Given the past few months’ challenging business climate for owners and operators in the dry bulk segment, even more focus should be paid to cost-efficient and safe operations. This article gives an overview of some important operational aspects in this context, along with practical guidance.
Main characteristics of bulk carriers Bulk carriers are ships designed primarily for the cost-efficient, large-scale transport of dry bulk commodities such as iron ore, coal, bauxite/alumina and grain. They have to fit perfectly into the overall logistics chain.
Bulk carriers’ sizes and configurations are optimised to allow the most economical use of these vessels in the typical trading routes and when carrying typical bulk commodities.
As a general rule, the market will always seek to use as large a vessel as the trade permits. This is due to economies of scale - bigger cargo parcels, faster loading and discharging operations and bigger vessels transporting the cargo will generate greater profit.
However, there are general limitations on the average ship size serving the different routes due to factors such as:
Port Restrictions: Berth limitations (e.g. draft limitations, air draft limitations, length of pier, etc) and lock limitations (e.g. Panama Canal, St. Lawrence Seaway, etc).
Infrastructure Restrictions: A less developed port and/or inland infrastructure hinders the quick distribution of large cargo volumes to and from the port areas.
Trade Restrictions: The demand for individual cargoes at various destinations is limited.
Consequently, bulk carriers have developed into well known size categories as shown in the table (overlapping and different size ranges may apply):
Design and operational considerations
In the past, the different bulk carrier designs have mainly competed on optimal steel weight and deadweight capacity, whereas today designers are focusing more and more on optimal operational flexibility and energy (fuel) efficiency.
Advanced ship technology and the introduction of direct strength assessments using the Finite Element Method (FEM) at the beginning of the 1980s led to reduced lightship weights and thereby a rise in deadweight capacities. The increasing use of high tensile steel (a higher ratio compared to mild steel) also contributed to lighter ships, with the side-effect that careful evaluation of structural fatigue became a more important issue. In retrospect, it could be argued that competition on steel weight, with the aim of maximising cargo intake, was one important reason for the many casualties at the end of the 1980s and the beginning of the 1990s.
A number of measures to enhance the safety of bulk carriers have been implemented by the IMO, IACS and the industry over the past few decades. The most recent of these is the introduction of the IACS Common Structural Rules for bulk carriers (“CSR Bulk”), according to which all new vessels are to be
constructed according to uniform acceptance criteria.
Today’s Rules and regulations provide increased safety and operational flexibility compared to the old standards. However, the challenge of combining improved safety with improved efficiency still remains.
Optimum size has already been mentioned as a main operational criterion, but other aspects may be of similar importance. The overall performance of a bulk carrier is determined by the vessel’s operational flexibility and efficiency and thereby its economic success in the shipping market. This is of particular importance in today’s market, where a large number of ships are competing for a limited transport volume.
From an operational point of view, the following aspects are to be looked at with regard to improved efficiency:
Ship Handling
Cargo Handling
Maintenance and Inspection
Ship Handling
The handling of a ship covers all aspects related to sailing on route, manoeuvring and berthing in an always navigationally safe manner.
The primary obligation of the master is to ensure that the ship, crew and cargo are not put into unsafe situations. The training and competence of the crew are essential to fulfil this obligation, and this is the reason for the introduction of the STCW Convention.
Load and discharge planning is one of the most essential tasks to be performed by a ship’s crew. It must be ensured that the strength and stability of the ship are not compromised at any time during the loading and discharge processes.
The planning of efficient loading and discharging by minimizing the berth time can only be performed within the strength and stability envelope-limits that the ship was designed according to.
It is recommended that a ship’s ability to cope with specified loading rates is stated and that the loading and unloading operations are to be time-wise synchronised with the ship’s de-ballasting operations.
New designs constructed according to IACS UR S25 have incorporated a 10% overshoot margin for high density cargoes based on the maximum cargo hold mass. This has been incorporated to provide an extra safety margin for any potential discrepancy between the actually loaded cargo and the planned cargo quantity, an aspect which is becoming more and more important as the loading rate and number of loaders increases. This extra margin is in general not incorporated into the design of vessels constructed prior to 1 July 2003, the in-force date for UR S25. The most sensitive areas with regard to the strength envelope limits are the outermost holds in alternate loading conditions. Consequently, efficient means to control the amount of cargo loaded into the individual holds are necessary to avoid overstressing and an unfavourable trim.
