Bulk Carriers

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The bulk carrier Berge Stahl.

The bulk carrier Berge Stahl

The bulk carrier was first developed to carry dry cargoes, which are shipped in large quantities and do not need to be carried in packaged form.  The principal bulk cargoes are coal, iron ore, bauxite, phosphate, nitrate and grains such as wheat.

The advantage of carrying such cargoes in bulk is that packaging costs can be greatly reduced and loading and unloading operations can be speeded up.  Before the Second World War, however, there was no real demand for special bulk carriers.  Seaborne trade of all mineral ores only amounted to 25 million tons in 1937 and this could be carried in conventional tramp ships (freight vessels).

By the 1950s, however, movements of bulk cargoes were increasing.  Very often ores and other commodities were found far away from where they were needed and the most convenient and cheapest way of shifting them was by sea.  Companies in the United States, Europe and increasingly in Japan began to build ships designed exclusively for the carriage of cargoes in bulk.

As demand increased and shipbuilding technology advanced so these ships tended to become bigger in size and carrying capacity.  This afforded the same economies of scale that were to make the Very Large Crude Carrier (VLCC) so attractive to oil tanker operators in the 1970s.  Doubling the amount of steel used in constructing a ship enabled the amount of carrying capacity to be cubed, yet the size of the crew required did not increase greatly and other costs, such as fuel, also rose relatively slowly, especially since speed was not vital to bulk transport.

The modern bulk carrier has evolved gradually but since the 1960s the standard design has been a single hull ship with a double bottom, large cargo holds with hopper tanks and topside tanks covered by hatches.  As with crude oil tankers the engine room, navigating bridge and accommodation areas are nearly always located at the stern of the ship.

By the 1970s, bulk carriers of more than 200,000 dead weight (dwt) were operating and rivalled the VLCCs as the largest ships afloat. There are several other similarities between bulk carriers and tankers, which help to explain the frequency with which they are mistaken for each other.  The simplest way of telling a bulk carrier from an oil tanker is that the holds of the bulk carrier are covered by hatches raised above the deck level, while the deck of the tanker is covered with fuel pipes.  A bulk carrier of 36,000 dwt may have five cargo holds while one of 250,000 dwt may have as many as nine.  Also, ships were being built which could carry oil, ore or other types of dry bulk cargoes.  This was done to increase operational flexibility.  One of the problems with the bulk trades (as with oil transportation) is that ships normally carry cargo one way but return in ballast because there is nothing to take back.  However, oil/bulk/ore (OBO) ships have never become as popular as dedicated bulk or oil carriers, partly because their complexity increases building and operating costs.

Today, bulk carriers transport a high percentage of world trade - and in most cases they do so safely.  According to the International Association of Dry Cargo Shipowners (Intercargo), in 1990-1994, 99.90% of dry bulk cargoes were delivered safely.  In the case of iron ore the figure was 99.71% and for both grain and coal reliability was 99.97%.

Text Box:  The post-war boom in Japan led to a huge increase in demand for raw materials and the ships on which to carry them. Here a bulk carrier operated by K Line prepares to take on a cargo of iron ore.

The amount of cargo carried is enormous.  In 1996, according to Intercargo, 1,092 million tonnes of iron ore, coal, grain, bauxite and phosphates were carried by sea.  A further 703 million tonnes of products such as steel, cement, pig iron, fertilizer and sugar were also shipped by bulk carriers.

Many different products are carried on ships in bulk.  Grains, such as wheat, maize, millet and rye have been transported by sea for centuries - the wheat trade between north Africa and Italy was a major economic feature of the Roman Empire, for example.  Since the last century, the grain trade has grown in importance and much of it is carried by sea, often on long trans-Atlantic or trans-Pacific voyages.

According to the International Grains Council, in 1996-1997 (July/June) total wheat trade amounted to 91.3 million metric tons, with the biggest exporters being the United States (26.5 million tons).  Other exporters are Australia (17.4 million tons) and Canada (17.0 million tons) while the biggest importers being Iran (6.7 million tons), Egypt (6.2 million tons) and Japan  (5.3 million tons).  In addition, 88.8 million tons of coarse grains including maize, millet and, rye were shipped in 1996-1997, the largest exporters being United States (53.1 million tons), Argentina  (10.6 million tons) and European Union (8.1 million tons) and the largest importers being Japan (20.3 million tons), South Korea (9.2 million tons) and Saudi Arabia (6.3 million tons).  Total grains shipped in the year 1996-1997 were therefore 180.1 million tons -- or just over 3,600 panamax-sized (50,000-dwt) shiploads.

Originally grain was transported in sacks, but by the middle of the 20th century the normal procedure was to carry it in bulk.  It could be stored, loaded and unloaded easily and the time taken to deliver it from producer to customer was greatly reduced, as were the costs involved.  However, there were problems.

Grain has a tendency to settle during the course of a voyage, as air is forced out when the individual grains sink (“sinkage”).  This leads to a gap developing between the top of the cargo and the hatch cover.  This in turn enables the cargo to move from side to side as the ship rolls and pitches.  This movement can cause the ship to list and, although initially the ship’s movement will tend to right this, eventually the list can become more severe.

