In article ,
"Grumman-581" wrote:

"Steven P. McNicoll" wrote in message
ink.net...
Doesn't seem any stranger than a boat sinking. I believe they're designed
to float as well.

These days, smaller boats often have flotation chambers filled with a closed
cell type foam (e.g. styrofoam) so that in the even that they are filled
with water, they might still remain on the surface, dependent upon what else
might be loaded in the boat... It wasn't always that way though... I've
helped recover sunken boats before that sank after hitting logs and such and
knocking holes in their bottom... Larger boats aren't required to have this
sort of positive flotation though... Don't remember exactly at what length
the requirement no longer applies... Probably around 25-30 ft or so, I
guess... It's quite possible that amphibs don't have this sort of design in
them...

*23.751***Main float buoyancy.

(a) Each main float must have‹

(1) A buoyancy of 80 percent in excess of the buoyancy required by that
float to support its portion of the maximum weight of the seaplane or
amphibian in fresh water; and

(2) Enough watertight compartments to provide reasonable assurance that
the seaplane or amphibian will stay afloat without capsizing if any two
compartments of any main float are flooded.

(b) Each main float must contain at least four watertight compartments
approximately equal in volume.