Notes on Bulkheads and Watertight Doors

Notes on Bulkheads and Watertight Doors

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BULKHEAD DECK: IS THE UPPERMOST DECK UPTO WHICH THE TRANSVERSE WATERTIGHT BULKHEADS ARE CARRIED.

MARGIN LINE: IS AN IMAGINARY LINE DRAWN 76MM BELOW THE UPPERMOST SURFACE OF THE BULKHEAD DECK.

PERMEABILITY: IS THE PERCENTAGE OF SPACE WHICH CAN BE OCCUPIED BY WATER TILL THE MARGING LINE, IF THE SPACE EXTENDS ABOVE THE MARGIN LINE.

WEATHERTIGHT: MEANS THAT IN ANY SEA CONDITION WATER WILL NOT PENETRATE INTO THE SHIP.

 

TYPES OF BULKHEADS:

  1. WATERTIGHT: SUBDIVIDE THE SHIPS INTO VARIOUS COMPARTMENTS AND THEIR NUMBER IS DICTATED BY CLASSFICATION SOCIETY REGULATIONS.
  2. NON WATER TIGHT: FORM THE BOUNDRIES OF TANKS USED FOR CARRIAGE OF LIQUID CARGO.
  3. OIL TIGHT: ARE ANY OTHER BULKHEADS SUCH AS, ENGINE ROOM CASINGS, ACCOMODATION PARTITIONS, STORES COMPARTMENTS ETC.

 

FUNCTIONS OF BULKHEADS:

  1. AS STRENGTH MEMBERS THEY GIVE STRENGTH TO THE HULL, THEY RESIST THE HULL FROM DEFORMING,
  2. HELP IN SPREADING HULL STRESSES OVER A LARGE AREA,
  3. DIVIDE THE VESSEL IN SMALL COMPARTMENTS, SO AS TO PREVENT PROGRESSIVE FLOODING AND ULTIMATE FOUNDERING OF THE VESSEL IN CASE OF FLOODING/COLLISION/GROUNDING.
  4. IN LIQUID CARRIERS THEY DIVIDE THE VESSEL INTO TANKS AND THUS REDUCE THE FREE SURFACE EFFECT,
  5. REDUCE / PREVENT DAMAGE CAUSED BY SLOSHING OF THE LIQUIDS IN THE TANKS,
  6. THEY ALSO PREVENT SPREADING OF FIRE, THEY ARE SPECIALLY DESIGNED TO WITHSTAND HIGH TEMPERATURES.

 

CONSTRUCTION OF WATERTIGHT BULKHEADS:

  1. FORMED OF SEVERAL STRAKES OF PLATING,
  2. WELDED TO THE SHELL DECK AND TANK TOP,
  3. STRAKES ARE WELDED HORIZONTALLY AND STIFFENED VERTICALLY,
  4. STRENGTH INCREASES TOWARDS THE BASE BY INCREASING THE THICKNESS OF THE STRAKES AT THE BASE,
  5. THE COLLISION BULKHEAD IS 12% THICKER THAN OTHER WATERTIGHT BULKHEADS,
  6. THE AFTER PEAK BULKHEAD IS ALSO THICKER TO REDUCE VIBRATIONS,
  7. THE STIFFENERS ARE GENERALLY VERTICAL BULB PLATES SPACED 760MM APART, IN CASE OF COLLISION BULKHEADS AND OIL TIGHT BULKHEADS IT IS SPACED 610MM APART,
  8. IT SHOULD BE OF SUFFICIENT STRENGTH TO BE CAPABLE OF REMAINING WATERTIGHT WITH A HEAD OF WATER UPTO THE TOP OF THE BULKHEAD,
  9. IT MUST EXTEND UPTO THE BULKHEAD DECK IN ONE PLANE WITHOUT ANY RECESS AS FAR AS POSSIBLE AND PRACTICABLE. ANY RECESS MUST COMPLY WITH THE APPLICABLE SUBDIVISION REQUIREMENT AS PER SOLAS,
  10. THE NUMBER OF PENETRATIONS IN A WATER TIGHT BULKHEAD MUST BE MINIMISED, ANY PENETRATIONS MUST BE AS INBOARD AND AS HIGH AS PRACTICABLE AND BE WATERTIGHT,
  11. SLUICE VALVES ARE NOT PERMITTED IN WATER TIGHT BULKHEADS.

 

LOCATION OF WATERTIGHT BULKHEADS:

  1. COLLISION BULKHEAD IN THE FRONT END,
  2. A AFTER PEAK BULKHEAD,
  3. WATER TIGHT BULKHEAD ON EITHER SIDE OF THE MACHINERY SPACE,,
  4. IF THE VESSEL IS LARGE, ADDITIONAL BULKHEADS ARE REQUIRED TO PROVIDE GREATER STRENGTH AND TO INCREASE THE AMOUNT OF SUB-DIVISIONS,
  5. PASSENGER SHIPS HAVE TO COMPLY WITH SOLAS FOR THE NUMBER AND SPACING OF WATERTIGHT BULKHEADS WHICH IS A STATUTORY REQUIREMENT.

