What is a dry dock and how does it work?

A dry dock is one of the biggest challenges in civil engineering. And not only that, but also all the auxiliary elements that compose it make dry docks a highly complex structure. From SYM Naval we want to approach, broadly, the operation of a dry dock in a shipyard as well as its main characteristics in this article.

The dry dock and its fundamental role in a shipyard

First of all, it is important to highlight that the dry dock is part of the facilities of a shipyard regardless of its main activity, being the ship building or repair of vessels. In order to carry out these shipbuilding and repair works, the shipyard also has a part of its own dry dock, additional equipment such as cranes, facilities such as berths and workshops that make it possible to repair or build a ship.

Regarding dry docks, we can differentiate several types according to their use:

• Repair and maintenance: Used for emergency and planned dry-docking surveys of ships.
• Shipbuilding: Docks destined mainly for the construction of ships.
• Shipbuilding and repair: Mixed dry docks used for both shipbuilding and repair works.

Taking into account the different facilities and equipment that a shipyard can or should have, a reasonable conclusion seems to be that the dry dock is the most fundamental part since it allows carrying out both shipbuilding and repair works on ships.

How does a dry dock work?

Generally speaking, a dry dock is a chamber separated from the adjacent port water by a gate. Its basic structure comprises the floor or plan of the dock, the side walls, the front wall and the gate that defines the dry dock.

The filling and emptying processes of the dock are carried out by pumps generally located in a pumping station. Starting with the dock filling process, and taking into account that the dock is dry and without any vessel inside, it is filled by the gravity until water level inside the dock is equal to the water level in the outer zone allowing the gate to open and the ship to enter to the dry dock. Once the ship is inside the dock, the gate is closed and therefore the process of emptying the dock begins by pumping water to the outside. During the process of emptying the dock, vessel is centered and positioned on the blocks and dry-dock is completely dry to make it accessible. These blocks where the ship is located and depending on its position, can be classified as: keel blocks, bottom blocks or side blocks. Both the number and type of these blocks will depend on the size of the ship that enters the dock.

Dry docking a ship is the most complex and dangerous operation to be carried out in a dry dock. Each ship to be docked, must have a dry dock plan, forward and aft draft condition, displacement, load disposition, stability conditions and detailed information of damages, if any, at the dock entrance. Based on this dry dock plan and with all the information about ship dry dock conditions, the necessary calculations are made for the proper positioning of the ship on the blocks.

Once the required work is completed and the ship is ready for departure, the dry dock filling process begins by pumping out water into the dock until the ship floats freely. At the moment when the water level inside the dry dock is equal to the water level outside, the gate is opened and the boat is towed out.

Although this article is informative about the concept of the dry dock, we hope that it has been useful to the reader. At SYM Naval, as a shipyard that also specialises in carrying out repair and maintenance work in dry dock, we will be glad to provide more information if you wish and send us your questions through our contact form.