As we have seen previously, dry docking is a commonly used procedure for the inspection, repair and maintenance of ships and boats. The primary objective of this method is to expose the parts of a vessel that have been submerged underwater for a long time. These submerged portions of the ship need to be checked regularly for damage they endure due to the sea water. Since the vessels are massive in size, dry docking is the most efficient way for the maintenance of ships.
Given that dry docking is one of the most frequently-used methods for repair and maintenance of boats, we shall see the complete procedure for dry docking and the scope of repairs that can be carried out, in this article.
Dry Docking Procedure
The procedure for the dry docking of a ship is not a spontaneous one. It takes months of planning, considering meticulous details about the ship and preparing the dock accordingly. Even the slightest mistake in calculations can lead to drastic consequences.
The phases of dry docking are as follows:
Phase 1: Pre-docking Preparation
The process of dry docking of a ship needs to be planned meticulously. Days before a ship is to be dry docked, the dock master will prepare a docking plan, taking into consideration all the minute details of the structure of the ship, i.e. hull structure of the ship, locations of the drain plugs, and echo sounders beneath the ship so as to not damage them during docking the ship.
Phase 2: Preparing a Docking Plan
The process of dry docking of a ship needs to be carefully planned to be executed with ease. Dock Masters and designers take aid of a series of sketches and detailed calculations about the ship’s height, weight, and structure. The docking plan explains how to successfully dock the ship and also how to easily undock it. It also reduces the risk of a ship capsizing during undocking.
Phase 3: Understanding the Stability Conditions
It is imperative for the ship to be stable while docking. The weight distribution of the ship that is to be docked needs to be calculated accurately. Since almost the entire weight of the ship is borne by the keel blocks, the slightest error in the calculations of the stability conditions can lead to a mishap. Hence, the stability condition of the ship is analysed perfectly before the actual process begins.
Phase 4: Arrival
The ship has to adhere to all the stability conditions on its arrival to the dry docking port. The propeller of the ship also needs to be immersed and the ship needs to have the least ballast. It is best to avoid dry docking if there is a chance of a rough weather. The cleaners and dock master then board the vessel.
Phase 5: The Actual Docking
Once the ship has successfully achieved the pre-docking conditions, the ship is to be tugged into the dock since its engine is not available. When the ship is inside the docks, the ship is moored and made secure. The crew then takes over and starts pumping out dock water, running the ballast pump, and removing the drain plugs, amongst other cleaning procedures.
What is the Scope of Dry Docking?
When a vessel is dry docked, the crew starts with checking the most important parts of the ship for any visible and internal damage. Repairing all major as well as minor faults in the ship goes a long way in increasing its productivity.
Here are some of the activities carried out in the maintenance procedure after a ship is dry docked.
The construction of the vessel hull needs to be carefully scrutinised for damages since it is in constant contact with the sea water. Even if the hull is not visibly damaged, its thickness must be tested to avoid any mishaps.
The docking crew measures the thickness of this hull using an ultrasonic gauge for the purpose. It measures the time interval between consecutive echo signals reflected from the surface of the hull. The paint on the surface of the hull does not hinder the calculations in this method; hence it is the most efficient way of testing the thickness of a ship’s hull.
Destructive & Non-Destructive Testing
Destructive testing involves breaking down or damaging certain parts of the ship just to test their strength. It involves rebuilding the same part to endure more damage and be more durable.
Non-Destructive testing evaluates materials and parts of the ship without disabling or destroying any of its features. It is a smarter and more efficient option when it comes to testing the materials aboard a ship. Some of the non-destructive testing methods include ultrasonic testing, visual inspection, and liquid penetration technique.
High Pressure Washing
This method is used to clean the ship’s hull of bio foul and dirt that have collected on the hull over time. The presence of algae and other bio foul on the surface of the hull increases its corrosion. It is important that the hull be cleaned and high-pressure washing is the most efficient way to do this. High-pressure washing involves the removal of the fouling with the help of manual gun systems and high-pressure water jets. They also make use of rotating nozzles to clean large areas of the hull.
Underwater Repair & Diving
Underwater repair deals with the inspection and repair of the ship while it is in the sea. A number of companies who offer these services specialise in examining the ship’s surface for flaws that can only be seen in water. They make use of advance machinery, such as underwater welding, to repair damaged propellers while the ship is in the water.
Blasting & Hull Painting
Blasting is the protective layer put on the hull to make it ready for the application of paint. It gives a good profile to the metal before it is painted. A good layer of paint minimises the corrosion of the ship’s hull.
Anchor & Chain Servicing
The chains and anchor on a ship are mostly used to stabilize it during times of rough weather. Over time, the anchor and chain which are mostly made of iron start to rust and erode. Hence it is necessary for the anchor and chain to be replaced or maintained regularly.
Inspecting a ship manually can be tedious at times. Thanks to the rapid development of technology, the inspection of an entire ship can be done quickly and more thoroughly with the help of robots. Robots have been developed to scan ships for inaccuracies, abnormalities and other faults. Such type of quick detection reduces the time needed to repair such damages.
The efficiency of a ship depends on how well all the machinery and operating systems of the ships are maintained. Hence, ships are expected to be dry docked twice in every five years. The process is obviously an important one, but the cost of dry docking a ship is massive. It is necessary for the ship to spend the minimum time being dry docked. The more time a ship spends on the dock, the lesser it will make financially.
To speed up the process of ship repairs, several ship repair and maintenance service providers now try to reduce the dry docking period for the ship.
There are several advantages of reduced dry docking. A reduced dry docking period will ensure a more efficient way of fixing ships. The faster ships are dry docked and repaired, the more vessels can come in. Using coating systems and abrasive blasting enables the surface of the ship to dry faster, thus considerably reducing the time of a ship in the docks.
Though it may seem like a simple process, dry docking is a complicated and an expensive procedure that involves intricate planning. The process is absolutely necessary for maintaining ships, submarines, and other vessels, so that they can function at optimum efficiency for a longer duration.
With reduced dry docking and the presence of several companies in India that provide quality repair and maintenance services, dry docking has become easier and faster than ever.
Cover Image Source: Cruisecritic