DNV GL - Service Suppliers Performing Tightness Testing of Hatches With Ultrasonic
Equipment on Ships, High Speed and Light Craft and Mobile Offshore Units .
“2.9 Operational procedures
— from 1 dB to 10% of OHV shall mean that the hatch cover is considered weathertight, subject to verifying
the design and the condition of the hatch cover, the coaming and the drainage arrangements
— above 10% of the OHV shall mean that the hatch cover is considered not to be weather tight and that corrective action to gaskets and drains is required.”
DNV GL states that anything under 10% of the open hatch cover reading is considered weathertight. This reading must be reported in decibel (dB) to comply with regulations.
As explained below, calculating 10% of the decibel scale can be complex. To counteract this problem, the Portascanner® WATERTIGHT can test for leak sites in both decibel (dB) and in the linear scale.
As you can see, in the below graphs showing both the linear and dB scales, the linear scale increases at a constant rate, unlike the decibel scale. It is easier to work out 10% in the liner scale because of this. Therefore, we suggest testing in the linear scale and then converting to dB as this is easier for the crew. The converted linear reading can then be used to comply with regulations, as per the above. The Portascanner® WATERTIGHT has a “MODE” button which instantly converts linear readings into dB readings, which is designed so that the crew can really easily comply with regulations.
Keywords:Shipping,Fire Safety,Fire And Sea,Ultrasonic Liquid Level Indicators