Text Box:  This picture shows what can happen when a ship’s cargo shifts to one side. A list can develop which, in extreme cases, can cause the ship to capsize.

In the worst cases, the ship can capsize.  This problem was well known and when the International Maritime Organization[1] came into being in 1959 one of its first tasks was to consider new measures for improving the safety of bulk carriers. These were incorporated into the International Convention for the Safety of Life at Sea (SOLAS), 1960. This was a new version of a convention that owed its origins to the Titanicdisaster of 1912.  The new bulk carrier regulations were more advantageous from an economic point of view than those adopted in SOLAS 1948 (which required a more extensive use of increasingly expensive temporary fittings and/or bagged grain) and many countries quickly put them into effect, even though the Convention itself did not enter into force until 1965. However, the new regulations still had some deficiencies as far as safety was concerned, for during a period of four years, six ships loaded under the 1960 SOLAS rules were lost at sea.  IMO began looking at this problem early in 1963 and asked masters of ships to contribute information to a broad study.  Further studies and tests showed that some of the principles on which the 1960 regulations were based were invalid -- in particular, it was shown that the 1960 Convention had underestimated the amount of “sinkage” which occurs in grain cargoes loaded in bulk.  This made the basic requirements of the Convention unattainable.  As a result, the IMO Assembly in 1969 adopted new grain regulations [resolution A.184 (VI)], which became generally known as the 1969 Equivalent Grain Regulations.

Voyage experience over a three-year period showed that the 1969 Grain Equivalents were not only safer but were also more practical and economical than the 1960 regulations and, with slight amendments, based upon operational experience, they were used as the basis of new international requirements which were subsequently incorporated into the 1974 SOLAS Convention. Although grain was the only bulk cargo to be given a special chapter in the 1960 SOLAS Convention, IMO also developed an international Code of Safe Practice for Solid Bulk Cargoes (BC Code), which was adopted in 1965.  The Code has been updated at regular intervals since then and is kept under continuous review by the Sub-Committee on Dangerous Goods, Solid Cargoes and Containers.  The practices contained in the Code are intended as recommendations to Governments, ship operators and shipmasters.  Its aim is to bring to the attention of those concerned an internationally-accepted method of dealing with the hazards to safety which may be encountered when carrying cargo in bulk.

The codes that are most relevant to the safety of bulk carriers are the revised BC Code and a new mandatory International Code for the Safe Carriage of Grain in Bulk (International Grain Code).  Like the original grain rules, the Code is designed to prevent the particular qualities of grain threatening the stability of ships when it is carried in bulk.  It applies to all ships - including existing ships and those of less than 500 tgt (tons gross tonnage) - that carry grain in bulk.  Part A contains special requirements and gives guidance on the stowage of grain and the use of grain fittings.  Part B deals with the calculation of heeling moments and general assumptions.

The revised BC Code deals with three basic types of cargo: those which may liquefy; materials which possess chemical hazards; and materials which fall into neither of these categories but may nevertheless pose other dangers.  The Code highlights the dangers associated with the shipment of certain types of bulk cargoes; gives guidance on various procedures which should be adopted; lists typical products which are shipped in bulk; gives advice on their properties and how they should be handled; and describes various test procedures which should be employed to determine the characteristic cargo properties.

The Code contains a number of general precautions and it is of fundamental importance that bulk cargoes be properly distributed throughout the ship so that the structure is not overstressed and the ship has an adequate standard of stability.  Loaded conditions vary according to the density of the cargo carried.  The ratio of cubic capacity to deadweight capacity of a normal ship is around 1.4 to 1.7 cubic metres per tonne and the ratio of volume of cargo to its mass is known as the stowage factor.  When high density bulk cargoes with a stowage factor of about 0.56 cubic metres per ton or lower are carried, it is particularly important to pay attention to the distribution of weight in order to avoid excessive stresses on the structure of the ship.

All bulk cargoes when loaded tend to form a cone.  The angle formed between the slope of the cone and the bottom of the hold will vary according to the cargo and is known as the angle of repose.  Some dense cargoes, such as iron ore, form a steep cone while others - such as grain - have a much shallower angle.  Cargoes with a low angle of repose are much more prone to shift during the voyage and special precautions have to be taken to ensure that cargo movement does not affect the ship’s stability.  On the other hand, the sheer weight of dense cargoes can affect the structure of the ship.

After dealing with general precautions, the Code then goes on to deal with cargoes having an angle of repose of 35 degrees or less and then with those where the angle of repose is greater than 35 degrees.  Cargoes with a low angle of repose are particularly liable to dry-surface movement aboard ship.  To overcome this problem, the Code states that such cargoes should be trimmed reasonably level and the spaces in which they are loaded should be filled as fully as is practicable, without resulting in excessive weight on the supporting structure.

Special provisions should be made for stowing dry cargoes that flow very freely, by means of securing arrangements, such as shifting boards or bins.  The Code says that the importance of trimming as a means of reducing the possibility of a shift of cargo can never be over-stressed.  This is particularly true for smaller ships of less than 100 metres in length.  Trimming also helps to cut oxidation by reducing the surface area exposed to the atmosphere.  It also helps to eliminate the “funnel” effect, which in certain cargoes, such as direct reduced iron (DRI) and concentrates, can cause spontaneous combustion.  This occurs when voids in the cargo enable hot gases to move upwards, at the same time sucking in fresh air.

