Gould 0738 wrote:

I don't dispute that- ergo the disclaimer.
But if the depth is measured from the keel and there is a depth indicator on
the sub it will never read zero. Is that somehow incorrect? That was why I
postulated *if* a depth guage read zero at the surface the reading would have
to be from the normally ballasted waterline. Since it apparently does not read
zero, that theory doesn't fly. Freely admitted.

It has never been part of submarine law that it must read zero on the
surface. Why should it?

The depth to keel is also an indication of freeboard. A submarine, after
surfacing, will use a low pressure blower to push the last bit of water
from the ballast tanks in order to increase the freeboard. The depth
gauge shows when it is as high as it will go.

Rick