Naval underway time would be hard to go back and retrieve, although I have the handwritten journals to do it. I spent 24 year in the canoe club and only five ashore.
However, warships do spend a fair amount of their lives in port. Pretty much same for my commercial time. And remember, unlike time underway on your personal vessel, you are not on the bridge most of the time underway, only during your watch. Now if you want to calculate hours afloat, not necessarily under way, well, about a third of my 72 years, and since time afloat is not deducted from your life span, I figure I am what, maybe 48?
Yes, and I've known ex Navy to have an extremely difficult time getting their sea time credit.