The Code then gives details of other dangers that may exist.  Some cargoes, for example, are liable to oxidation which may result in the reduction of the oxygen supply, the emission of toxic fumes and self-heating.  Others may emit toxic fumes without oxidation or when wet.  The shipper should inform the master about any chemical hazards that may exist and the Code gives details of precautions that should be taken.

Click here to enlarge pictureThe Code gives details of the various sampling procedures and tests, which should be used before transporting concentrates and similar materials and also contains a recommended test procedure to be used by laboratories.  There are seven appendices to the Code, giving information about particular cargoes.  A list of cargoes, which may liquefy is contained in appendix A to the Code, for example while appendix B gives an extensive list of materials possessing chemical hazards.  Some of the classified materials listed also appear in the International Maritime Dangerous Goods (IMDG) Code when carried in packaged form, but others become hazardous only when they are carried in bulk - for example, because they might reduce the oxygen content of a cargo space or are prone to self-heating.  Examples are woodchips, coal and direct reduced iron (DRI).  Appendix C deals with bulk cargoes which are neither liable to liquefy nor possess chemical hazards.  More detailed information concerning test procedures, associated apparatus and standards, which are referred to in the Code are contained in appendix D.  Emergency Schedules for those materials listed in appendix B are contained in appendix E.  Recommendations for entering cargo spaces, tanks, pump rooms, fuel tanks and similar enclosed compartments are shown in appendix F.  Procedures for gas monitoring of coal cargoes are contained in appendix G.

In 1990 the IMO issued a circular (MSC/Circ.531), which warned against the risks of shifting cargo and requested Member Governments to implement revised recommendations for trimming cargoes that were included in the 1989 edition of the Code and are intended to minimize sliding failures.
The actions taken by IMO undoubtedly helped to solve many of the problems associated with the carriage of bulk cargoes, such as cargo shift and the consequent loss of stability.  The number of accidents involving bulk carriers dropped during the 1980s and it seemed to many observers that the general problem of bulk carrier safety had been solved. 

A cross-section of a typical bulk cargo hold.
Cargoes such as iron ore are extremely heavy and can exert tremendous pressure on the ship’s hull.  Homogenous loading as shown below, is usually adopted for low density cargoes such as coal and grain, but may also be permitted for high-density cargoes under certain conditions.
Normally, however, cargoes such as iron ore are carried in alternate holds.  When a ship is floating in still water, there will be differences in the forces exerted upon the hull, which have to be taken into account when the ship is loaded. 
Alternate loading can result in shearing pressures, while uneven loading can cause the ship to “sag” or results in “hogging”.

Source:International Association of Classification Societies (IACS).  Bulk Carriers Guidance and Information on Bulk Cargo Loading and Discharging to Reduce the Likelihood of Over-stressing the Hull Structure.

Then, in 1990 the trend was dramatically reversed: 20 bulk carriers sank with 94 lives lost and in 1991, 24 sank with 154 dead.

  This development was so dramatic and so unexpected that alarm bells began to ring throughout the shipping world.  It became increasingly apparent that many of the bulk carriers lost - often without trace - had suffered from severe structural damage.  In some cases ships had simply broken apart like a snapped pencil.  What had gone wrong?  And what could be done to improve matters?

         The importance of age

There is no doubt that there is a clear link between accidents and the age of bulk carriers.  All but two of the ships lost in 1990 were over 18 years old.  In July 1995 the classification society Lloyd’s Register of Shipping published a table giving details of accidents involving 88 bulk carriers between January 1990 and December 1994.  Only three of the ships on the list were less than ten years old and nearly half were over 20.  What makes this so worrying is that the average age of bulk carriers had been rising steadily - from under nine years old in 1980 to more than 14 by 1995.  The reason for this upward trend is primarily economic.  During the 1980s there was a glut of shipbuilding, mainly because the industry greatly over-estimated the way in which trade would develop.  This was especially true of tankers, but it was true to some extent of bulk carriers as well and when trade increased much more slowly than had been forecast (and sometimes declined) the result was a fall in the demand for ships.  Some older ships were scrapped and others laid up waiting the return of more favourable trading conditions.  But throughout the period there has generally been a surplus of unwanted ships and freight rates have usually remained low.  This has discouraged the construction of new tonnage and has led shipowners and builders to explore new ways of cutting costs.

This trend is potentially worrying.  A survey of bulk carrier safety issued in July 1995 by the classification society Lloyd’s Register (entitled Bulk Carriers - an Update) pointed out that “an historically critical age group for bulk carrier casualties is from 14 to 18 years and that in three or more years’ time a large proportion of bulk carriers in service will be in this age group unless the age distribution is changed by, for example, a substantial scarpping programme.

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Causes of Bulk Carrier Losses, 1990-1997.
A study by Intercargo of bulk carrier losses showed that in30 cases the cause was plate failure and water entering the hull.  All the other causes added together accounted for the other 76 sinkings.


For straightforward economic reasons, there is little sign of such a mass scrapping taking place.  At the turn of the century, the great majority of the world’s bulk carrier fleet have reached the danger point.  More than half the world’s bulk carrier fleet is already more than 15 years old and one third is more than 20 years old.

