Deck Cargo on IHI Class Vessels

DECK CARGO ON “IHI” CLASS VESSEL

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KGJS

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Improvement

IHI class vessel has experienced a shift of deck cargo two times last year. As usual, to identify a single factor as the cause of this movement is difficult. One cargo was lumber on deck, other one pipes. Both times cargo was secured according Gearbulk procedures and under supervision of Supercargo. Obviously something went wrong, or procedure by itself was not perfect. Both times vessel’s rolling motion was up to 20O to 25O and cargo could not survive such angle accompanied with short rolling period. Evidently appropriate action to alter the course could have reduced rolling and prevent movement. It is important to emphasize that some navigational legs are constantly affected by high swell like Lirquen–Magellan Strait, and there isn’t much room to keep the vessel on favorable course. Therefore, advanced techniques for deck cargo securing should be considered.

January 2009 July 2009 IHI vessels due to design shows not so good seakeeping behavior, high GM, high roll amplitudes and accelerations. Therefore we have to think of an additional ways to secure deck cargoes and improve present ones. It is a fact that the lashing and securing of deck cargoes can become a matter of trial and error, which is not a professional way of safeguarding cargo. On 11th December 2008, the General Assembly of the United Nations adopted the UN convention on “Contracts for the International Carriage of Goods Wholly or Partly by Sea” The rules were signed in Rotterdam on 23rd of September 2009 and hence are known as “The Rotterdam Rules” It is intended that these new Rules will replace all the existing regimes i.e. the Hague, Hague-Visby and Hamburg Rules. The new convention aims at creating a modern and uniform law governing the carriage of goods which include an international sea leg, but it is not limited to port-to-port carriage of goods. Whilst there are many changes to the carriage of goods by sea regime in the convention, perhaps the most relevant to seafarers and ship owners regards the liability of the carrier. The list of defences available to the carrier has been significantly reduced, particularly by the abolition of the “nautical fault” defence which, under the Hague-Visby Rules, relieves the carrier from liability for any “Act, neglect or default of the Master, mariner, pilot, or the servants of the carrier in the navigation or in the management of the ship” Under the Rotterdam rules when a casualty is due to a navigational or management error, the “nautical fault” defence will no longer be available to the carrier. The major change is the issue of liability and the fact that the ship owner will become liable for almost all damage caused to the cargo whilst in his care. Accordingly a much higher burden is placed on ship managers, masters and crew to properly care for the cargo, which still is and always has been the best way to ensure that same is delivered in good condition. Sea voyages are made in variety of weather conditions which are likely to exert a combination of forces upon the ship and its cargo over a prolonged period. When sailing in adverse weather conditions, severe rolling motions are most dangerous for deck cargo. Even worst phenomena is when rolling motion is accompanied with downward heaving acceleration (when buoyancy falls and ship “sinks”)

Rolling angle 10O Rolling angle 30O Rolling angle 45O The rolling period is defined as the time taken for a full rolling oscillation from the horizontal to the left, back to horizontal then to the right and then back to horizontal. In vessels with a high righting capacity, i.e. stiff ships, rolling periods of ten seconds and below are entirely usual. Rolling and pitching of a vessel generate upward and downward acceleration forces directed tangentially to the direction of rotation, the values of which increase with distance from the rolling or pitching axis and are inversely proportional to the square of the rolling or pitching periods. At an identical distance from the axis, if the rolling or pitching period is halved, acceleration forces are quadrupled, while if the rolling or pitching period is doubled, acceleration forces are quartered. Rolling or pitching angles generate down-slope forces. During upward motion, stack pressures rise, while they fall during downward motion. Steeper tilting, as occurs during rolling, promote cargo slippage.

