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Marine Rubber Air Bag

Marine Rubber Air Bag

marine rubber air bag
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marine rubber air bag

marine rubber air bag is well known as ship launching airbag, marine airbag, rubber airbag, landing airbag, inflatable airbag, air balloon, rubber pontoon. It is composed by airbag body and terminal iron part. The airbag body is composed by natural rubber strength fiber material through vulcanization processing; The terminal iron part is made of cast iron, it is combined closely with the airbag body; One end is for pulling when moving the airbag, and the other is for charging and discharging the air.

marine rubber air bag size range: Diameter is 0.6-2.8m, Length is 5-24m, layers usually from 3-10layers.

Ship launching inflatable Roller Bags are widely used in ship launching, landing, lifting and moving heavy goods, salvaging stranded boats. And are very popular with shipyard, ship owner, and marine supplies company now.


Operating procedure

1 All obstacles shall be cleared along the way of the air bags, including the ship bottom.

2 The bow of the ship shall be tied to the windlass with mooring steel wire ropes. One end of steel wire rope shall be tied to the strengmember of the ship such as a bollard or a special horn, the

other end shall be tied to the pulley set of the towing system.

3 According to the planning of 6.2, air bags shall be placed underneath the ship.

4 The air bags are to be filled from the stern to the bow. Initially, the air bags are not to be fully

inflated. Having inflated all air bags and ensured that they made contact with the ship's bottom, the airbags shall be filled to the specified pressure.

5 When the ship bottom is lifted higher than the docking blocks and the air bags are bearing the weight of the ship, the docking blocks shall be removed. After all the docking blocks are removed, adjust the internal pressure of the air bags to make the force balance.

6 After the workers and other personnel who are going to stay onboard during the launching have boarded the ship, remove the ladders and gangways and so on.

7 Depending on the conditions of slipway and area water, one of the following launching methods may be used:

a) if the area water is wide enough, one can launch the ship by moving the ship to the water's edge, disengage the windlass, remove or cut the tow line and let the ship slides into the water by itself;

b) if the area water is not wide enough, use the windlass to control the launching speed and let the ship glide into the water slowly;

c) if the stern of the ship is built directly over the water and no windlass is available, the ship shall be secured to the ground anchor by the rope before filling the air bags. Tminimum water depth needed for launching is to be calculated. The ship may be launched by herself into the water by

cutting off the rope or letting off the ground anchor when there is enough water depth.

8 After the ship is afloat, tow and secure the ship to the wharf, measure the bow and stern drafts; inspect each compartment for leakage.

9 All air bags shall be retrieved.

10 All data of launching operation shall be recorded


How to arrange/choose the windlass when using the marine rubber air bags? 

* A windlass shall be used to control the movement of the ship. 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. 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).


1. F= Qg* Sinα-μQg*Cosα+ Q v/t

2. Fc≥KF/(Nc*Cosβ)


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.

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