New Oil tanker launch by Evergreen ship launching airbags

Eversafe Marine Engineering Company, the subsidiary company of Evergreen Maritime, successfully launched a DWT 11000 Oil tanker with marine airbags for Jiangsu Huanqiu Shipbuilding Company on Sept. 15, 2010.
The vessel named “Future Light” measures 142 meters by total length and 19.5 meters by molded breadth. Its launching weight reaches 4300 tonnes and has 3.6 meters draft at stern. The launching slipway has the variational slope: 12/1000 radian from vessel bow to the watergate, 25/1000 radian beyond watergate until end of slipway. The width of slipway also changes from watergate from 25 meters reduced to 12 meters. The average river water depth of watergate position is 0.8 meters. The distance between oil tanker stern and gateway is more than 30 meters.
The biggest difficulty of this launch projection is the special structure of slipway which may cause the vessel incline to one side or run into dock when it pass by the 12 meter width slipway part. No time to rebuild or do any remediation work to the slipway. The only possible launch solution is using Evergreen airbag launching technology.
Eversafe engineers researched this project for two weeks, from calculation to digital simulation by software. At last we found by adjust the gravity distribution of oil tanker can remedy the inclination moment when vessel pass by the 12 meter width slipway part. To reassure ship owner we also suggest the installation of two Evergreen pneumatic fenders on the dock. The discussion meeting with shipyard and ship owner is cheerful, all people here think the launch proposal is the best and safe way that we can do at that time.
According the scheme the oil tanker will be moved toward river for 20 meters by marine airbags then laid on marine airbags until next day morning when the water reaches appropriate depth.
At Sept. 14, Eversafe team completed the move forward work using 42 pieces YT-6 Evergreen marine airbags that have 1.5 meters diameters and 18 meters length. The next day 8 am people begin to adjust the air pressures of marine airbags to make vessel inclined with right angle. At 9 am the launch water area is blocked and two tugboats are ready. With the shot of starting gun the pulling steel ropes are cut down and oil tanker enter into water straight forwards with the rolling marine airbags and anchor at the appointed place after total refloatation. Hails from people and fireworks which resound across the sky accompany the magic launch process. There is no splash of water, no stern or bow fall off, no decline to one side phenomena happen during the launch.
The success of this marine airbag ship launch project verifies Evergreen airbag launch theory again. Without accurate calculation people can’t complete the launch on defect slipway so smoothly. For shipyard and ship owner they are glad to deliver or get oil tanker on time without extra cost of slipway repair or employ launch barge.
Evergreen airbag ship launch technology is invented initially for emergency launch such as during war or nature calamity period people can launch vessel without constructed slipway. Nowadays this ship launch technology is developed into a very flexible and effective solution and sometimes it becomes an essential for launch under imperfect condition.

