Prop ventilates while cornering

[MWMAKER]

I have owned a 98 pontoon with a 98 Evinrude 90 special since 2002. Recently the prop ventilates when corning, rpm's will rev high
and lose power. Changed prop to no avail. Any suggestions?

 

["G"]

Re: Prop ventilates while cornering

Pontoon boats have that problem for some reason. I'd bet the setup wasn't done right. You might try a Dol Fin but the setup is where I'd look to begin the diagnosis on cavitation issues on a turn.

Seems there was a post about this problem earlier this year. Look back in the threads for an answer on that problem/issues etc.

 

[trendsetter240]

Re: Prop ventilates while cornering

I have owned a 98 pontoon with a 98 Evinrude 90 special since 2002. Recently the prop ventilates when corning, rpm's will rev high
and lose power. Changed prop to no avail. Any suggestions?

Try adjusting the trim on your motor. Trim the motor all the way in/down before making tight turns.

 

[MWMAKER]

Re: Prop ventilates while cornering

I appreciate the quick reply from you both. This is the first time I have ever posted anything. I have read all posts I could find on this topic.The setup was done in 1998 at a reputable dealership and has worked fine for the past 6 years, only ventilating when trying to corner all the way. It has gotten worse this past summer to the point where if I try to turn as little as 30 degrees it ventilates. Trimmed all the way down has minimal effect. Don't know if this is a motor issue or boat issue. No changes on hull or transom. I am baffled. would anti-cavitation plate have an effect on this? Maybe?

 

[trendsetter240]

Re: Prop ventilates while cornering

I appreciate the quick reply from you both. This is the first time I have ever posted anything. I have read all posts I could find on this topic.The setup was done in 1998 at a reputable dealership and has worked fine for the past 6 years, only ventilating when trying to corner all the way. It has gotten worse this past summer to the point where if I try to turn as little as 30 degrees it ventilates. Trimmed all the way down has minimal effect. Don't know if this is a motor issue or boat issue. No changes on hull or transom. I am baffled. would anti-cavitation plate have an effect on this? Maybe?

The only thing that comes to mind is that the motor is higher up in the water now. This could be from removing a lot of weight from the boat, adjusting the motor mounts or ???.

Bit of a tough one for me as I've not spent a lot of time on pontoon boats. Hopefully someone more knowledgeable will be along soon.

BTW welcome to Iboats!

 

[walleyehed]

Re: Prop ventilates while cornering

Sounds like Prop trailing edge wear to me...If replacement prop was the same brand and style there may be other issues. One of them could be a bent skeg or a ding in leading edge of skeg, which in a turn will produce a huge air pocket and can cause ventilation.

 

[CharlieB]

Re: Prop ventilates while cornering

I've found one pontoon that had water in BOTH forward chambers leaking in from stress cracks alongside support bracket welds.

Water weight in fore chambers finally changed the balance, raising the rear to begin cavitation in turns.

Boat originally came in because of listing to one side, the cracks were worse, more water in the port side.

Rock the boat on the trailer and listen carefully for any 'slooshing' sound from within the toons.

Inspect, pressure test toons using a VERY controlled air supply limited to ONLY 2 to 3 PSI. Serious risk of toon bursting with more pressure.

If you are not confident in your ability then please take it into a reputable shop.

 

[Fun Times]

Re: Prop ventilates while cornering

I had one that the front of nose of the pod under the boat fell off in the lake and created a lot of air bubbles to the prop.

You also might want to look under the boat for anything that might be out of place.

Sorry, But need to ask just to be sure, But do you have more weight in the bow area, Like more passengers, ect???

 

[Texasmark]

Re: Prop ventilates while cornering

Since you had a functioning product and recently things changed, there should be an obvious answer and with the help you received you should be able to nail it. Additionally, you might get off the side while it is floating and see if it sits level in the water or has a forward tilt.

If the lower unit is all gungied up with algae/barnacles sort of stuff you could aggrivate the problem (ventilation tendencies) as would similar products on the toons themselves.

Can't really suggest anything additional as you had it working and now it doesn't.....but cupping the prop helps as I would imagine the whale tail suggestion. I never had one but in theory it makes sense as an aid in helping to keep the prop from sucking air from the surface of the water.....i mean that is the sole purpose of the antivent plate on the engine.

My 2c.

Mark

 

[steelespike]

Re: Prop ventilates while cornering

Wow 6 years and suddenly no more.I would carefully check the prop for a ding a subtle bend from contact with something.Maybe even a dent on the tubes.If you don't have a 4 blade pontoon dedicated prop that would help.Have you changed the weight placement.Aluminum props do wear out.Especially if you run in grundgy
water.

 

[MWMAKER]

Re: Prop ventilates while cornering

I thank you all for the suggestions. It is out of the water now and I will check for bent skeg or any lower unit abnormalities. Can the skeg be straightened if it is bent? The air test suggestion: question, do the pontoons have pressure in the chambers? or is it zero? If I do have water in one how do I remove it? evaporation? Any suggestions?

 

[steelespike]

Re: Prop ventilates while cornering

Toons don't have pressure they are basically atmospheric pressure.
If you do a pressure test be very careful I would use a hand pump and only a couple of pounds.I think there is a pic at the top of the page showing the results of too much pressure.Your boat may have access holes at the top of each section.
I would attempt to adapt a shop vac and suck any water out.

 

[Texasmark]

Re: Prop ventilates while cornering

Like Steelspike said, be careful with running a pressure test. I realize that most toons are round with curved end caps which helps to equalize the pressure over the entire tank but keep this in mind. Pressure is measured in lbs/inch/squared. Force is area x pressure. So 10# of pressure in the tires of your riding lawn mower might not seem like a lot, but if you pump up a toon cylinder to 10# you have just made yourself a bomb! Additinally, whereas a liquid filled vessel will yield a split/crack/hole and the liquid will come squirting out, an air box just blows up when the critical pressure is exceeded. Be careful.

Mark