Keeping hatch covers watertight

Water ingress from whatever cause is one of the main reasons of damage to cargoes onboard ships and occasionally, in extreme cases, can lead to the foundering of a vessel as highlighted in a number of recent bulk carrier casualties. The cause is often seawater entering cargo spaces through leaky hatch covers and any means to assist crews to check and maintain the weather and water tightness of hatch covers should receive maximum publicity. One such tool was recently launched by multinational company MacGregor. Its handheld ultrasonic tightness testing device, called Sherlog, enables a thorough and systematic checking of the tightness of key cargo access equipment such as hatch covers, bow, stern and side cargo doors and ramps. Testing is done easily and cleanly and, unlike hose testing, does not interfere with other shipboard activities during the short and busy time a vessel is in port. It can even be carried out with the hold already loaded. The manufacturer also claims Sherlog can be used to test bulkheads, portholes/windows and access doors and hatches to lower deck spaces and engine room spaces. Accuracy and reliability are claimed for Sherlog since it allows the user to identify a leak site quickly and without guesswork. The device has already received LR type approval and the hatch cover division the DNV service supplier approval certificate. Although ultrasonic-based leak detectors have been around for a number of years, a unique feature of the Sherlog system is its integrated data-logger. This allows data to be downloaded to a PC/laptop for subsequent use as a periodic survey information source that can easily be transmitted by email. For example, hatch cover leakage data can be downloaded for safe logging as required by IACS UR Z17 and classification societies. Consisting of two pieces of equipment, a portable ultrasonic multi-transmitter and a compact hand-held detector, the system can be used in a variety of situations. For example, when used to check hatch cover tightness, the multi-transmitter is placed in a central position in the cargo hold where it produces a uniformly distributed omni-directional sound field throughout the hold space. On deck, the hand-held detector is used to measure any sound energy leaking through the hatch cover seals, both around the hatch coaming and along panel joints. The transmitter sound is produced in a narrow frequency band and the detector is tuned to filter out just this band. So the inspector, wearing a headphone and reading a digital display, is not hampered by surrounding noise and can positively detect any leak greater than zero decibels. The detector logs the recorded dB values in its memory, which can then be downloaded. Surveyors, shipyards, shipowners and operators, charterers and P&I clubs will all find the Sherlog a valuable tool. The system is reliable in most weather condition even below freezing, says MacGregor, and has the advantage of providing a tamper-proof logging device requiring only one person to operate it. Experience has shown that since the early 1990s, when dry cargo ships were being increasingly inspected with this type of system, there has been a spectacular fall in reported damage to cargoes. Figures show that the number of incidences dropped from about 70% of all reported cargo damage in 1990 to almost zero (there was only one case last year). The ultrasonic technique is therefore extremely reliable, ergonomic and appears to be foolproof.