The
isolation raft is one method of reducing the noise produced by an
operating ship, usually a
submarine. As much of the large operating
machinery of the boat as possible (
cooling pumps,
oxygen generator,
steam turbine,
electric motors,
generators, etc) are placed inside the submarine on a free-standing platform that may span decks. This platform is isolated from the
hull at all points of contact by
buffers made of hard rubber or a similar material. Thus, the majority of the operating noise from the submarine will be deadened by the buffers before reaching the hull. This is important because any
vibration that reaches the hull is typically
radiated out into the water as from a
sounding board.
This technique is useful for nuclear powered and conventional diesel-electric submarines. It has an additional advantage of reducing the vibration experienced by a ship under way. While this is typically not an issue on a submarine, it can be on high-torque motors such as tugboat engines.
UPDATE: SkiBum5 notes that often on submarines the equipment is buffered from the raft itself by absorbent mounts, offering an additional level of noise-deadening. Thanks!