Problem with cavitation with new toon.

[noticon75]

OK we just purchased a new Sunchaser SS250 with a 115 horse Merc 4stroke. It has the 25" logs and we are experiencing cavitation problems.At first we only noticed it above 4500 rpm and but yesterday we had the bimini top up and had the cav problem at 3000 rpm. We had my wife and I and our 2 kids. I was at the helm the wife was in the back and the kids were towards the front. it was better when we moved them back but still had cav problems. Is this a problem with toons with larger logs or toons? The dealer is going to get in contact with the manufacturer but I was curious if others have had this problem and how they fixed it. TIA

 

[The Rooster]

Re: Problem with cavitation with new toon.

It is unusual to hear about a Toon w/ 115 hp. motor to experience cavitation. More common on 40-60 hp rigs that might be short shaft lower units. Yours should be long shaft. Assuming you weren't trimmed up too far, it's probably a simple fix for the dealer to lower your engine a notch or two. Good luck, and let us know.

 

[Bamaman1]

Re: Problem with cavitation with new toon.

You didn't say what kind of RPM's your pulling, and your motor's redline--per the manufacturer. Are your cavitation problems happening in a straight line, or in tight turns?

I also have some minor cavitation problems when too many people get on the front--with a 115 horse 20" motor. Most pontoon boats are using 25" motors. I seldom run with more than 5-6 people, so it's not been too much of an issue. My short engine is probably why I'm able to run relatively fast @ low RPM's with a 15 pitch prop.
I'm planed off @ 2500 RPM's, and seldom use more than 3500 RPM's cruising.

If you're pulling the specified RPM's and speed is as expected, I'd agree that your engine needs to go down a few inches. You can always raise it with the power trim. You might need a different prop if you're running a 25" lower unit.

When going into tight turns, pontoons will often cavitate due to the deep holes the pontoons are making in the water--causing the prop to grab air. There's really little you can do about that, however.

Good luck!

 

[lncoop]

Re: Problem with cavitation with new toon.

Not to put too fine a point on it, but what you guys are experiencing is ventilation, not cavitation.

 

[DJ]

Re: Problem with cavitation with new toon.

Not to put too fine a point on it, but what you guys are experiencing is ventilation, not cavitation.

Yup and pontoons are notorious for it.

 

[noticon75]

Re: Problem with cavitation with new toon.

OK IDK About shaft length but I have problems usually above 4000 rpm the motor is rated to 6400. it will run 5400 if I don't get the cavitation/ventilation problem BUT I have had the problem under 3000 RPM in straight line. As it sits now the motor cannot mount any lower.

 

[lncoop]

Re: Problem with cavitation with new toon.

What makes you confident it's ventilation? Can you give us a detailed description of what's happening? What does it feel and sound like when you experience the issue?

 

[noticon75]

Re: Problem with cavitation with new toon.

the RPM's go up but the toon comes to a stop while the motor is reving out of control.

 

[lncoop]

Re: Problem with cavitation with new toon.

Hmmmm. You referred to the boat as new. Is it brand new, or new to you? I ask because it sounds to me like a spun hub.

 

[DavenLC]

Re: Problem with cavitation with new toon.

Hmmmm. You referred to the boat as new. Is it brand new, or new to you? I ask because it sounds to me like a spun hub.

I'm having the same issue with my 2002 50HP Merc 2stroke 3cyl.
What do you mean "Spun Hub"?

 

[noticon75]

Re: Problem with cavitation with new toon.

Hmmmm. You referred to the boat as new. Is it brand new, or new to you? I ask because it sounds to me like a spun hub.

Brand new. and brand new to us! the dealer first thought it was a spun hub but it was fine. We do think we have the problem figured out. The lake we are on is up and is floating a lot of debris and the dealer is thinking it might be the trash in the water. Thankfully the lake is coming back down to conservation level.

 

[lncoop]

Re: Problem with cavitation with new toon.

I'm having the same issue with my 2002 50HP Merc 2stroke 3cyl.
What do you mean "Spun Hub"?

Over time the material between the prop and the hub will break down to the point that it can no longer hold the two together at higher RPMs. If that's your problem you can either replace the prop or have it re-worked. I think a re-hub is generally a little cheaper.

 

[lncoop]

Re: Problem with cavitation with new toon.

Brand new. and brand new to us! the dealer first thought it was a spun hub but it was fine. We do think we have the problem figured out. The lake we are on is up and is floating a lot of debris and the dealer is thinking it might be the trash in the water. Thankfully the lake is coming back down to conservation level.

Ah. That will do it. The first time we hit a floating stick at WOT my wife freaked out. Hope that's all it is. Keep us posted.

 

[TexasTriToonin]

Re: Problem with cavitation with new toon.

I was recently looking at the Mercury website at props. It said a 4 blade helps with cavitation on pontoons. Maybe worth a look since you have a Merc too.

 

[goboating]

Re: Problem with cavitation with new toon.

To the people who wonder about it...look inside your prop. You will see what looks like a rubber bushing around the center splines. This is the hub. It is the only thing that connects the splines to the prop. I have a 25HP Mercury. The first time I took it out everything was fine untill I tried to get on plane. Instead, all of a sudden the motor would go to max rpm's and the boat would settle back into the water. When I took it to my local boat store they put it in a test tank and that was the trouble. A new prop was going to be $120-$130 bucks, but I sent it off and had the hub replaced for $80 including shipping.

 

[rickdb1boat]

Re: Problem with cavitation with new toon.

Most newer 115 HP Merc 4 strokes will come with a Mercury prop, which has the Flo-Torq (Delrin) hub instead of the traditional pressed in rubber hub. If it's spun, you'd know it. Once they are gone, it will be tough to get much above idle speed (if that) in gear..