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.