Cavitation - End of My (Bleeping) Rope!

[Silvertip]

Re: Cavitation - End of My (Bleeping) Rope!

The prop hub is splined to the engine prop shaft. But the hub has a rubber cushion between it and the blade area of the prop. If that bond lets go you have prop slippage. If you have an XHS or similar hub system this is not an issue. But since you have tried different props, slippage is not the issue. Pontoons have very turbulent water at the rear and the prop needs to operate in that turbulence. The reason the Big Foot motors were made available is because they can swing bigger props and sit a bit lower in the water than the 1.83:1 gearcase. That setup is simply not meant for pontoon or work boat service. My Misty Harbor is powered by a 40 HP Suzy 4-stroke. It has a 2.27:1 gearcase, swings an 11-1/2x11 prop and does not ventilate. Think of the advantage a similar gear ratio of a Big Foot (or the 75/90 HP motor) and a 14 inch diameter prop would provide you.

 

[corm]

Re: Cavitation - End of My (Bleeping) Rope!

Hi,

Interesting posts.
I am with Silvertip for the most part.
One thing we used to do to help you problem was to put a "pontoon cup' on the prop. Some what like doing a double cup rolling it out to the out edge of the blades. It changes the rake a bit which is not all bad.
The other thing I noticed in your picture is that the transom vee is not low enough to flatten out the water before it gets to the prop. So you have to much turbulence getting to a small diameter prop. A big cup will help but not cure it. I think you will have trouble with a big foot too until you fix your transom. I know I had to tweak mine. I have a 25 ft Ercoa with everything on it running a 80 hp merc and a 18" P 20 degree rake prop. After I reformed my transom well vee to flatten out the water flow better it works great. I like the high rake props for their bite in an air/water mix. Not all high rake props work the same either. I tried 4 or 5 before I kept the one I have on now.
And yes I know that my hex pontoons perform different than the round tubes. So my propping may not work for others. I know the tweaking the motor well vee works on all boats that have a poor designed one.
It is hard to scale from your pictures but it looks to me like your transom vee should be 2" lower with that motor. Just free advice on the internet.

 

[sschefer]

Re: Cavitation - End of My (Bleeping) Rope!

I'm not qualified to talk toon boats but I agree whole heartedly with what Silvertip is telling you. I just went through a similar situation that I created when I put a 5" offset jack plate on my v hull. I could raise and lower that motor a full 7" and I tried 3 and 4 blade props but I still had cavitation. The problem was simply that the the prop was in turbulent water. I got rid of the jack plate and got the prop into cleaner water and the problem is gone. Now my four blade lifts the boat up and compensates for the heavy batteries up front like it's supposed to.
I don't know if moving the motor is possible for you but certainly Silvertips suggestion are.

 

[PolishPrince]

Re: Cavitation - End of My (Bleeping) Rope!

You might want to go back to the Tracker dealer with a tape measure and compare your measurements with a new "showroom" boat. I'd hate to see you spend another $3-$4K and have the same headache. You need to exhaust ALL the possibilities before dropping that kind of cash.

 

[lowell7963]

Re: Cavitation - End of My (Bleeping) Rope!

This may help or add more confusion. This my boat, a 24Ft Sweetwater, 22" diameter pontoons, 50 HP BF 4 stroke. Notice my transom is flat with minimal slope down towards the motor. Also see where my water line is.

 

[mayorjones]

Re: Cavitation - End of My (Bleeping) Rope!

I've said all along that I believe that the design of the Sun Tracker transom, and it's exaggerated "V" shape do definitely make my problem worse. I know there's a lot of turbulence back there - you can visually see it. But at the same time, it is what it is, unless there is some way of modifying it...

Here's where I'm at - I can't make my motor a Bigfoot. If I'm going to spend the money to upgrade, I guess I would likely make the move to the 90 hp 4 stroke to give me more performance for tubing, etc... I am not flush with funds and am not wanting to spend more money, but at the same time, I already have a very large investment that at the moment is basically useless to me.

