@RChiesa07Could i Cast Tiny Hut in The middle of Ocean or it needs a floor? There are other spells and effects that specify this. #dnd5e needs a floor – spell specifies dome, rather than sphere.
— Mike Mearls (@mikemearls) May 17, 2016
@RChiesa07Can Tiny Hut be cast on the deck of a ship as it travels or it is latitude/longetude stationary? #DnD5e it would move with an object it is cast upon
— Mike Mearls (@mikemearls) May 17, 2016
“A 10-foot-radius immobile dome of force springs into existence around and above you and remains stationary for the Duration. The spell ends if you leave its area.”
You don’t cast it “on” something, like an ocean or boat but rather around yourself in a location from which it does not move. So you could cast it there but I would think if on a moving ship or similar, it would leave the shelter behind where it was cast.
And you could anchor a ship to a Tiny Hut, RAW:
“Creatures and objects within the dome when you cast this spell can move through it freely.” So cast Tiny Hut, anchor the ropes somehow (an immovable rod or two perhaps), and tie off.
Or have the ropes away from the Hut and have others lash the ship to the outside of the Tiny Hut after its been cast since they cannot enter it and can looped around it. Use several (and/or some large netting) to keep the ropes from slipping.