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Old 03-12-2015, 17:31   #16
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Re: Catamaran Air Lift Bag

Interesting.
Why not use smaller cylindrical inflatable bags under each hull to lift a vessel off the sand/beach. The cat. could then actually be moved backwards or forwards if needed to vary access for hull processing, depending on keel etc. configuration. I suspect the cost of say eight to ten of these cylinders would be less than the cost of a single boat yard lift out. OK. yes a small compressor would be required although I have seen an arrangement for a small flatbed truck (called a "utility" in Aus.) that used the vehicle exhaust (directly connected from the tailpipe to a bag under the flatbed.) The air bag (about 1 meter diameter) tilted the hinged trailer bed that had a 3000 kg lump of concrete on board. Very impressive.
Any air bag arrangement would be easier on a hull than small area supports such as props or travel lift straps.
Incidentally, due to the beam of multihulls, the owner is often obliged to use and pay for very large travel lifts. In Cairns (Australia) this means that catamaran lift outs are seriously extremely expensive.

Even if the lift out is done by a travel lift, the catamaran could then be sat on the air cylinders to allow some movement backwards or forwards ... if needed.

The bags could be also used to achieve what is shown in the photo. That is, just to lift the aft or possibly bow or even just one side of the catamaran.

I can see an innovative opportunity here for some manufacture. They could be marketed as "Republican air bags" or just "Trumps". My friend suggested a lot of inflatable swimming pool lie-lows borrowed from the local kids. He's a worry. But it does imply that such bags may well have other uses. Fenders, soft seats etc.
Cheers
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Old 04-12-2015, 05:37   #17
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Re: Catamaran Air Lift Bag

The catamaran in the OP's picture is just assuming an inevitable position waiting for the multi-hating people to pile into this thread.

Mark
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Old 10-12-2015, 18:09   #18
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Re: Catamaran Air Lift Bag

Yanmar saildrives prior to the D50 models had a 100 hour oil change cycle, and the boat had to be hauled since the only drain was on the bottom of the drive. With the 50 they finally put in a chase so you can get it out of the top. Not to bright of engineering I think.

Did hear of one guy who changed old ones in the water. He would dive and attach a fitting to the drain hole with a tube above the surface. Figured that the weight / pressure of the oil kept water from intruding into the SD. between pulling the drain plug and attaching the hose fitting. Would then open the fill cap on the SD, pump the old oil out via the hose, fill with new oil and then dive down and replace the plug on the bottom of the SD.

From having both an SD31 and SD50 on my boat, I think this would probably work with no problems, but never tried it.
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Old 06-11-2016, 07:39   #19
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Re: Catamaran Air Lift Bag

Quote:
Originally Posted by ZipTie View Post
This is a nice way to avoid a Haul Out.
Fix a prop or a sail drive or Pull a rudder.

Nice to see an alternative method.

This is a picture of a 52 footer in St. Martin.

They 'haul' the aft end of cats by placing a huge Air Lift Bag beneath the bridgedeck, then inflating the bag.
When I look at this picture it looks to be as simple as I imagined it to be. That cat has fairly low bridgedeck clearance so the bag does not need to be particularly large to get it high enough. Keeping the bag in place is easy as it can only squirt out the back so it only needs to be held forward.

Steve.
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Old 06-11-2016, 07:48   #20
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Re: Catamaran Air Lift Bag

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Originally Posted by 44'cruisingcat View Post



Seems easier to me.
Seems a bit difficult to service saildrives sitting like that, still need to jack it up so airbags would still be useful. Fortunatly you have outboards.

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Old 06-11-2016, 07:53   #21
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Re: Catamaran Air Lift Bag

Quote:
Originally Posted by colemj View Post
This is the only way a catamaran is safe at sea.

Even then, it could just flip right over - I wouldn't stand near it.

And finally, your performance in that pic is for once meeting the expectations of all the experts here.

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Old 07-11-2016, 14:01   #22
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Re: Catamaran Air Lift Bag

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Originally Posted by clockwork orange View Post
Seems a bit difficult to service saildrives sitting like that, still need to jack it up so airbags would still be useful. Fortunatly you have outboards.

Steve.
I do feel fortunate in having outboards.

However most boats with saildrives also have minikeels, and can be beached, and saildrives accessed. I've helped friends replace anodes on their saildrives this way.
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