Bulk carriers potential hazards
Ingress of sea water into cargo holds poses significant threat to bulk carriers while on sea passage and in harbour. Effective means of monitoring hold bilges for presence of water are traditional practice. However New regulations now become part of the Safety of Life At Sea (SOLAS) convention and came into force on 1 July 2004. According to this regulation bulk carriers are now required to carry equipment that will give early warning of water ingress to the hull.
Introduction of Water Ingress Monitoring
Water Ingress Monitoring (WIM) is not a new concept. Masters will recognize that daily monitoring of bilges and tanks has been a feature of prudent seamanship since antiquity. However, this method of monitoring does not provide continuous information. Furthermore, when weather deteriorates the manual process is usually suspended because of the dangers to crew members taking the soundings. In such conditions the risk of flooding in the ship is increased and therefore some method of continuous monitoring should be introduced. The concept now adopted for bulk carriers by IMO monitors not only for the presence of water, but also, in the cargo hold spaces, the speed of ingress. To achieve this a two stage alarm is used, one at a low level in the hold, the second a short distance above it.
Methods of detection may vary. Some manufacturers use simple float switches, others may have other methods of detecting water. It is even permissible to install alarm points at the levels prescribed in the regulation in remote tank sounding systems.
The following guideline describe an example WIM system in more detail and how the provision should be used within the ship's Safety Management System. There are many variations in bulk carrier design. Each must be addressed individually. For example some ships do not have lower stools in which detection equipment can be positioned and thereby be well protected. In such cases WIM can be installed in protective tubes alongside existing sounding pipe arrangements.
Details of equipment for monitoring water ingress problem
Equipment designed for the purpose of monitoring water ingress to the hull of a bulk carrier must conform to a performance standard. Different manufacturers may design their equipment with variations in layout but all must be provided with certain minimum indicators and alarms.
All audible alarms should be connected to a mute button. This is to prevent interference with communication caused by loud alarms during the investigation process. The mute button cannot extinguish the indicator lamp, which must remain lit until the condition causing its activation is no longer present. An exception to this rule is in the case of spaces in which ballast is carried. The monitors for these spaces may be fitted with interlocks that disable the alarms and indicators but this interlock must be arranged so that when the (ballast) water level falls below the lowest alarm the monitor returns to the active condition.
The systems must be provided with internal monitoring arrangements aimed at detecting faults. The two principal types are open and short circuit and these should be detectable on each branch of the system so that for example an open circuit detected on a monitoring sensor in a hold is clearly identified in that part of the system. Furthermore the existence of such a fault should not affect the operation of the remainder of the system that serves other spaces.