. Is the motor low enough?

 

[tudunka]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

Your OB may not be deep enough and that could be causing the cavitation. You have a cavitational plate on your OB right above your prop. When underway, this plate should be at water level or just below, preferrably at water line, if it is too high, it will suck in air into the prop and that will cause the cavitating and pitting of the prop.

 

[Silvertip]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

To make the nose dive, you may be trimming in way too far. That drives the nose down and stern comes up thus ventilation (blow out) occurs. Trim up so the motor is more vertical or even out a bit. This will tend to raise the nose and settle the stern.

 

[Bamaman1]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

Most pontoon boats are built for a 25" outboard motor. From time to time, someone will mount a 20" motor (often off a bassboat), and the engine won't run deep enough in the water. Measure from the horizontal plane of the transom down to the anticavitation plate in inches to see if it's 20" or 25".

I have a 20" motor. It's very fast cruising, but I sometimes have to ask people sitting on the front seats to move to the rear. A fix is an adjustable jack plate, or cutting down the transom plate.

Another fix would be to put a new, proper pitch propeller on the boat. You didn't mention, but when your boat's not ventilating, can you pull the red line on the motor?

 

[lncoop]

Re: 25' Voyager Pontoon/150 HP Johnson with a serious cavitation problem.

One thing's for sure. We definitely need some deets from jimmy.