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The Ultimate Guide to Use Marine Airbags for Ship Launching

Airbag ship launching & dry-docking offer shipyards a cheaper, safer and eco-friendly option than traditional methods.

Ship launching airbag (refers to "air bags") that can be used for launching a vessel, this kind of air bags are made of synthetic-tyre-cord reinforcement layers and rubber layers, and are also known as marine airbags, they were invented in 1980. Xiao Qinghe shipyard launched a tank barge with marine airbags on January 20, 1981, and it is known as the first use of marine airbags. From then on, more and more shipyard began to use air bags to launching small and medium-sized vessels, especially in China and Southeast Asia.

Airbag launching refers to a method to launch vessels with marine air bags. It is a methodology for ship launching utilizing air bags. This kind of ship launching method has the advantages of requiring less permanent infrastructure, risk, and cost. The airbags provide support to the hull of the ship,air bags rolling motion take a vessel launch into water, thus it is arguably safer than other options like sideways launching.

The arrangements of air bags
Launching type
Based on the ship shapes, the ship may be launched, using air bags, by either end launching type or side launching type

End launching type
There are three ways to arrange air bags when using the end launching type. They are linear arrangement (see Figure A.1), staggered arrangement (see Figure A.2), and two-lines arrangement (see Figure A.3). As for which arrangement to use, it will depend on the ship¡¯s width and the length of the air bags.

1. When the ship¡¯s width is not greater than the effective length of the air bags, the linear arrangement shall be selected.

2. When the ship¡¯s width is greater than the effective length of an air bag and less than the effective length of two air bags, the staggered arrangement can be selected.

3. When the ship¡¯s width is greater than the effective length of an air bag and less than the effective length of two air bags, the staggered arrangement can be selected.

Side launching type

For small flat-bottom ships, the side launching method may be utilized (see Figure A.4)

Slipway

The gradient and the length of the slipway shall be determined according to the size of the ship and the hydrological condition of the area water.

The bearing capacity of the slipway shall be at least twice as strong as the working pressure of air bags.

For ships of more than 3,000 tons of length, more than 120m,the slipway shall be constructed with reinforced concrete and the height difference between the right and left sides shall be less than 20 mm. For ships of more than 1,000 tons but less than or equal to 3,000 tons in weight, or more than 90 m but less than or equal to 120 m in length, the slipway shall be constructed with cement concrete and the height difference between the right and left sides shall be less than 50 mm. For ships of not more than 1,000 tons in weight or not more than 90 m in length, the slipway may be an earthen slope and shall be compacted even by rollers. The height difference between the right and left sides shall be less than 80 mm.

The main slipway shall enable the ship to glide automatically when the ship is off the tow. The auxiliary slipway shall be determined according to the ship type, the water level at time of launching, the diameter of the air bags, and the safety requirements.

Towing arrangement

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 should be calculated carefully by technicians of ship yards or air bags company.

Ship launching process

AirbagTeam¡¯s Rubber Airbags are really cost-effective in launching a vessel, ranging from smaller sized barges to tug boats up to bigger sized chemical tankers etc. But it is very important to understand that rubber airbag launching is not a ¡®one-size-fit-all¡¯ method. In fact, AirbagTeam would need to understand all the necessary technical specifications of the vessel (or structure, as this launching method can also be used to launch caissons & floating jetties etc) and many external factors.

The first step is to identify the vessel size & dimensions.

Identify Main Dimensions & Types of Vessel

At AirbagTeam, we believe in listening before we jump to conclusions and putting our clients priorities first.

Before proceeding in advising, AirbagTeam staff would normally request our prospects to fill in a technical specifications form. Factors like length overall (L.O.A.), beam, draft, launching weight (light weight) of the vessel and working height (distance between ground and the hull of the vessel), just to name a few. This enables our team to understand the weight of the structure during launching and equally as important, the main dimensions so the airbags can be structured efficiently. Different designs of the structure plays a role in choosing the types of airbags.

Selection of airbags

After understanding the type of vessel and its principal dimensions, AirbagTeam staff is then able to recommend the types, sizes and numbers of airbags. A weight contingency of a certain percentage of the vessel weight is taken into consideration. This helps AirbagTeam ensure a safe launching process by not overexerting the rubber airbags and also have a safety margin, should there be any additional weight carried by the vessel during launching.

Based on the dimensions and structural design, the team can recommend the dimensions of the airbag in terms of length, diameter and type. Then, based on calculations and careful projections, AirbagTeam staff is able to determine the guaranteed bearing capacity per airbag. At this point, extra airbags for launchway mobilization will be included in AirbagTeam¡¯s recommendations.

General ground structure preparation

AirbagTeam airbag launching process requires a hard ground so that the whole structure will not sink during launching.

If the ground consists of sand or is soft, there are many options that our staff will recommend. Sandbags are a very commonly used option. AirbagTeam also helped many of our clients prepare concrete ground as launching slipway for airbag use. This would require a very delicate study of the nature of the ground and in-depth analysis on a case-to-case basis. Thus, it is crucial that this aspect should not be overlooked. Fortunately for AirbagTeam, we have helped our clients solve these issues in many years of our experience in ship launching. Contact us if you have such tricky issues with the launching slipway.

Other pre-launch conditions like power generation issues including the design & supply of diesel generator systems will also be discussed with our client.

Selection of slipway winch

The force needed to support the vessel motion into the water will be determined by taking into account the sloping angle. This enables the team to find out the type and strength of slipway winch required to hold the structure in place. The decision of whether to use an electric or hydraulic winch is also very important. A hydraulic winch may be more expensive but might be more durable and more suitable in certain cases. Though it depends on the user and conditions. Pulley blocks, shackles, suitable wire rope types and necessary equipments will also be recommended if needed.

