Airbag Ship launching can be adapted to launching of most ships, from flat bottom barges to V hull fishing boats , from hundreds tons tugboat to ten-thousand tons bulk carriers, they can rely on airbags for launching. Airbag ship launching has strong adaptability to terrain, and large tolerance for launch slope, ground bearing capacity, water level.,etc. literally a good technology should be like this, but this kind of large latitude can give people the illusion that airbag launching is omnipotent and does not need to be taken seriously. ISO17682 is the standard of ship launching utilizing air bags can give some basic principles for ship launching.
Eversafe Marine is one pioneer in airbag engineering fields, completed hundreds of vessels’ launching and dry docking with marine airbags. During their consulting and supervising jobs, they found and corrected many ship launching mistakes. They summarized ten common mistakes in airbag ship launching projects, which may help clients avoid failure and risks in ship launching projects.
1. Unreasonable ship launching ramps
Airbag launching requires a suitable ramp with a reasonable slope and proper bearing capacity, and generally the ramp needs to extend into water. The most easily overlooked factor in launching project is the ship launching ramp: some ramps are cliff shape without any extension into water, some with improper slope angle, some ramp can trap airbags. Those mistakes can cause accidents and get ship structure damaged during the launch. Below picture shows a typical improper launch ramp, the ship hull suffers a great bending moment and may even break into two pieces. In fact, a simple modification of the natural ramp can avoid or greatly reduce the damage to the hull during the launching process.
2. Insufficient water level for launching
The airbag ship launching needs to have sufficient water depth, which is not only a requirement for the smooth floating , but also a guarantee for the safety of ship. When ship launches at a insufficient water level, marine airbag may withstand 5 times of the normal pressure , which can cause airbag explosion accident and damage the hull.
3. Improper installation of winch holding system
When using marine airbag to launch the ship, it is necessary to have winch or ground anchor to hold the ship before final releasing. The proper installation and configuration of the winch is crucial to the safety of vessel launching. However, people can easily find careless or improper installation of winches in many ship launching projects. In the pictures below, there are typical careless winch installation cases.
4. Use airbags inflating or deflating to start ship launching
Such operation usually is done by experienced engineers, they know the critical point of ship starting but this operation is very dangerous. If on a slope with a suitable angle, the sliding force of the hull and the frictional force of the airbag reach an approximate balance, by adjusting airbag pressures it is possible to start the ship moving. But this is an unreliably controllable status: strong wind or other disturbances may break the balance, start the moving at unwanted time and people can do noting to remedy the irreversible consequences.
5. Irregular pulling lugs
Usually the pulling or holding system is connected to the hull by welding lugs/pad eyes at the keel position of the hull. The size of the lug plate, the welding position and the welding strength need to be verified by calculation. In the actual launching project, it is often found that the setting of connecting lug is very irregular. For example, as shown in the figure below, a hole is directly opened on the bilge keel , and then connected with a wire rope, even without one shackle.
6. Insufficient airbag quantity
This mistake happens often when people launch barges with airbags. Barge has wide flat bottom with light weight, people tend to use fewer airbags for barge launching.If airbags spacing is too large, the hull will be subjected to a large bending moment during the launching process, resulting in hull deformation.
The reasonable number of airbags required for boat launching is not only determined by vessel weight and airbag lifting capacity, but also the maximum allowable airbag spacing which varies for different vessel launching.
Regarding calculation of required airbag quantity for one ship launching, people may refer to ISO 17682 Ships and marine technology — Methodology for launching ship utilizing air bags.
7. Wrong selection of airbag sizes
For tugboats and fishing boats that have high gravity centers and small flat bottom areas, people should select small diameter airbags for the launching.If have to use big diameter airbags due to limit of using high support blocks, at least at launching moment, people need to low down airbag working height.
8. Inappropriate set of airbag working pressures
Before the ship is launched, usually it is necessary to adjust the pressure of the airbag according to the calculation results. Higher airbag pressure will not increase the launch safety, on the contrary it may cause ship hull damage.
9. Inappropriate set of airbag working height
Normally airbag working heights at launching should not exceed the ones when lift ship from support blocks.
10. Inappropriate set of airbag spacing
There are minimum spacing requirements for every diameter of ship launching airbags. If their spacing is too small, airbags possible squeeze each other during the rolling process and cause accidents. On the contrary, if the airbag spacing is too large, the hull will be subjected to a large bending moment.