Wednesday, 9 May 2012

Safety at Sea: Water Ingress Alarms

An interesting article from 'Safety at Sea' on water ingress alarms and their importance for bulk carriers. Derbyshire was a UK-flagged Capesize which sank with all hands (42 crew and 2 wives) on laden passage due to the progressive flooding of forepeak and foc's'le in a typhoon.

M/v Derbyshire
The successful search for the wreck of the Derbyshire and subsequent marine inquiry lead to a raft of safety measure being applied to bulk carriers, including raised forecastles, strengthened forward hatches, remotely activated pumping systems and water ingress alarms to alert the crew if water is where it shouldn't be.

The Antipodean Mariner

Bulker safety: Sink or WIM
Water ingress has been a problem for bulk carriers for several decades but, Dennis Barber argues, attempts to guard against the problem have not been watertight
Though liquefaction is a current focus of attention, it is not the only liquid problem facing bulkers. Stress on a vessel’s hull can lead to water ingress and even sinking. The problem was not fully recognised by the regulatory authorities until the early 1980s, and the mandatory warning systems are not as effective as they should be.
Early speculation about the disappearance of Derbyshire blamed liquefaction, although the cause of the bulker’s demise in September 1980 was later found to be loss of hull integrity and the flooding that resulted. At the time of the bulker’s sinking, Capesize vessels were sailing at the extremes of their shear force allowances with dry cargoes of iron ore. This fact should have led to an obvious deduction: that water entering the huge volume of space around the tiny heap of iron ore in the bottom of the hold would not only lead to a loss of buoyancy but also compromise the longitudinal strength of the hull.
The weight of water flooding into a hold, added to that of the borderline cargo weight, would lead to stress limits being exceeded rapidly. Also, the integrity of the ship’s sides and bulkheads (which are built to a static measure of strength related to pressure of still water) would then come under threat.
The significance of water ingress was highlighted at the International Collaborative Formal Safety Assessment (FSA) of Bulk Carriers when it reported to IMO’s Maritime Safety Committee during the period 2000–2004. The FSA found that the main reason for losses of bulk carriers, particularly large ones, was loss of hull integrity (LOHI). Put simply, if a hull fills with water, it will sink.
The fitting of water ingress monitors (WIMs) was one of the recommendations of the Reopened Formal Investigation (RFI) into the loss of Derbyshire. This finding was accepted and found its way into SOLAS, with WIMs becoming mandatory on all new and existing bulk carriers on 1 July 2004.
Initially, many manufacturers’ systems required penetration of the bulkhead of each hold and the installation of sensors at the critical heights required by the regulation. The idea was flawed from conception: it exposed the WIM to the cargo, which, by its dusty nature, was bound to block any orifice.
The IMO performance standard was focused on measurements being taken at the centreline to compensate for heel and trim. This is a minuscule and indistinct measurement in terms of the overall potential of a flooding scenario. It cannot be detected accurately in a rapidly rolling bulk carrier with the very ‘stiff’ stability to be expected when enormous weights are in the bottom of the ship, but it directed designers’ attention on to the centreline and resulted in bulkhead penetrations that became blocked with cargo.
A further mistake was the use of moisture, rather than pressure or float, sensors to detect the water. The hold in which the sensor was positioned would, once the hatch was closed, be subject to its own microclimate. Levels of humidity would often increase, particularly if the cargo was loaded wet. The instrument tended to mistake rising humidity for a flood in the cargo space.
Yet bulk carriers already possessed an efficient method of measuring water ingress that eliminated the blockage problem. By fitting bilge wells, usually in the corners of holds, solids could drop into the bottom of the filtered well. Any water remained there and could be measured from the sounding pipe entering the well space from above. On a well-run vessel, the well would be cleaned of solid residues before a cargo was loaded and soundings would be monitored daily.
Here the real problem was that the measurements were not continuous. To operate the routine in rough weather would risk the lives of the crew members charged with sounding the space from the open decks. The best WIM designs have merely tapped into the bilge well sounding system, placing sensors in recesses linked to the sounding pipes, not the bulkheads. This provides for continuous monitoring of an existing proven system. The sensor connections still allow free access by manual sounding methods.
When a WIM panel constantly sounds spurious alarms it is often switched off. This can lead to a port state control (PSC) deficiency or detention – assuming that the PSC officers are themselves sufficiently aware of the purpose of the instrument.
Three decades after Derbyshire’s sinking, some vessels still face the threat of water ingress occurring without warning. The response should surely be to provide the master with equipment fit for purpose, not to punish him for his inability to rectify defective design.
·  Captain Dennis Barber, consulting partner in Marico Marine, was the contracted specialist project manager at the UK MCA for the recommendations of the RFI into the loss of Derbyshire, serving as part of the project management team of the International Collaborative FSA for Bulk Carriers reporting to the IMO Maritime Safety Committee, 2001–2004

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