Marine Seacocks

[Miles]

I am led to believe that in the United States ball valves are preferred to gate valves. Apparently this is due to being able to determine whether they are open or closed just with a glance.
Now a lot of boats have direct discharge even if a sanitation tank has been added, not to mention water cooling through hull fittings.
I mention this as I have never noticed anyone changing their seacocks and I can't help but wonder why.