Flotation bags.

[burgundyben]

JFM got me thinking with his pumps discussion.

My boat displaces 4000 kgs. I had to write 4000 kgs as I could not remember tonnes vs tons.

So, if I hit something submerged and bashed a great big hole in the boat I could get pumps running, set off lifejackets in the hole, get a sheet under the boat etc.

I have to admit I've never experimented with the big sheet I have on board to know if its feasible to use it.

But all this might not be enough....glug glug glug.

If I had on board 4 air bags of 1 cubic metre each inflated quickly from a gas cylinder I could keep her afloat right? Realistically it could be kept on board.

One in the cabin, one on the foredeck, one on each aft cleat? Snap shackle on each? Gas cylinder? Automotive air bag type squib? Bish bash bosh.

As far as I am aware they are not available? (Have not actually looked mind!)

For my boat, its something I would consider, of course on JFM's boat its not quite such a practical solution, size of bags, weight, storage, gas cylinders.

I'm sure we've discussed this before.

Maybe something from these guys

http://www.seaflex.co.uk/

 

[peterg]

Couldn't you just have 4000 Waterbuoys attached all over the boat /forums/images/graemlins/wink.gif /forums/images/graemlins/laugh.gif

 

[jfm]

Hmmm. With my boat, it's just a plastic fantastic and you can buy another one from a catalogue any day of the week, so I suppose if the hull rips open I'll go for the liferafts and tender. My thinking on the pumps is that if the leak is small, ie pumpable, i'd prefer to stay in the mothership than get in liferafts, if 30nm offshore

Your boat is irreplaceable so worth saving. Hence the airbags seems a good idea. Catch is, i think you'd need 4 dive cyls to inflate them, which is quite a lot to carry. Crudely, if a dive cyl is 5 litres (that''s a guess) at 228bar then it will expand 200 times to fill an airbag at 1psi, which is all you'll need. That means it'll expand to 1000 litres, which is a cubic metre. So you'll need 4 dive cyls. With the bags themselves, that's a lot of kit to carry.

Alternative is inflate with a dinghy inflator, but that will take longer. Also you could have fewer airbags, and "save" the boat by having her just peeking above the top of the water but 99% submerged, using perhaps just one in the cabin. I wouldn't do that with the Squaddie - might as well let her sink and be done with it

Also, the transom ones wont keep the boat afloat. It'll be submerged before they work, and you'll then need another dive cyl to stop the bags deflating. The idea of having them inside/under decks seems better

Food for thought, but needs a bit more R&D!

1000kg = 1 tonne. The conversion factor tonnes to tons is 0.98 or summink, so the same thing in practice.

 

[benjenbav]

Lots of racing dinghies have buoyancy bags.

If you were going to inflate them in extremis rather than (as in the dinghy version) have them inflated all the time, then why not use helium to give more lift per cubic meter?

I think you'd need to look at restraining the bags so that when activated they didn't all move to, say, the cockpit and drift away.

 

[Scarron]

Why not blow em up with the exhaust..

You have two 6 litre engines right? if my sums are correct then they will pump 6000 litres a minute each at 2000 rpm [with some cooling water mixed in] so in theory you could fill your 4 x 1 cu m bags in 20 seconds.

Course you could always go to Henshaw and get them to make you something up, praps nail it around the rubbing strake and bingo, you wouldn't need fenders anymore.

 

[fisherman]

[ QUOTE ]
why not use helium to give more lift per cubic meter?


[/ QUOTE ]
That's an interesting question. The Helium filled bag would only displace its own volume, so no more lift. The difference is the weight of helium used would be less than that of the same volume of air...wouldn't it.....?

 

[burgundyben]

Hmm...nail it to the rubbing strake, I can see how that might look attractive...

Perhaps not cylinders, but fireworks, well squibs anyway.

Stand back!

 

[nonitoo]

My concern might well be the structural integrity when the buoyancy is applied to the underside of the decking.

I have no idea whether the deck, or whatever, is strong enough to cope with the pressure of, in your case, at least 4 tonnes of buoyancy pushing the 'wrong' way against the decking.

The other matter to consider, brutally, is whether the sodden hull is worth retrieving. The level of sophistication built in to large modern boats means that the hull would virtually have to be stripped bare and rebuilt from scratch.

It must surely be a toss up whether it might be better to write it off and take to the liferaft and let the insurance company take the strain.

Very much a personal decision.

Tom

 

[burgundyben]

[ QUOTE ]
My concern might well be the structural integrity when the buoyancy is applied to the underside of the decking.

The other matter to consider, brutally, is whether the sodden hull is worth retrieving. The level of sophistication built in to large modern boats means that the hull would virtually have to be stripped bare and rebuilt from scratch.


[/ QUOTE ]

I reckon my deck strcuture should cope with 1 mtr cubes as I described, I should know, I built it.

I quite agree, in the case of a modern ish grp boat, fully loaded with electronics and creature comforts it might well be best left to Davey Jones, in the case of my boat, I'd try to save her.

 

[Argonautical]

Talking about 'Flotation Bags'........I pumped into Jordan in Hay-Rods the other day, blimey, she'd sink now!!! /forums/images/graemlins/laugh.gif

Jas.

 

[nonitoo]

In summer '07 I followed a gorgeous Huntsman out of St.Kats and up river.

If she was yours I reckon I would try and save her too.

Tom

 

[benjenbav]

[ QUOTE ]
Quote:
--------------------------------------------------------------------------------

why not use helium to give more lift per cubic meter?



--------------------------------------------------------------------------------


That's an interesting question. The Helium filled bag would only displace its own volume, so no more lift. The difference is the weight of helium used would be less than that of the same volume of air...wouldn't it.....?



[/ QUOTE ]

Sorry, badly expressed. What I menat to say is the same size bag filled with helium would give more lift

 

[Seanick]

I have Flotation bags, made in America. Two Co2 bottles inflate 3 bags, one under the foredeck, and two under the aft deck. There is no makers name on them, but they were fitted to a 15 ton 45' yawl that did an Atlantic Crossing. They live in small wooden boxes with a canvas flap. The release was in the cockpit under a DSC style flap, a T-handle connected by wire to the Co2.
No I haven't tried them yet!