How to select marine airbags for your launch project

Marine airbags will cause people most interest once people have the experience of watching marine airbag ship launching. It looks like the magic show that big vessel run into water by riding rolling pneumatic rollers. In China most new built vessels whose DWT below 60,000 are launched with the “flexible ship launching technology” which definitely differ from traditional launch methods. Marine airbag ship launching technology gets the least limitation of landscape so it can save people most money and time.
The first difficulty for people to apply marine airbag for ship launching is how to decide if the vessel can be launched by airbags and select marine airbags. Most Chinese manufacturers will only tell you to do what but not why to do that when you consult with them for your launch project. In fact some manufacturers don’t know much of the marine airbag ship launching technology even they make marine airbags. Some real jokes: a manufacturer sold many marine airbags to a Turkish client and when people prepared launch they found no place to fit all marine airbags into bottom of vessel. Another joke sounds like that a manufactures sold 20 pieces marine airbags with 2.5 meters diameter to Malaysian shipyard to launch a 60 meters tugboat with only 700 tons. To avoid be fooled by some unprincipled manufacturers, there are some lies that people must know.
Lie One: Bigger diameter means better performance
People may be fooled by numeral tricks when they read performance data of marine airbags issued from manufacturers. People are leaded to believe that the bigger diameters of marine airbags have the better performance. In fact the performance of marine airbags is decided by the burst pressure which means the maximum pressure of airbags can bear. It is easy to understand that for the same material made bigger volume container will has less burst pressure. From the test data people can prove this prediction comes from common sense: the bursting pressure of marine airbags with 1.5 and 2.5 meters diameter is 0.67 Mpa and 0.23 Mpa respectively. When a 1.5 m diameter marine airbags and another 2.5 m diameter one are inflated to the same pressure, it is definitely the bigger diameter one will rise up heavier objects because of its bigger contact surface. But the bigger diameter one gets some problems that its pressure can not exceeds 0.23 Mpa and it will lift up vessel higher which will cause the extra demand of launch water level also its bigger contact surface with ground will need more slip force for vessel to start movement. In a word, marine airbags with the diameters exceed 2 meter are suit for some special lifting use not for vessel launching. During ship launching process marine airbags will be compressed and their inner pressure will rise to be nearly 2-3 times of initial pressure so marine airbags must have 3 time safety coefficient. Most 2-2.5 meters marine airbags can not get 2 times safety coefficient.
Lie Two: More plies means better safety
Some clients would like to believe marine airbags with more plies will ensure better safety. It is true that the 7 pliers marine airbags’ maximum pressure is higher than 6 pliers one. But good arrangement and maintenance will ensure much more safety of your marine airbags. The thickness and maximum pressure will increase no more than 8% when marine airbag’s plies increase one. So in most cases marine airbags with more plies can not offer a visible enhanced safety but the psychological effect. In fact the professional manufacturer has optimized the plies and structure of marine airbags. Most popular Evergreen marine airbags are 6 pliers. They have the best cost performance and more than 5 times safety coefficient which is enough for most marine projects.
Lie Three: More marine airbags employed for project means better safety
Like people always say going too far is as bad as not going far enough, too many marine airbags for the launch project may cause danger. There is a minimum space required for marine airbags arrangement. If marine airbags are placed too closer, they may huddle together and can not roll forward when they are compressed more during the launching process. Please note marine airbags will be compressed differently in the different launching period. Even marine airbags are not adjoining before the launch they can still huddle together in launching period.
After see through lies of marine airbags people may ask then how can we know if our vessel can be launched by marine airbags? The answer is simple: four conditions should be satisfied.
1. Vessel is prepared to be end launching
2. DWT below 60,000 tonnes
3. Launching channel’s width no less than 1.5 times of vessel’s length
4. For some special ship launching such as V-shape vessel additional brackets may be needed
To select suitable marine airbags for your marine projects you may refer the following.
There are two industrial standards for marine airbags in China.: one is product standard named “Air bag for ship up to or down to launching way “(CB/T 3795-1996 / CB/T 3795-2009); another is technology standard named “Technological Requirements for ship Upgrading or Launching Relying on Air-bags” (CB/T 3837-1998).The latter offer the basic calculation of marine airbags employed in a marine project.
According to Chinese industrial standards people will know the approximate quantity and specifications of marine airbags needed for their projects. There maybe optional specifications to be selected for a specific marine project and a good manufacturer should know the best choice. Suggestions from Qingdao Evergreen Maritime Company: for ship launching, the airbag’s diameter and length should not exceed 2.0 meter and 18 meter respectively; for caisson conveying, the 1.0 meter diameter is suitable for most projects.
The data of marine airbags’ blasting pressure will reveal the product’s quality level. For top quality marine airbags, such as one 1.5 m diameter and 7 m length Evergreen marine airbag, the blasting pressure is 0.67 Mpa which indicates the safe coefficient is more than 5 considering its 0.12Mpa working pressure. Never forget to ask for the maximum pressure from manufacturers if you want to buy marine airbags from them.
Full technical service is the qualification of a good company. Although general calculation formula or performance data of marine airbag can be got from most factories but detailed calculations based on mathematic model and experience is more important to the success of marine projects.

In a word marine airbags is a good powerful tool for lots of marine projects but people need to know some principles before using it.

