preparation for dry docking

docking

Preparation of Dry Docking 

For a vessel to maintain its class license, and comply with operational requirements, it must carry out planned dry docking every five years for the renewal of the license. In cases like collision or under water damage the vessel will be brought in for unplanned dry docking for repairs.

purpose

The main objective in carrying out dry docking is to ensure ships are operational and to maintain their class license. Structural machinery and various components are subjected to inspection and maintenance to ensure sea worthiness. Dry docking is also required if a ship has sustained damage to the underwater structure due to grounding, collision or any other damage which will affect the water integrity of the ship’s hull.

Dry Dock Periods

A docking survey should be carried out twice within a 5 year period. The intermediate survey must be completed within 3 years. One of the two docking surveys within the 5 year period should coincide with a special survey. A Docking Survey is considered to coincide with the Special Survey when held within the 15 months prior to the due date of the Special Survey. An in water survey may be accepted in lieu of the intermediate survey For vessels operating in fresh water special consideration may be given.

Preparing the Ship for Dry Docking
1. Make a repair and maintenance list, create or obtain a dry-dock handbook if required, and assign responsible ship staff to their duties on the list. Divide staff into groups to oversee the work carried out by yard gangs.
2. All spare parts must be checked and repair items kept ready for use.
3. Previous dry dock reports should be studied and previous clearance measures noted.
4. Clean engine room tank top and bilges.
5. Prepare sewage treatment tanks, dirty oil tanks and bilge tanks.
6. Flushing of bilge lines is to be carried out prior to dry dock.
7. The oil-water separator filter element should be renewed and the system checked for satisfactory operation.
8. For tankers, all cargo tanks are cleaned and gas freed.
9. Minimum bunkers (Fuel Oil and Fresh water) and ballast carried.
10. All heavy weights secured prior to dry dock.
11. All tanks and cofferdams must be sounded and recorded.
12. Fire fighting plans and safety measures discussed before dry dock
13. Fire fighting equipment on board should be checked and kept ready for use.
14. Emergency lighting and generator should be tested before entry.
15. Escape routes must be clearly marked.
16. All valves and chests to be overhauled must be clearly marked.
17. Shore connections for cooling water and fire line are to be readied.
18. Main engine, generators, and boiler are changed over to diesel oil.
19. CO2 total flooding systems are secured and locked before entry.
20. Vessel must approach dock with even keel.

Duties of ship's Chief Officer when entering dock

Sound round all internal tank soundings (wet soundings) before entering the dry dock

Communicate with the Dry Dock Manager regarding the vessels' draught and trim to suit the dock construction

Prepare all necessary documenation which may be required to complete the docking operation and the expected workload inside the dock

Calculate that the ship has adequate positive stability to withstand the expected 'P' force that will affect the vessel when taking the keel blocks. The GM should be large enough to compensate for a virtual rise in 'G' once the keel touches the blocks and the vessel enters the critical period

To enhance the positive stability all slack tanks, and subsequent free surface effects should either 'pressed up' or alternatively pumped out if possible

Any repair list should be completed and kept readily avialable to hand over to the dock authorities

All utilities required should be ordered in ample time to be supplied to the ship on docking

All store rooms, toilets and ships cmopartments should be locked for the purpose of security and any loose gear should be stowed away before entering the dock

Rig fenders around the vessel before entry into the dock

Plug and secure all upper deck scuppers to reduce the risk of pollution

Log Book Entries when entering dock

-Tugs engaged at rendezvous position
-Vessel proceeding towards open lock (usually under piolatage)
-Line ahore foward and aft
-Tugs dismissed
-Moorings carried up port/starboard
-Stern clears gates
-Vessel stopped making headway inside the dock
-Dock gates closed
-Moorings checked to hold vessel
-Moorings adjusted to align ship fore and aft
-Dock pumps commenced pumping out dock water
-Block contact made and vessel enters critical period
-Vessel sewed on blocks fore and aft
-Side shores passed to port and starboard
-Residual water cleared from dock
-Gangway access landed between shore and ships side
-Gangway walkable
-Pilot dismissed
-Pumping of the dock complete and dock floor walkable

The Docking Process

When it is decided that a ship is to enter the dry dock the first thing that is done is the keel block arrangement. This is done by the Asst Dock Manager. The centre keel block arrangement is always the same. However, the rest of the keel blocks are arranged according to the ships' structure. These are based on the ships construction drawings.

Docking of any ship depends on the ship's draught. It is important to note the draught of the ship so as to estimate the tide at which she should enter the dock. The draughts of container ships are usually 5-7m and for tankers about 3m.

When the ship is near the entrance of the dock, a crane is used to lift wires to secure the whip to the dock winches. Two winches are secured at the aft end and two at the forward end of the ship. These winches are used to guide the ship into the dock and bring it to the exact spot at which it should be laid on the keel blocks. A ship entering a dry dock is shown in the picture below:

Once the ship is braught directly above the keel blocks on which it will be laid on, divers are sent in the dock to ensure the ship sits exactly on the keel blocks as the water is being pumped out of the dock.

The pump room located at the foward end of the dock controls the rate of water being pumped out of the dock. This process can also be refered to as de-ballasting the dock. This is what a ship will look like after the dock is fully de-ballasted.

Once the ship sits properly on the keel blocks, fire hydrants, safety signs and a shore gangway is attached to it. Safety personnel then inspect the ship and mark dangerous areas on it with a Red tape. This is done so that hot work can be carried out with care. An example of such an area would be the fuel oil tanks.

