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

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.

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Old 04-12-2015, 04:37   #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.



You do not need a parachute to skydive. You only need a parachute to skydive twice.
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Old 10-12-2015, 17:09   #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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