Whats it like in an upturned catamaran ?

[mark_morwood]

Originally Posted by Mr B

My Motor cycle takes 3 x CO 2 cannisters to inflate my flat tyre to about 22 PSI, enough to ride on,

...

I need four big tractor tubes to cover what I am missing in permanent Bouancy in my floatation chambers to keep my Cat on the surface,
Yes I have calculated it out, The tractor tubes need to float one ton only, One cubic metre of air,

The contents of a 12gm CO2 cartridge will occupy 6litres at 0C and 1 atm.

So assuming I haven't screwed up the math, a very rough calculation is to displace 1 ton of water, you will need 1000l of C02 or 167 cartridges. This assumes the CO2 is only needed at 1 atmosphere, which is not correct as it will need to be under some pressure to displace the water so to be safe let's say 200 cartridges. You might want to think about hooking up to a bigger cylinder like a small scuba tank. 1000l is about 35 cu ft so about 1/2 a regular sized scuba tank of air.

[Mr B]

Originally Posted by mark_morwood

The contents of a 12gm CO2 cartridge will occupy 6litres at 0C and 1 atm.

So assuming I haven't screwed up the math, a very rough calculation is to displace 1 ton of water, you will need 1000l of C02 or 167 cartridges. This assumes the CO2 is only needed at 1 atmosphere, which is not correct as it will need to be under some pressure to displace the water so to be safe let's say 200 cartridges. You might want to think about hooking up to a bigger cylinder like a small scuba tank. 1000l is about 35 cu ft so about 1/2 a regular sized scuba tank of air.

Your getting carried away a bit here,
The example was purely to demonstrate how much air came out of a CO2 cylinder, Which is, 70mm long and 20 mm in diametre,
3 x CO2 cylinders carries almost 200 Kgs, at 22 PSI, My bike tyre, at 42 PSI it carries the same weight down the road, for the same volume,
At that rate, 15 cylinders would support one tonne of mass, at 22 PSI,
There is no pressure in displacement, Its cubic area,

One cubic metre of volume displaces one tonne of mass, seawater,
Approx if you want to be pendantic,

[Buzzman]

I'm not at all sure either of these 'calculations' is accurate, but I am definitely interested in learning what it would *actually* take to keep a cat afloat, or, perhaps more importanly, if acting on the mast, to help flip the cat back upright.

According to information published on Farrier's website, he calculated that his 40' cat could be righted from 180 degree flip to near-90 degree by the application of masthead buoyancy. Annoyingly (and perhaps understandably) he doesn't say how much, nor at what pressure etc etc.

I'm assuming leverage comes into as well, with the length of the mast acting as the levre, and the force being the buoyancy applied to the top of the mast. (Let's not get too sidetracked about how to get it there!)

So while our friends above are discussing the small 'cream foaming' size small CO2 canisters, there are much larger (and cheaper) canisters used to propel paintballs, that could perhaps do the same job.

Can anyone (who is actually an engineer and understands these things better) comment on this?

I'm imagining that one (or more) paintball cylinders (which I also believe are only compressed air, like the scuba tanks mentioned above) could be permanently let into a line that fed the masthead buoyancy bag, so once flipped, a skipper would only have to flip a lever to charge the buoyancy bag and get the boat back to near-90 degrees from 180 flip. [Note I am using near-90 as the measure because sure as **** physics won't allow the mast to get actually to 90 deg unless the in-water float sinks so that half the bridgedeck is entirely under water, and half entirely out - ie: the beam of the boat would then be vertical, and the mast horizontal to the ocean surface.]

But if (big if) this were possible, then theoretically at least the hull could be flipped back over to zero degrees (ie: beam horizontal to water surface, mast upright) and thereby "self-recover" - the apparent inability to perform which is the widely stated "Achilles heel" of cats and tris, as opposed to counter-weighted monohulls.

So there is some practical application of this science if someone can work it out....