Ship launching airbags are very popular way of launching ships ,especially in Asia, where many shipyards purchase airbags to launch their own ships. This method of launching ships has greatly reduced the cost of pre-construction preparations and the safety is guaranteed. It is suitable for all kinds of ship upgrading and launching, ship repairing and hauling.
Many customers don’t know how to calculate the number of used ship launching airbag. They may think that “my ship is only 100 meters long. Why do I need so many airbags?” Is it making me spend more money? In fact, the calculation of the number of ship launching airbags is a very technical operation. There are a lot of force data that need to be considered in the calculation process, and the process is pretty complicated. Today, Sunhelm Marine will share you the calculation method of ship launching airbag selection. Through this calculation guide, I hope everyone can understand how Sunhelm’s technicians provide recommendations for marine airbag solution and can check whether the solution given you by the other party is reasonable after you get the quotation. Avoiding encountering unreliable small The condition of the company's random quotation.
1.How does the ship launch airbag work?
Before we begin to understand the selection of ship launching airbags, let's take a look at how these rubber airbags launch a huge ship.
Ship launching project steps:
1.1Clear the obstacles that block the rolling airbag on the ship’s way to launching and obstacles that under the bottom of ship.Make sure the slide is smooth and clean.This step is not be obstructed by any objects during the launching process of the ship and to ensure the safety of the launching process of the ship.There may be some sharp and hard objects such as large stones or shells washed up on the coast.They may also pierce the airbags of the ship, so it is very important to clean them and level the slide.
1.2 Connect the bow part, mooring bollards and other strong components connect with the movable pulley block of the traction winch to hold the ship.
1.3 According to the operation plan by the technicians, place the ship launching airbag under the bottom of the ship and restart it to the specified air pressure. When the bottom of the ship is higher than the piers and the weight of the ship is all pressed on the launching airbags, remove all the piers and give the rubber airbags properly deflate to balance the force.This step is called"down f rom docking blocks"in the professional field.
1.4 All work-related crew members are ready to board the ship.
1.5 Consider the width of the water area, choose a suitable launching position and release the wire rope to move the ship to the vicinity of the water area, cut off the wire rope or unhook the shackle when appropriate, so the ship can automatically enter the water with the aid of the sliding force.
1.6 After the hull is completely in the water, drag the ship to the dock, measure the draught of the bow and stern and check whether there is water leakage in each cabin.
1.7 Recover all ship launching airbags and record the launch information.
2. Calculation method for choose ship launching airbag
After understanding the general ship launching process, let’s take a look at how Sunhelm’s technical engineers calculate the number of ship airbags used for everyone. When our technicians receive your quotation request, they need to know the following information:
- Type of ship
- LOA length of the ship
- The width of the ship
- DWT of the ship
- The angle of the ship launching ramp and the ground material
- Tide table, water depth, and flow velocity information of the launching sea area
For concrete ramps, the friction coefficient of the airbag to the ramp is 0.01-0.0125. For compacted natural foundations, the coefficient is 0.0125-0.02.
After knowing the above information, the technician will calculate the number of airbags required for launching your ship according to the following calculation formula:
Where N is the required number of airbags, K1 is the airbag coefficient, Q is the weight of the ship, g is the acceleration of gravity, Cb is the square coefficient of the ship, R is the maximum bearing capacity of the airbag per meter, and Ld is the contact length of the airbag with the bottom of the ship Value (m).
All calculation technicians will repeat the calculation more than 3 times to ensure the correctness of the values. Then the customer will be quoted according to the number of items needed. If you want to know the number of ship launching airbags required for your ship launching project, you can send email to Sunhelm and we can choose the type for you free of charge.
With this formula, you can also perform a calculation by yourself after accepting the selection recommendation to see if the number of airbags recommended by the other party is reasonable. However, it should be noted that when the ship moves, 2~4 redundant airbags should be prepared. This is pretty important and our corporation has calculated the number of ship airbags for you.
