Shipbuilding for the Arctic
(The following excerpt by Authors: S Navaneetha Krishnan & Antony Prince)
The Arctic region has a huge potential in terms of unexploited natural wealth and resources, though it accounts for a small area on the earth’s surface. Many countries, other than the eight countries which lay either completely or partially in the Arctic region, are interested in exploring the natural resources available in this region, and for various other economic, strategic and geopolitical reasons.
In addition, moving cargo from the west to the east (and vice versa) in the northern hemisphere can be undertaken through the Arctic region at lower cost. For any nation to have control over the Arctic, it will have to establish its physical presence in this region. Such presence can be demonstrated by reaching this ice / water bound zone through ships. However, not all ships can sail in the polar region; this is primarily due to the adverse climatic condition and presence of solid ice on the sea surface. Much of this region is covered with ice throughout the year; and in some areas, the ice melts and refreezes and thus multiple layers of ice exist. Therefore, ships transiting this region will need to be specially designed and constructed, so that they can navigate by breaking the surface ice. This essay will focus on the challenges and solution in designing and building such ships.
First, the ships need to operate in waters/ ice below sub-zero temperatures. At such temperatures, the normal shipbuilding steel will have very less fracture toughness value, and there is a tendency for the steel to develop crack and fail by brittle fracture; similar to the crack failure in the Liberty-class ships during the cold winter nights, when welded ships were being first introduced. The solution to this problem is usage of steel that has high value of impact energy (20 J at minus 10o C). During the construction of the ship, care has to be taken that the toughness does not reduce while welding.
Second, the forward part of the ship’s hull has to be carefully designed to ensure that it has the ability to pierce and break the ice during the forward motion. The ship generally breaks the ice by the power of its forward propulsion thrust. In certain case, where the ice is strong (multi-year ice layers are more than 50 mm thick), the ship’s bow rides over the ice and breaks it due to the ships weight, since ice has less bending strength. This warrants the bow of the ship to be specially designed to have the strength to break the ice.
Hydrodynamically, the ship’s bow is characterized by less flare at the waterline with more sloping or rounded stem. In addition, the hydrodynamic design of the bow should be such that, after the ice is broken / crushed, it is able to push the ice floes away from the ship side. The hull is designed in such a manner that the floes are mainly pushed below the ship. The forward part of the ship and the ship side at the waterline are build with strong material that are resistant to abrasion and corrosion. In certain cases, abrasion-resistant stainless steel is welded to this region of the ship. Therefore, ice strengthening of the ship’s hull is an important aspect for the ships designed and built to operate in the Arctic.
Third, in order to propel the ship along with breaking the ice, the propulsion train of the ship has to be appropriately selected after considering the speed at which the ship has to move, and the thickness of the ice that is to be broken. A diesel-electric engine with fixed pitch propeller (FPP) is one of the choices. Most of the Russian ships operating in this region are nuclear ships, where the nuclear-electric power is used to electrically propel the ship. Electric propulsion motors are preferred because of its good low-speed torque characteristics. In certain cases, direct drive through diesel or gas turbine connected to the Controllable Pitch Propeller (CPP) through gearbox is used, to take the benefit of less weight of the propulsion train.
Ships requiring more manoeuvrability are fitted with Azimuth or podded propellers. Such ships can create a wider channel in the ice, for passage of other ships following these. The exposed part of the propulsion system, such as the shaft and the propeller need to be protected from the floating ice and therefore, the aft end of the ship has to be designed accordingly.
Fourth, these ships have to operate for long duration in region which does not have adequate shore support for maintenance. Therefore, the reliability of all equipment and systems has to be very high. Rugged and dependable equipment / systems are essential in these ships. All the components in the equipment should function reliably at lower temperature; for example, rubber (used in equipment mounts) loses its softness and become brittle at low temperature. Similarly the systems which use seawater for cooling should be able to take in sea water, as well as ensure that this water does not freeze inside the system pipes. Therefore, reliable equipment, systems and quality construction is very critical for ships operating in the Arctic region.
In order to ensure that ships operating in the Arctic region have all these requirements addressed in the design and construction, the International Association of Classification Societies (IACS) has released unified class requirement for ships operating in the polar region. There are seven Polar Classes (PC) based on the severity of the ice conditions in which, the ships (other than Icebreakers) have to navigate. PC 1 is the most stringent, which caters for ‘all polar waters’ throughout the year and PC-7 is the least stringent one, where the ship has to operate during the summer / autumn in ‘thin ice’. International Maritime Organisation (IMO) is planning to put into place Safety of Life at Sea (SOLAS) and Marine Pollution (MARPOL) aspects for the PC before the year 2017.
Construction of polar class vessels needs quality workmanship. Majority of these ships are constructed by the Arctic countries, such as Russia, Canada and the USA. South Korean and Japanese shipyards are also building these specialised polar class vessels, since they have the international repute of building quality ships. There is a future potential for building polar class vessels, due to the availability of natural resources in the Arctic region. Indian shipbuilding industry can also look at this potential market, but its industry needs to first earn international reputation of building quality ships with reliable equipment and timely delivery.
(*S Navaneetha Krishnan is the first Admiral AK Chatterji Fellow at NMF and presently working with L&T Shipbuilding at Chennai, India. Prince Antony is President, GTR Campbell Marine Consultant Ltd at Nassau, Bahamas & Smart Engg. Design Solution Ltd at Kochi, India. The views expressed are those of the authors and do not reflect the official policy or position of the NMF. They can be reached at firstname.lastname@example.org)