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View Full Version : Cavitation Problems with Moombas



Djdompe
08-07-2009, 11:49 AM
Finally about to get my own boat!!! Looks like so far that the Outback V is the one for me, but am hearing that there are cavitation problems coming out of corners. Has anyone ever encountered this? Or for that matter, can explain to me exactly what this means? Any help would be appreciated

moombadaze
08-07-2009, 11:58 AM
Any boat can cavatate coming out of a corner-its just the prop getting some air and slipping. Not a real big deal-my lsv will do it sometimes.

Djdompe
08-07-2009, 12:02 PM
Sounds like something that can happen with any boat, whether a cheaper boat or a mastercraft... correct?

kaneboats
08-07-2009, 12:04 PM
I noticed it a heckuva lot more often with the old outboard boats than with any of the inboards I've been around. In fact, I can't recall ever noticing it in a DD boat.

Razzman
08-07-2009, 12:06 PM
I think what your hearing is someone who had an issue or thought they did and said exactly the same thing without knowing what they are talking about. If you think about, cavitation is generated by the propellors speed and mass, not by the hull. So in essence any boat is subject to it. Cavitation often occurs from poor propellor design or improper pitch for the application, that is not the case with modern inboards. Cavitation is often thrown out as a catch all when one of two things occur, the person saying so has no clue or the issue (if one exists) cannot be found.

Razzman
08-07-2009, 12:10 PM
Any boat can cavatate coming out of a corner-its just the prop getting some air and slipping. Not a real big deal-my lsv will do it sometimes.

When i test drove my LSV the dealer pulled a move on us and i swear we were going over! Ever seen an LSV in a high speed spin? I didn't think it was possible but it is and let me say i don't want to repeat it!

Anyway the point is even in that extreme turn/spin the prop did not cav or slip. I could see in rough conditions and a improperly trimmed boat the prop slipping. Dunno, i don't do powerturns as they have no purpose.

Razzman
08-07-2009, 12:11 PM
I noticed it a heckuva lot more often with the old outboard boats than with any of the inboards I've been around. In fact, I can't recall ever noticing it in a DD boat.

Your 100% right Kane and mostly because of trim.

moombadaze
08-07-2009, 12:17 PM
Ever seen an LSV in a high speed spin?


Nope i havent.

zegm
08-07-2009, 09:33 PM
I have owned 5 boats in the last 25ish years. I worked on a US Army rec. area where we rented out all kinds of boats that I got to play with. With this being said I have been on several outboards that I could get the prop to cavitate and we actually ordered short drives so that they would do it, it acts like a governer when you turn tight. But I have never been in an inboard and heard one do it. And I will and do crank them over at top end! If you get the prop out of the water on an inboard well then maybe you should be kissing you a&& goodbye!

Djdompe
08-10-2009, 01:19 PM
Sweet thanks a lot guys! Hopefully soon I will join the ranks as a Moomba owner

Ian Brantford
08-10-2009, 06:05 PM
Cavitation (http://en.wikipedia.org/wiki/Cavitation) is the formation of water vapour due to a very low-pressure area. It can happen routinely to a prop under heavy load if the prop is not properly cupped or pitched for the load to which it is subjected. The low pressure can damage the prop, although most commonly for small recreational boats, it will be limited to tearing some paint off of aluminum props. Low-quality or heavily-used props may acquire pits.

A completely different phenomenon is slippage due to air getting around the prop. This will typically happen in a tight turn when the water is choppy. The chop provides an opportunity for the hull, as it slides sideways, to close off a large air bubble between wave peaks. It is not a low-pressure phenomenon and does not pose the same risk of prop damage, although there could be small areas of low pressure as the water/air combination foams around the prop. Slippage is typically very short-lived. Since it involves an interaction of the water's surface and the hull, the hull design can play a part.

In real life, I notice no cavitation and only rare slippage in my Moomba XLV. The slippage only occurs when there is no ballast in use. Neither of these things are significant issues at all. Whoever is telling you about "boat quality" causing cavitation is experiencing a problem with "opinion quality". :-)

smokedog2
08-10-2009, 08:23 PM
add some weight to the center ballast

If you yank & bank tubes you can cause a little cavitation the weight pushes the prop down

jester
08-10-2009, 08:32 PM
I have owned an 08 OBV for over a year now with no issues on Cavitation. Does not matter if the boat is full or empty.

Razzman
08-11-2009, 02:18 PM
I'll still say it's not possible, the prop is too far under the boat. If your getting your prop out of the water then you have greater issues like NO water under the boat. Just my two cents.

Cav & slippage is common on outboards & I/O's. Cav & slippage is a problem or issue with large ships. Submarines have fought cav forever, BUT look at the horsepower & torque applied in these instances, our boats could only dream of those kinds of ratios.

Form&Function
08-11-2009, 02:27 PM
My lsv does not cavitate but it will suck air under the boat in a sharp turn with the ballast full.It also sucks are past the paddle wheel and freewheels the perfectpass into a false reading at idle.Granted the water has to be a little ruff for it to act up.

DDL
08-26-2009, 05:09 PM
We're running an XLV and any combination of tube or rider causes slipping in the corners. The kids like the whip on smooth water and I can't get the backside to stick long enough to get them around. Even doing a couple of quick hard turns to get them outside the wake will cause the slip. When pulling a couple of heavier riders on tubes it's noticably worse.