         Corrosion and Fatigue

The main reason why age is so relevant to shipping casualties is that corrosion and general fatigue increase, as ships grow older.  This is partly because of the stresses to which the ship is inevitably subjected by routine operations, cargo handling, weather and waves and partly to the effect of seawater on steel.  Although any water tends to causes metals such as steel to rust, seawater is much more harmful than fresh water because it contains so much salt.  The bulk carriers used in the Great Lakes of North America, for example, frequently survive to 50 or 60 years of age - up to three times as long as the average ocean-going ship.

Corrosion is a serious problem for anything built of metal that is exposed to the elements and for a ship it can be fatal.  Corrosion of metallic structure is likely to be more extensive and work more rapidly than on other structures simply because the ship is in continual contact with water, usually seawater.  It can also be accelerated by the effects of some cargoes, especially those carried in bulk.  The interior of cargo holds can be affected by humidity resulting from the moisture contained in some bulk cargoes.  Sulphuric acid can be formed from sulphur residues (which can come from coal) combining with water resulting from condensation.

There are various ways of preventing corrosion - or at least of preventing it from becoming a problem.  Tanks can be painted with special coatings and can be carefully washed out.  Above all, the condition of the hull and other structures can be continually checked for signs of corrosion or fatigue.  This, however, is much easier said than done.  There is, in the first place, a great deal of steelwork to be checked.  A bulk carrier of 254,000 deadweight tons (representing roughly the amount of cargo it can carry) might be 320 metres long, 54 metres in breadth and 26 metres deep.  The total hull area to be examined could thus be in excess of 54,000 square metres and that does not include the interior bulkheads, hopper tanks, brackets and other features.  All of this has to be surveyed and inspected - a daunting task that requires the use of special staging, artificial light and a considerable amount of stamina on the part of the surveyor or surveyors involved.

Certainly corrosion seems to have played a significant part in many of the bulk carrier accidents of recent years - especially the most serious losses.  An Intercargo analysis of 15 total losses in 1994 showed that 40% were caused by plate failure and subsequent ingress of water.  A further 6.7% of losses were never explained because the ships involved disappeared.  More than 70% of these losses occurred in heavy weather.

Intercargo found that of 29 fatal accidents involving bulk carriers between 1990 and 1994, 55% were due to plate failure.  In terms of lives lost 81% were associated with sinkings and disappearances.  In 12 cases adverse weather was a factor and in 67% of the cases, iron ore was the cargo.  Not surprisingly, the Intercargo report states: “The inescapable conclusion from this analysis is the fairly obvious one that it is plate failure, taking water and disappearance which cause the majority of fatal accidents.  Thus, although during the whole period losses related to human factors account for 33% of all bulker and OBO losses, such accidents comprise only 10% of fatal accidents and involve only 7% of the total fatalities...it is structural failure, aggravated by bad weather and the carriage of iron ore which causes the majority of the really serious accidents involving loss of life.”

The frequent references to iron ore are significant because once laden bulk cargo carriers get into trouble, the consequences can be very sudden.  The ships are designed to withstand bad conditions, but not to operate with several holds flooded and the combination of iron ore and a sudden inrush of seawater can result in more weight than the structure can stand.  Other investigations came to similar conclusions.  The American Bureau of Shipping said in 1991: “The recent spate of casualties on conventional bulk carriers appears to be directly traceable to failure of the cargo hold structure...”

Lloyd’s Register of Shipping concluded that the prime cause of most casualties is the inability of the side structure to withstand the combination of local corrosion, fatigue cracking and operational damage.  The evidence of the disastrous consequences of uncontrolled corrosion is overwhelming - but preventing it is not so easy as it sounds, if only because of the size of the ships themselves and the difficulties involved in assessing corrosion and plate thickness.

A report by Lloyd’s Register in the autumn of 1991 stated that the owner of one ten-year old Capesize bulk carrier estimated that the wastage rate of hold frames due to corrosion amounted to 0.5mm per year - and 1mm in some places.  Some frames had suffered metal wastage of 20%.  During one voyage from South America to Japan a bracket which was in good condition when the ship left became completely detached, leaving a 1.4mm crack.  It was not detected because “the rust scale adhering to the surface of the hold structures presented a smooth and regular surface to the eye on visual inspection, making it difficult to detect any cracking.”  Since the side plates of a bulk carrier may only be 20mm to 29mm thick the loss of a few millimetres can be disastrous.

         Operational Factors

Like many of the other studies carried out, the Lloyd’s Register report said that structural failures were due to a combination of factors.  Corrosion was important - but so was physical damage suffered during operations.  Bulk carriers are designed to withstand heavy seas.  The massive structures of the largest ships will bend with the action of the sea.  When the centre of the hull is higher than the bow and stern the action is known as “hogging”: the reverse is called “sagging”.  But the design assumes that the hull is sound.  Corrosion or other damage can lead to weaknesses developing that invalidate the calculations of the naval architect and imperil the whole ship.  Loading patterns can make the effect worse.  Dense cargoes such as iron ore are often carried in alternate holds in order to raise the ship’s centre of gravity and moderate its roll motions.  But this places greater stress on frames and girders and, because holds carrying iron ore are not completely filled, there can be greater side frame deflection.  The overall result is increased stress on inner hull components, according to Lloyd’s Register.  This might be perfectly acceptable in a new ship - but not in a ship that has suffered from 20 years of hard service and neglect.

