Importance of soundings: Throughout the loaded voyage, as at all other times, soundings of cargo spaces, ballast tanks, void spaces and bunker tanks should be taken and recorded daily by the same competent person.  The readings obtained should be inspected carefully for any unexplained increases or decreases in the values  observed. When the sounding positions are located on the open main deck and when the vessel is in adverse weather with a low freeboard, it is often unsafe to obtain soundings on the ship’s weather side or even on both sides. This is unfortunate, though unavoidable once the ship’s design has been finalised. In these circumstances the chief mate should be alert for any opportunity occurring when in the lee of land or because of an improvement in the weather to obtain a set of soundings. Failing this the hold bilges should be pumped daily until suction is lost. Reasons for any failure to obtain soundings should be logged.

During the 1980s and 1990s there were numerous indications that aboard badly-run bulk carriers a full set of soundings was sometimes not obtained for days or weeks on end. It is true that in almost every case soundings  when taken only confirm what the chief mate already knows – namely, that the ship is not leaking. But it is only when soundings are obtained daily, at the very least, that there is a reasonable chance that any damage or oversight will be detected promptly when it occurs. Water ingress detectors, if working properly, should detect serious flooding in forepeak or cargo holds at an early stage but will not detect water at tanktop level. Such water would seriously damage or even destroy a variety of cargoes and in addition would give warning that something was wrong. The safe delivery of cargoes can depend upon this seamanlike precaution and the daily taking of soundings should never be neglected.

High soundings in ‘empty’ tanks: Warning of a leak is provided by increased soundings in ballast tanks or void spaces and must be investigated promptly. First it may be necessary to pump out the compartment. Provided that the flooding is not too rapid such an investigation will normally involve entering the compartment – taking all the proper precautions when entering an enclosed space (see chapter 21) – and searching for the source of the leak. When the leak has been found, the problem can be assessed and the correct action chosen.

Interpretation of high soundings in a cargo space: When increased soundings are found in a cargo space loaded with bulk cargo there are a number of possible explanations and each should be considered. The water may have drained from the cargo or leaked through the hatch covers. It may have entered through an unbattened access hatch or an uncapped sounding pipe. Water may have leaked through a fracture in the deck or the hatch coaming or through a damaged ventilator.

It is regrettable that officers of many ships have no accurate idea of the capacity of the hold bilge wells. This means that they cannot say whether an increase in sounding of 0.5 metres represents 1 tonne of water, or 10 tonnes. That makes it more difficult to assess the significance of any increase in hold bilge sounding. The solution to this is simple. Measurements should be taken when the holds are empty to prepare simple calibrations. Of greatest value are the sounding of the bilge when full and the approximate tonnage of water contained by the bilge when full.

When preparing calibrations for the hold bilge wells two important points must be remembered. If the sounding pipe does not run vertically the actual full sounding will be greater than the vertical depth of the bilge well (Fig.  5.9): it is the actual full sounding which is required, since that is what the sounding rod measures. On some ships a number of the bilge wells may have exactly the same dimensions, but every one must be inspected in case the arrangements inside any are different. Details of design near the engine room or in a ballast hold, for example, sometimes require one or two bilge wells to be of a different shape and size to the others or to have the sounding pipe positioned differently and soundings will be very misleading unless this is known.

High soundings caused by drainage from cargo: Aboard a ship which is well operated and well maintained the most likely reason for an increased hold bilge sounding is that water has drained from the cargo into the bilge. If there has been a similar increase in most or all of the bilge soundings this suspicion will be a virtual certainty, particularly if the cargo is known to be self-draining. Water is reported to drain from most mineral and coal cargoes during the course of a long voyage with consequent weight losses of 1 per cent total weight of cargo or more. In a Cape-sized vessel carrying about 22,000 tonnes of iron ore per hold the water draining from the cargo in

one hold would average 5 tonnes/day during a 40-day voyage if the 1 per cent figure was found to apply. Water will also drain from a grain cargo which has been sprayed with a wet fumigant during loading.

When water does drain from the cargo there are two important requirements. The water must be pumped out of the bilge and not allowed to flood the hold, and the tonnage of water removed must be recorded. The reason for removing the water is to prevent damage to the cargo and increased corrosion of the tanktop and to reduce difficulties for the trimmers when discharging. It must also be remembered that once the water has filled the bilge well and flooded back over the tanktop, it is much more difficult to be sure how much water the hold contains. Flooding of the hold from a leak would then become more difficult to detect. For all these reasons the bilges must be pumped as frequently as is necessary to maintain them at a safe level – no more than half full.

