View Full Version : Vibration turning to right when pulling

06-01-2007, 11:26 AM
I've got an '01 Mobius V and have a weird vibration when turning to the right at speed and under a load, either with ballast filled making a turnaround or pulling a few kids on a (dreadful) tube. It almost feels like the transmission wants to slip, like it starts to give, but it never actually does.

Last summer the local deal went through it from bow to stern and didn't find anything wrong. This year I've found the same vibration/whirring sound when turning to the right, again only at speed with a load. A friend was telling me this is probably prop wash but I'm having a hard time believing that. The boat only has 200 hours, is always serviced and is in immaculate condition.

Anyone have any ideas what might be causing me the problems? Other than the right turn vibration thing it runs perfect straight line and left turns are nothing.

06-01-2007, 11:59 AM
The fact is only happens when turning right leads me to agree that it is cavitation or ventilation since that is the direction of force by the rotating prop. Both create a "shudder" as the prop over-revs and has periods of low and high force as the blades go through air-water-air-water....

You are probably turning too tightly. With a load of ballast, you should be turning wider since the hull is not riding as normally designed and more of it is out of the water. There were 2 threads about this a while back.


06-01-2007, 12:16 PM
Thanks - I did a search on the forums but didn't find any threads and I just joined today!

That's a relief to hear that is "most likely" the cause. My buddy also mentioned there is a certain brand of prop (Acme I think he said) that would help to eliminate this. Sound familiar at all?

06-02-2007, 12:56 AM
I've never heard that Acme is any better than OJ, or visa versa. Interesting thought though - they are shaped differently.


06-02-2007, 11:50 PM
It was probably a soggy chicken.


God I need to get to the lake.

06-04-2007, 01:57 PM
Hey Berg -

I have the same issue when doing the 'spiral of death' to the tubers. It is just cavitation. It is a little un-nerving the first couple of times it happens. There is nothing worse than breaking your boat pulling tubers!! That happened to my buddy Mem. Day weekend. While pulling a tube with his '04 Tige 21i, one of his swim platform mounts broke. The heavy teak platform started to swing out and destroyed his TAPS system. The boat is now in the shop for $1-2K in repairs. While it is in the shop they will also fix his bad starter, dead speedo, and transmission shudder. I told him to buy a new Moomba instead of the used (rental) Tige. We both bought them before last summer, and I have 80 trouble-free hours on my Outback. He has to hit his starter with a hammer to make it work. Who got the better deal?

Enjoy your boat, and be safe,


06-04-2007, 09:17 PM
Thanks Dave-

I have wondered if I'm actually sliding a little too much in the turns creating the white wash and if a fin or skag on the bottom would make any difference. Not going to mess with it though - would rather spend my money on other goodies.

Funny you mentioned the problems with the Tige. I was looking pretty hard at those before coming across my boat. I'd be driving one now if the seller hadn't backed out on me last minute. Kind of glad he did since I found this MobiusV instead.

06-04-2007, 11:41 PM
Put a few gal in the center bag - no more cavitation.

Not that I pull tubes or anything.


06-06-2007, 11:08 AM
I just purchased a 2000 Moomba Outback LS with 60 hours. Great boat but a little concerned about the "reving or slipping" while pulling towables. While in the figure 8 encounter a "rev" or feeling as though you
have a clutch engaged. The RPM gauge never moves...very strange.

Part II. Are you running Premium fuel? I fueled up with unleaded 89 octane and after a few minutes around the block the boat would not idle until I added a fuel additive.

Had no reservations about the boat (4th time on the lake) up until now, but kind of thinking twice about the Moomba. Can someone make relate?

Previous post about the reving sounds like my problem, but not sure.


06-06-2007, 11:55 AM
These boats are highly manueverable, but basically designed to pull a skier or boarder in a straight line.
Question: On a sterndrive, does the prop sit lower in the water once the boat is on plane more so than these ski boats? The only time my old I/O aerated was in hard turns pulling a toober.

06-06-2007, 12:08 PM
I think you are encountering the same problem I am. The more weight in the boat while pulling on the tube, the worse the revs or prop wash but the tachometer doesn't ever flutter. I don't think it's the tranny or the Vdrive slipping on mine.

Another friend of mine with a 2005 Mobius XLV just put on an Acme prop and just couldn't be happier with it. Rave reviews all around from him.

I have run 89 octane almost all the time with no problems. I will occasionally run 92, a bottle of treatment or octane boost through it for good measure but have never had any idling problems. Thing is - compare the cost of a few bottles of treatment to the extra cost of filling with premium. About $6 for 30 gallons. Might save yourself the hassle and just fill'er with 92.

06-06-2007, 12:22 PM
Man- you are dead on with that assessment! In fact, I had a lot of people in the boat pullng a "Big Mable" along with another towable so as you can imagine we had some weight going on.

So based on your comment, did you get a new prop? Or, are you kicking it around? I looked on the ACME website, but I don't have a clue as to what size to get, etc... Looks like about a $400 fix- huh?

I was all stoked about the boat until last weekend, but maybe this will do it. I liked your call on the gas treatment too.

