cazalea[Seiko Moderator]
20933
While researching my answer to your question, I dug out my U-N and set it
Reminding myself of one disadvantage of its claimed 200M water resistance -- an awkwardly difficult crown to operate as the seals on the stem are pretty tight.

(ok, it might be the fact that it's just before 6 am and my coordination could be faulty).
Another question to ask yourself (the warranty depts of watch companies certainly have this in mind)
WHAT IS A MARINE ACTIVITY?
Is it sailing?
Whale watching anyone?

River cruising?

"Diving" with marine creatures?

Running from a typhoon?

Off-roading in an English "rain forest"?

Spontaneous "cooling off" on a hot day at the marina?
Lighting the wood stove

Cleaning a crab?

Checking the time in the dark?

Fixing the shore transportation?

Restocking the booze locker?
Emptying the booze locker

Flying up to the boat?

Exploring glaciers?

to get ice for the drinks?

Fishing?

Figuring out where the heck you are?

Cleaning the prop?

Catching a fish in a rainstorm?

Calling it a day?