When we talk about Indonesia’s strategy to be the world’s maritime axis, there are some we need to consider. Apart from the readiness of marine infrastructure and services, we also need to take into account the number of vessels (legally) operating in our waters.
Now this number greatly depends on the capacity of the shipbuilding industry. Shipbuilding companies play an important role in building, maintaining, and repairing ships. According to the Indonesian Ministry of Industry, Indonesia is currently home to around 250 shipbuilding companies. However, only 20% of Indonesian ports have shipyard facilities. High investing and operating costs are the most substantial impediments to maintaining these facilities.
In general, shipyards have a docking facility, namely a graving dock, in the shape of a pool. This pool has to be wide and deep enough to accommodate the biggest vessels that may come into the dock and has a valve which opens to the sea. When a vessel is in construction, the valve is closed and water is pumped out to create a dry space for shipbuilding activities to take place. For repair or maintenance works, once the ship is in the pool, the valve is closed and water is pumped out. When the vessel is ready for launching (or relaunching), the valve is opened to allow water in. When the water in the pool has reached the same level as the water outside the pool, the valve is opened to launch the ship.
Some shipyards opt for ship railway and slipway, which is a rail to tow vessels to and from the sea. Building a slipway cost much less than building a graving dock. However, slipways are limited by the strength and capacity of the rail itself. Also, because the rail is fixed, moving the vessel around once it is on land will be difficult. Towed ships can also damage the rail and the rail requires costly maintenance, especially for the parts submerged in water.
In the 1980s, rubber airbags were invented to overcome the weaknesses of both the graving dock system, ship railway and slipway. Rubber airbags are tubular airbags with a cone at each end. This airbag is composed of two main layers. The inner layer is made of interwoven synthetic nylon thread covered with synthetic cord reinforced rubber. The outer layer is made of modified natural rubber to make it resistant to friction and pressure.
A rubber airbag is divided into three parts. The first part is the body, which is the middle part of the tube. The second part is the head, which is the cone at each end. The third part is the mouth, namely the metallic tip of the cone, that serves as air inlet and outlet.
The type of rubber airbag can be seen from the size and model. In general, there are three types of rubber airbags based on their diameters: 1.5 meters, 1.8 meters and 2 meters. However, there are also rubber airbags with diameters of 0.8 meters, 1 meter, 1.2 meters and more than 2 meters. The length of this product is adjusted to the needs of the customers.
Rubber airbags can also be categorized based on the number nylon thread layers in them. They usually consist of three to six layers of nylon thread. However, some airbags can have more than that even though they do not usually exceed 10 layers.
How do they work?
To pull the ship ashore, a rubber airbag is placed at the bottom of the ship’s front end. The ship is then pulled using a winch and as the ship moves ashore, another rubber airbag is placed in front the one already placed and so on until the ship reaches the repair or maintenance workshop. A supporting concrete block, called stow or keel block, is then placed under the ship. The rubber airbags are then deflated to store. When the ship is ready to relaunch, the rubber airbags are laid out, filled with air then the stow blocks are taken, and the ship is pushed to the sea.
Rubber airbags can be laid out in several arrangements:
- Linear Arrangement Method
For ships with width not exceeding the body of airbags, the airbags can be laid out in linear arrangement. The airbags are installed in a row from the front to the back of the ship.
2. Staggered Arrangement Method
For ships with width exceeding the body of airbags, but does not exceed the length of two rubber airbags laid end to end, the staggered method can be applied. The airbags are laid out in two alternating rows / zigzag (see picture).
3. Two Line Arrangement Method
For the ship with width exceeding the effective length of two rubber airbags laid end to end, the two-line method can be used. For ships with flat hull like barges, the width of the hull may exceed the length of two airbags.
With this method the rubber airbags are installed in two parallel rows (see picture) with at least 20 cm between the ends of the airbags.
To be able to use rubber airbags safely, shipyards must ensure that the launch site is flat, solid and free of sharp objects. Sharp objects such as pieces of iron or rocks can tear the rubber airbags. While the tear may be small at first, once you add the weight of a ship, the damage will be significant. However, airbags can still be used on sandy and sloping beaches or riverbanks. If airbags are to be used on floored surfaces, concrete flooring will be the best for optimum performance.
What are the advantages of the rubber airbag system ?
- Shipyards do not need to invest a lot to build graving docks and/or slipways. Flattening and hardening the launch site will be adequate.
- Rubber airbag maintenance is much cheaper than graving dock or slipway maintenance.
- Rubber airbags can be moved from one place to another quite easily.
- Without graving docks and slipways, a shipyard has a flexible capacity and can use the entire area of a sloping shoreline as a large manufacturing and docking facility.
Indonesian shipyards have been importing rubber airbags from abroad, especially China. However since 2019, PT Samudera Luas Paramacitra (SLP) in collaboration with BPPT, has successfully manufactured Indonesia’s first rubber airbags. It can be expected that the Indonesian shipbuilding industry will be more committed, competitive, bigger and stronger.
For consultation regarding the SLP airbags, please contact the hotline (+62) 823 2018 9998 or email us on admin@niri-rubber.com .
