Classification And Selection Of Life Boat Davit
There are many types of davits, and the currently used ones can be roughly divided into gravity type and inverted type (rotary type is not used on sea ships). The gravity davit can be divided into a slide type and a dump type. In these two types, depending on the position of the arrangement, it can be divided into a plurality of different structural shapes. The inverted rod davit can be divided into a straight rod type and a sickle type. Similarly, these two types can be divided into various structural shapes depending on requirements and arrangements.
Gravity davits, which are more commonly used on seagoing vessels, move quickly and safely. When the brakes are opened, the davits act as gravity, and the boat is released without the need for power. However, the disadvantage of this type of davit is that the lifeboat is usually suspended on the boat frame, which relatively increases the center of gravity of the vessel.
A reversing davit or a rotary davit generally requires the boat to be lifted to a certain height in order to pour the boat to the outboard. Therefore, the speed of the boat is slower and the deck area is also larger. Since the davit is placed directly on the deck, the center of gravity of the ship can be relatively reduced compared to the gravity type described above. The inverted rod davit is mostly used on rivers.
By means of its own gravity, the boat is sent out of the outboard davit, called the gravity davit. China's relevant regulations
If the weight of the boat exceeds 2,300 kg in the outbound state, the gravity davit should be used. For those weighing less than 2,300 kg, gravity or shake-out davits can be used. There are two basic types of gravity davits, the gravity slide type and the gravity dumping davit. The gravity dumping davit is rotated by the weight of the boat and the pylon to rotate the hoist around its lower hinge to lift the dinghy out of the outboard. The gravity slide type davit consists of a hanger, a slide rail, a davit and an attachment. The rails are two arcuate rails, one end of which is fixed to the side wall of the superstructure and one end fixed to the side. The upper part of the hanger is curved, and the lower end is provided with a roller, and the roller can slide along the track. The span of the cradle and the hull changes during the sliding process, thereby releasing the boat outboard. When the boat is towing, the sling of the dinghy is hung on the lifting hook of the overweight trolley of the pylon, the daviting machine is started, the steel cable of the hoisting pulley is twisted, and the dinghy is hoisted. Gravity davits are suitable for small boats of any size on any ship. The hoisting boats are fast and reliable, so they are widely used. The disadvantage is that the structure is complicated and the cost is high.
Relying on the manpower to shake the handle and drive the mechanical device, the hanger is poured out and the boat is sent out of the outboard.
The davit is called a shake-out davit. China's relevant regulations stipulate that the weight of the small boat in the state of being transferred is less than 2300 kg, and the gravity type davit can be used, and the plum-out davit can also be used. The hangers of the shake-out davit have various forms, and the common feature is that there is a set of screw transmission mechanism, which is composed of a screw sleeve and a screw. The human rocking handle drives the screw to rotate, and the sleeve is connected to the hanger. It cannot rotate with the screw, so it moves along the screw, thereby loading the hanger into the inboard or out of the outboard. The use of a swing-out davit to hang a small boat is similar to the use of a roll-out davit, only when the boat is sent out and retracted into the inboard, not directly by manpower but by mechanical means. The structure of the shake-out davit is more complicated, but the operation is time-saving and labor-saving than the roll-out davit.
In addition to the requirements for the arrangement and operation of the davit, the specification of the life-saving equipment for sea-going vessels also stipulates: passenger ships, aquatic processing vessels, scientific survey vessels and oil tankers with a gross tonnage of 1,600 tons and over 1600 tons. The davits should all be gravity. Davits of other ships: If the weight of the lifeboat exceeds 2.3 tons in the operation and out state, gravity type should be adopted; if it does not exceed the weight of 2.3 tons, it can be inverted or gravity type; if it does not exceed 1.4 tons, it is allowed to adopt spiral