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 rake consists of two flat iron knives, placed parallel to each other and joined on the shorter sides by two rectangles of iron rods. On the other side, these boxes are connected together by two crosspieces of the same metal, to form a parallelepiped. A shaft of beech or pine is hanging on the lower base, in order to bring four swabs and three weights six kilograms each.
Two iron arms, fixed to the top of the rectangles, are connected at the top by a rope forming the towing eye. A canvas bag is suspended at the bottom of the knives to collect what is taken from the seabed.
A net bag is inside the first and smaller, and forms a double bottom to avoid the contents is overthrown, should the rake turn upside down. The inner bag, also called the trap, ends at the bottom with a metal ring, that allows to collect the material going into the outer bag.
The towing cable is attached to only one of the supporting arms, so, if the rake encounters a rock, the tie can break, allowing to recover the entire tool.
The tie is done with one side longer than the other one, in order to decrease the resistance to towing.
The swabs are used to take small animals or algae that do not enter the rake, and the weights added to the wooden shaft keep the tool vertical when it is sunken. Also, the larger faces of the box are covered with canvas, to avoid damage to the bag when the rake scrapes the seabed.
To thoroughly study the coral it was necessary to have a rake that in addition to bringing up the coral, also took pieces of coral rock on which the animals attach, and so have knowledge on the exact nature of the seabed where they can easily propagate .The commander of the expedition Magnaghi invented a device in the form below.
Two iron rings 20 cm diameter and 230 cm apart, serve to hold together six curved bars of flat iron. The assembly forms a cage, about 80 cm wide.
Inside this cage, in the middle, it is suspended an iron ring with a diameter of 70 cm, which brings a net bag with the trap. The net bag is provided at the bottom with a canvas bag.
A sling of rope with four arms supports the bag from the top, while the bottom is connected to the bottom ring. On three of the six curved bars forming the cage, about two feet above the base, are suspended three chains with a length of 150 cm, each carrying a swab. Three other swabs are attached to the three remaining bars so that thet are at the height of the chains. Lastly to the top circle is fixed a handle with an eye to suspend and tow the tool.
This rake gave satisfactory results, as its narrow shape facilitates going through the obstacles, and the robust metal bars can easily break some materials, while those that penetrate among the bars are retained by the net.
In case the device passes between two rocks, the bars can bend, the rake squeezes and can be safely recovered with all the materials it contains. Moreover, as the tool works in a horizontal position, the portion of the inner ring that is between the two bars crawling on the bottom, rakes on its own, and if the obstacle is beyond its strength, the ring is free to disengage, and the net should not break. Furthermore, the swabs, arranged as explained, cover a large surface on seabed, that has already been moved by the rake, so that algae, crustaceans and corals that didn't penetrate into the bag, can be trapped.
Finally, this rake allows the ship to maneuver faster and in safer conditions, contributing to make less difficult the task.