It is advisable to keep a record of the tonnage of water discharged from the hold bilges, as recommended by the UN Draught Survey Code²⁴ and in some trades it is a charterparty requirement. This can be done by taking soundings before and after each pumping of the bilges if calibration tables for the bilge wells are available, or by pumping all the contents of the hold bilge wells into a holding tank where they can be sounded before being pumped overboard. Such a record, if kept in a seamanlike and professional manner and signed by Master or senior officer, will be evidence of the tonnage of water discharged and will explain apparent loss of cargo weight.

High soundings  due to leakage into hold: When one or several soundings are found to be rising for no obvious reason a  problem must be suspected and the hold must be investigated for a leak. Whether the hold can be entered will depend upon the amount of space occupied by the cargo and the safety of the operation from the point of view of speed of flooding, shifting cargo and hazardous gases. If the hold can be safely entered, taking all the precautions required for entry into a confined space, it may be possible to find an explanation for the flooding. Evidence of water flowing into the hold may be detectable in the cargo beneath hatch covers or ventilators or below a fracture in the steelwork of deck, coamings or ship’s sides.

If the hold cannot be entered, a thorough external inspection should be made of the boundaries of the compartment in search for any fitting which is improperly closed or damaged. If the sounding is found to increase whenever the vessel ships water on deck, a leak at deck level should be suspected. If the flooding continues at the same rate, or an increasing rate, at all times it suggests that the damage is below water level. By using all the information available the most likely explanation for the flooding can be found and appropriate action can be taken. (See below and Chapter 21 for action to take in event of flooding.)

High level bilge alarms: When high-level bilge alarms are fitted and working as intended they provide a useful service to back up the daily soundings and to provide for occasions when adverse weather prevents the taking of soundings. High-level alarms will give prompt warning if hold flooding starts suddenly and proceeds rapidly. However, high-level alarms may not be fitted or may be out of order. Each high-level  bilge alarm should contain a delay circuit which prevents the alarm from sounding continually when the water level is low but the ship is rolling heavily. If no delay circuit is fitted the alarm will sound continually during  heavy weather and is likely to be switched off. If it is switched off for this reason the sounding must be regularly checked by other means.

Water ingress detector systems (WIDS) and alarms: Introduced in 2004 in accordance with IMO regulations129 WIDS are now fitted in the holds of all bulk carriers and also in the ballast, dry and void spaces forward of their collision bulkheads. They are designed to give early warning of flooding and to provide an indication of the speed of flooding of a compartment. Flooding is one of the most serious hazards of which bulk carriers are exposed and there are situations in which a flooding bulk carrier can sink within minutes.

High soundings detected by hull stress monitors: It is claimed that hull stress monitors will detect flooding of a bulk carrier because flooding will cause a change in the ship’s average level of longitudinal stresses. When an observer at sea notes that the vessel is becoming more heavily loaded there is only one likely explanation: flooding is occurring.

High soundings detected by draught gauges: In at least one instance hold flooding in a forward hold has been confirmed by a high reading on the forward draught gauge. Readings from draught gauges, list indicators and any other devices which indicate a change in the vessel’s condition should be  promptly and thoroughly investigated.

From the records of bulk carrier losses it can be seen that in many of the cases the ships’ Masters appear to have been unaware of the imminent danger they were in. Ship losses were frequently so rapid that the ship did not have time to send a distress signal. Many mariners lost their lives as a consequence¹²⁴. Actions to be taken when flooding is suspected are described in Chapter 21 but can be summarised here. All personnel except those investigating the alarm and keeping systems running should be mustered at abandon ship stations. An URGENCY or DISTRESS signal as appropriate should be transmitted. The decision to abandon ship must be the Master’s and the vessel’s lifesaving craft must not be launched unless the specific order to do so has been given by him. That order should be based on the knowledge that the vessel is truly sinking, that the depth of water beneath the ship is deeper than the vessel’s hull and that the speed of sinking might prevent later launching.

Cargoes such as high sulphur coals, iron ore, sulphur and salt produce corrosive liquids when wet and can do heavy damage to the fabric of the hold. When cargoes which may be corrosive are being carried the hold bilges should be tested regularly for pH (acidity). This procedure is described in the section of Chapter 19 devoted to the carriage of coal.