I'm still waiting for a call back from Sun Tracker - I may call them back today and see if they have anything to report/suggest.

Again - I do GREATLY appreciate all of you taking the time to read through all of this and offer your input. Without you all, I'd be even more frustrated.

Thanks.
Dwight

 

[sschefer]

Re: Cavitation - End of My (Bleeping) Rope!

Best of Luck Dwight.. I know your frustrations.. Just keep working at it, you'll get it.

 

[lowell7963]

Re: Cavitation - End of My (Bleeping) Rope!

I've been looking around at the Sun Tracker site. Does your boat ride like this in the water? And does your pontoons have these "fins" on the outside?

This pic is from their site. It is a 2009 and a really nice looking boat, I hope you get it figured out.

 

[mayorjones]

Re: Cavitation - End of My (Bleeping) Rope!

Yes on the fins (I think), and no on the ride. The front of my tubes never leave the water that I'm aware of. I've looked up front along the side of the boat when it's running, and the front of my tubes are always in the water, I believe...

My boat is yellow, but yeah', it's a beauty... That's what makes this all so difficult. I absolutely LOVE the boat and would like to show it off to friends and family but am embarrassed to take anybody out in it because I know I'll have problems.

Thanks for the post.

Dwight

 

[PolishPrince]

Re: Cavitation - End of My (Bleeping) Rope!

I'm beginning to think you may be onto something with the transom design of your boat. I'm not a hydrodynamicist but while the bottom of the transom tapers down to push water into the prop, it seems to me that the "V" shaped floor would also direct water to the sides and decrease the amount of water directed at the prop.

 

[mayorjones]

Re: Cavitation - End of My (Bleeping) Rope!

Well, I'm not going to go so far as to say it's the problem, but it certainly doesn't help the issue. If you stand to the side when it's out of the water and the motor is down, it would appear that the "v" is going to move water away from the very spot that my prop is going to be looking for water to bite into. Add the fact that I'm likely not running the perfect prop and/or gear ratio and I think you've got the perfect "storm".

Again - the guy at Bass Pro Shops told me this is how they sell all of their 21 footers. However, I called another local Sun Tracker dealer, and he said that all of his go out the door with the Bigfoot. Let's remember that I am running this on the Mississippi River that holds a LOT of current, thus making the water a "moving target" from the get-go. If I were on a lake without current, it might be a different story? Who knows.

Called Sun Tracker today and talked to the gal I talked to - she had sent my info to her supervisor and was waiting for him to respond (to me). They can make themselves look really good or really bad with this deal - I know a lot of people read these posts. We'll see what they have to say.

Thanks again guys.

Dwight

 

[flycaster]

Re: Cavitation - End of My (Bleeping) Rope!

Well, I'm not going to go so far as to say it's the problem, but it certainly doesn't help the issue. If you stand to the side when it's out of the water and the motor is down, it would appear that the "v" is going to move water away from the very spot that my prop is going to be looking for water to bite into. Add the fact that I'm likely not running the perfect prop and/or gear ratio and I think you've got the perfect "storm".

Again - the guy at Bass Pro Shops told me this is how they sell all of their 21 footers. However, I called another local Sun Tracker dealer, and he said that all of his go out the door with the Bigfoot. Let's remember that I am running this on the Mississippi River that holds a LOT of current, thus making the water a "moving target" from the get-go. If I were on a lake without current, it might be a different story? Who knows.

Called Sun Tracker today and talked to the gal I talked to - she had sent my info to her supervisor and was waiting for him to respond (to me). They can make themselves look really good or really bad with this deal - I know a lot of people read these posts. We'll see what they have to say.

Thanks again guys.

Dwight

Last October I purchased the SUNTRACKER FISHING BARGE 21 foot.
The dealer would not sell the boat unless it had the MERC BIGFOOT. Got the 60 HP and have not had any cavation problems.
My prop site well below the "V" which contains a 30 gallon gas tank.

