Airbag System: The Blue Technology Breakthrough for Shipyard

Transcription

1 Airbag System: The Blue Technology Breakthrough for Shipyard Author: Daniel T., HAGE Director, PT. Inti Teknika Solusi, Indonesia dthage@intiteknikasolusi.com Abstract Developing shipyard will cost high investment for graving dock or floating dock or slipways. Airbag system comes as breakthrough to upside down this obstacle. This is an appropriate simple technology as our ancestor did when they moved the heavy materials to build their mega-structure at that time, rolling the load on timbers. Now, we use inflatable rubber sausage for this system. Using airbag systems will redefine the shipyards investment s need. Now, shipyards can be defined as simple as a workshop with the waterfront. Airbag system makes the docking and launching of the ships can be provided easily and low cost. Airbag system will expedite the development of shipyards in many remote islands and places. Engineer can learn and do the launching and docking easily. The equipment can be used for long time and the damages can be repaired to maximize the investment cost. This system also has some technical factors that should be noted and observed particularly for docking. This is a real breakthrough in Blue Technology that can boost the economic value. Keywords : Marine rubber airbag, ship launching, ship docking, airbag system. 1. Introduction Every shipyard need facilities for docking and launching such as: graving dock, floating dock or slipway. These main facilities are known as initial basic infrastructures of shipyards. To build these facilities will consume big investment and longtime preparation. Airbag System is able to substitute all of these requirements. Airbags can be used to launch and upgrading the ship for docking. Basically, this method is used by our ancestors. The ancient mega structures such as: Pyramids in Egypt and Borobudur Temple in Indonesia use timbers as wheels to move the heavy materials. Airbags are invented by this method also. The hard surface of timbers, which risky damaging the moved material s surface, are perfected by flexible and soft rubber materials. Marine rubber airbag are like inflatable giant rubber sausage. These airbags are inserted underneath the ship and pressurized. Ship or vessel can be moved on these rolling airbags. Figure 1. Ship Docking using Airbag System 1

2 2. Airbags The airbag s structure commonly is like at Figure 2a and Figure 2b. The effective length L is usually used as the length of airbag. The main specification of airbags are: Length (L), Diameter (D) and the thickness. The thickness means the amount of cords layers which are used. As standard the airbags must be referred to ISO [1]. Figure 2a. Structure of a typical airbag [1] Figure 2b. Marine Rubber Airbag 2

3 7 Layers Inteso Marine Rubber Airbag Bearing Capacity Diameter Working Guaranteed bearing capacity per unit length Working height pressure kn / m t / m Ib / ft 0.9 m (2.952 ft) m (2.624 ft) m (2.296 ft) D =1.5 m MPa 0.6 m (1.968 ft) (D =4.92 ft) (23.63 Psi) 0.5 m (1.640 ft) m (1.312 ft) m (0.984 ft) m (0.656 ft) m (3.608 ft) m (3.280 ft) m (2.952 ft) m (2.624 ft) D =1.8 m 0.14MPa 0.7 m (2.296 ft) (D =5.90 ft) (15.95 Psi) 0.6 m (1.968 ft) m (1.640 ft) m (1.312 ft) m (0.984 ft) m (0.656 ft) Table 1. Example of Airbag s Specification For conventional ships launching the quantity of rolling Air-bags can be calculated by formula: [2] Q. g N = K 1 + N 1... (1) Cb. R. Ld Where : N is the quantity of rolling Airbag, in pieces : K 1 is constant, K 1 = 1.2 ~ 1.3. Q is the weight of launching ship, t. g is acceleration of gravity, m/s 2. Cb is the block coefficient of launched ship. R is the allowable bearing force per meter of airbag length, kn/m. L d is the contact length between ship bottom and airbag body at the midship section, m. N 1 is the quantity of airbag replaced continuously, in pieces, normally it takes 2 ~ 4 pieces. The center distance of two airbag should meet the needs of structural hull strength, and avoiding overlapping of rolling Air-bag as well. As a rule, the center distance may be checked by using formula (2) and (3) : 6... (2) (3) Where : L is the length of launched ship, m. N is the quantity of rolling airbag, in pieces. D is the nominal diameter of rolling airbag, m. 3