For Lakesize bulk carriers, it is of great importance to have a high loading flexibility to cope with the draft restrictions when sailing on the St. Lawrence Seaway and the Great Lakes. Grain stability, permissible still water values and hold mass curves adjusted to the Great Lake conditions can improve flexibility. Further on, including hull girder deformations in the loading computer will give the master more reliable factors for planning the loading.
Another important aspect to be considered when talking about ship handling is the exchange of ballast water. The efficiency of ballast water exchange is mainly dictated by the design of the ballast piping system, including the pumps, valves and arrangement of the ballast tank.
An approved ballast water management plan guarantees that the exchange process does not put the ship in an unsafe situation if it is complied with. However, it is recognized that one step might take a very long time to conclude, time in which weather conditions can worsen. This is particularly the case for Capesize vessels, where the double bottom and top side tanks are generally connected and extend over two cargo holds in the midship area. Serving smaller tanks would definitely make this operation more efficient.
Cargo Handling
Cargo handling covers all the activities connected with the safe transferral, stowing, lashing and securing of the various cargoes to be transported. Careful consideration needs to be taken of the cargo’s typical behaviour and characteristics.
Driven by a fast turnaround time in port, cargo handling is an important design aspect. In general, design requirements are to be linked to the harbour conditions, such as optimum hatch openings providing easy access to the hold and shipboard cargo handling gear.
Lashing equipment in cargo holds and on deck is important for efficient cargo handling as is appropriate cargo hold ventilation and humidity control.
Cargo variety is a typical feature of the smaller bulk carrier segments up to the Handymax size. The smaller vessels may carry all kinds of dry bulk as well as break bulks, such as steel products, forest products or project cargo. In general, dry bulk cargo is handled by port side equipment, whereas fitted shipboard cranes are used for handling break bulk and project cargo. If the cranes are also to be used for handling dry bulk cargo, this should be taken into account during the design phase and grabs should be stowed on board.
The cleanliness of cargo holds prior to loading is an important issue, particularly for bulk carriers which change their type of bulk cargo very often, such as Handysize and Handymax vessels. Operational efficiency is improved by the ability to perform fast cleaning of the cargo spaces. Providing appropriate cleaning tools and the necessary water and air supply are necessary preconditions. Hence, sufficient pump capacity and a dedicated wash-water holding tank may be important design requirements.
Maintenance and Inspection
It is well known that a lack of maintenance will lead to more rapid structural deterioration and, in the worst case, to loss of life and property. It is a fact that the lack of maintenance and improper inspections by ships’ crews were contributory factors to the massive bulk carrier losses in the past.
Costly repairs combined with off-hire may be reduced if a regular inspection and maintenance plan is in place. Such a scheme should focus on typical areas that require attention in bulk carriers, enabling the owner to better control the condition of the ships.
With the introduction of the enhanced survey program (ESP) for bulk carriers in 1992, class surveys are carried out much more thoroughly than in the past. However, they cannot replace continuous maintenance, which is still the owner’s responsibility. It should be noted that, through the resolution A.744(18), the ESP requires the ship owner to maintain onboard documentation relating to any inspections carried out by the ship's personnel with respect to structural deterioration and the condition of the coating.
To assist the owner in doing so, the IMO has developed A.866(20) - “Guidance to Ships' Crew and Terminal Personnel for Bulk Carrier Inspections” - to provide guidance to ship's crew and terminal personnel with respect to the principal areas on bulk carriers that are likely to be susceptible to corrosion or damage. This guidance is supplemented by the IACS recommendation No. 76 on “Guidelines for Surveys, Assessment and Repair of Hull Structure – Bulk Carriers”.
The maintenance of bulk carriers’ cargo hatch-covers became mandatory with the introduction of regulation 7 of the revised SOLAS Chapter XII, which entered into force on 1 July 2006. This is also part of the ISM scheme.
Nevertheless, there is a trend today towards charterers being concerned about the condition of the bulk carrier they are going to charter, and rating schemes similar to the ones used for tankers are becoming more and more popular.
With respect to the operational efficiency, a structured inspection and maintenance plan combined with crew training will maintain the availability and reliability of the ship by:
Detecting deficiencies at an early stage
Dealing with problems while they are still minor
Being able to document the ship’s condition
Maintaining a uniform standard across the fleet
In DNV, we have the expertise and experience needed to help owners ensure their bulk carriers are operated efficiently. Our philosophy is that a safe and reliable bulk carrier is more easily obtained if it is properly designed, constructed, maintained and inspected.
This article will be followed up with more in-depth articles on each operational aspect in coming issues of the DNV Bulk Carrier Update.