In water survey of ships afloat
All without an exception of ships are exposed to influence of the water sea element and their structural components are worn out and need constant preventive and scheduled repair.
So that the ship was in a state of constant service readiness, it is necessary to inspect her at certain periods including the underwater survey and timely repair works.
The underwater survey is a scheduled or unscheduled inspection, but necessary due to the certain circumstances, expertise of risks. The underwater survey of the ship's hull state is a procedure which is required for each ship irrespectively of her type and cargo-carrying capacity. The underwater survey is necessary for estimation of the general and detailed technical state of the hip's hull underwater part before docking, purchase or sale of the ship as well as a compulsory part of a package of measures approved by the Classification societies.
The ships are inspected in dock and as well as afloat. According to the official rules the underwater inspection (survey) as well as estimation of state of the ship's hull underwater part when the ship being afloat is possible only with special instruments and equipment by means of which the measurements should be carried out, video and television shot, transmitting system of the captured image to the monitor in mode of real time (CCTV or underwater television). Such a fault detection of the ship afloat without necessity of docking enables to carry out a qualitative examination of the hull shell plating, moreover to check its anode and cathodic protection and fasteners, state of plates in the shell plating, to define availability and localization of dents, cracks or fractures, to inspect the sea valve gratings, to inspect the propulsion/steering unit by measuring the bearings sag of the rudder blade stock and stern gear. Inspection afloat makes it easier to identify the possible risks and better to define the list of the forthcoming repair works.
Each ship is itself individual, each has her own history and fate, that's why every time the underwater survey is carried out with taking into account the peculiarities of the object.
In most cases the ship's underwater inspection is carried out under supervision of the Classification society inspector, and the diving companies performing the inspection are pre-tested for competence in a required Classification society and have its recognition at the hands for performing the works as to surveying the ships.
Here is the approximate description of the list of arrangements which the divers carry out when the ships' underwater inspection is required.
- As a rule the specialists-divers, equipped with special instruments and video-equipment according to the approved survey program, are dived into a required depth.
- Then those places and objects which should be checked are shown to an inspector.
- The inspector observes the inspection and constantly sees the image on his screen as well as he can adjust the divers' work and direct their actions. The underwater part of the hull, bottom and side openings, bilge keels, welded seams, riveted joints and many others are examined, in a word everything that requires checking and inspection.
- The propellers are thoroughly examined, their state is estimated and availability or unavailability of cracks, corrosion on the surface of blades are defined.
- If there is necessity for discussion of the disputable matters, more detailed or repeated examination, all detected defects are captured by photography and video-record.
- Besides the underwater inspection (survey) can detect the hull dents which a specialist-diver measures by means of the special meters, magnetic strips and other instruments.
- Sometimes the underwater inspection is accompanied by simultaneous repair works in the case if the defects can be eliminated at once afloat. Such partial and urgent repair helps to prolong the reliability of the ship's operational characteristics and to decrease the emergency risks to a considerable extent.