Marine airbags are often called ship launching airbags that indicates they are most used for launching ship into water. Inspired by ship launching, people developed many applications of marine airbags in different fields, the most remarkable one is heavy lifting and moving with marine airbags.
SPMT stands for self-propelled modular transporter, a platform vehicle with a large array of wheels; it is equipped with Power Pack Unit which provides the propulsion.
Obviously marine airbags are not as famous as SPMTs in heavy lifting and transport fields. The main reason is that marine airbag is not a high developed industry product yet; its ISO standard was issued only at 2011 years. Due to special manufacture technology marine airbags can only be made in China which also limited its worldwide development.
Marine airbags heavy lifting and load out has similarity with SPMTs but more difference. A comparison may help people to know their individual characters.
●Heavy Lifting
●Lifting Capacity
The SPMTs consist of four-axle units or six-axle units, the maximum allowable axleline payload is 30 tons per line. Then we can know:
Air bags' diameters are available from 1 meter to 2.5 meters and maximum length is 25 meters. Its lifting capacity is decided by below formula:
Then we can see airbag's lifting performance is decided by its working height and inner pressure.
Airbag specification | Load | Lifting height | Airbag pressure |
1.0 ×15 m | 471 tons | 0.5 m | 4 bar |
1.5 ×15 m | 235 tons | 1.0 m | 2 bar |
2.0 ×15 m | 420 tons | 1.0 m | 1.8 bar |
Provided there is a caisson with follow dimension needs to be lifted.
Length(m) | Width(m) | Height(m) | Weight(t) |
20.45 | 13.45 | 17.3 | 2357 |
To lift this caisson at 0.5 m high from ground people may choose 6 pieces airbags (1.0×15 m). The total 6 pieces airbags' lifting capacity is 422×6=2533 tons. Air bags can be positioned with 4 m space.
To lift this caisson with SPMTs, people will need 2357/180=13 units 6 line modules but the structure dimension decides maximum 12 units modules can be deployed. Then SPMTs is not suit for this caisson lifting and moving.
Lifting Heights
Deflated airbags can be inserted into 20 cm height space underneath structure and when they are inflated they can lift structure up to 2 meters height.
The trailer deck of Kama g and Scheuerle SPMTs can be lowered to 1.2 m, so they can only be driven into higher space. The lifting distance of SPTMs is about 50-60 cm.
Operation
Marine airbags heavy lifting needs to place and inflate airbags piece by piece so the operation is not as quick as SPMTs. However this character enables airbags to fit into very limited space for lifting, such as vessel holds.
In a conclusion, SPMTs will generally need extra lifting systems to put the load onto the trailer decks due to limited lifting capacity or space. Marine airbags are better at heavy lifting (Jack up).
●Heavy transport
●Load out
By heavy load out, we mean the process of moving a structure from land to a barge. Normally, the structure need to be lifted from support then skidded or rolled onto barge.
Marine airbags heavy load out need the structure has flat bottom which enable airbags can roll underneath. For frame works people need to create the solid flat bottoms for them by placing steel plates under structures.
SPMTs are peerless for load out of frame works and odd size modules.
Marine airbags load out need winches to pull and hold load to move. SPMTs do not need extra winch systems.
SPMTs allow each wheel to telescope independently of each other, so that the load can be kept flat and evenly distributed while moving over uneven terrain. Marine airbags can also achieve this effect but need to be operated manually.
Steering
Each individual wheel can swivel independently from other wheels so SPMT can turn, move sideways, or even spin in place.
Marine airbags heavy transport can also be steerable by manual adjusting airbags inclined angles. Obviously this performance is not as convenient as SPMTs do.
Steering radius
From theory calculation the possible steering radius of airbags and SPMTs of load transport should be same. Considering load capacity/meter of SPMTs is not optimal, SPMTs steering radius should be bigger than marine air bags.
Speed
SPMTs often move at under one mile per hour while fully loaded. Marine airbags heavy transport speed is decided by the winch speed which is often less than 0.6 KM one hour.
In a conclusion, SPMTs is good at heavy load out or transport. Marine airbags heavy transport only suit for regular structure with possible flat bottom and short distance transport.
As mentioned before marine airbag is not a high developed industry product but that can not cover its advantages for some heavy lifting and transport or load out applications. Such as concrete caissons load out projects, marine airbags are found to be most convenient and economical method to be used. Marine air bags can roll a load into water directly which can even save the semi submersible barge. Steel cofferdams weighing 3000 tons had been transported from construction spot to river bank and launched successfully.
The SPMT is a classic solution for heavy load transport. It is versatile, extendable and often the only viable solution for large structures. However, the classic SPMT has some drawbacks: it is ill suited for indoor operation due to its combustion power source. It has a high deck height, making access to the cargo difficult or requiring extra lifting systems to put the load onto the SPMT. It's load capacity/meter is not optimal and it needs a lot of space. Many SPMT types are not fully omni-directional and it is not easily automated. Their hydraulic circuits of the hydraulic motors experience high pressure peaks which often lead to oil leakage, the same goes for the hydraulic suspension. The classic SPMT requires a high maintenance schedule resulting in high costs. On the whole they come to be not cheap.
English
