Monday, June 21, 2010

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.

Wednesday, June 16, 2010

DWT35,000 cargo ship launched by Evergreen marine airbags

Eversfae engineering company successfully launched a DWT35,000 cargo ship with 48 pieces Evergreen marine airbags on June 15 2010.This vessel named “Five continents 05” was built by Five Continents Shipbuilding Company located in Jiangsu province.
Marine airbag ship launching projects are commonplace but to launch a big vessel is still an exciting work. “ Five continents 05” measures 178 meters long and 28 meters width, its launching weight is 9,000 tons. This vessel is built on a 0.01 radian concrete slipway which has abrupt down end, a very dangerous structure for marine airbag ship launching. The drafts of stern and bow are 4.2 meters and 2.4 meters respectively.
The difficulties of this launching project are as follows: bad slipway, heavy weight, long length. A vessel will not start to move relying on gravity’s slipping down component of gravity force if its inclined angle is 0.01 radian. Long vessel will need careful arrangement of marine airbags to ensure the safety of hull structure.
After negotiating with shipyard, Eversafe engineers supervised the modification of slipway end structure and got two tugboats to handle with any emergency during the launching. At June 14 Evergreen team began to inflate well arranged marine airbags to raise vessel and remove wooden blocks. Firstly, eight pieces marine airbags under the bow were inflated to be 0.20 MPa pressure then twenty pieces marine airbags were inflated to be 0.18 Mpa and left airbags were inflated to be 0.16 Mpa. So the vessel was lifted by total 48 pieces marine airbags easily.
As the high tide time of June 15 is at 9 AM the launching time is set at 8:45. In the morning of Jun 15, Eversafe team began to adjust pressures of 20 pieces marine airbags under stern to be 0.12 Mpa and 28 pieces marine airbags under bow to be 0.2 Mpa. Then the vessel got an approximate 0.013 radian inclined angle. At 8:40 am, people began to chop up the steel ropes which were attached to winches to pull ship to avoid unexpected slip. As soon as the ropes broke down vessel started to move into water by riding rolling marine airbags smoothly. It took 2 minutes from the vessel’s movement start to fully float.
From this ship launching project people can easily find irrefutable evidence of Evergreen marine airbags’ excellent quality. During the vessel lifting up period, pressures of eight pieces marine airbags reach 0.2 Mpa and holding these pressures more than 10 hours. It means each marine airbag bears more than 300 tons weight and no air leakage occurs in 10 hours.
Evergreen Maritime is devoted to be excellence. Up to date technology and new material are constantly applied to manufacture of marine airbags to assure Evergreen marine airbags can always satisfy customers’ increasing demands.

Sunday, June 6, 2010

Tunisian 950 Ton Ferry launched by Evergreen Marine Airbags

950 Ton newly constructed Ferry by Societe De Constructions Industrielles Et Navales was to be launched in Sfax, Tunisia with Evergreen Marine airbags.
After an initial study of various methods of ship launching, Evergreen Marine Airbags proved to be the pioneering and promising technology for this launch.
ISEAS being a representative of Evergreen in Middle East, Africa and India Region, was pleased to get this opportunity to do a technical feasibility study for the launching of this newly constructed Ferry.
At an initial stage, ISEAS’ representative carried out technical feasibility study by personally visiting the site. Various aspects of launching the ferry with Evergreen Marine Airbags were considered and discussed in detail.
Considering the shape of the bottom of the ferry, V shaped hull, it was critical to choose the right size of airbags as well as to design the slip way appropriately. The size of Evergreen Marine Airbags to be used was advised after a careful and systematic study. Accordingly the slip way angle was suggested.
It was also noted that this Ferry was constructed on a flat ground in Tunisia. Fortunately the flexibility of airbags proved remedy to this practical limitation; the slope could be created by adjusting the inner air pressure of the Evergreen Marine Airbags.
With all the necessary recommendation a complete report was submitted by ISEAS in order to ensure the safe and certain launch with this technology.
Prelaunch Preparatory and Evergreen Marine Airbags Inspection was carried out at an intermediate stage. ISEAS’ engineer effectively pressure tested all the Evergreen Airbags and inspected all other pre launching preparation.
Finally on 26th of May 2010, Vessel was ready to be launched with Evergreen Airbags Technology and as anticipated after all the necessary preparation under the supervision of ISEAS personnel, Mr. Krishan Kumar, the vessel glided into the water effortlessly as expected. The launch was Successful.