3. Arrangement of ship launching airbags
When the ship is launched, it is not only necessary to calculate the required number, but also to determine the arrangement of the airbags.The arrangement of ship launching airbags can be roughly divided into two types: longitudinal launching and lateral launching. What kind of arrangement could be used will depends on the ship types and site conditions.
Let's take a look at the requirements for the layout of various launching airbags.
3-1 Longitudinal launch
When the ship is launched longitudinally, the marine airbags can be arranged in three ways: single row arrangement, staggered arrangement and double row arrangement. It is necessary to decide which arrangement to use according to the width of the ship and the length of the ship launching airbag.
3-1.1 Single row layout
When the width of the ship is less than or equal to the effective length of the marine airbag, a single row arrangement is adopted. This is the most common arrangement of marine rubber airbags for the upgrading and launching of ships.
3-1.2 Staggered arrangement
When the width of the ship is greater than the length of one ship airbag and less than or equal to the length of two ship airbags, the staggered arrangement is adopted. This arrangement is suitable for ship types with a relatively wide ship width. When the safe working length of the ship airbag may not reach the same length as the ship width, it is necessary to arrange two rows of ship airbags to be longitudinally launched in a staggered manner.
3-1.3 Double row arrangement
When the width of the ship is greater than the length of two airbags, or when ships such as catamarans and open mud barges are launched with airbags, the double-row arrangement is the best choice to ensure safe launching. There should be a gap of more than 0.2m between the ends of the two airbags.
3-2 Horizontal launch
Small ships with flat bottoms with wide ships and sufficient length at the bottom can be launched laterally. When the ship is launched laterally, airbags of the same model, the same diameter and the same length need to be chosen.
The ship launching airbags are divided into two groups, placed under the bottom of the bow and stern, with the same spacing between the airbags and there should be a gap of more than 1m at the ends of the airbags. It is recommended that not to exceed one-tenth of the length of the hull. The towline at this time should be fixed at the center point of the two airbags and perpendicular to the hull.
What method to choose to arrange the ship launching airbag, in fact, the technicians at this step have already considered comprehensively when selecting the model, everyone does not need to worry about which method need to be chosen. Or you can visit our ship launching airbag page to learn about the basic specifications of marine airbags.
If you want to know which launching method is suitable for your project, please send us an email so that Sunhelm technical team can give you professional technical support.
4. Safety precautions of launching ship
Four major problems may arise during the launch of the airbag vessel.
First, if the buoyancy of the water does not lift the stern in time, the stern may collide with the berth or the seabed. Therefore, it is very important to know the water depth of the launch area in advance.
Secondly, when the stern rises, the bow may fall to the ground, and the airbag under the bow cannot withstand the pressure. This may be caused by the slope being too large when calculating the downslope angle. When the stern is tilted up, the airbag in the bow will burst due to excessive pressure. At this time, it will be very dangerous if someone is around.
Third, due to the friction of the airbag stuck in the soft seabed, the ship may sink into the water.
Fourth, if the ship goes too far in the water, it may hit the other shore. This is also a serious accident caused by not calculating the position and angle of the launch of the ship.
If you want to know more about the things you need to pay attention to during the launch of the airbag, you can contact us and we will help you avoid all risks.
5. Summary
The construction of the ship launching project is a complex project that requires precise calculations. It seems to be simple and requires the support from many years of working experience technicians. Sunhelm Marine has a professional technical team and every technician has more than 5 years of field command experience participating in ship launching projects. Ensuring the safe implementation of customers' projects is our important mission. If you have never tried airbag launching before, you can make your first attempt at Sunhelm! Sunhelm's ship launching airbags adopt a new cross-wound process and have passed ISO14409 certification. They are good quality and affordable products. In fact, the price is not the most important thing when buying airbags, the most important thing is making sure the safety of the ship, isn't it? You will get what you paid for, Sunhelm's ship launching airbags will not make you disappoint.