hull technology - 1 - docking

8/4/2019 Hull Technology - 1 - Docking

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Hull Technology



Docking

• Reasons for docking include Inspection / repair

of:-

– Under water hull structure – Under water valves/suction

– Under water hull appendages

– Cathodic protection system

– Hull coating

– Maintenance of rudders, stabilizers, shaft brackets and

shaft



Types Of Docking

• Programmed

– Normally part of AMD, Refit schedule .

Duration depends upon MMS routines andknown defect rectification time required.

• Un-Programmed

– Generally of short duration. Dock is madeavailable for shorter duration, specifically to

carry out a single defect rectification



Type of Docks

• Graving Dock

– Permanent facility, an integral part of the shipyard. Can

be covered or uncovered• Floating Dock

– A mobile platform which can be towed any where and

berthed at a suitable depth

• Ship Lift / Synchro Lift – Immobile arrangement. A platform which can be lifted

mechanically after a vessel has docked in it



Types of Docks

• Heavy Lift Ships

– These are basically self propelled floating

docks, like the one used to transport USS Coleback to USA

• Slip ways

– Used mainly for building ships hulls beforelaunching and retrofitting. Small vessels are

generally docked on slip ways



Ship Lift Dock



Graving Dock



Floating Dock



Heavy Lift Ships



MEO’s Responsibilities - Before

• Read BR 3000 for details on this topic, it will be includedin final examination

• De-fuel vide BR 3000

• Ensure safety measures BR 2000(60)

• Be aware of docking / undocking procedure for the type of ship and type of dock

• Study the docking plan. A docking plan shall contain

– Ships profile – Deck plans (arrangement of keel blocks etc)

– Sections of ship where shores are to be used




• Know the lines of responsibility

– Ship is upright. Plumb lines / level indicators rigged toensure uprightness

– Trim is as per the requirement of dock authorities

– Davits / Gangway to be stowed inboard (Exo)

– Sonar Dome to be drained (WEO)

– Rudder locked amid ship

– Shoring positions marked on weather deck

– Propeller at docking position and blades at 0 pitch

– Ship de-fueled and de-ammunition. Liquid state must berecorded

– Fin angles at 0

– Cathodic protection switched off




• Start / Allow de flooding only if shore supplies

(power / fire main /HP air/ air-conditioning) are

available

• Ensure availability of alternate source of fire main pressurization such as ship’s engine driven pump etc

• Check availability of the following in dock

– Crane

– SW supply

– Sewage

– Normal jetty supplies, water etc

• Check draughts immediately prior to entering dock




• Permission for fuel - machinery policy

• Propeller polish (iaw S2022a 4386/1)

• Ensure logs are ready – Dock bottom log

– Movement of weights

– Underwater valve log

• Record initial weight positions• Note liquid tank state

• Get a brief from the Dock master



Documentation Available

• BR4000 - MOD(N) Docks UK

• BR4001 Foreign Dock Book

• D231 Docking Certificate

• D231a Undocking Certificate

• D231b Ammunition Certificate

• D238 Docking Report• NES 850 General Dock Block Arrangements



Docking Tips

• Have a good breakfast, it’s a long day

• Make sure all doors are open

• For the dockmaster this is a regular

evolution

• You must be sure how you will control the

evolution



Ships Stability While In Dock

• You should be familiar with the diagram

below

Z

B B1

M

K

G




• When ship inclines a small

angle, buoyant force will act on

B1 towards M

• Weight of the ship continues toact from G but will be parallel

and opposite to B1M direction

• GZ is the righting arm of the

ship

Z

B

B1

M

K

G




• When a ship settles on keel blocks and waterlevel continues to fall, some buoyancy is lost.Just like the term parallel sinkage, the ship

experiences parallel rise• Docking can be considered as weight being

taken off of the ship

• As soon as the ship touches the dock blocks,the parallel rise starts

• As the force acts on the keel it is assumed thatthe weight is being removed from the keel




• A ship of draught 0, floating with G0 and

B0, will experience a reaction force Fr upon

touching with the keel blocks.• Magnitude of this force will be equal to the

weight (w) of the layer W0 WD BD L0

• It will actually be the weight of the volumeof water layer, third dimension added will

be the length of the ship).




