when the stern drops abruptly, airbags may burst or launch ramp end collapse due to strike moment then vessel bottom collide with ground. On the other hand, if stern drops much down the bow will rise high that make airbags under bow can not support it anymore. When bow drops down at last there will be a big strike moment imposes on balloons so balloons may burst and cause the bow collide with ground.
Airbag burst when stern drops fast
Airbag bursted when stern dropped down
Airbag burst when bow drops fast
  Bow rised high during the launch
 Slipway broken due to ship bow impact
To launch a ship at deficient water level is dangerous but if have to do it peole may take some remedy solutions such as extending slipway of underwater part or increasing ship buoyancy by adding buoyancy tanks/airbags.
Other important factors effect airbag launching safety:
Ship launching risks analysis-Â ramp,
Ship launching risks analysis-hold system
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