They are heavy-duty forklifts of the sea, and can reach up to 200m in length.
Semi-submersible barges are used in the marine industry to carry cargo or equipment to oil rigs, or ferry other vessels.
For example, if a shipyard is in shallow waters, the semi-submersible barge can transport ships from the shipyard to open waters.
What makes the semi-submersible barge different from others is that its main deck can go several metres under water to "pick up" floating cargo such as oil rigs or other ships.
A semi-submersible barge made the news after it sank near Batam last Friday during a submerging trial. Three crew members, one of them a Singaporean, died while six others were rescued.
Dr Arun Dev, 60, a senior lecturer at the Singapore campus of Newcastle University's School of Marine Science and Technology, said these barges work by having water pumped into ballast tanks, which causes the barge to submerge partially. For the barge to float to the surface again, water is pumped out of the ballast tanks.
Vessels or cargo can be placed on the barge by lifting the load onto it or by submersion, said Captain Mohd Salleh, 54, the deputy director of Singapore Polytechnic's Singapore Maritime Academy.
The barges can be moved by tugboats or placed on other self-propelled transportation vessels.
Captain Salleh added that when testing such barges at sea, how well they perform depends on their stability, buoyancy and watertight integrity.
"Since the vessel is made of heavy steel, it must have sufficient buoyancy. Stability is a definite prerequisite, it is part of the ordinary practice of seamen," he said.
These barges are normally tested in open waters with sufficient depth to do the submersion, added Dr Dev.
Out at sea, the standard operating procedure is to don life jackets and all personal protection devices during operations, said Captain Salleh.
Dr Dev said crew members should not stand on the main deck of the ship while it is submerging as it is dangerous, so crew members would be located in the four pillars.
Semi-submersible barges are becoming increasingly common, added Dr Dev, as more shipyards are picking up this technology.
Large-scale barges can carry cargo such as ships, oil rigs or equipment for offshore industries.
There are four control towers, one at each corner of the barge.
To move the barge to the location, it is either towed or loaded onto other self-propelled transportation vessels.
The barge takes in ballast water to lower itself so that cargo can be loaded on it.
After cargo is loaded, ballast water is expelled to raise the barge.
This article was first published on July 24, 2014.
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