Fairplay Solutions magazine Issue 123 December 2006

 Next month sees water ingress monitors star to become compulsory on small single hold cargo ships.  Solutions looks at some of the issues surrounding this new equipment.

is most usually achieved by installation inside a pipe opening to the deck. With single hold ships it should be possible to locate the sensors inside the hold on the aft bulkhead with cables passing through into the engine room behind.

As with most SOLAS required equipment, water ingress monitors are expected to be working

WATER ingress monitoring systems have been mandatory in bulk carriers since 2005 and with effect from 1 January 2007 they will also become compulsory on smaller new and existing single hold dry cargo ships.

Water Ingress in small single-hold general cargo ships is often the cause of tragedies with casualty rates in this group being much higher than in the larger bulk vessels.  So the new legislation should not only save lives but help prevent some of the losses that less informed media put down to bulk carriers giving that sector such a poor public perception.

When the initial legislation came into force in 2005, there were just four companies able to supply type-approved systems. Attracted by the money to be made from a huge retrofit programme, the number of suppliers with approved systems had burgeoned to more than 50 in just a few months.  Once the initial rush brought about by the 2005 rules had subsided, many system suppliers left the market, but they or other newcomers may be enticed back by a new retrofit bonanza that could run until early 2010. Costs for installations will vary depending upon the choice of system but from what solutions has learnt from different suppliers, a figure of about $5000 for a single hold ship should be the upper limit.  

Geoff Taylor MD of UK-based PSM Instrumentation agrees with that view and adds that in conversations with classification societies he has been told that in a rush to get systems approved in time to meet the earlier deadline some products that have subsequently proven not to be reliable were given class approval. “However, it is unlikely that these systems will have approval withdrawn”, Taylor told Solutions.

Taylor also points out the effect of poorly performing systems on the crew saying

Most systems consist of a high and low level sensor or switch connected to a control panel which is in turn connected to both visual and audible alarms on the bridge. The switches and their cables need to be protected from damage by cargo and cargo handling equipment which

 at all times and in many ports PSC inspectors will require to see the devices tested before allowing the ship to put to sea.

This in itself can present problems for some types of system since they ca only be tested with the hold empty.  The simplest float switches for example might be tested by immersion in a bucket of water but that is hardly practical once the hold is full and the switch located near the bottom of the hold. Some float switches are also liable to corrosion and this can be a big problem with some bulk cargoes.

Both these problems are claimed as having been overcome in Martek Marines’ Bulksafe system which is constructed using Delrin a non-metallic plastic material and has an integral testing device that also serves to clean the sensor’s filter and which can be used even in full holds.

PSM Instrumentation by contrast uses a pressure switch in it’s system that requires just a single sensor to determine the depth of water present in the hold. As the water depth increases so does the pressure on the sensor’s membrane increasing the current as t does so. PSM claims that the sensor is accurate enough to show the gradual rise in water depth in a flooded hold allowing the situation to be better monitored than those systems that just have low and high level alarms.

Testing of the system can also be performed with a full cargo and this is done by applying a vacuum which pulls the pressure membrane upward activating the alarm. PSM’s system also goes under the name Bulksafe but the two systems are not connected in any way and the manufacturers are competitors.

There are other types of system that use different technologies. Ariston of Norway employs microwave sensors in it’s Surveyor system while French firm Enraf relies on water sensing switches with no moving parts measuring conductivity. Yet another type relies on a Squing with vibrating forks that operate constantly and whose vibration frequency is affected by a moist atmosphere.

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Who's affected and when?

The requirement to install water ingress monitors in single hold dry cargo ships comes from a change to SOLAS regulation II-1/23-3 adopted in May of 2005. The new rule applies to existing cargo ships of less than 100m in  length built before 1 July 1998 and all new and existing ships less than 80min length built after that date. Systems in existing ships need not be fitted immediately on 1 January 2007 but must be installed during the first intermediate or renewal survey after that date.

The wording of the new regulation - referring as it does to cargo ships and not specifically bulk carriers - will mean that owners of ships such as container vessels, timber carriers and other general cargo ship types are required to fit the devices. Since many of these small ships also carry bulk cargoes of grain, feedstuffs and minerals, the new rules will remove the anomaly that allowed them to exempt themselves from rules affecting 'pure' bulk carriers. 

For PSM's Bulksafe Solution click here