Thanks for the mention, Burgess!
I just googled "Energizer Sea Beam" (the US market name) and I see pictures of the MkV.
Bizarrely, this is mostly sold there in packs of 3. (Huh? One for home, one for the car, one for the boat???????????)
It's big, but that's because it has to float with the not inconsiderable ballast of 4 alkaline F cells on board. So the "empty space" has grown in recent years.
Keep googling; you should be able to find one for about US$10 if you shop around.
Lumens, if the bulb is the same as the Australian-market Mark 5 will be the KPR113 at 51 bulb lumens.
Whilst you CAN change that for a TLE-1F LED dropin (50 lumens), I would strongly recommend a Mag Xenon 4-cell LMSA401 bulb which will give you your required 81 bulb lumens, still with plenty of runtime. (Incidentally, a rough equivalent to this is bulb is now OEM in the newly-released Mark VI.)
Changing the subject slightly, Eveready have just released the "Mini Dolphin" (2D) and "Micro Dolphin" (2AA), for those who require a floating lantern but require something smaller. Either of these would be beaut with a TLE-1F.
I would love to say "I'd never go boating without one", but tbh, I get seasick on a 5000-ton ferry.