 

TESTING OF WATERTIGHT BULKHEADS:

  1. THOROUGH INSPECTION OF WATER BULKHEAD SHALL BE CARRIED OUT,
  2. HOSE TEST SHALL BE CARRIED OUT AT THE MOST ADVANCED STAGE OF FITTING UP OF THE SHIP,
  3. TESTING MAIN COMPARTMENTS WITH WATER IS NOT COMPULSORY,
  4. IF TESTING NOT CARRIED OUT BY FILLING WATER, HOSE TEST SHOULD BE CARRIED OUT WHERE PRACTICABLE,
  5. IF HOSE TEST NOT PRACTICABLE DUE TO DAMAGE TO MACHINERY OR ELECTRICAL EQUIPMENT IT IS REPLACED BY CAREFUL VISUAL EXAMINATION SUPPORTED BY MEANS SUCH AS DYE PENETRATION TEST OR ULTRASONIC LEAK TEST,
  6. FORE PEAK, DB TANK INCLUDING DUCT KEEL AND INNER SKINS SHALL BE TESTED BY FILLING UP WITH WATER,
  7. TANKS INTENDED TO HOLD LIQUIDS SHALL BE TESTED FOR TIGHTNESS WITH WATER TO A HEAD UP TO DEEPEST SUB-DIVISION LOAD LINE,

 

COLLISION BULKHEAD

  1. EVERY SHIP SHALL BE FITTED WITH A COLLISION BULKHEAD IN THE FORWARD UPTO THE FREEBOARD DECK, AT A DISTANCE OF 5 % OF THE LENGTH OR 10 MTRS (WHICHEVER IS LESS) FROM THE FORWARD PERPENDICULAR,
  2. WHERE THERE IS A BULBOUS BOW OR ANY OTHER STRUCTURE EXTENDING FORWARD OF THE FORWARD PERPENDICULAR, THE ABOVE DISTANCE SHALL BE MEASURED FROM A POSITION:

     

    1. AT THE MIDLENGTH OF SUCH EXTENSION, OR
    2. AT A DISTANCE OF 1.5 % OF THE SHIP’S LENGTH FORWARD OF THE F.P., OR
    3. AT A DISTANCE OF 3 MTRS FORWARD OF THE FORWARD PENDICULAR,

WHICHEVER FROM THE ABOVE 3 IS AFT.

  1. THE COLLISION BULKHEAD MAY HAVE RECESS OR STEPS, PROVIDED THEY TO COMPLY WITH RULE (1) AND (2) ABOVE. PIPES PIERCING SUCH BULKHEADS SHALL BE FITTED WITH VALVES WHICH ARE OPERABLE FROM ABOVE THE FREEBOARD DECK AND THE VALVE CHEST SHALL BE SECURED TO THE BULKHEAD IN THE FOREPEAK. THE VALVE MAY BE FITTED AFT OF THE COLLISION BULKHEAD WHERE SUCH VALVE IS EASILY ACCESSIBLE UNDER ALL SERVICE CONDITIONS, BUT THE SPACE SHALL NOT BE A CARGO SPACE. NO DOORS, MANHOLE, OR ANY OTHER OPENING SHALL BE FITTED IN THE COLLISION BULKHEAD.
  2. IN EVERY CARGO SHIP PROVIDED WITH A LONG SUPERSTRUCTURE IN THE FORWARD, THE COLLISION BULKHEAD SHALL BE EXTENDED WEATHERTIGHT UPTO THE DECK IMMEDIATELY ABOVE THE FREEBOARD DECK. THE EXTENSION SHALL BE WITHIN THE LIMITS SPECIFIED IN (1) AND (2) ABOVE.
  3. IN EVERY CARGO SHIP PROVIDED WITH A BOW DOOR OR SLOPING LOADING RAMP FORMING PART OF THE EXTENSION OF THE COLLISION BULKHEAD ABOVE THE FREEBOARD DECK, SHALL BE WATERTIGHT AND THE PART OF THE RAMP WHICH EXTENDS 2.3 MTRS ABOVE THE FREEBOARD DECK MAY EXTENDS FORWARD OF THE LIMITS SPECIFIED IN (1) AND (2) ABOVE.
  4. THE NUMBER OF OPENING IN THE EXTENSION TO THE COLLISION BULKHEAD ABOVE THE FREEBOARD DECK SHALL BE CAPABLE OF BEING CLOSED WATERTIGHT AND SHALL BE RESTRICTED TO MINIMUM, COMPATIBLE WITH THE DESIGN AND NORMAL OPERATION OF THE SHIP.

