During the campaign conducted by the hydrographic vessel "Washington " in 1881 between Sciacca and Pantelleria (Maritime Magazine 1882), studies were carried out on coral reefs to study the extension, the shape and the conditions in which animals can grow coral.
The ganga is a device consisting of two iron tubes that connect together two iron flats in the shape of a horseshoe. Of the two tubes, the upper is bigger and the lower one is fixed at the center of the crossbars.
The iron frame is used to support a rope luff to which is sewn a net bag long enough. Inside this one is a smaller and finer net bag, that forms the trap to collect the fish in the double bottom and prevent the contents go away if the ganga goes upside down.
Just below the rim that forms the bottom of the trap, on the sides of the larger bag, also known as seine , is set another trap with even finer net, whose bottom is closed by a canvas bag.
Its purpose is to stop small fishes and crustaceans - once entered into the seine - that could pass through the mesh.
Also, the canvas retains the mud collected in the ganga, avoiding that it is carried away by the flow of water.
To lower and tow the ganga a sling is used: it's a piece of wire with 0.07 m circumference, 25 m long. It carries at its half a thimble , and is conveniently tied to the top of the tool.
Finally, the ends of the sling, also equipped with a special thimble, are tied to the bottom of the seine while supporting a weight of 40 kg.
To make the frame of the Ganga heavier, four soundings , weighing 6 kg each, are fastened to it.
The ties at the ends of the frame should be weaker than the sling, so that, when the ganga meets a rock, the ties are broken and the tool may be recovered without damage, as the sling remains attached to the bottom of the net.