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 pump
s, oxygen generator
, steam turbine
, electric motors
s, 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 buffer
s 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!