Preparation For Air Bag Used For Ship Launching

Airbag is more and more widely applied in ship docking and launching. The application method is ceaselessly improved. The airbag application method for common medium ship launch is described as follows:

1. Based on calculation result, enough rolling airbag and lifting airbags, towing machines and air compressors are prepared. Before use, an airbag shall be inflated and tested without load (inflating pressure can be 1.25 times safe work pressures). In case of air leakage, the airbag must be repaired before use.

2. The roads for ship movement, including the road from the shipbuilding berth to ramp, must be cleaned up and flattened. Sundries must be removed from the roads, especially sharp iron nails and stone on the road, to avoid piercing the airbag. The ramp shall be enough long and wide in water.

3. All the protruding sharp corners and burrs on castings like “A” bracket and stern post and so on shall be ground flush.

4. Fasten the hull with the steel cable of traction winch.

5. Close all the sea chest valves on the ship, fix the rudder and propeller.

6. There are many ways to remove all blocks and fill in the rolling airbag. Here we propose two methods as follows. User may choose one based on the equipment conditions such as ship weight, amount of the airbag and so on.

(1) For light ship, the bearing capacity of the airbag is large enough to lift the ship away from blocks and therefore blocks can be removed directly and fill in the rolling airbag.

(2) For heavy ship, lifting airbag(or its combined force) can be adopted to lift the bottom. Before the lift, firstly specify the optimum position of the pre-pivot and lifting airbag. According to the figure, the closer the pre-pivot to the center of gravity the better, however, it will cause too many blocks in front of the pre-pivot which means large workload to remove the blocks manually. Therefore, the position shall be determined reasonably considering such elements as ship length and so on. The lifting airbag shall be located in the end if possible. However, the location is also subject to line shape of the stern as the lift of the lifting airbag will not be large enough if the bottom is too far away from the ground. Under this circumstance, it would be better to move forward. Therefore, the optimum position of the pre-pivot and lifting airbag shall be decided after specific calculations as case varies from ship to ship.

7. Adjust pressure in the airbag so that the bottom can be lowered to appropriate working height.

Make sure that the bottom will not touch the ground while moving the ship. For average small-sized ship, the working height could be chosen within the range of 0.2-0.3m.

8. All airbags shall be pointed at the center of the ship and perpendicular to the launching direction.

9. Start the traction winch to release steel cable slowly followed by slow movement of the ship. When the forefront airbag located in the front part separates from the bottom, it shall be put into the stern immediately and fill in the airbag according to the arrangement space of the airbag defined in the calculations.

10. Repeat the above process to move the ship to waterside slowly. When the airbag can’t be filled in, block the river and no ship is allowed to pass.

11. Evacuate personnel in the dangerous zone, inform staff on the ship to get ready. When conditions such as water depth and so on are enough, cut cable or unhook so that the ship can launch quickly. If the river is too narrow to realize quick launching, release the cable slowly by traction winch to launch the ship slowly.

12. For large ships, it’s necessary to install anti-slip device.