bottles

[Mark42]

Re: bottles

I understand your argument, and I'm not trying to be a smart-ace, but if your bottles are a couple of feet below the surface, you are already pretty much screwed, are you not? As a couple of other posters have pointed out, you can't have enough buoyancy to save a catastophic hull breach anyway. If you are unsure of that, just refer to the various boats that do sink each year in freshwater around the country.

Having said that, I believe I would take the route of bottles combined with pour in foam. The bottles would reduce the amount of foam required drastically, while the foam would stabalize, add some buoyancy, and may even privide a seal on the caps of the bottles.

One of the contributing problems with the bottles is that they are already about 1 or more feet below the water surface when the boat is at rest. If there is a hull breach, and the boat swamps, then the bottles sink to 2 to 3 feet below the surface. Foam at this point will not compress and maintains its buoyancy, and by CG regs, the boat will float level at the surface (full of water, but its not sinking). The bottles compress a bit at that depth, reducing their buoyancy, making the boat sink a little more, compressing the bottles, etc. The problem is to figure out how much air compresses at the depth the bottles will be at when the boat is swamped so it doesn't slowly dive.

They will compress some, but think of it this way, even compressed to half their size, that bottle will still contain more trapped air or buoyancy than a chunk of foam of equal size, even not compressed. Then take into account that the foam may one day be water logged to some degree, the bottles seem the way to go.

I have to disagree, because a bottle of air and a chunk of foam the same shape and size will behave completely differently under water. The foam will maintain its size (and therefore buoyancy) due to the structural strength of the foam cell structure itself, down dozens of feet. A bottle will be flat at that point, and will loose any significant buoyancy.