4 Figure 3. Ready for Launching Figure 4. Protected from sharp edges 2.1. How to select airbag technically Some factors must be specified to select the airbags which will be used as follow: 1. Specify the most common ship s particular which is serviced. The length of airbag will be suited to the width of the vessel. 2. Specify the height of docking blocks. The diameter of airbags are defined by the height of these docking blocks. Sometimes it can use two kinds of diameter. The smaller diameter can be used as rolls and the bigger ones can be used as jack. Airbags don t work on their full inflated diameter. The diameter should be at least 30 (thirty) % bigger than the height of docking blocks. 3. Specify the weight of vessel. This data will be used to select the thickness of the airbags. 4. Specify the application of the airbags. Are they for launching or docking? Launching can use normal safety factor for choosing the thickness. The Table 1 can explain the bearing capacity of the seven layers airbags. The thicker airbag has higher bearing capacity. This table is suitable for launching process, since the clean and smooth hull surface of new ship. For ship upgrading or ship pulling, we must use thicker airbag due to sharp fouls (oyster and clam) on ocean going ship s hull. We can use one or two layers thicker than normal bearing capacity. Fresh water or river vessel doesn t have sharp fouls on its hull How to maintain and repair the airbag Airbag as rubber products must be handled in proper ways. Some factors that take effect on airbag s lifetime such as: 1. The rubber is aging faster under ultraviolet or sunshine. The airbag must be stored in shady condition. 2. Airbag must be used in clean shipyard and free from sharp material such as: steel snipping, trashed glass bottle. 3. Airbag must be moved carefully. Avoid friction of airbag s surface against shipyard s floor. Dragging the airbag on concrete surface of shipyard can damage the rubber airbag. Pulling the airbag at the airbag s end plug can loosen the steel part of the airbag. The broken or punctured airbag can be repair easily. There are two methods for repairing the airbags: 1. By cool system. Using the rubber glue to patch leakage. This method is suitable for small hole or tear, less than twenty centimeter tear or shred. This method is very simple and fast to be applied. It also can use Trichloroethylene cement based for this system. 4

5 2. By hot system. Using the heater and un-vulcanized rubber sheet to patch the shred and hole. This process will take long time but the result is very reliable. The burst airbag can be repaired using this method. Figure 5. Damage Airbag Figure 6. After Repaired Airbag With the proper maintenance and repairing procedures the rubber airbags can be used more than seven years How to select airbag quality Selecting the airbag s quality needs some experiences which sometime make exhausted. All airbags manufacturer are in Mainland China. Many of them are small company and do not mention to ISO standards. The business situation in China put the price as a floating standard. Whatever price standard we want, they will try to reach it. It s difficult to deal with real good company. We cannot judge from their website appearance only. Some guidance which useful to make decision regarding the airbag quality are: 1. Make sure that we get exactly correct dimension which we had purchased. The Length is always the effective length which can be loaded, instead of the overall length. 2. Make sure that the used nylon cords is as standard ones with 30 kg breaking load. 3. Make sure that we can contact and get response easily from the supplier, since we cannot know the condition of our airbags until it burst (to know the inside rubber structure) Land preparation and pulling system The land for shipyard must be prepared to have good flatness, inclination and proper soil compactness. The slope of the land should be 2-3 degree. This slope is related to the power of the pulling system. The land must be free from all things that can break and puncture the airbag. In many islands in Indonesia, the soil compactness is poor, since it is peat soil. To build the shipyard with concrete work area also an expensive effort. Having airbag can be a good system. Airbag also can be used as jack to add the docking blocks when it moved down. Winch is the best combination with the airbags. The layout of shipyard can be arranged to handle many ships. Well prepared layout can maximized the capacity of shipyard. Many shipyards in remote area also use heavy equipment (bulldozer or excavator) to pull the ship. It makes the docking process so easy and simple. The foundation is needed to put the pulley to add the pulling capacity. 5

6 Figure 7. Crane Barge Pulling Figure 8. Pulley Figure 9. The Worst Condition 3. Discussion Using airbags as a smart breakthrough also need further discussion on engineering side. Some consideration need to be taken are: 1. Launching process calculation which slightly different than the ordinary launching by slipway. The ship s weight is not well distributed load, the load between two airbag must be calculated due to longitudinal construction strength 2. Ship construction calculation due to concentrated load during ship pulling. 3. Standardized procedures due to appraisement from insurance company. 6

7 4. Conclusion 1. Airbag system is able to take as a smart breakthrough to expedite the growing of shipyards. The simple technique makes this system is easy to be learnt and applied in many shipyards. 2. This system has been proven as smart system that give flexibility in shipyards investment. 3. Advance study to this method should be done to make perfect the empirical experiences. 5. References [1] International Standard Organization (2011), Ship and Marine Technology Ship Launching Airbags, ISO (E), First Edition [2] China State Shipbuilding Corporation (1998), Technological Requirements for Ship Upgrading and Launching Relying on Air-Bags, CB/T , [3] Prasodjo, Budi Setyo (2012), Analisa Peluncuran Bangunan Apung Menggunakan Balon Bertekanan Untuk Peningkatan Efisiensi Galangan kapal Nasional, Badan Pengkajian dan Penerapan Teknologi, F