For more than a century, mariners have calculated the weight of cargo loaded on vessels by comparing visual marks painted on the outside of a ship’s hull both before and after it’s loaded.
The practice has its drawbacks, however, since observers have to take those readings while standing at water level on the deck of another vessel or on the port’s quay, a process that’s prone to inaccuracy and can expose the observer to dangerous conditions. But the industry has stuck with the practice, since mariners can’t very well park a ship on a scale, like a tractor-trailer at a highway weigh station.
Now one company says it has a better way. New Jersey-based inspection and certification firm SGS has created a draft survey tool (DST) that allows inspectors to take draft mark readings for a ship or barge while standing on the deck of the vessel itself, improving both precision and safety.
After pilot-testing the invention for 18 months, SGS is now marketing the device for use in the fertilizer trade across North America, where the old-fashioned “hit or miss” approach has occasionally led to serious disputes between the shipper and receiver due to inaccurate measurements, the company says. Users can choose between the original DST device, which automatically saves measurement results to a cloud database, and the slim-sized DST Lite, which is small enough to fit into the narrow gaps between barges on the Mississippi River and transmits its results to an app on the surveyor’s smartphone.