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The safety of the container ships, An increasing concern
Intervention of Afcan at the General assembly of the French Maritime law Association in Paris
With the increasing volume of consumables produced in the Far East, in China in particular, the regular lines operators ask for increasingly large ships. At the same time, one sees incident reports implying massive losses of containers and impressive fires that give good reasons to worry. Will the container ships continue to grow, and what are the main concerns industry must face?
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The container ship did not cease becoming increasingly large since its introduction at the end of the fifties. Regularly the largest ship ordered beat the record of the previous year, the last order of China Shipping Container Lines and Seaspan being for a ship of 9200 EVP increased to 9600 EVP. Since the end of the fifties the maximum size grew more or less regularly until the beginning of the nineties.
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The advent of post-panamax accelerated growth rate. It is almost what occurred with the development of the VLCCs in the seventies, where it seemed that there was no limit with the increase in size. We know, however, that the “million tons” tanker never materialized and that the typical VLCC was stabilized with the actual 300.000 tons, which seems the most current size for the VLCC. Will the growth of the container ship continue or will the curve of growth stabilize?
It is the cost per EVP per mile which is the leading force, and it is the economy of scale which will feed the growth, but the marginal profits will probably decrease with the increase in size. Thus according to the probabilities there is an optimal size that the largest ships will reach. In the same way, in the segments of the different sizes, there will be an optimization that will be carried out, just like with panamax. There are a few years largest panamax were of the 4000-4500 EVP.
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The last designs published by Aker Ostee can carry 5600 EVP. The superstructure is divided into two sections, which makes it possible to have more containers in the hold and decked, reduced torsional stresses and gives a better field of vision from the bridge.
Up to where the container ship will grow? There are technical constraints that fix the current maximum size. The existing design is a ship with only one propeller, with the largest diesel engine manufactured (12 cylinders), maximum boring (980 or 960 mm), the power available is approximately 93.000 BHP (68500 kw), which gives a maximum speed of approximately 24-25 knots, which is required by industry.
However, in August 2004 it was heard that a 14 cylinders engine had been ordered in Korea by Odense Staalskipsvaerft. We do not know yet on which size of ship it will be installed, but press articles let think that one would cross the limit of the 11000 EVP. This engine can deliver approximately 80.000 kw, and even if there is the 16 cylinders on the drawing boards, it is noted that only one propeller cannot withstand this size of engine.
Most ports around the world have draft limits lower than 14 meters. Currently the scantling draft is 14,5 meters for an operating draft of 13-14 meters. Dredging and development of the terminals will be able to modify that in the future, but in a foreseeable future this limit should remain.
The large engines require propellers of a diameter close to 10 meters. With a safety margin for the depth and a margin for the upper edge, the depth of 13-14 meters is necessary to accept the propeller even if the ships are at slow speed in narrows and shallow waters. In fact the propeller could be the factor which currently limits the size of the ship.
For the time being, it is the single propeller design which prevails. Optimization for fuel savings can be incompatible with few vibrations and the alternative practice just acceptable. Why then not turn to a double propulsion (2 engines, 2 propellers) like certain small draft tankers did successfully ? Various sources indicate that the initial investment is about 10 percent of a new building. The improvement of the efficiency of the propeller reduces the exploitation costs but the economic reasons always seem to discourage taking such a risk. The system with two propeller shafts offers obvious advantages, such as double independent propulsion and the possibility in case of emergency to continue on one propeller. It is a strong argument if it is considered that the ascending values of the ship and the cargo represent an increase in risk for the insurance.
The breadth of the ships was limited by the outspreading capacities of the gantry cranes and the lifting capacities in ports around the world. Until the delivery of post-panamax, it was not a problem. The maximum breadth increased by steps from 32,20 meters to the current value of 42,5 meters for the the 8500 EVP class and to 45,80 meters for the 9600 EVP class and over. The terminals installed new gantry cranes, some being able to be lengthened later. The lifting capacity is important not for the maximum weight of the containers but rather for the handling of hatch covers. The weight of the pile increased logically involving an increase in the weight of hatch cover. Currently hatch covers of nearly 50 tons are installed.
Plans for 12.000 EVP and even 16.000 EVP (malaccamax) were announced in the press. Any design beyond the limit of the 9.500-10.000 EVP requires another propulsion, that it is to say with two propellers or the combinations with contrarotating pods or propellers. This increases the investment cost and thus the impact of the economy of scale offered by the increase in size is reduced. If that occurs, there will be probably a jump in the increase in size to compensate for the increase in the initial cost. With exploitation and respect of the schedules, reliability requirement it is not a surprise if the industry feels reluctant to try this solution. Various studies were published and it seems that the alternative of two propeller shafts is most likely to be adopted. This is what happened with VLCCs where draft restrictions inspired the solution increased width and double propulsion.
