USS GRUNION SS216

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USS GRUNION (SS-216)
ANALYSIS OF CONNING TOWER FAILURE

• ANALYSIS OF CONNING TOWER FAILURE
• C. A. THOMPSON

BY C. A. THOMPSON SEPT 2008
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• USS GRUNION CONNING TOWER FAIRWATER WAS IN
  NEARLY ORIGINAL GATO DESIGN CONFIGURATION WHEN
  SHE WAS LOST. THIS INCLUDED
• AN ENCLOSED PILOT HOUSE AREA FORWARD OF THE OPEN
  BRIDGE. THIS INCLUDED A HELM, MAGNETIC COMPASS,
  GYRO REPEATER, ENGINE ORDER TELEGRAPH, ETC
• AN ENCLOSED CIGARETTE DECK AFT OF THE BRIDGE. THE
  BULKWARK WAS FABRICATED OF SHEET METAL.
• IT IS POSSIBLE THAT THE PERISCOPE SHEARS HAD BEEN
  UNPLATED.

PLATED SHEARS?
ENCLOSED PILOT HOUSE
OPEN BRIDGE
BULKWARK
CIGARETTE DECK
FAIRWATER ACCESS
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END HEAD REINFORCEMENT RING
CT HELM MAGNETIC COMPASS OPTICS (NOT INSTALLED ON
USS COD
CT HELM PENETRATION
CT END HEAD
TOP OF ENCLOSED PILOT HOUSE
USS COD FWD CT END HEAD

• The conning tower is a cylinder sitting above the
  control room.
• The fwd end of the CT is a convex end head. The
  after end is a convex end head. The after end
  head was replaced during WWII, in most GATO subs
  such as USS Cod, with a concave end head.
• When the forward battery collapsed, much of the
  conning tower fairwater collapsed, revealing the
  conning tower cylinder.
• Connecting the end head to the CT cylinder is a
  very heavy duty metal reinforcement ring.

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CONNING
TOWER

• The Conning Tower is mounted atop the Control
  room with a series of saddles.
• The Saddles forward of the periscope shears are
  smaller, and mounted directly to the hull
  reinforcements for the control room.
• There are three massive supports for the
  periscope / antenna shears. These supports are
  not required for conning tower reinforcement.
  Their probable function is to supports the
  periscopes and keep them from vibrating while
  submerged.

CR HULL
REINFORCEMENT
SADDLE
CONTROL
USS COD PORT SIDE LOOKING AFT
ROOM (CR)
PERISCOPE SHEAR SUPPORT
USS COD PORT SIDE LOOKING FWD
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LOOKING FWD
LOOKING AFT

• THE THREE PERISCOPE SHEAR SUPPORTS SIT ATOP THE
  CONTROL ROOM (VIEW OUTLINED BY ORANGE LINES),
  ENCIRCLE THE CONNING TOWER AND ARE MAJOR
  SUPPORTS.
• SHEAR WEBBING RESTS ON TOP OF, AND IS WELDED TO
  THE CONTROL ROOM, THE TANK TOPS, THE CONNING
  TOWER CYLINDER, AND FAIRWATER SUPPORTS. EACH
  SUPPORT WEBBING HAS 4 HOLES, PORT AND STARBOARD,
  UPPER AND LOWER.

CONNING TOWER
TANK TOP
CONTROL ROOM
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SHEAR SUPPORTS ARE WELDED TO THE CONTROL ROOM
REINFORCEMENTS, TO THE TANK TOPS, TO THE
FAIRWATER PLATING AND TO THE CONNING TOWER CODs
FAIRWATER PLATING IS ARMORED, AND WELDED TO
SUPPORT STRUCTURE. GRUNIONs FAIRWATER PLATING
WAS MUCH THINNER, AND RIVITED TO FAIRWATER
SUPPORTS
FAIRWATER
PLATING
REINFORCED HOLE IN WEB
SHEAR
SUPPORT WEB
CONNING
TANK
TOWER
TOP
WEB WELD
TO CT
CR REINFORCEMENT
CONTROL ROOM
REINFORCEMENT
OVERHEAD
USS COD PORT AFT SUPPORT
USS COD PORT AFT CT
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THE PERISCOPE SHEAR SUPPORT WEB STRUCTURE
CONTINUES UPWARD AROUND THE CONNING TOWER
FAIRWATER
PLATING
CONNING
TOWER
WEB WELD
CONNING
TOWER
WEB WELD
TO CT
TO CT
SHEAR
SHEAR
SUPPORT WEB
SUPPORT WEB
REINFORCED HOLE IN WEB
FAIRWATER
USS COD LOOKING UP BETWEEN PORT SHEAR SUPPORTS
USS COD LOOKING UP BETWEEN PORT SHEAR SUPPORTS
PLATING
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THE PERISCOPE SHEAR SUPPORT WEB STRUCTURE
CONTINUES AROUND THE TOP OF THE CONNING TOWER, TO
THE PERISCOPE/ANTENNA REINFORCEMENT
FAIRWATER PLATING
UPPER PORT WEB HOLE
CIGARETTE DECK
SUPPORT WEB
SUPPORT WEB
FORE/AFT SCOPE
REINFORCEMENT
CONNING TOWER
USS COD PORT UPPER AFT SHEAR SUPPORT
CONNING TOWER
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USS GRUNION CT ANALYSIS

