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.
A round iron rod, 2 meters long, is fastened at the ends in the center of two flat iron rings.
Six steel cables or chains are hanging from the rod at equal distance. Each one of these has three or four swabs , arranged one after another, and each swab has in the head a weight of three kilograms.
A sling with a thimble allows to support and tow the unit, while the iron rings help in preventing the tool from getting caught on the seabed.