201122 Hazards of under-declared cargo weights

Case 1: Timber Loading

A tween-decker cargo ship was chartered for a voyage from West Africa to load a mixture of logs in the lower holds, packaged sawn timber and plywood in the tween decks and several containers of coffee and cocoa beans on the hatch covers. As is common in these regions, the logs were floated down-river in the form of large rafts. These were marshalled by small tugs and secured to the vessel while anchored in estuaries and coastal lagoons. A gang of stevedores commenced loading the vessel, skillfully standing atop the floating logs and slinging them in ones or twos, depending on the size of the logs and capacity of the ship's cargo gear. They, along with winchmen, signalmen and tallymen worked in 12-hour shifts and the tugs would ferry them to and from land twice daily.

The master received very scant information on the quantity and types of logs to be shipped, partly due to non-existent or unreliable communications with the forestry plantations in the interior, inland hauliers, stockyards up-river and shippers. A historic table of stowage factors for common species was handed to the vessel. The stevedores could not communicate in English and the ship's crew could not understand their rudimentary French and local dialect. The charterer's port captain stationed himself ashore after the initial visit at the first loading port. As it later turned out, the ship's managers and crew lacked detailed knowledge about this trade while the charterer's super-cargo wrongly assumed that the ship's crew was fully conversant with the nuances of timber loading in West Africa and offered no advice to the vessel.

The ship's crew accepted the stowage factors as stated in the list, not realising that the data was only for 'dry timber' and accordingly prepared a rudimentary stowage plan and stability condition. They were unaware of the fact that in most timber loading operations, a 'surcharge' or extra weight will affect the stowage factor, often caused by water absorption when logs are floated down-river, inaccuracies in the measurement of each log and deliberate under-declaration of weights by shippers. Such surcharge can sometimes be 35 per cent in excess of manifested cargo weight. Cargo was worked day and night and the tallymen handed a daily summary of cargo loaded figures at 0800 every morning. This process was repeated at
two anchorage ports.

The holds were duly filled with logs and the vessel berthed at a wharf to load the sawn timber and plywood in the tween decks and the containers on the hatch cover. It was at this late stage that the master noted excess deadweight from daily draught surveys. A revised stability calculation showed that after loading the containers on the hatch covers, the vessel would fail to meet Solas minimum stability criteria. When the master refused to load these containers, a lot of commercial pressure was put on the owners and vessel, and finally, a scheme was worked out whereby all double-bottom (DB) tanks were pressed up with sea water ballast. Despite this, the vessel had insufficient stability and two empty DB fuel tanks were also filled with sea water to ensure the vessel met IMO stability criteria without being overloaded. At the discharge port, a slop barge was hired and the contaminated ballast from the fuel tanks was duly disposed ashore.

Case 2: Containers

A large container vessel was loading at the final load port before commencing a trans-ocean voyage. The exit channel from the terminal had a draught restriction and sailing was subject to a narrow tidal window. Pre-arrival loading information listed some 350 containers, most of them going on the deck stacks. Being a regular vessel at the port, the terminal's computer system provided a departure stability condition with the sailing draughts allowing for adequate under-keel clearance (UKC) as per company's SMS. However, during the latter half of the 12-hour loading period, the chief officer realised that there was substantial under-declaration in the manifested container weights (later estimated to be an average of 12 per cent). This meant that after loading the manifested boxes, the ship was in serious danger of grounding in the channel. Thanks to quick thinking by the master, a total of about 850 tonnes of ballast was discharged before sailing from the twin auto-heeling tanks, which due to their high location and narrow width resulted in a safe even-keel trim and an acceptable stability condition. The ballast was restored in the heeling tanks after reaching deep waters but unfortunately, it was realised after sailing that stack-weight limits had been exceeded in many deck stacks.

Lessons learnt
Shore cargo weights must always be treated with caution. Accurate draught surveys and evidence of draught and stability calculations must be preserved by the vessel;
Charterers/terminals must be issued a written note of protest immediately once under-declared cargo weights is suspected;
The vessel's officers must fully familiarise themselves with the cargo types before arriving at the load port(s). Shore management must actively communicate to the vessel, expert advice obtained from industry sources, P&I club etc. Guidance documents such as the publication Thomas' Stowage must be carried by and consulted by the crew on board every dry cargo vessel;
With timber cargoes, a careful investigation must be made in the early stages of loading to establish the 'surcharge' or excess weight of cargo, especially if the logs are floated down-river;
Container terminals must be queried about the accuracy of manifested weights of loaded containers. Nevertheless, the ship's officers must work out displacement calculations frequently to monitor the 'missing' cargo weight;
Such excess weights may impose unsafe stresses on the tanktops, tween decks and hatch covers;
On modern container vessels, if the excess weight on hatch covers is not accounted for, the deck cargo lashing configuration as determined by the on-board software may prove to be insufficient.