• FAILURE PATH
• ANALYSIS OF CT PROVIDES ONLY ONE LIKELY PATH FOR
  FAILURE
• CT AS DESIGNED HAS 9 MAJOR PENETRATIONS
• 8 OF THESE ARE IN TWO LINES OF 4 EACH
• 4 AT THE UPPER TOP DEAD CENTER (GOLD LINE)
• 4 AT THE LOWER BOTTOM DEAD CENTER (BLUE LINE)
• THOSE 4 AT THE BOTTOM DEAD CENTER ARE MASSIVELY
  REINFORCED.
• THEREFORE, THE ONLY LIKELY FAILURE PATH IS THE
  PENETRATION LINE AT THE UPPER TOP DEAD CENTER
  (TDC)

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USS GRUNION CT ANALYSIS

• THE LOWER HULL PENETRATIONS RECEIVE ADDITIONAL
  SUPPORT
• SADDLES WHICH HOLD CT IN PLACE
• LOWER CT HATCH MANWAY
• PERISCOPE/ ANTENNA PENETRATIONS (WELDED TO BOTH
  CT CR)
• THIS ADDED SUPPORT SHOULD PREVENT COLLAPSE FROM
  BELOW

SADDLES
PERISCOPE/ ANTENNA (3)
CT HATCH
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USS GRUNION CT ANALYSIS
1 SCOPE SPOOL PIECE
FORE-AFT SUPPORTS

• UPPER CT SUPPORT
• FORE-AFT REINFORCEMENT
• PERISCOPE 1 SPOOL PIECE
• ANTENNA SPOOL PIECE
• PERISCOPE SHEAR SUPPORTS (3 WRAP AROUND SUPPORTS)
• THE FORWARD HALF OF THE CT DOES NOT HAVE NEARLY
  THE REINFORCEMENT AS THE AFTER HALF

ANTENNA SPOOL PIECE
PERISCOPE SHEAR SUPPORTS
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USS GRUNION CT ANALYSIS

• IF FAILURE WERE ALONG THE UPPER CT FAILURE LINE,
  WHAT WOULD WE EXPECT TO SEE?
• DOWNWARD, INWARD COLLAPSE ALONG THIS LINE
• DISTORTION OF OTHER STRUCTURE CONSISTENT WITH
  THIS FAILURE
• CT END HEAD (S) PULLED INWARD
• POSSIBLE ROTATION OF CT HATCH

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• NOTE LINE OF FAILURE (DEPRESSION) FROM CT HATCH
  TO 1 PERI-SCOPE, AFT TO ANTENNA (YELLOW LINE)
• NOTE FAILURE OF ALL SIX BRIDGE DECK SUPPORTS AND
  SUPPORT WEBBING DOWNWARD

ANTENNA MAST
PERISCOPE 2
COLLAPSED DECK SUPPORTS (6)
PERISCOPE 1
UPPER CT HATCH
LINE OF FAILURE (COLLAPSE)
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BRIDGE DECK SUPPORTS
FAIRWATER PLATING
HOLE IN SUPPORT WEBBING
BRIDGE DECK SUPPORT WEBBING
USS COD PORT SIDE LOOKING FWD

• NOTE THAT THE BRIDGE DECK SUPPORTS ALONG WITH
  THEIR SUPPORTING WEBBING HAVE FOLLOWED THE
  PERISCOPES AND ANTENNA DOWNWARD. THE WEBBING IS
  LITERALLY TORN IN HALF. THE DECK SUPPORTS AND
  HOLE IN THE WEBBING ARE CLEARLY VISIBLE IN THE
  PHOTO OF THE WRECKED BRIDGE

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USS GRUNION CT ANALYSIS

• THE COLLAPSE IS MOST SEVERE IMMEDIATELY INBOARD
  OF THE UPPER CT HATCH COAMING. NOTE HOW THE HULL
  DEPRESSION DEEPENS AS YOU PROCEED FROM THE FWD CT
  RING, TO THE HATCH TO THE FORE/AFT STIFFENER,
  WHERE THE HULL APPEARS TO START BACK UPWARD.
• THE 1 PERISCOPE PENETRATES THE CT JUST AFT OF
  THE FORE/AFT STIFFENER. THERE IS A SPOOL PIECE
  RUNNING FROM THE UPPER CT PERISCOPE PENETRATION
  TO THE CT LOWER PERISCOPE PENETRATION. I BELIEVE
  THIS SPOOL PIECE IS RATED AT THE SAME PRESSURE AS
  THE HULL (IN CASE IT FLOODS). THIS WOULD PROVIDE
  SIGNIFICANT ADDITIONAL STRENGTH. 1 SCOPE IS ALSO
  SUPPORTED BY THE EXTERNAL WEBBING.

