Every machine needs repairing, maintenance and constant upkeep for smooth functioning. Dry Docking is the process followed for the periodic repair and maintenance of ships, boats and watercrafts.
Dry Docking is a method of ship repair being practiced for decades. It is a process of manufacturing, repair and maintenance of ships in an area known as the ‘lock’. In simple words, a lock is like a ‘garage’ for repairing ships. The only difference being, a lock is constructed aligning the shore for easy manoeuvre of the ship and sea water drainage.
The main purpose of a Dry Dock is to expose the underwater parts for inspection, repair and maintenance. The ship to be repaired is hence manoeuvred into the lock and the gates are sealed post which all the sea water accumulated in the vessel is drained for better inspection and repairs.
According to SOLAS, active ships that fall under the 100A5 category have to be subjected to a bottom survey twice every 5 years. Also, a Merchant Vessel which is older than 15 years needs to be checked for breaches or any defaults twice in every five years. In case of Passenger Ships, the repair period is every two years.
The primary goal of a Dry Dock is to carry out effective repairs and maintenance of the parts that are in constant contact with marine water and not visible unless the water is flushed out. Subjecting vessels to this process is a must if the Classification Society finds it necessary to carry out Dry Docking, in spite of the schedules outlined by SOLAS.
This is usually the case if the ship has met with a collision, was grounded in past or has been subjected to poor maintenance practice. Inspection during dry docking is also carried out if the ship is to be sold.
Types of Dry Dock
There are about 5 known different types of Dry Docking techniques, of which the Floating and the Graving Dock are most common.
Graving/ Excavated Dock
The graving or excavated dock is constructed on the land near the sea shore using concrete to build walls, blocks and gates. This is the most basic form of Docking technique, where in the ship is manoeuvred inside the dock and rested on the blocks post which the gates are closed and water is released from the ship.
Floating docks are specifically used to repair vessels that have met with accidents or broken down in the middle of the sea. A U shaped structure called pontoons are used to salvage ships from mid sea. These U shaped structures are filled with water, which makes the dock go under water helping the ship to sail. Once the ship is secured and brought to the repair area, the water is released, making the dock to rise up and exposing the parts of ship that are otherwise underwater.
Syncrolift / Shiplift
A syncrolift or a shiplift docking method is incorporated on ships that weigh from 800 to 25000 ton ship-weight. A floating dock makes use of the buoyant force of the pontoon, but in the Syncrolift, the ship is transferred onto a platform placed on the bed of the graving, and both ship and platform are heaved up on the land by winches installed on either side of the platform.
Slipway, patent slip
Specifically meant for smaller boats, in Slipway, the hull is placed on trolleys and pulled ashore on the inclined surface using winches. The Marine railway is another type of Slipway docking technique, where an inclined plane extends from the shore to the water and the boat is hauled onto the cradle. This technique is usually used in case on repairs for larger ships weighing about 3000 ton in ship weight.
Why is it Necessary to have Dry Docks?
Dry Docking is necessary to view and correct mechanical defects in the vessel in its original, dry form for better results and effective functioning. Basically to clean, scrub and prepare the ship by de-scaling all rusted areas of the hull, and finally paint the ship’s hull so that speed and fuel consumption are restored to it’s original.
Before a ship is taken for repair, a surveyor inspects the vessel in clear water where the hull is visible on the outer surface. The surveyor analyses and points out defects which are then corrected through Dry Docking.
Dry Docking Boats and Watercrafts
Aside from saving the boat hull and drives, proper dry-docking also greatly enhances access to the watercraft for boarding, fueling and maintenance. Plus a dry-docked boat needs no lines or bumpers and avoids scrapes and bruises from bouncing around in a tied-off wet slip mooring.
Preparations and Parameters before Dry Dock
There are various detailed steps to be followed before Dry Dock, as given in sector-specific manuals and literature. But, for our better understanding, here are the three most important aspects to be followed.
- Balanced G.M component: While the ship is brought to the dock, the centre of gravity (G) increases as a result of the ‘contact’ with the docking surface. This, subsequently changes the metacentric height (M). For a smooth docking process the values of G and M need to compensate each other or in, simple words – balance out.
- Position of the Vessel: During the Docking process, the vessel is supposed to be in an upright position. Care should be taken to ensure that there is no port or starboard list while the ship docks.
- Small or Moderate Trim Aft: The slight trim allows the accenting of stern and bow in tandem rather than simultaneously as it will reduce the load and pressure on hull and the keel of vessel.
Safety measures to be followed
Dry Docking is a massive and risky activity. Getting the ships onto the dock, repairing them and then putting them back involves high risk to the life of the workers and to the equipments being used on the dock. Before starting the dock process, Dry Docks need to follow a set of safety rules:
- Escape route. Two fixed gangways, independent of each other.
- Safety plan of the vessel available at gangways.
- Suitable communication system and routine for alarm in emergency situations
- Ship watch round regularly
- Contact with fire-brigade ashore.
- Water under pressure to the vessel’s fire-hose and sprinkler system.
- Hot work permit
- Fire watch at least during hot work plus two hours
- Portable extinguishers and a connected fire-hose where hot work is performed.
- Secondary fire alarm system where necessary
- Debris contributing to fire load sent ashore
- Fire-doors or WT-doors fully operational at all time
- Gas free certificate
Choosing a shipyard for repairing your vessel
While all the above mentioned information will help you understand what Dry Dock is all about, choosing a shipyard that best suits your requirements is a decision that requires evaluation of multiple parameters.
- Trading area
- Safety record
- Technical ability
- Local infrastructure
- Financial situation
- Weather/season in the area
- Operational restriction – tides
Dry Docks in India
India is surrounded by two coastlines – the east and the west. That being said, the density of docks on the western coast is a lot more than that at the eastern one. This forces ships to travel all the way to the western coast or to China and other southeast asian countries like Philippines, for repairs and maintenance, thereby skyrocketing the costs.
Shipping is still in a growing phase with the prestigious Sagarmala project leading the country towards development. That being said, India currently houses seven dry docks – Two at Mumbai Port Trust, One at Vishakhapatnam, owned by Hindustan Shipyard, a floating dock at Panaji, Goa, one dry dock at Mormugao, Goa, One at Kolkata and one at Port Pipavav, Gujrat.
New Dry Docks under development
Under the Make in India initiative, in order to serve the growing scope of shipping, the govt. is building two more dry docks – one at the Cochin Shipyard and another one at the Andamans – both to the tune of 1800 crore each.
Developing Dry Docks in India
Given the fact that shipping in India is on an upward growth trajectory, the government is moving rapidly towards ensuring that shipping in India is managed holistically, in house, thereby promoting the Make in India initiative. Developing Dry Docks and other shipping service stations across the Indian coastline will not only reduce the costs for Indian Shipping companies, but also attract foreign freight carries to stop by for a juice up, emergency repairs or basic maintenance.
Having our own Dry Docks will bring down our services and repair costs tremendously, benefiting India Inc. on the whole.
Did you know that SHM Shipcare has their own Dry Docking services?
Functioning under Homa Engineering Works, SHM provides Graving dock services for vessels weighing a maximum 30,000 tone. Length of the ship that can be accommodated is about 1000 feet long and 100 feet wide.At SHM, we offer a quick and efficient turnaround for any type of vessels, watercraft, boats and life rafts for services at our port that include:
- Thickness Gauging
- Destructive & Non-Destructive Testing
- High Pressure Washing
- Underwater Repair & Diving
- Blasting & Hull Painting
- Anchor & Chain Servicing
- Robotic Scanning
So the next time your vessel or boat needs a quick fix, stop by our shipyard at Mumbai.