Pulling force plays a huge role especially for certain launching projects that require a slow and steady approach, needing the winch to be able to operate long periods of time.

Placing of rubber airbags

AirbagTeam uses 3D projections to determine the placement of rubber airbags at ready-launch position.



This helped give a 3D view on how to evenly distribute the weight of the vessel/structure for AirbagTeamimum safety. AirbagTeam takes into careful consideration the distance between components and how to coordinate the metal strut/stand locations.

Launching of the Vessel

First time clients usually require AirbagTeam consultation crew to be on ground to help them launch their vessel. We are able to facilitate the whole preparation together with supervision of the launching process at a small consultation cost for our clients. Equipped with decades of experience in launching and careful projections, our team ensures the project success and the safety of the crew. With its advantages, launching of structures up to 10,000 Tonnes using this method is pretty common these days. It is widely acknowledged that these launching bags are able to be used up to more than 5 years and is super cost efficient compared to most traditional launching methods.

Using marine airbags to launch and land ships

The use of marine airbags to launch a ship and to land it back in a dock is a very novel process. The concept was developed in the year 1981 in the Jinan province of China. In these past thirty years, this concept has undergone a lot of development and revolution and is now one of the most recognised methods of launching and landing a ship.

Airbags help remove the hindrance of using tows and tugs as launching and landing instruments. Moreover since the airbags use synthetic rubber and a high defined system as their core design, it has become easy to use such airbags for any ship that has a DWT (Dead Weight Tonnage) of less than 55,000.

Additionally, the revolution carried out in the process of using airbags as launching tools also has the advantage of being used for any kind of ship. This factor is very important because in the initial days when the marine airbags were newly launched in the shipping industry, only small boats which were flat-bottomed could use the facility of a marine airbag.

Since these airbags come with abrasion-free coating and are resistant to any sort of piercing, they ensure that the process of using marine airbags can be repeated many times over. This again contributes to the investing rate of a shipping company or owner being quite less than what they would be contributing while opting for the more conventional methods of plunging a ship into the water.

A marine airbag is something that has come up a long way in the three decades of its first being used. Given the way the technology is peaking in today¡¯s times, it is very obvious that could achieve even more development in the days to come. Further development and up-gradation for this particular system, would mean that naval hauling and trucking could be something that even non-naval users be proud and appreciative about. 

The following are some of AirbagTeam Marine¡¯s insights about airbag launching and how to ensure success, rather than a catastrophic and embarrassing failure.

1) Identifying the type, size & weight of the vessel before you launch.

It is surprising that many take this step of granted. Main factors like types, sizes, vessel weight, working height (distance between the hull of the ship and ground) affects your choice of airbags. The main structure of vessel is vital in determining the placement of the inflatables too. Many fail due to the ignorance of such details as they think that airbag launching is a ¡°one-size-fits-all¡± technique.

2) Type, length and number of airbags have to be chosen carefully.

There are many types of airbags. They are different in number of rubber layers, rubber quality, strength of the layers etc. The dimensions of rubber inflatables in terms of diameter, length and layers determine its lifting/bearing capacity. It is highly advisable that a weight contingency should be taken into consideration as a safety margin so that the inflatables will have a longer lifespan in the long run because they are used well within their lifting capacity. Extra airbags for mobilization proposes should also be considered. AirbagTeam Marine also uses an in-house built software to check the type, length and number of inflatables proposed.

3) Ground structure/ slipway has to be free of sharp objects and preferably, a small degree slope.

First and foremost, a hard ground is a must to have a safe and successful launching. The suitability of the launching area must be considered and steps taken to prepare it. Although some launch their vessels on soft ground, it is not worth the risk and is not advisable. Additionally, the launchway must be free of hard & sharp objects like sharp metal plates, big stones etc. These may damage the rubber launching bags during launching.

4) Slipway Winch to provide pulling force needed.

A slipway winch is needed to hold the vessel in place (prevent it from slipping into the water) during the placement of airbags. Slope angle, weight and type of ships should be carefully considered to determine the winch capacity. A choice of electric winch or hydraulic winch also depends on the facilities of the shipyard and the aspects of its usage.

5) Determine the accessories needed for ship launching using airbags.

Accessories like pulley blocks, shackles, steel wire rope and AirbagTeam Marine¡¯s innovative Quick Release Shackle may be needed. The types of accessories and volume depends on the situation.

6) Determine whether a slow launch or quick launch.

Some inflatable launchings are done by releasing a quick release shackle (the connection between the winch & the vessel) and the vessel is allowed to slide into the water facilitated by gravity. However, for trickier situations, a slow launch may also be practised. This is where the winch slowly releases the rope and the vessel is allowed to slide slowly. For slow launches, the balance of the ship is ensured so if at any point of time it falls out of balance, the winch will be immediately stopped and corrections can be made.

7) Rubber inflatables are versatile

Aside from ship launchings and used to facilitate pulling vessels out of the water, these rubber inflatables can be used to mobilize heavy structures like caissons, floating jetties and other equipment. Moreover, it is very commonly used in marine salvage projects where it is used to float or lift. Many shipyards are pleased that aside from using these rubber airbags for their ships, they are able to use them for other purposes as well. This versatility has served them well.

8) Cost advantage due to flexibility.

Launching using rubber inflatables have relatively lower costs, especially upfront investment. The most interesting aspect is its ¡°scalability¡±. Many ship repair yards in Asia prefer this method as they can increase their ship repair capacity whenever they want and not be restricted by say, the dimensions of the dry docks they own.


Reference: Airbag for Ship Launching and Airbag for Dry-docking or Haul-out

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