Implications of double hull bulk carriers and ballast water management

In the last few decades when the subject of maritime trade and ships has been in the media it has normally been focussing on the damage to the environment caused by oil spills from tankers. Legislation such as OPA 90 and initiatives to fit oil tankers with double hulls was seen as the answer, with the focus being to keep the oil inside the vessel.

In January 2004, Mr. Hans Viig, Senior Vice President of the Classification Society Det Norske Veritas, gave a presentation to over 50 Hong Kong branch members and guests on the subject of double hull bulk carriers and ballast water management.

Structural Safety – a growing concern on bulkcarriers

Attention has now turned to the use of double hulls on bulk carriers for reasons of safety and the survivability of the vessel rather than minimising pollution, by keeping the seawater outside of the ship’s hull.

The threat to the environment not by oil pollution but through the global transportation of invasive aquatic species in ballast water is being addressed by legislation for the control and management of ballast water and sediments on ships.

Mr. Viig used a series of slides to show how the modern day bulk carrier is in fact a “delicate” vessel and not the strong sturdy ocean going workhorse that had for too long been the perception.

Images of bulk carriers split in two whilst alongside berths, as well as stricken vessels at sea and an eerie photo of the bow of the “Derbyshire” on the seabed after being lost with all hands due to accidental hold flooding in 1980, provided stark reminders of the major casualties and loss of life that has befallen bulk carriers.

In order to simply explain to those in the audience more accustomed to driving a desk, than a ship, Mr. Viig showed how on a 1:100 scale model of a typical 289m long Capesize bulker having 20mm steel plating, the side shell on the model would only be 0.2mm thick – the same as normal printing paper!

A bar graph showed how the individual risk to crew on bulk carriers was significantly greater than the risk to crew on oil tankers with the risk of foundering around 16 times greater.

A closer look at bulk carrier fatalities between 1978-1998 showed that 45.8% had occurred due to side shell failure, with 9.4% due to a collision, 18.7% had been due to hatch cover failure with failure of other deck openings accounting for 3.5%.

The challenges identified if the number of bulk carrier fatalities were to be reduced include preventing the accidental ingress of water, mitigating the consequences of such accidental ingress and evacuating the crew in a timely and safe manner.

To meet the challenges, Mr. Viig explained the new IMO and IACS requirements for future bulk carriers which includes the use of double side skins, improvements to hatch covers and coamings, water ingress alarms and dewatering equipment and free fall and free floating lifeboats as well as clearly defining the bulk carrier as a ship type, assigning Class notations dependant on cargo type and stricter control of loading conditions. These will be brought into force by the IMO’s amendments to SOLAS ChXII and by unified requirements of IACS. As for existing bulk carriers, new requirements have included, amongst others, the strengthening of the transverse bulkhead between hold numbers 1 and 2, improvements to hatch cover securing arrangements, smaller hatches and side shell frames, water ingress alarms and stricter survey requirements.

As well as increased safety levels the installation of double side skin structures should enable double hull bulk carriers to obtain preferential charter rates. This is because the smooth sided cargo hold structure will reduce unloading time, and will be easier to clean and hence increase the operational flexibility when compared to the conventional single hull design with exposed framing in the cargo holds.

On the downside, boxing in the side framing necessitates additional steel weight due to the internal cell structure within the double hull space made up of the supporting webs and girders and access platforms. During the life of the vessel this means more structure and welded seams to inspect and an increased area to coat.

Mr. Viig ended this part of his presentation by reminding the audience that bulk carriers lead stressful lives and a safe and efficient bulk carrier is only obtained if it is properly designed, constructed, manned, operated and maintained.

The dangers inside ballast water

Mr. Viig then turned his attentions to the impact of invasive aquatic species and the latest IMO Regulations to combat them.

Over 70% of the Earth’s surface is covered by sea with around 60% of the human population living in coastal areas with over 90% of world trade carried out by sea. Mr. Viig advised that billions of tonnes of ship’s ballast water is transferred globally each year, which means thousands of species of microbes, plants and animals are transported from one part of the world to another with each vessel.

The impact of this transfer of so many organisms is staggering. Diseases such as cholera can spread and the invasive species such as the European Zebra mussel are now present in more than 40% of U.S. waterways, fouling up water intake pipes of industry at a huge cost to the U.S. economy.

The IMO ‘International Convention for the Control and Management of Ships’ Ballast Water and Sediments,’ is due for implementation from 2005 onwards. This will require vessels to have an approved Ballast Water Management Plan and maintain a valid International Ballast Water Management Certificate, and the vessels adherence to the Ballast Water Management Plan will undergo regular surveys as well as checks by Port State Control inspectors.

However, present ballast water exchange methods and equipment will not totally prevent the transfer of harmful organisms. Various research and development projects are underway around the world, including the used of heat and chemical treatment. Ships constructed before 2009 will have until 2014 to comply with the Ballast Water Performance Standard. However, ships constructed after 2009 will need to comply once built if vessel’s ballast capacity is less than 5,000m³, or by 2011 if the ballast capacity is greater than 5,000m³.

Ballast water exchange has brought inherent dangers to the vessels themselves. Unsafe ballast exchange sequences have resulted in undue stresses on the structure of a ship. One picture slide in the DNV presentation showed the forward half of the bulk carrier ‘Flare’ which broke in two during a ballast water exchange with the loss of 21 crew members. Safe exchange sequences have been developed and if followed should reduce the further loss of vessels and crew, whilst adoption of double hulls and continuing improvements in design and procedures should increase the safety of bulk carriers.