Cavitation - End of My (Bleeping) Rope!

[Zeeter]

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

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

though it is SO weird that the guy at Bass Pro would tell me this is the same motor they use on all of them.)

That doesn't surprise me a bit. Those guys cant fix a sandwich. What Silvertip said makes perfect sense. He knows more about boat set up than most Ive read on here. You may have the option of just switching out lower units. Dont know. Thats got to be cheaper than an engine swap.

 

[rickdb1boat]

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

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

Looks like an extra long shaft motor to me.

 

[mayorjones]

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

I have read (maybe in this post?) that the Big Foot comes in a 2 stroke and 4 stroke - is anybody knowledgeable on the ability to just get a Bigfoot lower unit and put it on my existing two-stoke motor? If that's an option, I would be interested in that, I guess.

I called a local Mercury dealer - they wanted somewhere in the range of $6500 for a new 60 hp Bigfoot, and would give me $3000 for mine. Hate to pay $3500 to fix a problem that I inherited, but that's how life goes, I guess?

For what it's worth - I put the original 3 blade prop back on today - it definitely behaved better than it had with the four blade, but once a little gas burned off, it started cavitating again, even at only about one-quarter throttle with the engine all the way down.

Keep the thoughts coming guys.

Thanks.
Dwight

 

[Bass Tracker TX17]

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

Sounds like wrong setup BUT I might be way off base here. I couldn't see a good side view of the motor. Is your stop bolt for trim in the closest hole to the boat ???? If it's not put it there and try it one more time.. trim that puppy all the way in.

 

[Zeeter]

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

The bigffots came in 2 and 4 stroke as far as I know. The whole difference is the gear ratio and the being able to use a larger diameter prop. as silvertip mentioned.

 

[svilla]

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

If your boat is running better with weight in the stern, you could add ballist. I know it is a band aid fix, but 150 - 200lbs worth of dumbells would only cost you around $100 bucks. The up side is you can also move the weight around to balance your boat. Or simply remove the weights when you are going to run at max capacity.

 

[mayorjones]

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

Well, in regards to adding weight, the problem is that it is so sensitive that I couldn't keep up with it. If someone, even a child, walks to the front to get a drink from a cooler, it is enough to set it off.

I called Sun Tracker today and gave her my sob story. She got the serial # and was going to check on some things. Since I'm not the original owner, I don't know how helpful they'll be, but it's worth a shot.

As mentioned - the guy before me only used the boat a couple of times (didn't even put numbers on it), so I'm thinking this has been a problem since day one and he just didn't want to deal w/it. Sure wish I wasn't

 

[svilla]

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

well I wish you luck, hope tracker will help. If you lived closer I would volunteer to put my fat rear (260lbs) in the stern of the boat to see what weight would do for you .

 

[mayorjones]

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

Appreciate the offer on the fat rear - thank goodness we're not next door neighbors

I have found a 2006 Mercury 90 hp 4 stroke at a local marine shop. He's offering to trade motors, swap em' out and do the full set up with a new prop for $3825. Doesn't sound like a bad deal to me. As a reminder, I now have a 2008 50 hp 2 stroke.

Anybody have any comments on that trade - good, bad or otherwise?

Thanks again everybody.

Dwight

 

[flycaster]

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

Appreciate the offer on the fat rear - thank goodness we're not next door neighbors

I have found a 2006 Mercury 90 hp 4 stroke at a local marine shop. He's offering to trade motors, swap em' out and do the full set up with a new prop for $3825. Doesn't sound like a bad deal to me. As a reminder, I now have a 2008 50 hp 2 stroke.

Anybody have any comments on that trade - good, bad or otherwise?

Thanks again everybody.

Dwight

Is it a BIGFOOT???
If not you may be tying a knot into the end of your rope.

 

[lowell7963]

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

The motor you have should have a 3 or 5 year warranty. Be sure what you are getting from the marine shop.

I found a 60HP BF with 3 year warranty on ebay for $5,800.

I can't see from the photos, but can you post measurements from the botom of the transom - "V" to the center of the prop. I'll compare to mine tonight, On my 24FT with 50HP BF. I do remember the lowest bolt is right at the very bottom of the transom, yours seems a couple of inches above that.

The real issue is getting the motor lower in the water, not the HP.

And lastly, how did you diagnose your problem as cavitation? Any chance the prop is slipping on the hub or something similar?