 

WATERTIGHT DOORS

 

OPENING ARE NOT ALLOWED IN WATERTIGHT BULKHEADS BUT WHEN IT IS NECESSARY TO HAVE AN OPENING IT IS IN THE FORM OF A WATERTIGHT DOOR. WHERE AN OPENING IS CUT IN THE FORM OF A WATERTIGHT DOOR, CARE MUST BE TAKEN TO MAINTAIN THE STRENGTH OF THE BULKHEAD. THE OPENING IS TO BE FRAMED AND REINFORCED. IF THE VERTICAL SPACING BETWEEN STIFFENERS IS INCREASED TO ACCOMMODATE THE DOOR OPENING, THE SCANTLINGS OF THE STIFFENERS ON THE EITHER SIDE IS INCREASED TO GIVE AN EQUIVALENT STRENGTH TO THAT OF AN UNPIERCED BULKHEAD.

THESE DOORS ARE MADE OF MILD STEEL OR CASTE AND ARE EITHER VERTICAL SLIDING OR HORIZONTAL SLIDING TYPE AND CAPABLE OF BEING OPERABLE UPTO A LIST OF 30 ON EITHER SIDE. THESE SHOULD BE CAPABLE OF OPERATION FROM THE VICINITY OF THE DOOR AS WELL AS FROM A REMOTE LOCATION. POSITION INDICATORS SHOULD BE PROVIDED NEAR THE DOOR AS WELL AS AT ALL REMOTE OPERATING POSITIONS. THERE SHOULD BE AN AUDIBLE ALARM, DISTINCT FROM ALL OTHER ALARMS IN THE VICINITY, WHICH WILL SOUND WHEN THE DOOR IS BEING REMOTELY OPERATED. REMOTE OPERATION CAN BE IN THE FORM OF A VERTICAL THREADED SHAFT GOING UPTO THE DECK OR CAN BE HYDRAULICALLY OPERATED BY MOTOR AS WELL AS A HANDPUMP AT REMOTE LOCATION AND ALSO NEAR THE DOOR. DOORS WHICH ARE NORMALLY CLOSED AT SEA BUT ARE NOT PROVIDED WITH REMOTE OPERATION SHALL BE MARKED “TO BE KEPT CLOSED AT SEA” ON BOTH SIDES OF THE DOOR. DOORS WHICH ARE TO BE PERMANENTLY KEPT CLOSED AT SEA SHOULD BE MARKED “NOT TO BE OPENED AT SEA”.

 

BOW DOOR

  1. THE OUTER RAMP SECTION AND THE OUTER BOW DOOR ASSEMBLY ARE MOUNTED ON INDEPENDENT HYDRAULICALLY OPERATED FRAMES,
  2. FIRST THE BOW DOOR IS OPENED, THEN THE OUTER RAMP FRAME IS UNFOLDED, THEN FINALLY THE COLLISION BULKHEAD DOOR OPENS AND SITS ON THE RAMP FRAME AND COMPLETED THE RAMP ASSEMBLY,
  3. THE RAMP FRAME IS LOCATED FORWARD OF THE COLLISION BULKHEAD DOOR,
  4. INTERLOCKING OF VARIOUS PARTS PREVENTS ACCIDENTAL / OUT OF SEQUENCE OPENING, i.e. FIRST THE BOW DOOR WILL OPEN, THEN THE RAMP FRAME AND FINALLY THE COLLISION BULKHEAD DOOR.
  5. WHEN CLOSED THE DOOR IS CLEATED BY HYDRAULICALLY OPERATED WEDGES AROUND THE ENTIRE OPENING, IN ADDITION STRONG LOCKING DEVICES ARE POSITIONED IN THE LOWER PART OF THE DOOR SECTION AND THE HULL,
  6. FULL WATER TIGHTNESS IS ENSURED BY A SINGLE LIP RUBBER SEAL MOUNTED AROUND THE DOOR OPENING.

 

CONSTRUCTION AND INITIAL TESTS OF WATERTIGHT DOORS AS PER SOLAS

  1. IN PASSENGER SHIPS THE FRAME OF VERTICAL WATERTIGHT DOORS SHALL HAVE NO GROOVE AT THE BOTTOM IN WHICH DIRT MIGHT LODGE AND PREVENT THE DOOR CLOSING PROPERLY.
  2. IN PASSENGER SHIPS THE WATERTIGHT DOOR SHALL BE TESTED BY WATER PRESSURE TO A HEAD UP TO THE BULKHEAD DECK OR FREEBOARD DECK.
  3. IN CARGO SHIPS A HOSE TEST IS ALSO ACCEPTED.

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