Evergreen Marine airbag ship launching process

Evergreen marine airbag is widely used in the ship building, ship repairing, oil and gas, marine salvage companies nowadays.
Now we are making a brief introduction of Evergreen airbag ship launching procedure as follows:
1. According to the calculation, prepare enough marine airbags, towing winch machine, air compressor and other instruments needed.
Before using, all airbag should be inflated with 1.25 time inner pressure of working pressure to test its safety and air tightness. If there is air leakage, it should be patched before using.
2. Clear all the obstacles and sharp iron nail from the slipway.
3. Check on the uneven scar caused by welding of heavy steel structure to ensure ship’s bottom is smooth.
4. Fasten towing winch with ship.
5. Close all the valves, fix the helm and screw propeller.
6. Take out all the wooden stands under the ship, insert rolling airbags. There are many ways to do it. Now we introduce two most used ways as follows. The user may choose one of them according to the weight of ship and quantity of marine airbags.
A. For the light weight ship, airbags can fully lift the ship and make it to detach with the wooden stands. Then it is easy to insert other airbags and remove the wooden stands.
B. For the heavy ship, we use airbags to lift the ship at the stern of ship. So we must find the best point for bow supporting point and lift airbag. From the figure, we can know the bow supporting point should near to ship’s transverse gravity center. But consider the workforce of removing wooden stands before bow supporting point we should select that point at a reasonable place. The lifting air bag should far away from the gravity center to get a bigger lift moment. Sometimes we have to consider the figure of ship’s bottom to decide the lifting point. In one word we should find the best lifting point to get the maximum lifting moment.

To lift the ship the following condition should be satisfied
Q•LQ〉W•LW
Q-bearing capacity
W-weight of ship
LQ-distance from lifting point to bow supporting point
LW-distance from gravity center to bow supporting point
C. First take out all the wooden stands in front of lifting airbag and bow supporting point. Insert the lifting airbag and start to inflate and stop charging as soon as the bottom of ship dispatch with the wooden stands. Then take out the wooden stands from the ship middle to stern, insert more airbags at planned positions. Repeat above process to remove all the wooden stands and place air bags.
In order to ensure the safety, we should insert some flexible wooden stands. When the air bags can lift the full weight of ship, we can take out these stands.

Not finished. Please contact author to get whole edition.

Marine Airbags: Innovative and Versatile Marine Tool (part 1)

Introduction
Marine airbags are widely used in China for ship launching ,caisson conveying and marine salvage nowadays. It is estimated that more than 80 percent new built ship whose DWT below 60,000 and about 50 percent caisson fabricated for gravity quay are launched by marine airbags.Not only in China but also other Asian countries marine airbags are acknowledged as the powerful and versatile tool for marine works.

The history of marine air bag dates back to 1990s. A Chinese ship repair and building shipyard launched a 60 DWT tank barge with marine airbags on January 20, 1981 and it is known as the first use of marine airbags. The invention of marine airbags was expected to develop a flexible, less limited ship launching method.

Over the past twenty years, marine airbags have made great advancements in the manufacture and application. The first generation marine airbags employ rubber dipped canvases as reinforcement material and two cone-shaped ends are stuck to the chamber trunk. Now the top marine airbags are seamless and their performances are about 15 times of the first generation with the same specifications. Regarding the launching/landing technology, marine airbags have also achieved a significant leap. In the beginning, only small and flat bottom ships located on a fabricated slope could be launched with marine airbags. Now this technology is more flexible and less limited by the ship and landform. The DWT of launched ship reached 55,000 and launching ramp can be aclinic. Not only for ship launching marine airbags are widely used for heavy conveying also. Marine airbags contributed much to the success of famous Nanhai No.1 ancient ship salvage project. The 4,800 tons cassion which hold the invaluable ancient ship landed from the semi-submersible barge and transported to the museum named Crystal Palace riding on 16 pieces marine airbags.

Marine airbags -Interview with Evergreen Maritime (1)

What were the first uses of marine airbags in the launching of ships?
People can trace the history of airbag ship launching back to 1981 year,over 20 years ago. Xiao Qinghe ship repair and building shipyard,located in Jinan city of Shangdong Province, launched a 60 DWT tank barge with marine airbags on Janu. 20, 1981. Seven marine airbags were employed in that ship launching project,one is 2 meters in diameters and 6 meters long used for elevating and the left six air bags are 0.8 meter and 6 meters long act as the rollers. The initial intention of that ship launching trial is for warfare purpose to develop a prompt,less landform limited ship launching method.

