What is Dry Docking?

Dry docking refers to the process of entirely removing a sea-going vessel from the water and placing it on a dry dock to facilitate repairs or maintenance. This procedure is critical for maintaining the structural integrity and operational efficiency of ships, especially when significant repairs are required on a ship's hull. In this article, we explore the practical aspects of dry docking, including the process for smaller boats, the costs involved, and potential issues that can arise during the transition.

Dry Docking: A Simplified Explanation for Smaller Boats

The concept of dry docking can be easily understood by looking at a standard 14-foot jon boat. Instead of dragging the boat to the shore and setting it on sawhorses, you can essentially simulate a small version of dry docking for minor repairs. However, for larger vessels, a more complex procedure is necessary.

Process for Larger Vessels

For large ships, the process of dry docking is quite intricate. Typically, the dock used is a specially constructed cement structure that is intermittently flooded with water. Before the vessel is placed in the dock, detailed ship drawings are reviewed to identify the pre-planned support locations.

Preparation and Setup

Large blocks, usually made of wood, are built at these locations, designed to support the ship’s weight. The blocks are positioned with precision and then the docks are flooded with water. This is done through controlled valves to ensure that the structure remains stable. Divers then inspect the blocks to confirm they haven't shifted.

Transferring the Vessel

Once the dock is ready, tugs and pusherboats are used to carefully move the ship into the flooded dock. The ship is secured with mooring lines to ensure it remains centered over the blocks. A coffer dam, a temporary watertight barrier, is then placed at the end of the dock. Slowly, water is pumped out, and divers or remote drones monitor the ship’s settling to ensure it is properly supported.

Adjustments and Final Preparations

If necessary, the ship can be shifted back and forth using mooring lines and winches to ensure it is perfectly centered over the blocks. This process continues until the ship is fully supported and the dock is free of water. Pumps are used to remove any water that manages to seep past the coffer dam.

The Cost of Dry Docking

The cost of placing a large tugboat in dry dock can range significantly. For example, in Japan, at Sumitomo or MHI, the cost of just putting the vessel in the dry dock is around $250,000. This does not include the actual repairs that need to be carried out.

Issues with Damaged Hulls

In cases where the hull needs repair due to damage, such as being bent, the costs and logistics significantly increase. At professionally managed shipyards, European, Japanese, and Korean yards, this kind of damage is rare. However, in lesser-equipped shipyards in third-world countries, or some U.S. shipyards, such damage is more common.

Conclusion

Dry docking is an essential process in ship repair, ensuring that even the largest vessels can be maintained and repaired efficiently. Whether it's a small jon boat or a large tug, the principles of dry docking remain the same—precise planning, controlled water levels, and thorough monitoring. Understanding the intricacies of this procedure is crucial for anyone involved in maritime maintenance and repair. The costs associated with dry docking can be substantial, reflecting the complexity and importance of the work involved.