Design features originally chosen for operational reasons may also have safety implications.  Many bulk carriers are fitted with very large hatch openings to facilitate cargo loading and unloading.  Yet these openings may represent points of weakness in the hull since they reduce the torsional resistance of the hull.

Cargo handling methods have also been criticized.  These have changed considerably in recent years, with the emphasis being to load and unload the ship as quickly as possible so that the berth can be cleared for the next ship.  In some loading terminals iron ore can be loaded at up to 16,000 tons an hour by means of conveyor belts often several kilometres long.  Stopping the loading process for some reason cannot be done simply by pressing a button - it has to be very carefully planned and can take several minutes to carry out.  In these circumstances it is not surprising that bulk carriers can sometimes be overloaded.  The International Association of Classification Societies (IACS) says that there is no evidence that high loading rates causes physical damage to the interior of cargo holds (assuming that they are in good condition to begin with) but “high cargo loading rates under an uncontrolled process could result in inadvertent overloading which could cause local or global damage.”  Dramatic proof of what can happen if something goes wrong during loading came in 1994 when a bulk carrier broke in half while being loaded at a port in South America.
 
Text Box:  From a distance, it is possible to mistake a bulk carrier for an oil tanker, but there is one crucial difference: although both ship types are divided into a series of huge cargo holds, bulk carriers have hatch covers which have to be opened when cargo is loaded and unloaded. These extend almost the width of the ship and can represent a point of weakness in the hull structure, especially in severe weather, when the hull is subject to considerable wave action. This photograph shows just how huge the hold of a bulk carrier – and its hatch cover – can be. The International Maritime Organization is now intensively studying hatch cover strength.
 
Credit: Bergesen

A study carried out by IACS members showed that a 5% overload placed in various holds could increase the stillwater bending moment by up to 15% and the sheer force by up to 5% while a 10% overload could increase the still water bending moment by up to 40% and the sheer force by up to 20%. A 10% overload, according to IACS (in reply to questions submitted by the Nautical Institute) could be caused by a five to eight minute delay in stopping a conveyor belt with a capacity of 16,000 tons an hour.  At the other end of the voyage, other problems can be waiting. Bulk cargoes are removed from the hold by means of huge grabs, which can weigh up to 36 tons.  The last tons of cargo, which may be caught up in frame webs and other parts of the hold, are often removed by bulldozers and hydraulic hammers fitted to the extending arms of tractors.  There is always a danger that the hull - especially if it is suffering from corrosion or fatigue - may inadvertently be damaged in the process.  Part of the problem is that modern loading and unloading techniques were developed long after the ships they are intended to load were built.  The need for speed may have compounded the problem in some cases.  An article in the August 1995 edition of the BIMCO Bulletin, the magazine of the Baltic and International Maritime Council, observed that, “there has been a growing body of evidence that terminals, which were often owned by the cargo owners or charterers of the ship, were putting pressure upon the ships to amend their loading plans or to load cargo to suit them, with little consideration about the overall safety of the ship.”

Text Box:  This graphic, based on the Intercargo study, shows how safety of bulk cargo carriers has improved since 1990. Nevertheless, the number of losses has fluctuated and is still worryingly high, especially when the increasing number of ageing ships is taken into account.







         A Question of Attitude

The idea that commercial considerations could threaten safety has been noted by other sectors of the shipping industry.  A study by Lloyd’s Register discovered that “operational damage was accepted as the norm by the operators of bulkers and OBOs; second, there was little awareness as to the significance of this damage and its likely consequences on the capability of the ship under adverse operating conditions.”  This might be put down to simple thoughtlessness, but that excuse cannot be made for shipowners who purposely move their vessels from one trade to another - to escape increasingly vigilant port State control inspections.  That is what happened when Australia, alarmed by a number of accidents involving elderly bulk carriers visiting its ports, tightened its port control procedures.

The result was a rapid switch of tonnage from the Pacific to the Atlantic where inspections were apparently not as rigorous.  According to Lloyd’s List  “in the first nine months of 1989 there were nine voyages with Capesize vessels aged 20 years or more in the transAtlantic trades.  In the corresponding 1993 period that figure had increased to 152.”  It is difficult to avoid the conclusion that the owners of at least some of the ships concerned moved them because they knew that the ships were in such bad condition that they would not be allowed to operate in Australia - or even leave port - without being repaired.  The owners were presumably quite content to allow the crews to risk their lives on ships which they knew were unseaworthy.

It is not surprising in the circumstances that, when Lloyd’s Register of Shipping began to investigate bulk carrier losses in 1991 it found that “one of the biggest problems facing LR ...is the general attitude of the industry.  It is thought by some in the industry that cracking in these structures is inevitable due to the harsh nature of the cargoes and the rigorous operational procedures throughout their service life.”

               High tensile steel

Most of the concern about the condition of bulk carriers has focused on old ships, especially those aged more than 20 years.  But young ships are not immune to neglect and corrosion and there is also evidence that changes in the steel used on some relatively young bulk carriers could present even more serious problems than those experienced by earlier designs.