The building costs for new large ships are about 80 to 100 M US$ according to the market rates and country of construction. American Institute of Marine Insurers raised the problem of the increase in risk for the insurance. They indicated an average value about 45.000 US$ for each container (EVP), which gives the cargo value at approximately 430 M US$, making a total of about 500 M US$ for a 9.600 EVP type. The value ratio of the cargo to that of the ship is about five. That means many eggs in the same basket !
What is thus the risk table for these large ships?
FSA studies (Formal Safety Assessment) give information on the dangers associated with container ships. First comes damage to the hull and to the engine followed by collisions and fires. The total cost is estimated to 359.000 US$ per ship and per annum for a 4500 EVP ship (panamax size). Transposing the statistics of small ships to new large ones gives figures of about 700.000 to 800.000 US$ per ship and per annum value of the cargo not included.
Some of the most outstanding accidents relating to container ships are collisions, fires in containers, fatigue of the platings, damage caused by impacts on the bow, loss of containers, parametric rolling and various complaints on the cargo, often relating to refrigerated containers.
A modern bridge, well designed, checked and approved by the classification society is essential for a safe navigation. These ships frequently enter and leave ports and are often in a dense traffic. The qualification of the officers is another problem. Because of the fast expansion of the trade, the best are very much required. Simulators for training on the largest ships will perhaps not be available in time and in sufficient number to face the request. The size itself and the enormous windage of these new ships could prove to be a challenge for the captains as well as for the pilots.
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Fires in containers were the subject of many press articles these last years. Enormous fires involved the abandonment and the loss of large ships, such as HANJIN PENNSYLVANIA in December 2003. Fires are often associated with sensitive cargoes such as the calcium hypochlorite, an oxidising agent which can ignite spontaneously under certain conditions. Extinguishing such fires can be a real problem because oxygen is released by the burning product, which contributes to feed the fire. A current fighting method against these fires consists in isolating the pile of containers on fire by drowning it with water to prevent fire extension, and letting the pile burn until the end. The damage is generally considerable, such as the case of CMA DJAKARTA. The ship had a hold completely destroyed by fire, and had to be rebuilt at the same price as a new ship.
The integrity of the hull is normally not a problem for container ships. We record only one accident concerning a container ship which broke in two parts, namely MSC CARLA. The container ships were always built with double side plating, double bottom and watertight bulkheads.
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It is the best means to stow a box in the shapes of the ship. That gives also a fine designed hull integrity. Regulation wants to impose the double hull on large tankers and bulk carriers, and that will take a few years before it is applied to all ships.
Fore part is an an exposed zone on large ships. The cant continuously increased to reach values well over 45 degrees to increase the number of containers on deck. The decked stowage and the size of the ship prevent the bridge from watching the fore deck. This, combined with speed, make it more vulnerable to hull damages. This problem was noticed by the DNV on large tankers in the Seventies and the formulation of the rules was adapted and modified through the years to make sure that sufficiently solid bows were built. However it is a very difficult task for the officer on watch to adjust speed and course to preserve the ship and the cargo while maintaining a tight schedule under changing weather conditions. The DNV is currently testing with three container ships operators an installation on the bridge which will help the captain in its decision-making process. The purpose of “Active Operator Guidance” (AOG) is to help and advise the officers on watch during navigation in heavy weather.
Parametric rolling was the cause of very heavy losses of containers these last years, the example of APL CHINA seems to be the traditional case about it. Parametric rolling can occur by head seas with an unfavourable combination of wave height, length and period according to the ship length. Sudden rolling may occur without notice, making the piles of containers rock like dominos, producing severe losses. A more constant attention from the sailors seems to have reduced the number of incidents last winter. But more research and attention paid to this problem are perhaps still necessary. The DNV AOG System will prevent also the risk of parametric rolling.
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Plating fatigue is a damage which was submitted to industry these last years.
Serious cracks were discovered by German ship-owners on panamax type after only a few years in service. This problem is well-known on large tankers and bulk carriers but had not been, until now, observed at large scale on container ships. Although the technical cause of the cracks is different from that of the tankers, the remedy is almost the same. With the increased use of high-strength steels, the problems of fatigue must be studied carefully, because for the everyday use either the steel is ordinary or high-strength the lifespan is the same facing fatigue. So when the level of the efforts is increased when high-strength steel is used, it is necessary to pay special attention to the details of structure and concentration factors of the efforts to maintain the same lifespan in front of fatigue.
Problems must be solved by design. For ships already built and in service, it is necessary retrospectively to calculate fatigue, an inspection program must be established paying attention to the detail before getting to the stress limit. That will make it possible to prepare budgets and plans and to carry out repairs in a controlled way. The alternative can be the occurrence of hull cracks which, if it happen on a fuel capacity, can cause an awkward pollution in port, involving an immediate suspension of charter party and repair expenses. Such unexpected incidents will certainly have a cost higher than planned and well prepared repairs.
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Even if the container ship is a type of reliable ship, the fast development of new larger designs and the ascending value of the cargo require taking the initiative in order to treat the specific dangers of the container ships. The whole industry must concentrate on these problems and find the suitable solutions.
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