How has the technology advanced since then?
During the past over twenty years, the marine airbag ship launching system make progress not only the airbag but also the ship launching/landing technology.
The first generation airbags use rubber dipped canvas as reinforcement layer , the trunk and two cone-shaped ends are made separatelly. People lapping rubber and dipped canvas to form the air chamber trunk and stick strips to molds to make the air bags’ ends ,then stick them together.
The latest marine airbags use the rubber dipped synthetic-tyre-cords as the reinforcement layers and take the whole-enlacing-technology for manufacture. The trunk and two cone-shaped ends are made at the same time and enlaced together so the whole air bags have no joints. Due to the development of rubber chemistry the performance of rubber employed in the latest air bag is highly enhanced also. The performance of the latest airbag is 15 times of the first generation one with the same specification.
Regarding the launching/landing technology, it developed most during the past 20 years. From the beginning, only small and flat bottom ship located in fabricated slope can be launched with air bags. And now this technology is more flexible and less limited by the ship and landform. Any type of ship DWT below 55,000 at a place with enough launching space to the water can be launched with air bags. And the launching slope even can be aclinic. The air bag ship landing technology developed from applications in some stranded ship salvage projects and then it comes into a cutting edge one especially useful for some marine emergencies.
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Evergreen airbags successfully launched a 32,500DWT Bulk Carrier

On 16th.Jan.2010, the 32,500DWT Bulk Carrier “NO. 6 Dongze” was successfully launched by Evergreen ship launching team with Evergreen Marine Airbags in Nanjing Dongze Shipyard. It is the sixth ship launched by Qingdao Evergreen Maritime Company using airbag launching technology for this shipyard.
This Bulk Carrier with 210 meters length and 34 meters molded breadth weight 9,500 tons. January is the dry season of the Yangtze River Valley, so there is long distance between the stern with the tide point. Fortunately the launching slipway was initially constructed in the light of Evergreen team’s design, so the calculation of launching start point came to be easier. Finally the ship was moved forward about 30m to reach the best launching point by the control of mooring winches.
Total 64 pieces Evergreen Marine Airbags D1.5xEL18 (YT-6) were employed to launch this Bulk Carrier. And all airbags’ inner pressures were adjusted to the required value before the launch. After a simple ship launching ceremony, the workers cut off the wire ropes to release the ship. Then the Bulk Carrier went into river by riding marine airbags smoothly. Different from the traditional end-on ship launching, the “stern dipping” and “stern rising” phenomena are not obvious anymore during airbag ship launching.
Qingdao Evergreen Maritime is preparing another 55,000DWT vessel launching project which will be performed after three weeks. Keep an eye on our website www.evergreen-maritime.com to know the latest news.

Hydraulic burst test of Evergreen Marine Airbags

Hydraulic burst experiment is the ultimate test for the Marine Airbags’ performance, material, manufacturing technique and structure type. Meanwhile, Hydraulic burst test also can be used to confirm the safety working pressure. But, there hasn’t been any other manufacturers done this test with regular products because of the high cost and lacking of confidence of their airbags’ performance. Generally they employ a small size airbag to do the hydraulic burst experiment and then infer to all sizes.
At the request of research department of China Shipbuilding Industry for the amendment of CB/T3795, Evergreen-Maritime did this “Hydraulic burst test” with regular Evergreen Marine Airbags. As per the requirement of industry standard, we randomly selected three pieces D1.5xEL8m YT-6 type Evergreen Marine Airbags to do the bursting test orderly under the same condition.

The result is as follows:
For the first Marine Airbags, the Hydraulic bursting pressure is P1= 0.73 MPa
For the second Marine Airbags, the Hydraulic bursting pressure is P2=0.71Mpa
For the second Marine Airbags, the Hydraulic bursting pressure is P2=0.72Mpa
Thus, the average bursting pressure is P= (P1+P2+P3)/3= 0.72 Mpa.

Then we select the safety working factor 6 (the industrial standard demands this factor for 4.5)
Pe = P/n= 0.72 Mpa / 6= 0.12 Mpa

Thus, we define the “Safety Working Pressure” of YT-6 type Evergreen Marine Airbags with 1.5 m diameter as 0.12 Mpa. For airbags with other diameter sizes, we did the same Hydraulic burst experiments to define the safety working pressure data.
To get more information, please don’t hesitate to contact us by sales@evergreen-maritime.com