basic floatation

[trueblue]

My boat only has sealed pockets inside the hull. I've always wondered about this and whether or not I really should have foam but the boat builder made a pretty strong statement to me that the sealed air pockets were quite acceptable/

Does anyone know about this aspect of flotation?

Cheers

Mick

[gofishin]

Mick, there's an old saying that is pretty useful; "you can't sink a cork"...

Air pockets are fine until they get a leak, whether that is from a major event like a collision, or a leaky bung, hairline crack or a screw/hole drilled where it should not be! It doesn't matter how well the boat is built, how meticulous the pressure test was, or for how long it held pressure for, to satisfy the main regulations acceptable to the ABP (for boats 6m or less), the two largest air chambers must be discounted for buoyancy calculations.

This pretty much rules out this form of flotation for smaller boats, and hence a buoyant material should be used to provide positive flotation, i.e. EPS, PU or PE/PP sheet etc (which is becoming popular).

Depending on the regulation, the type of foam allowable differs too. For ABYC you are not allowed to use naked EPS (styrene) for the first 4” in the bilge, as it is prone to chemical attack. For EU requirements your not allowed to use it at all. From memory, for ABYC, EU and AS1799 (& USL/survey) it must be fuel resistant with a minimum density of 32kg/m3, and with a minimum allowable compressibility etc.

It all gets a bit complicated really. There should be a level playing field, one mandatory ‘regulation’ that all manufacturers build to. At least then the consumer can compare apples with apples etc and know what he/she is getting in a boat!