Thursday, November 19, 2009

A Submarine Mystery for the Astute Only


Yesterday's Mystery Questions of the Week were answered correctly by the SonarMan. One question involved identifying something striking from the ship's underway photo, other than 3 items M.E. mentioned.


There was something else remarkable in that photo. Think hydrodynamic flow and observe the HMS Astute's unusual bow configuration. Note the freeboard (height of ship's hull, excluding sail, above the waterline). We do not know Astute's speed, but compare the sea turbulence on the sub's flanks to that of our SSN-21. Let's assume the underway Seawolf was at a higher surface speed.

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Does surface turbulence even matter for a nuclear submarine? Like U.S. boats the Astute's hull is hydrodynamically rounded for higher speed with lower drag, turbulence and noise generation.
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The forward fairing on Astute's bow no doubt covers specialized equipment (space is never wasted). Does it also provide another purpose? Is it a flow diverter to reduce sonar transducer noise. M.E. suspects so.

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Submarines are always silent and strange

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2 Comments:

At 30 July, 2015 10:21, Blogger Jandanagger Laterrobinson said...

The fairing serves no purpose except hydrodynamics. British submarines have a “chin” mounted sonar and a steel forward outer hull – as opposed to the spherical sonar array and composite bow dome of their US counterparts. The foremost part of the submarine is high-strength steel and can then withstand considerable collision stress with only minor damage as opposed to the damage that can be inflicted on a US boat. Think USS San Francisco. The picture of Astute underway was on her initial contractor sea trials out of Barrow heading to Faslane. No weapons, minimal stores and stocked only for the short trip. The fully equipped operational sub has a much smaller freeboard.

 
At 30 July, 2015 16:51, Blogger Vigilis said...

J.L., thanks for underscoring my observation about the unusual hydrodynamic flow: "There was something else remarkable in that photo. Think hydrodynamic flow and observe the HMS Astute's unusual bow configuration. Note the freeboard (height of ship's hull, excluding sail, above the waterline)."

Your clarification of unusual freeboard in Astute's sea trial is also interesting because you cite an unusually light load, which is incidental unless purposefully unadjusted by routine ballasting.

As to the extensive damage to USS San Francisco's bow, however, preservation of bow-mounted sonar in any fast attack submarine is unrealistic in a head on, flank speed collision with a seamount. SSN-711's pressure hull not only withstood, it preserved the lives of all but 1 of its 99 impact-injured sailors.

 

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