• Therefore the buoyant force will now act at

BDock such that

FB

= 0

-FR

= 0

-w

• Shift in the C.G due to this removal of weight

will be

KGDock = (

0 KG0-FRKg)/(

0 – FR)• Since weight removal is assumed to be at keel

therefore Kg=0

KGDock = (

0 KG0)/(FB)




• Thus

GMDock =KMDock -KGDock

=(FBKMDock -0KG0)/FB

• The righting moment in docking situation

will now become,

FBGZ =FBGMDock Sin

=(FBKMDock -0KG0)Sin



Docking Plans

• So at any time during docking a ship must maintainthe following to ensure positive stability

FBKMDock > 0KG0

• If the above is not possible then brest ropes must beapplied before the critical draught is reached

• A dock plan contains dimensional details of the dock itself. Including the dimensions of the blocks being

used• Used to determine if the ship will fit in the dock

• Every ship has a dock plan, a copy of which is keptwith the dock master



Docking Plan

• Profile section

– Location of decks, bulkheads, tanks and main longitudinals

at the ships side

– Proposed position of the shores – Navigation data for the U/W hull only

– Position of shore services connections

• Section Plan

– Section of the ship, including sections recommended for

shoring

– Details of ships U/W projections

– Recommended position of blocks if using a single line of

blocks at centre line



Docking Plan

• The docking authority is to prepare the dock

and relevant hardware, after matching up

both dock plans• Markings are painted on dock sides for

shore spars and stern of the ship



Docking In A Floating Dock

• When a ship is to be docked into a floating dock, centreline of the ship must coincide with that of the centre line of the dock

• The principal applied in a floating dock is – The lift available in any section of the dock must not be less than

the weight of that part of the ship that is to be docked over it

• By observing this principal longitudinal bending momentsand stresses on the dock structure are kept to a minimum.

• Lift curves are normally available for floating docks forthis purpose




• Distribution of weight of a ship is not uniform

along its length whereas the floating dock has

uniform lifting capacity along its length

• Therefore the displacement of the vessel is

considerably less than the lifting capacity of

the dock

• Once a ship is lifted then it becomes part of the

dock, thus the previously discussed special

stability considerations have to be kept in mind




• Floating docks have a bottom pontoon and lower

sections of the walls divided into a number of

tanks• These tanks are remotely flooded or de-flooded to

achieve sinking / rising of the dock

• Upper parts of the walls contain control

equipment, workshops, offices, accommodation

etc



MEO’s Responsibilities – In Dock

• Keep record of all shifting of weights 250Kg or

more, and details of weights moved forwarded to

dock authority prior un docking• Keep in mind any UxE operation while in dock

• Record opening and closing of all water tight

valves, glands or other U/W openings

• Avoid any spillages onboard and on dock floor.

Clean the same as immediately as possible




• Carry out survey of U/W hull with Keyrates

• Note condition of anti-fouling and otherprotective coatings, zinc anodes, suctionstrainers, propellers, U/W shaft bearings(This is done as soon as possible)

• Monitor progress of all work being carriedout with time critically in mind




• U/W valves

– During intermediate dockings 25 % of total valves

must be repaired

– During Refit/Repair period all remaining valves

must be repaired

– All valve’s maintenance must be completed during

refit – From inspection point of view, always check

valves in the closed position, check for operation

and efficient operation



Docking Preparations

• Check keel blocks

– Remove those in way of any U/W fitting

– Placing extra blocks in way of higher loading

– Check security of blocks




• Check shores are spaced 30 – 40 Ft apart

• Shores are cut 6in short to allow wedges

and packing at their heels• Shore spars are prepared as per the location

where they are to fit exactly

• Shores are placed such that their positioncoincides with that of bulkheads, decks orframes to prevent local straining

hull technology - 1 - docking

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