emergency hull flotation device?

[hansp77]

Just before I take my sleep deprived brain to bed, to get up for work in about 5 hours,
I had a rather silly thought.
Feel free to shoot it down in flames-
its just a thought.

Would it be possible, but more to the point practical, to design a device that upon catastrophic breaching of a hull, would inflate some sort of air bag, or chain of such, for the purpose of stopping the boat sinking?

Now obviously a half sunk boat kept up by a few balloons is not going to sail very well, and any motor would likely be submerged, but it might still be as safe as a liferaft (or moreso). With the added bonus, that if or when you get rescued, you can salvage your boat too.

I have been trying to think exactly how much air would be required to float a boat.
Would it be the volume of air inside the hull below the waterline?
If so, then I would think that it may be feasible.
Or, as the boat sinks, would the extra wheight underneath the water change the calculations?

I don't know.

Of course where to put the compressed air might be problem.
Possibly, liquified air in tanks, being rather heavy, could be incorporated into the ballast, keel or deadwood section. Ideally the flotations bags would need to be as low as possible, and fixed, so that they stopped the boat sinking at a point, hopefully with at least the decks still out of the water, but ideally with some cabin space and shelter available. Much like a big comfy air-bed .

Similar to a concealed air bag in a car stearing wheel, a longitudal bag could be designed to rise out of the floor.

as I said.
Just a silly idea.

take your shots...
Hans.

[westlawn5554X]

Actually, that is not really silly.

I have the same idea watching documentary of sunk ship being salvage by ballon lifting.

If let say your yacht is facilitated with a couple of ballon with pressure trigger, then when the yachts start sinking to a certain pressure the ballon would at least deter the further progress of sinking, buying time for quick escape.

Student

[Ike]

Actually there are such devices on the market. But the bigger the boat the more difficult it gets.

Oh yeah, one cubic foot of air will float 62.4 lbs in fresh water, 64.4 lbs in salt water. Whether you boat will float depends on what it weighs underwater. For small boats under 20 feet it's a fairly simple calculation. Bigger boats are more complex. Also when you start getting into bigger boats and using air bags then you have to think about structural loads. If the bags aren't arranged right they can break stuff.

[westlawn5554X]

I thought salt water is 64 lbs? your right about the breaking from misplace ballon.

Student

[Frosty]

I got one in the car,--- its in the steering wheel apparantly.

[westlawn5554X]

Would be nice trying to sink one and see it float just pulling your leg pal.

Student

[bhnautika]

Hansp77 have a look at this site http://www.floatpac.com/

[Poida]

That's a great idea. Now we were talking about pirates on the other thread, the first thing I am going to steal is hansp77's idea, patent it and make a killing and I won't need a gun.

Actually instead of a bag the boat could be fitted out with layflat hose which could be stored under the decking secured with plastic clips that would break when the air pressure is pumped in. A dive cylinder is all that is required to supply enough air, it holds 30 bar ie you would end up with flotation of 30 times the volume of the cylinder at atmospheric pressure. I think a cylinder is 2 cub ft so the flotation would be 60 cub ft and support 3,840 lbs. I think 1.7 tons. I live in a metric country. Or 64 ft of 4" layflat hose.

But I'm sure if my calculations are wrong someone will soon let me know.

[bntii]

Don't head to the bank just yet

A company called Yachtsaver provided these for quite some time. They went belly up due to low sales.

[Poida]

Why bntii, couldn't they keep their head above water.

[SeaSpark]

I'v been playing with the idea of fast curing and expanding foam in a thin bag.

An gas filled bag will have to be very strong not to be punctured by boat inventory when inflated. Foam when expanded in a bag would do no harm to inventory and once cured will stay in the bag when it is punctured. Part of the foam can be carved out to reach supplies.

Have been unable to find a foam that fits the requirements for this:

-Fast expanding for in case the boat sinks rapidly.
-Fast curing for the same reason.
-It should not develop to much pressure when expanding to prevent the boat from beeing blown apart.
-Preferably it should not be flamable so it can also be used in case of fire, perhaps it can assist in starving the fire from oxigen.

[Ike]

You probably won't find it either. The problem here is heat. Foam made by mixing two chemicals is an exothermic reaction, that is it generates heat which accelerates the reaction. To much heat and the cells become extremely thin and fragile and break. (they look like broken glass) Also the foam expands way beyond the normal two pound density, so instead of 1 cubic foot you get more at a lesser density, and it's very porous and absorbs water. To get the fast reaction you want you need a lot of heat. What you'll get is bad foam that won't support the weight and will be be very fragile. Plus that if you put this in plastic bags, that much heat would probably damage the bags allowing water in.

However, I suppose you could talk to the people at BASF or the half a dozen other foam manufacturers to see if it can be done economically.

[Ike]

PS: you can do what you want with air!

[timplett]

Perhaps not a very functional idea, it just popped into my head now. What if the hull was lined with a fairly thick rubber bladder, directly on the inside of the hull. It would be fastened along the upper edge of the hull, the keel, and sandwiched between the hull and bulkheads. The idea would be that say you struck a rock and pierced the hull, the rubber should be flexible enough to to simply stretch out of the way and absorb the impact without being punctured. It should hold enough air inside to keep the boat afloat, and most of the boat should still be accesible. This would obviously only be practical to apply to a new boat during construction, retrofitting it to a boat would be too much work to be worth it. I think that it would only work on smaller boats, if at all. Anyways, like I said, just an idea that popped into my head.

Tim Plett

[ernie]

I like the flat hose idea Poida had, wrap the boat just above the water line with enough to lift the full displacement, use either compressed air or a chemical reaction to produce enough gas to inflate the tube to 4 – 6 psi. like a ridged inflatable. When inflated you may not sail well, but you should be able to maintain steerage way and maybe even get home or pump out and execute repairs at sea.

Also, if you have an air pump to inflate in non emergencies, this would be a very protective fender system.