Dry Docking of Ship-Why we need it and What is done there

Dry Docking is an important practice that is associated with all the vessels that float on the water. In this article we will focus on the merchant ships only. When ship is sailing on the sea, there are several maintenances that cannot be carried out when ship is floating on the water. Mostly under water spaces are checked and repaired when ship is on dry dock. According to different classification societies, a ship needs to do dry dock twice in five year. Now it depends on the ship owner as when to do this. Generally normal procedure is that after 2 years, ships get in to the dry dock. But those vessels who sails in fresh water only, dry dock period may extended further, depending on the classification society because the salt content in the fresh water systems are very less as compared to the sea water.

In water surveys are also carried out by surveyors from time to time. All the deficiency that surveyor points out during this inspection are corrected when ship is taken for dry docking. In water surveys, a ship is carried to a location where water is clear enough, that its hull is visible from outer surface. So, this type of survey can only be carried in certain geographical location of world.

Preparations done before dry dock

Well as soon as the ships come out of the dry dock, a new file is maintained for another dry dock. All the necessary things like what type of maintenances we have to carry out on ship when it is in dry dock is accomplished. By doing so we are reducing the last minute hassle as what to maintain and what not. Before the dry docks, a full report of ship is sent to the dry dock department. This ensures that there are fully equipped according our need. A sketch of how ship will be made to rest on wooden blocks, are decided prior to ship coming.

Dry Docking, How to do Dry Dock
Now when ship starts coming, most of the things like fresh water tanks, fuel tanks etc are kept at minimum low level. Reason behind this is that we do not want ship to have a high draught. Now a platform just like you bath tub but having dimensions 100 times more than this is there. It is
completely full of water and ship enters in to this space, it is sealed tightly from all spaces. Now in order to keep ship on the wooden blocks, water from this big water reservoir is slowly drained out. This is the critical part of the dry docking. Ship due to its own weights, starts getting downward and subsequently is laced with tight ropes. Once the ship is properly seated on the wooden blocks, rest of the water is also taken out.
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Maintenances carried out on ship during dry docking

There are handful of maintenances that is being carried on the ship and they are as follows:
First of hull of ship is cleaned with blasting method and all the marine growth sticking to the ship hull is removed. A new paint is applied on the hull. This is special paint.
Rudder bearing clearance is also checked and bearing are removed if needed.
All the opening liked sea chest, out let of boiler blow down valve etc are checked and replaced if needed.
Sacrificial anodes, if they are installed and had worn out, needs to be replaced. Nowadays we used the impressed current cathodic protection.
Propeller condition and sealing of glands are checked for its leakage. Properllar Drop is also checked.
Anchor cables are check for their efficiency by surveyor.
All other machineries that cannot be operated when ship is on the way are checked at dry dock like main engines units, any major fault on any ship machinery etc.

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Mark Eriscson

Love to write about topics related to maritime sector. Was born in sailor's family, so love to ride on those high seas. In free time i would like to go for a good sunbath and some soothing guitar music. Want to have my own boat one day.

One thought on “Dry Docking of Ship-Why we need it and What is done there

  • September 25, 2017 at 1:06 pm

    Thank you Mark for an interesting topic.


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