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Ship launching and haul out with airbags

Gneral introduction of Ship launching with marine airbags



The traditional ship launching methods include end on launching,side aunching and dry dock floating.Most airbag ship launching are end on launching.


To launch a vessel with marine airbags,people should set up holding system first,then lift vessel from keel blocks,remove blocks and move the vessel with airbags into water at last.



      Set up holding system for airbag ship launching                                            Jack up vessel from keel blocks


General airbag ship launching is carried out on a ramp,with suitable angle the vessel can move into water by the sliding force its gravity once the holding system is released.


There are two methods of holding system releasing correponds to 'free launching'and'controlled launching'separately.The free launching means the connection of holding system with vessel will be unlashed when vessel is launched,it needs wide water area.



           Free ship launching with airbags                                                                             Ship floats after launching


 In case the launch water area is limited, the controlled launch is preferred. Wincheswill be released slowly to control the movement of vessel,once vessel floats,it will be stopped by winches’pulling.




Applicability ofairbag ship launching


The airbag launching feasibility of aspecified vessel should be calculated first but there are some simple rules mayhelp people to know launch feasibility quickly.


The majority of airbag ship launching isend launching but side launching is feasible only when some rigorous conditionsare satisfied.


Vessel whose DWT below 70000 tonnes may belaunch with airbags. Regarding bigger vessels only by calculation people canknow the launch feasibility.


Airbag shipdocking/beaching introduction


Airbag ship docking means people haul outvessels to the land with pulling winches and rolling airbags. Comparing withtraditional trolley docking method. This system has less demand of ramp/slipwayand also the pulling winch.




Generally people will ground or nearlyground vessel then insert airbags to lift the bow first in low tide time.Whenwater level increasing,vessel will be pulled forward thus more rooms underneathvessel become to be aviliable for more balloons. Step by step vessel will beentirely suppoted by ballons.




When vessel arrives at first its finalposition, by deflating balloons slowly vessel sits on keel blocks steadily.


Facilities forairbag ship launching and beaching


Winches


Winches are deployed to hold vessels beforethey can be launches or pull vessel out of water.Generally speaking winchesdeployed in airbag ship launching or beaching project are electrical, low speedtype. Their pulling speed is below 10m/minute.


For safety reason winches should beequipped with one extra set of manual brake. In case of electric brake systembreaks down or power loese accidentally people can brake thee wire ropes withmanual brake.



Groundanchors(winches foundations)


Ground anchors are designed to fix winches.Ground anchors can be cast concrete structure or buried heavy objects.

The safe load of ground anchor should haveat least 1.5 times safe coefficient.


To enable the instllation of winc andpulleys, ground anchors should have the connection pad eyes.


Wireropes


Wire ropes should have at least 3 timessafe coefficient. The use of rotation-resistant wire ropes will not likely berequired.


Pulleys(Blocks)


Pulleys are deployed in airbag shiplaunching or ship beaching projects to magnify winches ’pulling force.Generally traveling blocks will connect with vessel, standing blocking willconnect to pad eyes on ground anchor.


There are many techniques to reeveblocks.But most important purpose is to avoid the twist of blocks,especially tetraveling blocks.


Conventional wire ropes will twist or unlayslightly when they are tensed.To eliminate odd-part reeving where th wire ropedead end is on th traveling block is very important because wire ropetorque,from the application of load, is greatest at the rope dead end.


Aircompressors


To pump airbags, the air compressor needsto have 7-8 bar inflating pressure and not less than 2 CBM per minute flowrate.


Airbag Arrangement


Airbagarrangement is very important for sefe ship launching or docking.All conditionsinclude vessel dimensions, the weight distribution ,launching slipway and waterlevel shoule be considered to decide airbag arrangement.


Vessel length


Allairbags should positioned center to center with the vessel. More airbagsdeployed for the project is better for the safety, The maximum space of airbagsshould not exceed 6 maters. The minimum spaces of airbags are decided byairbags’ diameters. The follow chart shows minimum spaces of different airbags.


Airbag Diameters

1.0m

1.2m

1.5m

1.8m

2.0m

Minimum Spaces

1.5.

1.8m

2.2m

2.8m

3.0m

 

Vessel Width


Whenairbags’ length is longer than vessel’s width, airbags should be positionedcenter to center with vessel.


Whenairbags’ length is shorter than vessel’s width but longer than 1/2 vessel’swidth, airbags should be positioned as crossover type.


Whenairbags’ length is shorter than 1/2 vessel’s width,arebags should be arrangedas two rows.We don’t suggest arrange airbag in three rows even for extra widevessel or platform launch.



Vessel Gravity Distribution


It iseasy to understand that under heavier part of vessel, There should be moreairbags.


Launching Slipway and Water Level


The waterlevel and slipway affect the working height, space of airbags arrangement.


Slipway Ramp Design


The slipway’sparameters which include length,width ,slope angle ,bearing capacity andelevation should be desgined base on calculation results.


 They are decided byvesssel’s parameters and water level.


Thelength and width of airbag launching slipways’ can refer to traditional endlaunching slipway because airbags get more contact area than traditional launchtrolleys.


Generallyslipway for airbag launching and haul out will have shore part and under waterpart. The shore part has small slope angle and the underwater part has biggerangle which can give launched vessel more slide forward force and enableairbags roll out of bottom of vessel. The length,angle  and structure of underwater part are veryimportant for the success of launching and airbags’ safety.


If possiblecorrete slipway is the best for airbag launching and haul out.For temporaryvessel launching ,strong enough ground is acceptable but slope angle shouldsatisfy the demand.

 

Basic informationneeded for design of ship launching procedure.


1.       Type of vessel?

2.       LOA and length of vessel?

3.       Molded breadth of vessel?

4.       Vessel’s actual launched weight(gravity weight)/weight without cargo?

5.       Block coefficient of vessel

6.        of stern and bow

7.       Gravity center position

8.       Type of ground ship is builton?(Dirt, concrete, etc)

9.       Height of wooden blocks thatsupport vessel

10.   Angle degree of slipway?(Land,notunder water)

11.   Water survey data of end ofslipway area

12.   Tide schedule at site

13.   Distance from vessel stern to theend of slipway

14.   Picture of vessel(stern, bow)andslipway


Risks Aanalysis




There arerisks of ship launching with airbags. When accidents occur the marine airbag ismost often blamed. But according to our investigation more than 80% accientsare caused by inappropriate airbag arrangement and bad launch conditions.

The mainfactors that affect launch satety are launch ramp ,water level and facilities.