Changlin Ship Launching Air bag — How to Select Air bags?

 

The type code and specification of air bags should be selected according to ship type, dimensions, and launching weight of the ship.

 

Air bag bearing capacity:

The bearing capacity is different if the air bags' type code and specification are different. To guarantee safety, air bag's capacity should meet the requirements of the ship launching weight. Before the ship launching using air bags, launching calculation should be carried out. The total air bag bearing capacity should be calculated by ship launching weight. According to the total bearing capacity and ship bottom area, the quantity and type code of air bags will be selected.

Table 3 shows the corresponding relation of ship launching weight, air bag unit length bearing capacity and relevant type code.

Air bag diameter

The air bag diameter is mainly decided by the ship blocks' height. Ship lifting from blocks is the most important stage in the air bag launching process.  At this stage, the ship whole weight is to be lifted by air bags, and the air bag working height must be larger than the block height. The air bag diameter should be selected according to the block height. The air bag diameter must be increased by 0.5m-0.7m, which is based on the block height, otherwise the air bag bearing capacity may be not enough.

At present air bags with diameter less than1.2mcan only be applied on small ships. Air bags with diameter1.5mor1.8mare used to launch over 10,000DWT ships. For block height larger than0.9m, diameter1.5mair bags are mostly chosen for the launching. For block height larger than1m, diameter1.8mair bags are preferred.

Air bag length

For small ships, the air bag length should be slightly larger than the ship molded breadth. Air bag length can be decided by the formula: B<L<B+D (where: B is the ship molded breadth; L is air bag length; D is air bag diameter) (see fig.5)

When moving a tug, a fishing boat and the like ship with small block coefficient, air bag ends must extend out of the ship sides, to get good stability of the ship moving. The extended length at each side should be slightly larger than air bag diameter. 

For medium ships, the extended length at each end shall not be very long. For example, a normal ship like cargo ship with block coefficient CB > 0.75, airbag should be equal to the breadth of flat bottom at mid-ship (the breadth excludes arc part at bilge).

For large ships, if existing airbag length is shorter than the flat bottom breadth, the longest air bags should be ordered. The airbags layout can be interlaced mode or twin-row mode. We would like to provide advice and suggestion according to customer's specific situation.