The present invention generally relates to the field of underwater painting and, more particularly, an improved method of an apparatus for efficiently carrying out underwater painting of ships and offshore constructions.
In recent years, there has been a remarkable tendency seen to make ocean going ships more full in the hull scale as typically shown in the case of oil tankers. Also, it has become increasingly more frequent today than before to build an offshore construction such as an oil drilling rig or the like.
As such tendency develops, there have been increasing difficulties encountered. For example, with ships having a fuller hull size, a shortage is indicated of accordingly larger scale docks and docking accommodations. Additionally, the docking interval of ships has today been greatly prolonged in comparison to the past, and in accordance with this, various problems have now been presented concerning the mechanical maintenance of a submerged portion of the painted shell surface of the ship's hull. In the case of offshore constructions such as oil-well platforms for example, once it is towed to the prescribed sea area and settled thereat, the construction cannot with ease be towed or otherwise transferred for a maintenance operation. Thus, with an under water operation for the prevention of corrosion or rust generation, or for cleaning, maintenance and so forth are present. Thus, the necessity has now grown to be greater for efficiently carrying out underwater operation for the maintenance of ships and offshore constructions, and a solution effectively answering such necessity is universally called for today.
With regard to the art for underwater painting, there has not yet been an established technique. In some instances, underwater painting is worked by way of an manual operation done by divers manually coating an in-water curable paint, or it is effected by use of a spatula of the type in which the paint is fed under pressure. However, those operations are inefficient: They are only of a nature by which underwater painting can be done but no satisfactory painting performance can be obtained with regard to the thickness of the coated film, evenness of the coating and strength of the adhesion of paint (it is only 1/3-1/4 of the strength in the case of a painting under atmospheric conditions).
In order to overcome the shortcomings of such old art, some underwater painting machines have been developed, an example of which is disclosed in Japanese Patent Application No. 51-26649 laid open under publication No. 52-111196 on Sept. 17, 1977. The painting machine of such prior art is as illustrated in FIG. 1 of the accompanying drawings, and in brief it has the following features:
The underwater painting machine includes a main body as indicated at 101 in FIG. 1, which has driving wheels 102 for driving the machine in back and forth or longitudinal directions and similar wheels 103 for driving in left and right or transverse directions, each wheel comprising an inflatable material such as a rubber type. By inflating the tyres by sending air into the same, the machine is lifted up, and by actuating an air motor or electric motor 104 and supplying power across an electromagnet 105 and 106, the machine can be driven to run in longitudinal and transverse directions without being detached from a surface of a construction to be painted. The main body 101 includes electromagnets 105 and 106 for preventing the machine from falling or floating away the surface for painting and a water valve 107. Within the body 101, further, an open-bottom box structure 108 is provided, internally defining a painting chamber 110, and between the body 101 and the box structure 108, there is formed a buoyancy tank 109. The box structure 108 has at its top a portion 111 for mounting thereto nozzles for injection of washing water for cleaning the surface for painting, air to be supplied at a high velocity for drying the washed surface and an in-water curable or hydro-curable paint. About the lower end periphery of the box structure 108, an inflatable sealing tube 112 and an outer covering 113 are extended, and by supplying air into the sealing tube 112 to have it inflated, the painting chamber 110 can be sealably shut from the ambient water. When the box structure 108 is thus intimately attached to the surface for painting, air will be sent into the painting chamber 110 through a flexible tube 114 to remove away the water within the chamber 110, and then the paint will be jetted through the nozzles fixed to the portion 111 to thereby paint the surface for painting.
The method of underwater painting utilizing an automatic painting apparatus as above described is more efficient in comparison to the manual painting operation of the old art. However, even such method has shortcomings for example as follows:
1. The painting machine is maneuvable only in longitudinal and transverse directions, whereby it is difficult to freely turn the machine or move it as desired. PA0 2. The magnetic force of electromagnets is relatively low and the attenuation of magnetic force proportional to increase in distance is of a relatively high degree, so that particularly when there lies a relatively great distance between the electromagnets and the metal surface for painting, it is difficult to freely run the machine. PA0 3. The machine is not adapted for changes in the buoyancy it receives when water is filled in the painting chamber or discharged from the same, and it is therefore difficult to maintain the machine in a stably settled condition in water. PA0 4. The jetting nozzles are immovably secured at the top of the painting chamber, so that it is difficult to perform a uniform painting or to provide a relatively wide space for the painting chamber. PA0 5. During the stoppage of painting operation, paint is permitted to stay in the piping, and the pipe is often permitted to undergo clogging. PA0 6. The buoyancy adjusting mechanism limitedly comprises a buoyancy tank only, so that it is difficult to freely let the machine be submerged, floated or maintained in a stably settled condition.