The majority of ships operating today are built of mild steel.  But since the early-1980s increasing use has been made of high-tensile (HT) steel, especially in the construction of bulk carriers.  HT steel has been used in shipbuilding since 1907 but its recent popularity is due to the fact that plates can be thinner without losing any strength.  Whereas a normal side plate will be 24-29mm thick, this can be reduced to 20mm by using HT steel.  The weight saving - which might amount to several thousand tons - cuts building costs and also enables the ship to carry more cargo.  However, for these savings a price has to be paid.  One is the simple fact that HT steel corrodes just as quickly as mild steel.  Since HT plates are thinner than those of mild steel, corrosion is likely to reach the danger point more quickly.  A second problem is that HTS-built ships are more prone to structural problems caused by the way in which load is transmitted through the ships’ structural components and the inter-dependency of the structural response.

IACS observed that the most common example where failure had occurred on HTS-built bulk carriers was at side longitudinal connections to web frames.  According to Lloyd’s September 1995 Shipping Economist, HTS-built ships are also prone to a phenomenon known as “springing”: because the ships are flexible and tend to vibrate with short sea waves.  The article stated that “classification society rules have always been based on empirical evidence from previous generations of ships, but the increased use of HTS changed the characteristics of vessels and therefore represented a step into the unknown.”

It is clear from the above that HTS ships need at least as much care and maintenance as those built of mild steel, especially as they too are frequently subject to greater stresses in cargo loading and unloading than was originally envisaged.  Many shipping experts believe that whereas mild steel bulk carriers usually begin to experience major problems at the age of 20, those built of HTS will do so much earlier.  Since most of those built in the early 1980s are already in their late-teens, the danger is that there could be another rise in bulk carrier casualties, unless action is taken to prevent it.

The sudden increase in bulk carrier losses in 1990 and 1991 caused considerable alarm in the shipping industry.  In response, the IMO Assembly adopted Resolution A.713 (17) (“Safety of Ships Carrying Dry Bulk Cargoes”) which contains interim measures designed to improve the safety of ships carrying solid bulk cargoes.  The preamble expressed concern at the continuing loss of bulk cargo carriers and the heavy loss of life incurred.  The resolution noted that the nature of cargo and ballast operations could subject bulk carriers to severe patterns of bending and sheer forces and also to significant wear.  It referred to the dangers posed by some bulk cargoes through their high density and tendency to shift.

The importance of not overstressing the ship’s structure during cargo operations was emphasized and governments were advised to pay particular attention to the structural integrity and seaworthiness of ships when port State control procedures are carried out under SOLAS.

Shipowners were encouraged to fit vessels with equipment to monitor the stresses on the ship’s structure during the voyage and during cargo operations.  They were also encouraged to install equipment required by the Global Maritime Distress and Safety System (GMDSS), which entered into force on 1 February 1992 but which did not become mandatory for most existing ships until 1999.

The impact of this resolution and action initiated by major classification societies was immediately beneficial.  The number of bulk carrier losses dropped to just two within the next year.  What is most significant about this improvement is that the resolution did not introduce any new measures but simply stressed the importance of implementing existing standards.  From this it is possible to conclude that at least some of the casualties that occurred in 1990 and 1991 were due not to defects in the regulations covering bulk carrier safety but to the ineffective way in which they were implemented.

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Loss of life on bulk carriers
This graphic based on the Intercargo study shows that 637 seafarers lost their lives in bulk carrier accidents between 1990 and 1997. Of these 227 died when the ship sank through taking on water or plate failure. A further 150 were lost as a result of disappearances (usually associated with bad weather) while another 119 deaths were attributed to adverse weather.



1 Sinkings Taking water and plate failure
2 Sinkings Disappearances
3 Adverse weather
4 Navigational Strandings not by engine failure
5 Navigation Collisions
6 Other fire and explosions
7 Engine room accidents Fire and explosion
8 Engine room accidents Stranding

Poor implementation of regulations is a problem that concerns all forms of shipping and is one that IMO has been treating with even greater urgency.  Successful implementation depends upon a number of factors, but to be really effective it requires everybody involved doing their job efficiently and with the necessary commitment and dedication.

Those involved in implementation are:

  flag States the Governments which have ratified conventions and thereby promised to put them into force
  port States which have authority under conventions to check that foreign ships visiting their ports comply with IMO requirements
  shipowners who own the ships and have the greatest responsibility - and opportunity - for ensuring that they are maintained in good condition.
  seafarers
whose training and skill are vital to shipping safety and who stand to suffer most if something goes wrong.
Actions taken by IMO to improve implementation have been particularly important such as:
    established a Sub-Committee on Flag State Implementation, which spotlights some of the problems Governments have in enforcing IMO conventions and provides guidance in overcoming them
    encouraged the establishment of regional port State control systems. Regional systems are especially useful in improving port State control because ships normally visit more than one country in a particular region.  Regional co-operation in inspecting and surveying ships ensures that few sub-standard ships avoid the net - and that ships in good condition are not inspected unnecessarily adopted guidelines on management for the safe operation of ships and for pollution prevention
    These were replaced by an International Safety Management Code (ISM Code) which became mandatory in 1998 through a new chapter IX of SOLAS
    complete revision of the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW) in 1995 and became effective in February 1997.  The Convention introduce strict new controls which will enable IMO to validate the training and certification procedures of Parties to the Convention.
     
