As the main cause of vessel loss is sinking, the maintenance, testing and monitoring of watertight hatches, doors and multiple cable transits on vessels is essential. A watertight hatch cover is designed to prevent the passage of water in either direction under a head of water for which the surrounding structure is designed. Many mariners may think hatches are robust, monolithic structures, thereby failing to appreciate the small tolerances on panel alignment and gasket compression. It is better to think of hatches as complex, finely-made structures, to be handled with care.
This has been recognised recently by marine insurers. The Swedish Club has released a report warning bulk carrier operators to pay attention to water damage. The 2018 Swedish Club report, Wet Damage on Bulk Carriers, which has been prepared in cooperation with DNV GL, and MacGregor, identifies heavy weather and leaking hatch covers as the most common and the most costly type of wet damage claim. With the average cost for a wet damage cargo claim being almost $110,000, this is alarming.
According to the report, wrongly applied and poorly maintained cargo hatch covers and sealing systems increase the risk of cargo becoming damaged by water. The most common wet cargo problems include leaking cross joints, and compression bars, rubber gaskets, hatch coamings, drain channels and cleats in poor condition.
As stressed in the report, proper weathertightness is a key factor in keeping cargo dry. To ensure that the hatch covers are weathertight the sealing system needs to be in a good condition.
This is demanded by the regulations: SOLAS Reg II-1/11.1 it states that hatches and watertight seals must be regularly tested: “Where a hose test is not practicable [sic] it may be replaced by [sic] an ultrasonic leak test or an equivalent test. In any case a thorough inspection of the watertight bulkheads shall be carried out.” The importance of continually maintaining seal integrity must take a more prominent position in ship maintenance scheduling.
How have seals been tested traditionally?
Chalk testing is used traditionally for visual inspection of the compression integrity of doors and hatches on vessels that hold the potential for flooding. Chalk is applied evenly around the knife edge, coaming compression bars or panel cross seams of doorways. The door/hatch is then closed and sealed. Once re-opened the rubber gasket which pushes against the knife edge is visually inspected for the chalk line. Any breaks in the chalk line indicate a lack of compression in that area. It must be noted that chalk testing is NOT a leak test, but only provides an indication of potential compression issues
The International Association of Classification Societies states that a chalk test must be followed by a hose test. The hose test is used in conjunction to determine the weather tightness of doors and hatch covers. The spray from a nozzle of 12mm diameter is sprayed from a distance of 1 to 1.5 meters with a water jet pressure of 0.5 ms-1 This test should help identify any leakage from the hatch joints, although the exact location of the leakage sight cannot be pinpointed. Various drawback come with this test, for instance;
Both of these tests are time-consuming and sometimes completely impractical. Some circumstances have been highlighted that prevent this test from being conducted such as the hose test if dry cargo is within the hold being tested but these tests conducted at port or in dry dock will never reproduce conditions when the ship is at sea and therefore cannot expect to achieve the same standard. Claims resulting from water damage due to leaking hatch covers still contribute a huge part of the overall loss figures on dry cargo ships. This method is neither accurate nor time effective.
The accuracy of results is open to human error. The application of the chalk must be very accurate in order to avoid misdiagnosis. A false application of chalk could be construed as a compression issue.
In fact, the limitations of using chalk and water hose testing have been demonstrated in case studies from the Swedish P&I Club’s Recent Report:
CASE STUDY 1:
Before loading with grain the cargo hatch covers had passed a water hose test. Once the vessel was fully loaded the cargo hatch covers were then sealed with tape. The cargo was mostly damaged underneath the cross-joints. During the voyage the vessel encountered heavy weather at Beaufort scale 10 with large waves and a swell which covered the hatch covers in water. A visual inspection of the cargo hatch covers, rubber gaskets, securing devices, valves, ventilators and drainage channels found them to be in order. During the voyage the tape by the cross-joints between the forward and aft hatch panels of two holds had peeled off. A chalk test was carried out and this did not show any imprints on the rubber gaskets. At the discharge port it was found that part of the top layer of the cargo in a number of the cargo holds was damaged by seawater. Further investigation revealed that there was no contact between the compression bars and rubber gaskets on the cross-joint panels. In addition, an ultrasonic test identified that the cross-joints between the forward and aft hatch cover were also leaking.
CASE STUDY 2:
A vessel had loaded wire coils. After loading was complete the crew taped across the transverse beams of all the cargo holds. The vessel sailed through heavy weather that lasted for about two days. During this time the vessel was pitching and rolling heavily. The cargo hatch covers were covered in water. When discharging at the destination port it was found that the steel coils in the top tiers were corroded. The coils below the centre line and folding seams were the most affected. The surveyor tested the water integrity of the cargo hatch covers with an ultrasonic device which detected significant defects to the sealing arrangements.
How can ultrasound change this?
The Swedish P& I club recommend using Ultrasound. As stated in their 2018 report “A much more effective method is to use an ultrasonic device, which is designed for this purpose and can pinpoint the area which is leaking, and if the compression of the gasket is sufficient. The advantages of using this type of equipment are evident, since ultrasonic tests can be carried out during any stage of the loading without risking cargo damage. The test can also be completed in sub-zero temperatures. The ultrasonic test should be carried out as per the class requirements.”
Ultrasonic testing is a dramatically more sensitive, accurate and reliable method for testing cargo hatch covers, bulkheads and doors for watertight integrity on all vessels. A multi-directional ultrasound emitter is placed in a hold. The opening being tested is then sealed and the receiver switched on ready to receive any leakage of ultrasound via a set of headphones. An increased reading of ultrasound signal signifies an issue with the integrity of the door/hatch. Further, and closer inspection will allow identification of any specific leakage sight along with the severity. This test will take approximately 10 minutes and requires only one operator.
Ultrasonics is proven to be the quickest, easiest and most efficient method of testing watertight & weather-tight seals of hatch-covers, doors, multiple cable transits. The Portascanner® WATERTIGHT is the most accurate model of its kind – proven to 0.06mm (+/-0.02mm). This is designed primarily to enhance the ease and accuracy with which critical watertight, airtight or weather tight seals can be inspected for leak sites or areas of reduced compression in the seal. The ultrasound generator emits a modulated signal of a specific frequency of ultrasound (in most cases 40,000Hz). The receiver then picks up the signal and converts it into a result indicating watertight integrity. The easy to use Portascanner® WATERTIGHT allows crew member to check for failing seals whilst at sea which allows for prompt maintenance.
Coltraco Ultrasonics focus on benefitting the crew; designing innovative ultrasonic solutions which the crew will be happy to use by being easy to operate, quick, accurate and a better method to traditional techniques. Thus increasing the likelihood of tests being regularly conducted, in line with regulations and even going above and beyond for more frequent testing. By so doing, the crew will be creating a safer ship.