I also find the boat sticks the corners better doing a left turn over a right.

Is this prop related or the general design of the competition hull?

mmandley
08-26-2009, 05:16 PM
Only related to the tubing portion of your post.

I find it best when people want a hard ride or thrown to the flats, take a 45 degree turn and that will toss them outside the wake, then gradually keep turning and it will put so much force on the tube it forces it to glide out as fare as the rope will allow to the flats. I do this till i get the 180 turn done, then you end up crossing your own rollers and thats a bumpy ride also but the tub is behind the boat. Turn the opposite direction and toss the tube to the other side of the boat into the flats and cross your rollers and there bound to catch air.

Ive tried S turns and such and it just seems like the boat is working harder to get the tubers what they really want.

Sled491
08-26-2009, 05:16 PM
The left and right thing is the prop rotation.

I ski with a couple of guys who each own MC's, the one does cavitate the other no. My Outback, Never!

Ian Brantford
08-27-2009, 03:46 PM
We're running an XLV and any combination of tube or rider causes slipping in the corners. The kids like the whip on smooth water and I can't get the backside to stick long enough to get them around. [...]

I have an XLV, and only one of the 5 tubes that I have available has a problem getting outside the wake. It has an inflated bottom that is ribbed, and this helps it to track too straightly. However, it still gets outside the wake with just a bit more effort.

A good way to get a tube outside the wake is to speed up a bit, go into a turn to give the tube some sideways momentum, then slow down a bit (and possibly stop turning). The tube's momentum will carry it outside the wake, and only marginal speed/turning is needed to keep it there indefinitely.

By "speed", I do not mean a lot. When I upgraded from a smaller boat, I found that I was consistently misjudging speed and going about 5 MPH too fast in the XLV for what the tube and rider required. I learned to pay attention to the speedometer more than "feel". Most spirited tubing (where you are pulling lots of turns and dragging the rider over your own wake from 30 seconds earlier) is best done at 10-20 MPH. 10 MPH to build the wake and 15-20 to drag the tube over it for a good bounce.

That's for braver adults, who dare you to bounce them out of the tube. For lesser folk who want a moderate bounce without the ejection, you can just let off the throttle at the last moment, so the tube goes over the wake under its own momentum, without tension in the tow rope. The rider and tube will bounce up, down, and resume.

DDL
08-27-2009, 11:25 PM
Thanks for the comments and advice gang.

I find I'm always having to adjust my speed slower than faster with this XLV. This boat certainly behaves differently than the 20' Bayliner we were running previously. I've never been a driver that tubes at high speeds (for obvious safety reasons) and I have to admit I was pretty good at giving tube riders all they could handle with that old girl.

Even on moderate or extened turns, the backside of this XLV will pop out frequently. This past weekend we were operating on a smaller lake. As we approached the end of the lake I started into a slow right right with my 100 pound nephew on a single, round tube. He was outside the wake and I wanted to keep the momentum going to get his speed up. As I accelerated through the turn, the backend pop out at least three times. I ended up having to slow right down to get the backend settled back in the water.

It will just take a bit of time to learn the the intricacies of this boat.

Thanks again,
DDL

Hillbilly
08-28-2009, 12:29 AM
Could they be mistaking cavitation for chine lock?

I know when I have my LSV dumped it is a pig in the corners and will sometimes get caught for a second. You really have to muscle it around every once in a while. But like I said it is only sometimes and when it has over 3k in weight not including ppl and gear.

Ian Brantford
08-28-2009, 12:54 AM
Even on moderate or extened turns, the backside of this XLV will pop out frequently.

This may be because of the low deadrise at the transom. What is it -- 10 degrees or less? Your old boat probably had something like 15 degrees.

Solution: you've got a ballast system. Use it! :-) At least, fill the rear ones partway to put a few hundred pounds on the stern. That should help to hold it down.

DDL
08-28-2009, 07:02 PM
This may be because of the low deadrise at the transom. What is it -- 10 degrees or less? Your old boat probably had something like 15 degrees.

Solution: you've got a ballast system. Use it! :-) At least, fill the rear ones partway to put a few hundred pounds on the stern. That should help to hold it down.

I'll give the ballast a try this weekend.

JoeTechie
09-08-2009, 03:00 AM
Ever seen an LSV in a high speed spin?


Nope i havent.


You boys need to come take a ride w/ me. :) Power turns have a perfectly good use... "FUN". :) I understand and appreciate my boat's limits, and I never push them, but people's limits are far exceeeded by the boats - so that makes for a great equation. V-drives cant do real 180's, like the old 17' MC's...but for the average rider - they can't tell the difference siting inside the boat.


Direct-drives, v-drives, and any number of crafts can get 'prop aeration' (cavitation is sorely missused term). I've done it any number of times. It is slight and only noticable a small % of the time. Heck, just riding with the wakeplate all the way up and running too fast can cause porpoising and that can cause aeration and cavitation. Rough water and hard tubing at speeds exceeding what we all like to accept as normal can cause aeration. No matter how "low in the water" the prop is, air gets under your boat - it is not glued or to the water. The amount and longevity of that air is where you go from managable to aeration to cavitation.

-J