IMO's Sub-committee on Ship Design and Equipment (DE) began work on measures to do with constructional safety, especially the hull integrity of large ships and installation of a monitoring system that would provide information to the master of the ship while the ship was under way and during loading and unloading operations. Such a system might prevent the accident from happening in the first place.  The recommendation was subsequently issued as MSC/Circ.646.  The Circular contains guidance on the fitting of hull stress monitoring systems (HTMS) and recommends that they be fitted to bulk carriers of 20,000 dwt and above.  Governments were asked to provide IMO with information on experience gained.

The Sub-Committee also considered ways of combating corrosion of seawater ballast tanks, a problem shared by both bulk carriers and oil tankers.  It included the regulation 14-1 in Chapter II-1 of SOLAS, which requires all dedicated seawater ballast tanks to be provided with an efficient corrosion prevention system, and the relevant guidelines.  These guidelines were adopted by the IMO Assembly in 1995 by resolution A.798 (19).  The regulation itself was included in amendments to SOLAS adopted by the 66th session of the MSC in 1995 which entered into force in 1998.

Resolution A.713 (17) emphasized the importance of regular inspections of bulk carriers, especially of older ships, and in 1993 guidelines on an enhanced programme of inspections during surveys of bulk carriers and oil tankers were adopted by the 18th Assembly by resolution A.744 (18).  It was originally intended that the guidelines would apply to tankers but because of concern about the loss of bulk carriers they were extended to them as well.  The guidelines were regarded as so important to safety that amendments to SOLAS to make them mandatory were adopted in May 1994 and entered into force on 1 January 1996.

The guidelines apply to existing tankers and bulk carriers of five years of age and over which means that the vast majority of the world tankers and bulk carriers are affected.  The enhanced surveys must be carried out during the periodical, intermediate and annual surveys prescribed by the SOLAS Convention.  The enhanced survey programme is mandatory for oil tankers under Regulation 13G of Annex I to the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 relating thereto (MARPOL 73/78).  The guidelines pay special attention to corrosion.  Coatings and tank corrosion prevention systems must be thoroughly checked and measurements must also be carried out to check the thickness of plates.  These measurements become more extensive as the ship ages.  The guidelines go into considerable detail to explain the extra checks that should be carried out during enhanced surveys.  One section deals with preparations for surveys and another with the documentation which should be kept on board each ship and be readily available to surveyors.  This should record full reports of all surveys carried out on the ship.

Annexes to the guidelines go into still more detail and are intended to assist implementation.  They specify the structural members that should be examined, for example, in areas of extensive corrosion; outline procedures for certification of companies engaged in thickness measurement of hull structures; recommend procedures for thickness measurements and close-up surveys; and give guidance on preparing the documentation required.

Guidance on planning the enhanced programme of inspections was adopted by the MSC in May 1994 and issued by means of MSC/Circ.655.

IMO's Sub-Committee on Dangerous Goods, Solid Cargoes and Containers (DSC) considered ways of improving the safety of loading and unloading operations.  One aim was to amend Chapter VI of SOLAS so that ship masters would be provided with sufficient information on cargoes to be able to assess stress limitations.  A questionnaire, issued as MSC/Circ.611 deals with the loading and unloading of bulk cargoes based on a model plan prepared by the Nautical Institute and the International Federation of Shipmasters’ Associations (IFSMA).  Other organizations were also working to improve bulk carrier safety, including the leading classification societies, most of whom are members of the International Association of Classification Societies (IACS).

Three other circulars were issued in December 1994.  MSC/Circ. 665 is concerned with the duties of Chief Mate and Officer of the Watch at bulk cargo loading and discharge ports.  It contains checklists that are designed to ensure that loading and unloading is carried out safely.  The circular was superseded in June 1995 by MSC/Circ. 690, which contains an improved model ship/shore safety checklist.  MSC/Circ. 666 contains a cargo operation form, which is intended to ensure proper planning and calculation prior to the commencement of cargo operations.  MSC/Circ. 667 contains general advice on bulk carrier safety.  It stresses, for example, the importance of reducing corrosion within holds and ballast tanks by maintaining paint coatings and gives guidance on where corrosion is most likely to occur.

Click here for Details on MSC Circulars 667 and 690

The 1997 SOLAS Conference

A new chapter XII to SOLAS - Additional Safety Measures for Bulk Carriers, adopted by the November 1997 SOLAS Conference entered into force on 1 July 1999.  It covers survivability and structural requirements to prevent bulk carriers from sinking if water enters the ship for any reason.  Existing ships which do not comply with the appropriate requirements will have to be reinforced - or they may have to limit either the loading pattern of the cargoes they carry or move to carrying lighter cargoes, such as grain or timber.

The regulations stipulate that all new bulk carriers 150 metres or more in length (built after 1 July 1999) carrying cargoes with a density of 1,000 kg/m3 and above should have sufficient strength to withstand flooding of any one cargo hold, taking into account dynamic effects resulting from presence of water in the hold and taking into account recommendations adopted by IMO.

