breeches buoy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An apparatus used for rescues and transfers at sea, consisting of sturdy canvas breeches attached at the waist to a ring buoy that is suspended from a pulley running along a rope from ship to shore or from ship to ship.

from The Century Dictionary.

• noun In the life-saving service, a name given to an apparatus, like a short pair of breeches, moving on a rope stretched from a wreck to the shore, for the purpose of landing persons from the wreck.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a ring lifebuoy, fitted with canvas breeches, rigged between ship and shore, for rescuing seamen when a ship is in danger of breaking up; also used for transferring people from ship to ship at sea

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a life buoy in the form of a ring with short breeches for support; used to transfer people from a ship