How to arrange/choose the windlass when using the marine airbags?
* A windlass shall be used to control the movement of the ship when use the marine airbags. Tow system that comprises windlass,
steel wire rope and pulley set shall be securely fastened to the ground anchor in front of the berth.
In general, a slow windlass shall be selected for ship launching when using marine airbags. The veering speed of the windlass
shall be 9 m/min to 13 m/min.
*The forces of the windlass and the steel wire rope are shown in below picture when the ship is being
launched and before gaining any floatation. The maximum tensile force of the steel wire rope shall be
calculated in accordance with Formula (1). The hauling force of windlass’s steel wire shall be checked in accordance with Formula (2).
Using marine airbags to launch a ship
1. F= Qg* Sinα-μQg*Cosα+ Q v/t
F is the maximum pulling force of the steel wire rope when the ship is being launched (kN);
α is the angle between the ship, which is borne by air bags, and the horizon (degree);
μ is a friction coefficient of the rolling air bags on the slipway. It shall be determined according
to many factors such as gradient of the slipway, condition of the ground, configuration and
internal pressure and arrangement of air bags;
v is the speed of the ship in motion (m/s);
t is the time for the windlass to brake the ship motion (s);
Fc is the tensile force of the steel wire rope of the windlass (N);
K is the safety coefficient, in general, K = 1,2~1,5;
Nc is the number of the hauling wire ropes on the moving tackle;
β is the angle between the direction of maximum pull force (F) and the steel wire rope (degree).
In general, it is not to be greater than 6°.
* Windlass shall be securely fixed to the ground anchor. The design load of ground anchor shall
meet the requirement of the calculated pulling force (F).
* The steel wire ropes shall meet the requirements of ISO 2408, with capacity of the calculated
maximum pull force (F) or the calculated tensile force (Fc). The allowable load of pulley set, shackle, steel.
* wire rope and rope clip shall meet the calculated pulling force.
* Windlass shall be checked and maintained on a regular basis. Steel wire ropes shall be inspected
and, according to the manufacturer's specification, be replaced on a regular basis.