For existing ships (built before 1 July 1999) carrying bulk cargoes with a density of 1,780 kg/m3 and above, the transverse watertight bulkhead between the two foremost cargo holds and the double bottom of the foremost cargo hold should have sufficient strength to withstand flooding and the related dynamic effects in the foremost cargo hold.

Cargoes with a density of 1,780 kg/m3 and above include iron ore, pig iron, steel, bauxite and cement.  Less dense cargoes, but with a density of more than 1,000 kg/m3, include grains such as wheat and rice, and timber.

Chapter XII allows surveyors to take into account restrictions on the cargo carried when considering the need for, and the extent of, strengthening of the transverse watertight bulkhead or double bottom. When restrictions on cargoes are imposed, the bulk carrier should be permanently marked with a solid triangle on its side shell.  The date of application of Chapter XII to existing bulk carriers depends on their age. Bulk carriers which are 20 years old and over on 1 July 1999 have to comply by the date of the first intermediate or periodical survey after that date, whichever is sooner. Bulk carriers aged 15-20 years must comply by the first periodical survey after 1 July 1999, but not later than 1 July 2002. Bulk carriers less than 15 years old must comply by the date of the first periodical survey after the ship reaches 15 years of age, but not later than the date on which the ship reaches 17 years of age.

Formal Safety Assessment

Following the publication of the report on the 1980 sinking of the bulk carrier Derbyshire in the South China Sea with the loss of all on board, a formal safety assessment (FSA) study of bulk carriers by the United Kingdom to aid future IMO decision-making on bulk carrier safety.

FSA is a process for assessing the risks associated with any sphere of activity, and for evaluating the costs and benefits of different options for reducing those risks.  It therefore enables, in its potential application to the rule making process, an objective assessment to be made of the need for, and content of, safety regulations.  The FSA consists of five steps: identification of hazards (a list of all relevant accident scenarios with potential causes and outcomes); assessment of risks (evaluation of risk factors); risk control options (devising regulatory measures to control and reduce the identified risks); cost benefit assessment (determining cost effectiveness of each risk control option); and recommendations for decision-making (information about the hazards, their associated risks and the cost effectiveness of alternative risk control options is provided).

The entry into force on 1 July 1999 of the new Chapter XII to SOLAS on Additional Safety Measures for Bulk Carriers was a significant step in improving bulk carrier safety and was the culmination of a lengthy process involving Governments, shipowners and classification societies in looking at all aspects of bulk carriers, from operational issues to their design and structure.

The ongoing FSA study on bulk carriers will go some way to helping IMO in the process of deciding which regulations – or amendments - will be appropriate. Indeed, this is part of IMO policy to move to a more pro-active approach.  Instead of solely responding to disasters, a preventive and prospective approach is necessary by using statistical analysis to identify potential problems and ensuring that new measures are safe.  The results of the FSA study which are due in 2001 will help analyse the likelihood of occurrence of disasters such as the Derbyshire, and the measures needed to prevent it.  The work on bulk carrier safety is also being carried out against the broader context of IMO’s moves to improve implementation of existing IMO instruments and in reducing human error – still seen as the cause of most accidents at sea.

The industry view

The organization that represents many of the world’s dry bulk carrier operators at international meetings is Intercargo. In May 2000 Intercargo published its latest Bulk Carrier Casualty Report giving details of losses in 1999 and ten years of data for the period 1990-1999.  This showed that “the trend in the number of bulk carriers lost can be said to be declining; however, the statistical significance of this decline remains marginal.” The greatest number of vessels lost in one year was 22 (1991) and the least was 8 (1995).

The report shows that older bulk carriers are much more at risk than those under 15 years of age. The average of bulk carriers lost at sea during the decade was 19.5 years. Although weather is often associated with losses at sea the Intercargo report says that “a well-found or well-navigated ship should be able to survive all but the most severe weather conditions. In nearly all cases weather is unlikely to have been the primary cause of loss.” This is generally related to the age and condition of the ship.

The report says that the primary cause of bulk carrier losses and loss of life in bulk carrier casualties are related to structural failure. Although the loss record of bulk carriers is no worse than that for other sectors of shipping, the loss of life associated with rapid sinking “is too high and is preventable.”

Intercargo says that bulk carrier casualties “have their genesis in the failings of shore-based ship managers.”
 
click here to enlargeclick here to enlargeAverage age of bulk carriers lost 1990-1997(Left)


Lives lost in bulk carrier accidents 1990-1997(Right)
The graphic shows the strong link between structural failure and loss of life. Because of the density of the cargo carried, bulk carriers are particularly vulnerable is the ship’s structure is seriously damaged and water enters the cargo holds.
 


For further information about bulk carriers, please go to these links:

The Library of IMO has prepared an extensive bibliography of Internet links and other information about bulk carriers, which can be found at:
http://www.imo.org/imo/Library/bulksafe/bulksafe.htm
The International Association of Classification Societies (IACS) has published Bulk Carriers: Guidance and Information on Bulk Carrier Loading and Discharging to Reduce the Likelihood of Over-stressing the Hull Structure. It is available for downloading on the IACS web site at http://www.iacs.org.uk/publications/bulkguid.pdf.


[1] Add link to the paper entitled International Maritime Organization