1Sq. ft. of air will give you how much flotation?

[CUDA]

Like One sq. ft of air is = to x lb. --Any one know the answer?Thanks jim

[Kavalk]

One CUBIC foot of air will give you 64lbs of positive bouyancy in salt water. Minus the weight of the container.

[shadowman]

Flotation is based on water displacement, so 1 S.F of air should float the weight of 1 S.F of water minus the weight of the container. If its not in a rigid container you would have to account for compresion, and that would get complicated quick!!:D

This is just the way I look at it, Could be wrong.

[CUDA]

Thanks Kavalk now how about fresh water?

[Jimboat]

The answer is in the difference in specific weights of air and water. The Specific Weight of air is 0.076 lbs per cu. ft. The Specific Weight of water is 62.4 lbs per cu. ft. So in (fresh) water you will get approximately 62 pounds of "floatation" with each cubic foot of air you provide. Salt water is heavier than fresh water by 3% (ie: specific weight is 64.3). So, in salt water you will get approximately 64 pounds of "floatation" with each cubic foot of air you provide.

[CUDA]

You Folks are great Thank You;)

[Scream And Fly]

I love it when Jim gets all technical like that... Very cool!

Greg:)

[Trikki1010]

I still have that 62.4lbs/cf pounded into my head from HS Physics:eek:

[FrenchPhil]

Yes, but is air really flotation :o ? Give me 2 part foam anytime :D

[Techno]

How much is needed to keep a boat swamped? Not float it but just keep it at the surface.
I'm wondering if a 1200 lb boat needs this much floatation or can get by with the third less amount since it is displacing water and weighs less.

[shadowman]

Thats why I look at it as displacement. It would'nt take alot of captive air space to keep a light boat on the surface.
Somebody please tell me If I'm looking at this the wrong way But, If you have enough captive air space to displace the boats weight in water It should be unsinkable. Famous last words.....
I think the subject is interesting and would love to hear more.:)

[Kavalk]

The only trick here is keeping the air captive.
Find out the weight of the whole rig. Divide by the appropriate bouyancy number, lets use 62 (lbs per cubic ft) and you have the required number of cubic feet of air to keep this thing afloat(awash)
Of course you'll have to remember the weight of the container and add it to the weight of the boat.
Also you have two types of containers.
Flexible. And rigid.
Flexible tend to be easier to install, but more fragile and prone to chafing and leaks. Also if the boat gets pushed a few feet under, the flexible container will compress, lose volume and therebye bouyancy. Remember a baloon at the surface(1 atmosphere) will be half the size at 33ft of sea water(2 atmospheres) So if your boat has only enough bouyancy to barely keep it awash, and three people are sitting on it and a wave comes by and they stand up, the boat may disappear.

Rigid, is more robust, tougher to fit to the boat, heavier.
For the most part is fairly immune to the pressure thing. Of course eventlually, anything will implode given enough pressure differential.

Don't get too theoretical on the calculations. ALWAYS allow a fudge factor. On the side of additional bouyancy, and strength.

[Techno]

I remember something about an object weighing less when submerged. If its a third less then this means I would only need enought to float 800 lbs instead of 1200. This may not seem like a big deal but do the math and this floatation becomes rather large.
1200 = about 20 cu. ft /2 for both sides and its a square foot 10 feet long!
For 800 its only 7 feet.

I would only want the boat near the surface so it can be recovered easily.

Another thing I noticed is where its put and how its attached. A bunch of loose pop bottles could easily float out. A fastened tank, or netted. Or foam if in the part that breaks lets the rest sink.:eek: If the foam is attached to the deck and this splits from the hull you have a deck and lost the boat.

[Jimboat]

The object will weigh less when submerged, because of the floatation realized when it displaces the weight of the water. So you're already getting your advantage with the flotation (you can't count it twice).

[shadowman]

The boat itself will displace a certain amount of water. The big problem would be to figure out how much. Thats probably the reason for the safety factor. I like the idea of air being used for flotation in a rigid container. It could'nt soak up water and it could also be drained.

[stokernick]

I remember my son`s 18 ft Hustler had a big airbag under his deck.:cool:

[Tom D.]

Nick,
What the heck was David doing under the deck?

Tom:D

[Kavalk]

Years ago I used to get a hold of large "Dunnage Bags" that were made by Goodyear. They were heavy duty, had inflate inlets like an inflateable boat, and available in various sizes.

The story I heard was that these things were originally used as dunnage or padding between loads being shipped by rail.

I used 'em in salvage operations.

Vacuum 'em flat, roll'em up, jam 'em in somewhere and inflate.

Look like large black vulcanized pillow when inflated.

Maybe could also consider a system that deploys when needed.
Like an F1 boat.

[stokernick]

it was BIGNICK`S Hustler,and David hadn`t bulked up yet!!!