 

[MikDee]

Re: Cavitation - End of My (Bleeping) Rope!

Watching all this, IMO, your motor is not deep enough in the water. The only thing I can say is, when on plane at WOT, look over the back (transom) to see where the waterline is, then measure it from a fixed point on the transom, or try to make a best "guesstimate" as to where? Then reset the height on your motors cavitation plate to that point, or just a bit below it, and then try it.

 

[mayorjones]

Re: Cavitation - End of My (Bleeping) Rope!

Everything appears to me that it is as low as it can go - how/where would I find additional adjustment to move it down even further to meet your suggestion regarding the cav plate vs water line?

Thanks.
Dwight

 

[lowell7963]

Re: Cavitation - End of My (Bleeping) Rope!

MJ,

Maybe you should start an additional post, a poll if you will of all the 21Ft Suntracker owners to see what motors they are running and any issues. The post title needs to catch their attention so something about 21Ft Suntracker Bass Buggy. The "Cavitation - End..." title may not net those happy owners without problems.

Good Luck, the answer is out there!

 

[Silvertip]

Re: Cavitation - End of My (Bleeping) Rope!

The shape of the engine pod, the position of the AV plate, engine mounting height, and the general construction of this pontoon is perfectly normal. I have a Misty Harbor with virtually an identical pod and my engine is mounted identically to yours and the AV plate is in about the same position (about 5 - 6 inches below the pod) and I have no ventilation problem unless everyone dashes up front for some reason. But that's an issue with any pontoon. Make people sit down when under way. As you have determined, one dealer tells you they sell all their pontoons in that model with a standard engine. If you contacted those people I wonder what they would say about the performance. On the other hand, one dealer refuses to let the unit go without a Big Foot. My money is on the Big Foot. As for the picture of the pontoon with the nose of the tubes in the air, those fins on the side (the very long fins) are called lifting strakes. Standard tubes have shorter fins up front but those are simply spray deflectors.

 

[ozarkglen]

Re: Cavitation - End of My (Bleeping) Rope!

Before I spent a lot of money on a new motor, I would definetly try a transom jack. Sure sounds to me like your motor is too high. I found a boat salvage yard in the local area and picked up a transom jack for $100. You can find a new one in the $300 - $400 range. Even if this doesn't solve your problem (but I believe it will), it will work on your new motor and give you more fine tuning options later. Good luck!

 

[mayorjones]

Re: Cavitation - End of My (Bleeping) Rope!

I am more than willing to try a transom jack - can anybody give me any pointers on what I'd want to look for? I looked at them briefly on E-Bay, and it looks like there are some different "sizes" of "offset" or something?

Any advice would be greatly appreciated.

Thanks.
Dwight

 

[Jeep Man]

Re: Cavitation - End of My (Bleeping) Rope!

Yes on the fins (I think), and no on the ride. The front of my tubes never leave the water that I'm aware of. I've looked up front along the side of the boat when it's running, and the front of my tubes are always in the water, I believe...

My boat is yellow, but yeah', it's a beauty... That's what makes this all so difficult. I absolutely LOVE the boat and would like to show it off to friends and family but am embarrassed to take anybody out in it because I know I'll have problems.

Thanks for the post.

Dwight

Dwight, my '08 definitely does not have these "fins". To me, they look like lifting strakes which, I am told, are ineffective with smaller (less than 120 hp) motors. I'd be surprised if your boat has them.

 

[mayorjones]

Re: Cavitation - End of My (Bleeping) Rope!

Yep - no fins here either.

After leaving four phone messages and two e-mails for the Customer Service Manager at Sun Tracker, I got a response today asking if I had a local Sun Tracker dealer. Our closest is an hour away, and I responded with that info but have not heard back yet. I'll keep you posted.

Wish me luck!

Dwight