 

[mayorjones]

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

I tried a different prop - I guess that's what told me it wasn't a prop problem, slippage, etc...

I'll measure it up per your suggestions and post it. I understand that the motor needs to be further in the water - I guess I thought I would be happier overall with a larger motor anyway, especially a 4 stroke, which would be much quieter than what I've got now. Even when it is "working", it still screams pretty good at 5500 rpm (WOT).

Thanks for your assistance.

Dwight

 

[Silvertip]

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

Flycaster -- There is no 75/90 HP BigFoot. In fact the 40/50/60 BigFoot motors have the 75/90 gearcase. So a 75/90 are suitable in standard 20 inch versions. However I would still specify Mercury's pontoon prop.

 

[svilla]

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

How much would it cost to make your motor the big foot? Is it just a lower unit change? If so it may be cheaper since you could still e-bay your good parts.

 

[Thad]

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

I am not a pontoon guy, but I found this so interesting that I could'nt stop reading.
I see where everyone is hung up on the measurement from the transom mount. I looked at the pics and it appeared that the bottom of the log is lower than the cavitation plate. The aft pic is somewhat of an illusion as the motor is trimmed in. The side pic, although only showing one log and a partial was enough to give the appearance of a potential culprit which could explain some of the "cavitation" issue. As weight moves forward, the logs will absorb that weight and dig, bringing the aft portion of the logs up, in return raising the prop closer to the surface.

Like I said, not a pontoon guy, and this is mearly an uneducated observation, but maybe a new set of eyes isn't always a bvad thing.
Please don't be too hard on me:redface:

 

[mayorjones]

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

Though I own the one in question, I am not a pontoon guy either. If anybody else is in agreement w/what he's saying, I would gladly take pics from other angles if it would help in determining this.

I posted a question regarding converting to Bigfoot both here and on the Mercury outboard page, but no responses as of yet...

Thanks guys.

Dwight

 

[mayorjones]

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

I just called Mercury and no, it is not an option to convert this to a Bigfoot. The innards are different

 

[Jeep Man]

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

Appreciate the offer on the fat rear - thank goodness we're not next door neighbors

I have found a 2006 Mercury 90 hp 4 stroke at a local marine shop. He's offering to trade motors, swap em' out and do the full set up with a new prop for $3825. Doesn't sound like a bad deal to me. As a reminder, I now have a 2008 50 hp 2 stroke.

Anybody have any comments on that trade - good, bad or otherwise?

Thanks again everybody.

Dwight

In your shoes, I would very seriously consider this deal. Just going from a 50 to a 90 is worth close to 3K. Then moving from 2 stroke to 4 stroke is worth a couple as well. The 4 stroke is going to be a lot quieter and give you better performance. There is a wiring harness adapter needed for your new control to work on an older motor (14 pin to 9 pin), but I think it is for pre-2005, but check it out anyway. My '08 Sun Tracker has an '02 motor so I needed it. Also, see if he will give you a warranty that would match the '08 your trading.

 

[98psi700rmk]

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

Before you lose your mind and trade motors and spend a ton of money you don't need to spend calm down a bit and check a few things over.

I am around these boats every single day of my life. It sure sounds to me like your prop is slipping.

Think about it....

Your problem gets worse when you have more weight on the boat and when more stress is put on the motor.

Your RPM levels fluctuate erratically for basically no reason. I would assume your gas tank is around 12-14 gallons so the extra 75lbs of gas weight shouldn't make that big of an RPM difference.

How did you re tighten your prop??? what did you use to hold it in place when you put it on? Did you use a proper wrench to tighen it or did you just use a regular wrench?

The difference between a prop that can slip and a prob that is tight isn't as much as people would like to believe. You need to make sure you hold the prob steady when you tighten it, you cant just hold it by hand and tighten it up. This potential solution is basically free so I would try it.

Make sure this is with the 3 blade also. Your lower end gear ratio wasnt designed for a 4 blade. A 50 should run your boat just fine, a 90 on that boat is going to be big time overkill.

 

[mayorjones]

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

I'm interested in talking about prop slipping, but if the "spline" has teeth and the prop itself has teeth, how would it slip? I'm not that smart of a guy, but looking at how things are attached, I'm struggling to see how unless the prop fell off it could slip.

Thoughts/explanation? Please believe me - I'm not trying to sound cocky or obnoxious. I am just admitting ignorance and looking for some words of wisdom...

Thanks.
Dwight