06-06-2007, 12:27 PM

Since both outboards and sterndrives are planing, the prop is lifted close to the surface, it is MUCh easier to cause aeration (not cavitation) on a OB or SD, then on towboats. Turning hard actually lifts the prop out of the water.

Towboats tend to get cavitation vs aeration because they sit much lower in the water and do not plane out as much... but because of the ability to change the ratio and shift in weight, when turning they can lean over more.. the more ballast, the more they tend to lean. The wakeplate can help this a LOT, but bubbles under the boat cause cavitation and you then feel the effects.

So, the more ballast, the wider the turns need to be.

Simple rule.

When unweighted, and with the wakeplte set properly - you can spin these boats 180 and not cavitate one bit. Can't do that with an I/O !

Hope this helps,


06-06-2007, 12:35 PM
Great explanation. This is my first inboard moving from I/O boats and it has been an eye opener. Don't get me wrong..positives with both, but I see exactly what you mean with the cavitation. I guess with the rope attached to the tower it exaggerates the leaning effect too.

The remedy is a new prop and wider turns. Do you know anything about ACME props and the size I would need for my 2000 Outback LS?


06-06-2007, 12:38 PM
I'm torn on what I want to do. I bought my boat last June and put about 30 hours on it. I think the prop is the original and it is absolutely flawless minus two little nicks that are maybe a half mm or so. I don't have perfect pass yet or any big boomin' stereo system so of course I've got a big wish list and a disproportionate budget.

Depending on how things go this summer I may break down and buy the prop - keep this one for a spare. We'll see.

You might consider taking your Outback into the dealer for a full systems check & tune-up. Who knows - it could be some temperature sensor telling the fuel injection to cut off the fuel or air mixture to make your idle rough. Right after I bought mine I had the local dealer go through it from end to end and check everything out and give it a tune. I do (most) of that all myself now, but initially I felt it was worth the investment considering the cost of the boat and the thousands of $$ of gas I'd be putting through it... Plus I've pulled more than one person off the river with a boat load of :( when there pride and joy wouldn't start or stay running.

06-06-2007, 12:42 PM
Thanks jc,

but I'm Joe, not Butta.


And NEVER tow inflatables from the tower !!! Designed for much less stress - you can cause all sorts of stress cracks and damage. Inflatables are the hardest thing to pull, and shoi;d only be attached to the pylon, rear tow point, or a bridal across the two rear lift eyes.


06-06-2007, 01:21 PM
Very true with towing from the tower Joe. However, if you ever have never tried it, you can really whip a tube when pulling from the tower! We tried it just once with a buddy (in his late 20's - no kids) and it was the wildest ride I have ever seen on a tube. We could have gotten him clear out in front of the boat coming out of a turn with just a little more finesse. Not encouraging any recklessness - just had to share - because we would have killed him for sure if we had kept it up...

06-06-2007, 01:23 PM
Aerate, not cavitate. I stand corrected, and thank you on that Joe. Even made the edit on me previous post.
btw, Joe could only want to be Butta, he could never actually be B.

08-27-2007, 12:27 AM
my buddy has a 2002 moomba kamberra and he is having this same problem. today it seemed a lot worse then it normally is but it was very windy and choppy. could that be why it was worse than it normally is or could it be something else and if so what could that be? thanks

08-27-2007, 01:06 AM
I would say yes to that based on my experience. Running on glass the vibrations are minimal or non-existent when cranking through turns. Out in the chop trying to whip a tube around over your own wake and others really seems to bring out the whine and whir.

I actually have a small bend on one of my fins from a close encounter with a log over the 4th of July. Funny thing is that it's not causing any new vibration. Last run out it seems to actually be cancelling out the vibration coming from tight turns when I'm loaded down like I was experiencing earlier. Weird... I was also checking out a Malibu and Mastercraft floating next to me who both run 3 skags down the bottom. Helps to keep them from sliding in the turns, etc. I'm wondering if the Moomba hull would benefit from that but there's no flat mounting spot on these years (like the newer Moombas have) if anyone were considering adding some on.

New prop is coming soon - hopefully before summer is dead and gone!

08-27-2007, 06:35 PM

I too have come across this problem. First time was in fairly choppy water, pulling a tube with three kids on it, going about 22 mph. Would only happen on right turns and when it did, I notived that the engine speed would shoot up about 200 rpms. When I pulled under the same conditions but increased speed to about 24-25, it didn't do it. On my boat, it felt as if the transmission was slipping. I don't recall any significant shuderring. It happened again this weekend, again while towing a tube and only when turning right.

I called the dealer and the first thing he asked is it happened at other times. I said no, and commented that we surfed later on with no problems. He said that it's definitely cavitation (or maybe aeration?) because if it was the tranny slipping, it would definitely have done it also when we were surfing, as that puts a lot of load on the tranny.

Someone on the board suggested filling the front bag to prevent this. I'll try that next time.

Ditto with what Joe said - the tower is designed to pull one wakeboarder. I always use the pylon when pulling the tube and have no problem whipping them back and forth across the wake.