Bulk carrier losses in the early 1990s were dramatic: ships sank rapidly, often with the loss of all lives. Many were old and had suffered structural damage. A study by IACS (International Association of Classification Societies) found that after flooding in the foremost hold, the bulkhead between this hold and the adjacent hold can collapse from the pressure of cargo and water, leading to progressive flooding and sinking.
The dangers with two holds flooding:
A study by the U.S. Maritime Administration (MARAD) found that a typical midsize bulk carrier should survive all one-hold flooding so long as the ship is not suffering from metal wastage and undetected cracks but flooding of any two holds would have disastrous consequences.
Fig: Dangers of hold flooding
Reason of abnormalities
If a ship takes on an unusual trim or heel, or if her motions become changed, breach of the hull envelope should be suspected immediately:
i) Unusual collections of water on decks may be indicating trim or heel abnormality.
ii) Sudden changes of heel or trim will indicate flooding or in smaller ships with lighter cargoes it may indicate cargo shift.
iii) Jerky lateral motions can be indicative of large scale sloshing as would be the case if a hold were flooded.
iv) On smaller ships, slowing of the ship's roll period may indicate excessive water within the hull - a serious threat to stability. Ships fitted with GM meters should be able to identify any unexpected changes in GM.
v) Increases of water boarding forward decks may indicate flooding of a forward compartment. Trim and freeboard changes are notoriously difficult to assess from an after bridge.
Methods of detection
i) Hatch covers may be dislodged by pressure and/or sloshing from within a hold if flooding occurs through side shell or bulkhead.
ii) Sudden pressurization of compartments adjoining those that are damaged or flooded will indicate failure of internal subdivision, most notably bulkheads.
iii) Spaces may be monitored, either using gauging or bilge/water level alarms. Forward store spaces can also be monitored audibly using "talkback" telephones that may be fitted in forward spaces. Anchor impacts and water in the space can be detected using telephones of the type that remain active until switched off from the bridge.
iv) Hull Stress Monitors, where fitted, may be able to detect unexpected longitudinal hull girder bending. Torsional stresses may also be detected through differential changes between port and starboard strain gauges.
v) Visual monitoring from the bridge using binoculars, where fitted, by closed circuit television, can give indication of abnormal water on deck and local damage. However, assessment of trim or freeboard using this method is difficult.
vi) Assessment of trim changes can in certain conditions be detected by noting the level of the horizon, when visible, against a known reference point on the foremast.
vii) Draught and trim can be assessed using draught gauges. Changes are much more discernible using this method than by visual means from above decks.
Early readiness for evacuation
In the event of identifying or even suspecting that the ship may have sustained damage, ship's personnel should immediately be called to their emergency stations. A high priority should be placed on preparing equipment for evacuation. Abandonment should however only be invoked on the spoken orders of the master following assessment of the risk.
Contact with a Maritime Rescue Co-ordination Centre (MRCC) and/or owners should be made early if the master has any suspicion that the ship is damaged. An URGENCY signal is justified and this should be upgraded to DISTRESS if the ship is confirmed as damaged.
Masters should place a strong emphasis on evacuation training so that donning of protective suits and lifejackets, launching of survival craft, and operation of EPIRBs and SARTs is a familiar process to all ships' personnel. Also included should be shutdown procedures for main and auxiliary machinery, which can, if left running, hinder launching of survival craft.
Warning against flooding
Seafarers have been lost when bulk carriers have sunk due to having insufficient time to evacuate the vessel. Bulk carriers have, on occasions sunk so fast that not even distress signals were sent out. The facts made it mandatory on board functioning of water ingress alarms. If alarms frequently malfunction, the equipment should receive priority attention to rectify the fault. Crew members should not be reticent to muster.
If an alarm is false, the crew can be stood down, but if it is genuine and crew are not mustered, there could be insufficient time to do so if flooding progresses rapidly loss of sleep is less serious than loss of life. These are principles that are well established with fire alarms.
Flooding is potentially more serious than a fire that can be fought. Only the most serious fires can threaten the survivability of the ship in terms of buoyancy but flooding is the beginning of sinking. It should therefore be afforded higher status than fire.