Drydocking of Ships

WHAT IS DRY DOCK? NECESSITY OF DRY DOCKING

dry dock

 

WHAT IS DRY DOCK? NECESSITY OF DRY DOCKING

– BY A.K.RAMANUJAN

Reasons for dry-docking?

Dry dock dry docking necessity.

The  dry docking  activity  of  cargo ships  on  a  regular basis  is  a  requirement  for  efficient  and  safe  operation  of ships and  has  two  main  objectives  which  are  as  follows :-

  • To  clean, scrub,   prepare  by  de -scaling  all  rusted  areas  of  the  hull,  and  finally   paint  the  ship’s hull so  that  speed and  fuel  consumption  are  restored  to  the  original
  • To examine  all  underwater  critical  components  as  well as  the  entire under water  hull for  defects  and  take  suitable  corrective.

Regulations on Dry docking

The  question  that  is  frequently  asked  is  whether  it  is  mandatory  to  dry dock  a  ship on  a  regular basis.  The  answer  is  yes  and  it  is  in  accordance   with  cargo  ship  safety  construction rules  based  on  the  1974  SOLAS  regulations. The  rules  state that  cargo  ships  have  to be  dry docked  twice  in  an  interval  of   five  years  with  the  interval  between  consecutive  dry dockings  being  not  less than  two  years  and  not  more  than  three  years.  The  classification  societies  have interpreted  this rule by  providing  a  regular  interval  of   thirty  months  with  a  window  period  of  + or –   six  months  from  the  anniversary  date  so  as  to  suit  this  requirement.

HISTORY OF DRY DOCKING

About  sixty  years  back  all cargo  ships  were  being  dry docked  on  an  annual  basis  and  this  was  being  done  in  accordance  with  classification  rules  existing  then.

With  advances  made  in technology, steel quality and  paint  materials  have  improved  considerably  making  them  more  reliable. In addition  to  this  it  the  pattern  of  world  wide  shipping  has  changed   whereby  ships  are at  sea  for  longer  periods   in  a  year  as  compared  to  conditions  sixty  years  before. The Administrations  and  classification  societies  have  therefore  amended  the  rules  accordingly.

In addition to  the  above  change.  The  classification  society’s rules  for  periodical  surveys  have  now  been  amended  to  operate  in  accordance  with  the  harmonization  of  surveys so  that  surveys  and  repairs  are  carried  out  conveniently  without  hindrance  to  the  operation  of  the  ships.

DRY DOCK SURVEY

Accordingly  in  a  five  year  cycle  of  survey  the  two  dry dockings  are  programmed  as,  the  first  dry-docking  during  the  intermediate  survey  layup  and  the  second  dry-docking  during  the  special  survey  layup for  renewal  of  class  certificate.

The above stated facts  apply  to  regular  and  routine  dry docking. As  per  classification  rules  as  well  as  rules  for  issue  of  safety  construction  certificate,  the  routine  dry-docking  cannot  be  substituted  by  an  afloat  underwater  inspection . Such  inspections  are recommended  in  special  circumstances  especially  when  the  ship  has  missed  the  scheduled  dry docking  for  various  genuine  reasons  and  this  inspection  by  the classification society is  carried  out  only after  obtaining  a  suitable   recommendation  from  the  Administration. This recommendation is  limited to  issue  a  voyage permission for  the ship to  reach  the  shipyard  stemmed.

OTHER REASONS FOR DRY DOCKING

Dry docking  has  to  be  carried  out after an  accidental  grounding  or  collision  involving   underwater  damage .This  dry docking  will only  involve  the  requirements  for  satisfactory  completion  of  the  repairs  for  the  under water  damage. If , however  this  accident  has  occurred  within  close  proximity  of  the  scheduled  dry docking  date ,  the    dry docking  activity  (regular)  may  be  suitably  advanced  which  the  administration  will  agree.

It  should  be  understood  that  during  dry docking the  normal  repairs for hull and  machinery as  scheduled  and  listed  out will  continue but  they  are  not  considered  as  work  relating  to  the  dry  docking  activity. This  is  being  stated  here  especially  so  that students  answering specific  questions  on  drydocking  do  not  list  out  jobs  or  work  which  do  not  require  drydocking.

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One thought on “WHAT IS DRY DOCK? NECESSITY OF DRY DOCKING

  1. Subodh Patil says:

    Dear Sir
    I am appearing for my Masters Orals and one of the questions being asked is how do you prepare for an emergency dry dock after a collision. Who will advice the vessel to be docked and what precautions will have to be taken if there is breach in the hull.

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