Application for all the necessary permits are then made. These permits include hot work permit, cold work and enclosed space permits. Gas checks are also carried out in enclosed spaces every day to ensure maximum safety.

The Undocking Procedure

When the docking work is near completion, the ships personnel as well as the shipyard personnel will need to carry out their respective checks on the vessel and around the dock area. Once the ship has finished dry docking it may not be immediately ready for normal trading. There are many tests which must be carried out first. These tests engine tests and sea trials and will be explained further in this section. The dry dock is not the loading port of the ship and hence the ship would leave the dock in the ballast condition on route to its loading port.

There are various duties and logs that need to be taken before and when the ship is leaving the dock. These are summarized in the topics descussed below:

Duties of the Chief Officer prior undocking

Ensure all the listed work is completed to a satisfactory standard. In particular that all 'survey work' is completed, prior to leaving the dock. To this end a final internal inspection of the vessel would be the order of the day.

Carry out an external inspection of the hull and enter the Dry Dock. This final visit to the dock floor would also encompass the replacing of any tank plugs that have been drawn. This task should not be deligated to a junior officer as the Chief Officer must sight all the tank plugs being replaced.

The Dry Dock Manager would accompany the ship's Chief Officer on final inspections and ensure that no vehicles, materials or personnel are remaining in the dock, prior to commencing any flooding operation.

Inform the ship's Master of the expected departure time and the crew would be engaged in activities to make the vessel ready for sailing. These activities would include odering the Navigator to plan the ships movement from the dock, posting the sailing board and cancelling shore leave, placing the engine room and respective personnel on standby, carrying out checks on all navigation equipment and making relevant entries into the deck and offical log books.

Ensure that a full set of tank soundings have been taken and that adequate supplies of fresh water, fuel and lubricating oil are on board to suit the ships movement needs. These tank quantities would then be applied to a complete stability check to ensure that the vessel has an acceptable GM once she floats clear of the keel blocks. Stability checks are the sole responsibility of the ships personnel and comparison should be made between the entry soundings when the vessel was last afloat.

All hatch covers would be closed up and the watertight integrity of the uppermost deck assured. Anchors and cables would be heaved up and stowed correctly aboard the vessel. All pipelines, power lines etc. would need to be disconnected and relavent manpower should be made available both ashore and aboard the ship in order to release these safely and at the appropriate time.

Tugs, the marine pilot and linesmen would need to be ordered to standby for the time of departure. Ships crew would be placed on standby on the fore and aft ends to tend moorings.

Finally, the chief officer would sign the Authority to Flood Certificate. This is provided that he is satisfied that the Dry Dock Authority has completed the docking specification and that the ship is in a seaworthy condition. This certificate should then be completed to allow the flooding of the dock to commence.

The Undocking Process

Before water is pumped into the dock, there are a few checks that must be made. Bottom plugs must be closed and sea chests should be in full working condition. Also, ballasting of the ship must be done. This is to ensure that the ship does not have an even keel draught (the aft draught is usually greater than the forward draught).

The pump room, which is usually located at the forward end of the dock controls the amount of water being pumped out of the dock. This is also referred to as ballasting the dock.

The gangway is lifted sometimes by means of a crane once the dock personnel have cleared the ship. Fire hydrants and all shore connections are disconnected.

The forward and aft ends of the ship are attached to shore based mooring lines which are winch controlled. A crane lifts these lines and places them on the deck so that they can be attached. These help to control the movement of the ship as it leaves the dock so as to ensure it leaves smoothly.

When the level of seawater in the dry dock reaches the sea level, the dock gates are opened.

A tug boat attaches a tug line to the aft end of the ship and begins to pull the ship backwards (out of the dock). The shore based mooring lines help to guide the ship smoothly out of the dock. Another two tugboats are on standby on either side of the ship.

Once the ship is halfway out of the dock, the aft shore based mooring lines are disconnected and the standby two tugboats attach themselves to the ship by means of tug lines.

When the ship has cleared the dock gates, the front shore based mooring lines are detached and the tug boats turn the ship around.

Once the ship is some distance away from the dry dock, the tug lines from all three tug boats are detached and the tug boats move away from the ship. The propeller is then started and ship moves away on its own propulsion.

Dry Dock - Glossary

Keel Blocks
The term given to the center line blocks of the dry dock that the docked ships keel will come to rest on. They are usually made of 'oak' wood and may not always be on the docks centre line, especially when more than one vessel is being docked

Dry Dock Manager
A dockmaster who retains the ultimate responsibility for the complete working of the dry dock

Hot Work
Any work which involves a source of ignition or temperature sufficiently high enough to cause ignition of a flammable gas mixture

Cold Work
Work which cannot create a source of ignition

Hot Work Permit
A document issued by the authorities permitting specific hot work to be carried out in a specific time period in a deifned area

Critical Period
The period of time from the critical moment when the keel of the vessel first touches the line of blocks and ommences to achieve the position of being 'sewn' on blocks.

Shores
Horizontal supports, usually timber employed between the stepped sides of a graving dock and the ships side shell plating. Ideally shores would be positioned in way of deck stringers and framed intersections of the ships steel work.

Authority to Flood Certificate
A certificate which must be presented to the shipboard representative for signature, usually the Chief Officer, prior to the action of re-flooding the dock space and returning the vessel to a floating condition. Chief Officers are advised to ensure all required work is completed to satisfaction prior to signing such a certificate. The Chief Officer would also take time to check that all plugs have been returned to any tanks and that no personnel are still inside the docking area.