The need for a large dry-dock was realized by the Indian Navy with the induction of Aircraft carrier INS Vikramaditya, for its maintenance and upkeep as required for keeping it at sea.
By Milind Kulshreshtha
Indian Navy boasts of being in the group of few of the largest navies in the world and operates hundreds of small and large warships and submarines. Endeavour is to maintain most part of this naval asset at sea 24/7, round the year for protecting the 7516.6 km Indian coastline and for various other Power projection roles around the globe. Technically warship and a submarine are very complex types of machinery, which require highly talented manpower to operate and maintain them at the combat readiness level at all times, a mammoth task keeping in mind India’s huge area of interest to be protected even during the peacetime.
Mumbai Dry Dock
The dry-dock at Naval Dockyard, Mumbai is the latest asset in India’s pride as a seafaring nation. It was nearly a decade long effort to create this unique structure. The need for a large dry-dock was realized by the Indian Navy with the induction of Aircraft carrier INS Vikramaditya, for its maintenance and upkeep as required for keeping it at sea. The dry-dock construction was a mammoth challenge since it is surrounded by sea on all three sides, with dock basin jutting out 300m into the sea. This required cofferdam construction to undertake the work on dry-dock area. It is understood that the dock floor is about one and half meter thick concrete and huge amount of steel and concrete was used for its construction. It is a modern dry-dock with high automation, and can be dewatered in less than three hours and filled back within just one and a half hours. Overall, the dry-dock measures about 280m in length are 45m wide and 17 m deep, enough to meet the forthcoming requirement of dry-docking INS Vikramaditya and the indigenously built Vikrant. This dry-dock surely is a pride of the Indian Navy for times to come.
What are Dry-Docks?
Drydocking of a ship is a highly planned activity and the process involves taking a vessel to a dry dock basin, locking shut the caisson gates, and draining out the water in the basin using high power water pumps, so that the submerged portions of the hull can be cleaned, inspected and repaired. Every sea going vessel has to mandatorily undertake this dry-docking procedure for preventative maintenance or for any urgent underwater repairs, as required. The steps involved in this are:-
(a) Entering the Dry-Dock. A Dock Master prepares the dock floor for each ship by placing special blocks (for the ship to sit on) as per the ship’s underwater profile. The keel blocks, as well as the bilge block are placed on the floor of the dock in accordance with the ship’s approved docking plan. It is extremely important that all the supporting blocks conform to the ship’s structural members to avoid a ship being damaged when its weight is supported by the blocks. The blocks are made of specific height so that ship’s sonar dome is under hung well above the dock floor to avoid damages. With the help of tug boats, the ship is brought into accurate position over the blocks, and caisson gates closed. The dry-dock water is drained out gradually, taking precautions that the ship is slowly settled down on the blocks at an even keel. All alignment checks are carried out by the team of Dock Master so that ship is balanced vertically before this operation. While still with some water around the ship, the hull cleaning team takes to the water to clean the ship’s sides for marine growths etc.
(b) Hull Inspection & Maintenance. Once all the water is pumped out from the dry-dock area, necessary underwater Hull maintenance and repairs are undertaken, along with routines on underwater equipment like Sonars, sea valves, etc. No machinery is allowed to run on board when the ship is balanced on the blocks in a Dry dock and special electrical Earthing arrangements are made for the ship since the Hull (being the universal Ground for a ship) is no more in the conductive seawater now! Blasting of Hull is done primarily to remove rust or defective paint from the ship side and old paint is removed to expose the bare steel. Once the blasting is completed, the entire vessel is cleaned and painted to protect the integrity of the steel and prevent future corrosion. The sea chest is a hull recess for seawater intake for the cooling systems in the Engine Room and this too is cleaned along with overhaul of the sea valves. Routine and repairs on the Rudder, Propellers or shafting too are completed. Finally, the underwater side is painted with anti-fouling paint to prevent marine growth. The ship is usually inhabitable during the dry-dock period as no air-conditioning the system is running but the shore power supply is made available for work progress.
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(c) Alignment Checks. Ship’s Radar and Weapon alignments are completed during the dry-dock period using various techniques like Star alignment (to overcome parallax errors), Horizontal alignment checks etc. Ship’s Fore & Aft and Horizontality validation checks are completed for gyroscopic alignments and ship’s Datum Records re-established. Ship’s heading marker for course measurements w.r.t. True North alignment is undertaken. Alignment checks for propeller shaft too are undertaken during the dry-dock period using Laser alignment tools. The Degaussing of the ship is also planned during this period so as to reduce ship’s magnetic signature (as protection against activation of magnetic mines). The sacrificial anodes for Hull corrosion prevention system, like ICCP (Impressed Current Cathodic Protection) system is replaced during the dry dock period. There are a plethora of many activities undertaken as SOPs during the dry-dock period.
(d) Flooding of Dock. After all maintenance work is completed, especially the underwater work package, the sealed dock is slowly flooded back using the high-pressure pumps, and during this activity movement of personnel onboard is restricted for ensuring a balanced vertical rise of the ship. When the ship is completely off the blocks, the caisson gates are opened and the ship moved out using Tug boats.
Maintenance of Ships & Submarines
The ships and submarines undergo a highly advanced maintenance plan which is contemporary and hi-tech. The maxim of Float, Move and Fight is a no mean task for a seafaring warship due to challenging sea environment which is equally harsh to men and metal. Very stringent maintenance schedules are followed by these warships and submarines be it as onboard upkeep or a well-defined sequential pattern of Short Refits (SR) and Long Refits (LR). These are primarily designed around machinery overhauling and repair routines as specified by respective OEMs. These also include SAMs, SSMs, Gas Turbines or Steam Boilers and such large highly complex systems and failure of any of these critical systems while ships and submarines are at sea, is seen as highly significant Organisational flaw. As per Naval SOPs in place, any incident of major machinery failures results in a thorough investigation as part of Technical Board of Inquiry for the Root Cause Analysis.
It may be interesting to note here that each and every machinery fitted onboard has a maintenance schedule, i.e. from a small motor to the Ship’s propellers and the large steel hull. The hull of the ship and various appendages like underwater valves & glands, sonar domes, etc. are critical parts of ship and these have a fixed overhauling maintenance schedule prescribed by the OEMs or, as and when some failures call for the underwater repairs. The record of all repairs and overhauls are meticulously maintained as sacrosanct documentation onboard and put up for Inspection by Headquarters regularly. Each logbook and repair sheets of equipment give its life story and manpower onboard is personally attached with these parameters and ensure that the peak performance is achieved by all systems onboard. For the inaccessible equipment and ship’s hull which remain submerged in water always, special maintenance is undertaken on a regular basis through dry-dock facilities.
Interestingly, there is a unique type of dry-dock with the Indian Navy, called Floating Dry-docks Navy (FDN). These specialized docks are used for ship’s dry-docking while in the sea itself, using the concept of a pontoon. These FDN can be towed by ships, to places as required. Whenever a ship has to be dry-docked into them, FDN valves are opened and the chambers filled with water, causing the dry dock to float lower in the water. The FDN becomes submerged and this allows a ship to be moved into position inside. When the water is pumped out of the chambers, the dry dock rises and the ship is lifted out of the water on the rising deck, allowing underwater work to be undertaken.
(The author is Artificial Intelligence and C4I expert. Views expressed are personal.)