FWD CT RING
FORE/AFT SCOPE STIFFENER
CT HATCH COAMING
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CONNING TOWER DAMAGE

• CONNING TOWER COLLAPSE
• CT STIFFENER (WHITE ARROW) RUNS UPWARD FROM PORT
  (RIGHT), THEN DROPS SHARPLY DOWNWARD TO CT HATCH
  COAMING
• INBOARD SIDE OF CT COAMING SIGNIFICANTLY LOWER
  THAN OUTBOARD SIDE (ORANGE LINES)
• CT HULL TORN IN AREA OF AFT END OF CT COAMING
• INBOARD OF UPPER CT HATCH, YOU CAN LOOK DIRECTLY
  INTO THE CONNING TOWER.

GRUNION CT LOOKING AFT
OUTBOARD SIDE
CT STIFFENER
INBOARD SIDE
TORN PLATING, HOLE IN CT
FORE/AFT SCOPE STIFFENER
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USS GRUNION CT ANALYSIS

• PORT/STARBOARD UPPER SHEAR SUPPORT DISTORTION DUE
  TO COLLAPSE OF CT, PULLING SHEARS DOWNWARD.
• ATWARTSHIP UPPER SHEAR SUPPORTS ARE ALSO
  DISTORTED DOWNWARD (VISIBLE IN DVD)

STARBOARD
PORT
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• ROTATION OF UPPER CT HATCH
• YELLOW LINE (TOP) INDICATES ORIGINAL ORIENTATION
  OF HATCH
• NOTE ALSO PINCHING OF SHEAR SUPPORTS DURING
  COLLAPSE (WHITE ARROWS)
• NOTE DIFFERENCE IN ANGLE OF STIFFENERS (2 WHITE
  LINES, BOTTOM PHOTO). CT IMPLODED INBOARD OF
  UPPER HATCH CAUSING HATCH TO ROTATE

SHEAR PINCHING
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AFT CT END HEAD

• THE TOP OF THE AFT CT END HEAD HAS BEEN DISPLACED
  FWD AS CT COLLAPSED. NO CLEAR PHOTO OF THE AFT
  END HEAD FROM AFT IS AVAILABLE.
• THE CT HAS TWO FORE/AFT HORIZONTAL LOGITUDINAL
  SEAMS, AT 3 AND 9 OCLOCK. NOTE FAILURE OF CT
  LONGITUDINAL SEAM (YELLOW ARROW).
• LOWER PHOTO - VIEW OF AFTER CT END HEAD FROM
  PORT. BULKHEAD HAS COLLAPSED FWD TO ANTENNA
  (WHICH IS SUPPORTED INSIDE CT BY SPOOL PIECE.)

LONGITUDINAL SEAM?
AFT CT BULKHEAD RING
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• THE AFT END OF THE GRUNION CT, FROM THE 1
  PERISCOPET TO THE ANTENNA, WHICH IS SURROUNDED BY
  THE THREE MASSIVE SHEAR SUPORTS, HAS ALSO
  COLLAPESE DOWNWARD. NOTE THE MASSIVE KINK IN THE
  THREE PERISCOPE SUPPORTS, WHICH SHOULD FLOW
  SMOOTHLY UPWARD (SEE SLIDE 7). THEY, AND THEIR
  ASSOCIATED WEBBING HAVE COLLAPSED WITH THE CT.
  NOTE SHARP BEND ANGLES OF THE SUPORTS

AFT CT BULKHEAD
SEVER KINK IN SHEAR SUPPORTS
FRACTURED CT HULL SEAM
GRUNION CT LOOKING STBD TO PORT
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USS GRUNION CT ANALYSIS

• BASED ON THE ABOVE, IT IS MY CONCLUSION THAT THE
  USS GRUNION CONNING TOWER COLLAPSED RAPIDLY AS A
  RESULT OF HYDROSTATIC PRESSURE
• IT IS PROBABLE THAT ASSOCIATED SUPPORT MEMBERS,
  PRIMARILY CT SADDLES AND PERISCOPE SUPPORTS,
  ABSORBED AVAILABLE ENERGY, AND PREVENTED THE CT
  FROM COLLAPSING COMPLETELY