Stealth: Raft Mountings in submarines
In submarine warfare stealth means quietness. Submarines mostly detect each other passively, by listening. Therefore a quieter submarine can hear the enemy before they are heard themselves; during much of the Cold War US and British submarines had a material advantage over their Russian counterparts because of the attention paid to quieting. One of the ways this is achieved is by mounting machinery on noise-absorbent materials to prevent noise being transferred to the hull and from there into the water around the boat – this is termed raft mounting.
Because of the sensitivity of the subject, raft mountings are rarely photographed and even less discussed. I could not find very much information on the internet, so here is a quick overview. Feedback and corrections welcome. Contact
Raft mountings for submarine quieting were first developed by the British in the 1960s, based on similar mounts used to protect the Ton Class minesweepers’ from acoustic mines. The technology was shared with the US Navy and implemented on both country’s nuclear powered attack submarines at about the same time.
US Navy submarines are renowned for the attention paid to quieting. Here a raft platform for machinery being inserted into the hull of a Virginia Class attack submarine.
Among the first countries to implement raft mountings was Sweden. By the 1970s they were not only raft mounting the diesel generator (engine), but almost the entire inside of the submarine. The raft mountings on the Nacken Class are visible in HMS Neptun which is on display at the Naval Museum, Karlskrona . This is one of the few opportunities to actually see this for yourself but you have to look carefully:
A heavy rubber noise-absorbent mounting between the top of a diesel generator and the hull.
A raft mount under the upper deck. This one was located in the torpedo room.
Even the platform at the bottom of the ladder between the upper and lower torpedo tubes has a rubber mounting. Note also the pipe seals above.
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The frame-like chassis for raft mounting in the French Triomphant-class ballistic missile submarines
Originally only the propulsion and noisy machinery was raft mounted, and on some submarines this had to be locked in place during high speed operations. Nowadays in some designs whole deck modules are raft mounted, even in the accommodation and control spaces:
Royal Navy HMS Astute Class SSN construction showing a raft-mounted module being inserted. Excellent photographs by Alex Howe - alexhowe.com
A Russian patent illustration showing raft mounting.
Another modern Russian design, this time related to the Project 885 YASEN Class SSGN. Note the rubber mounts on the upper image.
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