Jere Lull wrote:
In article ,
Peggie Hall wrote:
Otoh, I just learned that a lot of cockpit drain through-hulls are
also below the waterline...which makes no sense to me either...sigh...

More than you might think: Ours are above the waterline at rest. At hull
speed, they're a foot under the stern wave. And I can't easily change
them because they're structural members.

All my 30' yachts and under have had the cockpit drains
underwater. To have a cockpit that is designed to be within
normal proportions of height, the depth of the drain fitting
in the cockpit, with a tube clamped and led away under the
cockpit sole to it's opposite hull outlet, you're already
below water level, usually on the curve away.
Not everyone has a larger boat with high freeboard and
consequently a high cockpit sole.
The major problem is from having the corresponding valves
open when leaving the boat for any length of time, unlike
all others, which can (should) be closed.
BrianH.