Airbag Launching System Frees Ship From No-Fixture Ramp

Evergreen Shipping Supplies Co. Ltd. (Qingdao, China) recently announced that it successfully launched a new-build 20,000-deadweight-tonnage ship from a no-fixture ramp with its airbag launching system in Jiangsu province, China.

The 150-meter-long by 21.6-meter-wide cargo ship was built on a 200-meter-long concrete ramp without a fixture or anchor block. The angle of the concrete ramp was 0.86 of a degree. The inland river on which it sat was 350 meters wide with water depths of seven to 11 meters, and the distance between the ship stern and the end of the ramp was 15 meters. Because there was no anchor block on the ramp, no winch was available, Evergreen representatives said. The main challenges of the project were starting the ship launch and keeping the ship from slipping when moving it off the wooden blocks, they continued.

In a low tide period, the river was dredged and sandbags were placed to fill pits in the riverbed, Evergreen representatives explained. Thirty-four marine airbags 1.5 meters in diameter and 18 meters long were placed between wooden blocks according to a computer-simulated calculation, they continued. The airbags were inflated in such a way as to limit the ship’s slipping to a maximum of 0.57 of a degree when raised, Evergreen said.

Airbags were inflated from the stern to midship, one after the other, until the center of gravity was exceeded, Evergreen said, and further inflation from bow to midship lifted the entire ship. According to Evergreen, after all supporting wooden blocks were removed, airbags at the bow were deflated to adjust the ship’s gradient angle to 0.45 of a degree, which would make the ship safer from any unexpected slipping.

As the tide rose, airbags were inflated and deflated to keep the ship’s gradient angle at 0.57 of a degree, Evergreen said. An excavator grab, with its shovel wrapped in tires, was used to push the bow, the company said. After two pushes, the ship started to move slowly by riding the rolling airbags, and the movement was self-accelerated until the stern floated because of the ship’s increasing gradient angle, the company continued. It took 62 seconds from the start of the ship’s movement to total float, while the preparation took more than 12 hours, according to Evergreen.

The company said the main instruments of its airbag launching system are marine airbags, air compressors and regular winches. The sausage-shaped marine airbags are made up of rubber layers with rubber-dipped synthetic-tire-cords as reinforcement material. They have one to two-meter diameters and are six to 20 meters long. One marine airbag 1.5 meters in diameter and 18 meters long can hold more than 200 tons, Evergreen representatives said. For more information, visit http://www.evergreen-maritime.com.