Maybe a boat could be very impressive but think about it, Store the seamoth in the Cyclops, and then the Cyclops in the boat. first i think it's unecesary a big boat cause it's as @Astromancer said an Undewater game, and beacuse why do you want a boat if the map is very small, if the map would be infinite or bigger could be the possibility and then imagine the quantity of materials used to build it
Don't sweat it. There's just a lot of people making topics about wanting vehicles that are "more" rather than "different". A boat could be an interesting addition from a "mobile island" perspective, but more as a peer of the Cyclops than its superior. An enclosed Seaglide sort of already is present due to the Seamoth.
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Coding that would probably be unpleasant as well.