Are you allowed to hang a towel on the side of a boat that the walls are 10 tfachim high on shabbos?
Answer:
Yes, this is permitted.
Best wishes.
Sources:
See Aruch HaShulchan 355:11. Although it is not permitted to throw something overboard (this is transferring from a reshus hayachid to a karmelis), it is permitted to place something on the walls of the boat, and even if it falls in the sea there is no prohibition involved.