DECK CARGO ON “IHI” CLASS VESSEL

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KGJS

Continuous

Improvement

Pre-planning, stowage and securing, plays a vital role for successful delivery of cargo. Nevertheless, lack of care during sea passage can nullify proper stowage and securing. Thorough attention to securing elements has to be given while carrying deck cargo. Standard Gearbulk procedures for re-tightening and an additional chocking must be strictly followed. Whole cargo should be compact and to act as one solid block. Minimize rolling at given circumstances has crucial part of proper care during sea passage. Example, 700 mT of lumber on hatch cover 5 with rolling angle of 10O and rolling period of 10 sec creates force of 490 kN (50 mT). Cargo by itself (without lashing chains) balancing this force with 2060 kN (210 mT) of static friction. But we have to remember that this is just static friction, not dynamic. If we add just downward movement of rolling component friction goes down to 1890 kN (192 mT). This is simplified calculation from complex mechanics of lashings on deck lumber. Up-and-over lashings of this type do not adequately prevent sideways movement. They provided downward force on the deck cargo and this, in association with the friction between the deck cargo and the top of the hatch cover preventing transverse shift. In both accidents there was an additional wooden stanchions slotted into the sockets to restrict sideways movement. When you break down the transverse forces on the deck stow and make comparison with lashing forces applied, there is certain imbalance. If a rolling force is applied tending to move lumber packet over another or over the hatch cover, the opposing friction force brought into play is tangential to the surfaces in contact and is just sufficient to balance applied force. There is the limit beyond which the friction force can not increase. When this limit is reached sliding (collapsing) is about to start. And friction force reaches the limiting value. After sliding starts the direction of the friction force is opposite (still exist) to that of the resultant motion. The kinetic value (sliding resistance) of friction force is usually slightly less than the static or limiting value. In theory we can divide deck cargo into three sections – upper, middle and lower. Chain lashings balance upper section, stanchions or lumber chocks balance lower section and middle section shows the tendency to distort into rhomboid or collapse under the influence of transverse (rolling) force – because there is nothing except friction which opposing the transverse (rolling) force! The force of static friction increases up to a maximum value, after which the object "breaks loose" and begins to start moving.

Several proposals on how to improve securing of deck cargoes on IHI vessels.

1) To strictly follow Gearbulk instructions referring to deck cargo pre-planning, stowage, securing and sea passage care. 2) Supply hydraulic chain pullers and speed sinchers 3) Increase “non-skid” paint area on hatch covers 4) Arrange stock of “non-skid” material on board 5) When loading pipe packs/bundles on deck, than an additional securing of pipe packs in fashion of Olympic lashings 6) IHI class vessels have slightly higher container fittings on hatch covers; this should be considered when dunnage floor is made 7) To supply steel stanchions “H” beam, and have them permanently on board 8) To fabricate and use “pull back anchors” with hog wires 9) Use of software (LashCon, Marhydro or similar) to monitor and estimate max rolling criteria 10) Be aware that sudden change of ships course can cause violent rolling in heavy weather.

Pipes on deck

The force of static friction increases up to a max value, after which the cargo “breaks loose'' and begins sliding!

Photo shows magnitude of the force, the socket wall has been bent before stanchion was sheared off.

Olympic lashing of pipe bundles with webs tied down to D-rings.

Steel stanchions on both sides

Up and over chain lashings

DECK CARGO ON “IHI” CLASS VESSEL

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KGJS

Continuous

Improvement

“Pull back” anchor is completely new idea and approach to lashing of deck cargoes. Starboard side “pull back” anchors should be connected to port side lashing point with wires, which are run between two layers of cargo. On the end of the wire, turnbuckle as tensioning device must be attached. Port side arrangement is opposite to starboard. The weight of the cargo will help to hold the wires in place, and this arrangement will provide a rigid box structure, which has resistance to racking and transverse shift.

If a timber deck cargo does shift, the “pull back” anchor lashings will tighten and, providing they don’t break, will eventually arrest the shift. Other benefits of “pull back” anchors are:

- prevent slack in the stow which could cause the lashings to slacken - produce a binding effect within the stow; and - reduce to a minimum the permeability of the stow

This size steel “pull back” anchor has a weight of 7,3 kg and maximum securing load MSL of 40 kN which is approx. 4 metric tonnes. The size and shape can be changed. One “pull back” anchor set would include: - 1 anchor - 1 corner protector plate - wire rope dia.16 mm - 3 shackles of MSL 4 mT - 1 deck lash turnbuckle

PRACTICAL APPLICATION ON BOARD OF “IHI” CLASS VESSELS

A little extra time and money spent ensuring a really secure deck stow could well pay dividends on passage, especially in the heavy weather! Prepared by: Capt. Leo Tvrde and Ian Broad, Master Mariner, Operational Manager Chile