Introduction
Dry docking vessels with airbags means hauling out vessels to dry land with marine airbags and winches. This technology suits for ship repair and ship recycling industris, also good for emergency precautions of vessles. With airbags people can haul out vessels from water then move them to another place for repair, breaking or store. After repair or modification , the vessels can be re-launched using airbags. The basic principle of airbags ship launching or haul-out is changing the force of sliding friction into rolling friction to save energy, just like ancient Egyptian using logs to transport heavies.
Advantages
- Flexible. Using airbags people can haul out vessels at temporary land or beach and re-launched them after repair. In remote areas without infrastuctures, using airbags to dry dock vessels is the most economical and fast way. Airbags act like foldable dry docks enable people haul out ships everywhere.
- Fast. No need cradle, rails or concrete, set up winch system then can pull ships to the land. For one vessel with 1000 tonnes lightweight, the hauling takes no more than three days.
- Safe. Marine airbags are made from rubber ,they have much bigger contact area with vessel bottom compared with cradles or shiplifts, so much safer for vessel.
- Economical. Minimum infrastructure required for airbag ship drydocking, save time and money.
- Green. No harm even no change to the environment, easy to get appoved by authorities.
Limitations
- Tidal change. Big tidal change is favourable to airbag ship drydocking operations, especially for big ships with deep drafts but is not the prerequisite.
- Hauling capacity. It is limited by the winch pulling capacity and ramp angles. LT 6000 tonnes vessel had been succesfully pulled to land by this technology.
- Vessel bottom. Flat bottom is favorable, fishing boats and tugboats can be dry docked with airbags but the boat weight will be limited.
Basic Equipment
- Marine airbags. Airbags with 1 meter diameter are most often chosen since working heights of airbags for haul out usage are about 30-40 centimeters. And shorter airbags are convenient to operate.
- Pulling system. Winches with blocks are relibale and recommended, bulldozers and excavators are alternatives.
- Air compressors. The bigger the better, minimum requirement is 0.7 MPa and 3 CBM per minute.
General procedure of ship hauling with airbags
- Clean ship bottom and landing beach.
- Move the ship get near the shore at high tide time.
- Fasten the vessel with guy ropes and wire ropes from the winch. Generally ships need to be controlled by 4 ropes from 4 directions to ensure its precise landing spot.
- Select a reasonable position near the bottom of bow to insert marine airbags which will act as the fulcrum for winch to move the ship. If it is difficult to insert airbags at the bottom of bow, people may insert them from one side to another side. For heavy ship the quantity of bow lifting airbags should be added until they can lift the bow. For V shape bow vessel the bow lifting marine airbags should be inserted at the position where they can have bigger contact area with the bottom of vessel. Also, people may place airbags at appropriate positions at low tide and position the vessel upon marine airbags at high tide, and then inflate airbags to lift the vessel. People should make the vessel haul-out plan according to the practical situation.
- After the bow lifted, start the winch to pull ship towards lands and insert more marine airbags under the ship until ship is pulled to the land completely .
- Pump marine airbags further to lift ship bottom higher then insert keel blocks according to plan.
- Deflate airbags slowly to make the ship rest on keel blocks. Generally lower bow first.
- Remove airbags.
Ramp or slipway for airbag ship docking
The slipway’s parameters which include length, width, slope angle, bearing capacity and elevation should be designed base on calculation results.
- The length and width of airbag launching slipway can refer to traditional end launching slipway design.
- The bearing capacity of airbag launching slipway can be lower than traditional slipway because airbags get more contact area than traditional launch trolleys. And that is why airbag ship launching can save slipway investment.
- Generally slipway for airbag launching and haul out will have shore part and under water part. The shore part has small slope angle and the underwater part has bigger angle . The length, angle and structure of underwater part are very important for the success of launching and airbags’ safety.
- For temporary launching or dry docking, compacted natural ground with suitable slope is accepatable.
- For freuqently launching or docking ramp, concrete is the best.