Ship details

"The Bree is about forty or fifty feet long and fifteen across; I suppose it draws five or six inches. It's made of lots of rafts about three feet long and half as wide, roped together so they can move freely — I can guess why, on this world."

"Hmph. So can I. If a ship that long had its two ends supported by waves while the middle hung free up near the pole, it would be in pieces before long whether it started that way or not. How is it driven?"

"Sails; there are masts on twenty or thirty of the rafts. I suspect there may be centerboards on some of them too, retractable so the ship can be beached; but I never asked Barlennan."

Hal Clement, Mission of Gravity