Description SHIP WITH BOTTOM WORK SPACE FOR WELDING

Technical Field

[1] The present invention relates to a ship including hull parts constructed independently and combined together at the end of construction and, more particularly, to a ship having a welding-purpose bottom work space formed with such a height as to ensure that joint portions of the hull parts to be welded can lie above a water level when the hull parts are launched into water. Background Art

[2] As is generally known in the art, a ship is far greater in size than a typical building structure and is constructed through a complex process. The ship goes through a construction process in which many different members and devices are combined together. Nowadays, most of large ships are constructed in a dock which refers to an installation provided in a shipbuilding yard or a harbor for building or repairing a ship.

[3] The dock is largely classified into a dry dock and a floating dock. The dry dock is situated near a sea area having a sufficiently great depth and is formed by excavating ground into a length, width and depth great enough to accommodate a ship. The dry dock has side walls and a floor formed of a reinforced concrete and sheet piles. A dock gate is installed in a gateway of the dry dock. The floating dock is a steel-made box having a generally "U"-like cross-section and is provided with a plurality of water tanks. The buoyancy of the floating dock is controlled by changing the quantity of sea water stored in the water tanks.

[4] Due to the restriction in the size of the dock, a large building structure such as a ship or the like is constructed on a block-by-block basis unlike the manufacture of a motor vehicle. In other words, the first step of building a ship is to prepare a multiplicity of individual small blocks (about two hundreds blocks in case of a supertanker having a dead weight of 300,000 tons). The individual small blocks are grouped and assembled together to produce a plurality of medium- sized mounting blocks. Thereafter, the mounting blocks are assembled into a ship in the dock. However, in case of ultra large- sized ships that enjoy an increasing demand in recent years, e.g., heavy lift vessels and ultra large crude oil carriers, there is a limit in assembling blocks within a conventional small dock and completing the overall process of building the ships.

[5] Figs. 1 and 2 are front and top plan views illustrating a conventional shipbuilding method in which left and right hull parts are combined together to build a ultra large- sized ship.

[6] As can be seen in Figs. 1 and 2, left and right hull parts are produced in different

docks and launched into sea water. Then, the left and right hull parts are combined together in a floating state. This shipbuilding method makes it possible to overcome a restriction imposed by the size of a dock in building an ultra large ship. Furthermore, the shipbuilding method helps shorten the use cycle time of a dock and increase the dock use frequency, thereby enhancing the productivity of an ultra large ship.

[7] In order to complete the shipbuilding process, it is necessary to weld joint portions

Cl of the left and right hull parts. When the left and right hull parts are launched into sea water for a welding purpose, however, the joint portions Cl of the left and right hull parts are partly positioned below a water line (WL) and submerged in the sea water. Therefore, a welding work for bonding the left and right hull parts together needs to be performed under the sea water.

[8] In the underwater welding, a base material is melted by an electric arc and the melted base material is covered with a flux as is the case in a ground welding. A direct current source, cables, a circuit breaker, a welding rod holder, a grounding clamp and a welding rod are needed to perform the underwater welding. One of the cables is connected at one end to a negative terminal of the direct current source and the other cable is connected at one end to a positive terminal of the direct current source. The cables are connected at the other ends to the welding rod holder and the grounding clamp via the circuit breaker.

[9] As the welding rod on the clamp makes contact with the base material, an arc with a temperature of 6,000 to 10,000 ⁰ C is generated to melt the end of the welding rod and the portion of the base material around the welding rod. The melted metal of the welding rod is moved toward the base material along the flow of the arc under the influence of gravity, electricity, electromagnetism, gas diffusion, surface tension and the like.

[10] However, the underwater welding shows a low welding quality in most cases. This is because a large number of air bubbles are generated around the arc in the course of underwater welding and a hydrogen gas present in the air bubbles is introduced into the welded metal, consequently causing cracks to the welded hull parts. Setting aside the welding quality problem, the underwater welding is more difficult to conduct than the ground welding, thereby posing a problem in terms of workability, safety and cost. Disclosure of Invention Technical Problem

[11] In view of the above-noted problems, it is an object of the present invention to provide a ship that allows joint portions of independently constructed hull parts to be kept above a water surface when the hull parts are launched into the water and makes it possible to weld the joint portions of hull parts above a water level.

Technical Solution

[12] In accordance with one aspect of the invention, there is provided a ship including hull parts constructed independently of one another, the hull parts having joint portions to be welded together and stepped portions to form a bottom work space for welding when the joint portions are welded together, the stepped portions having such a height as to ensure that the joint portions can lie above a water level when each hull part is launched into water. Brief Description of the Drawings

[13] Fig. 1 is a front view illustrating a conventional shipbuilding method in which left and right hull parts are combined together to build a ship.

[14] Fig. 2 is a top view illustrating a conventional shipbuilding method in which left and right hull parts are combined together to build a ship.

[15] Fig. 3 is a front view showing a ship having a welding-purpose bottom work space in accordance with the present invention.

[16] Fig. 4 is a top plan view of the ship having a welding-purpose bottom work space shown in Fig. 3. Best Mode for Carrying Out the Invention

[17] Hereinafter, one embodiment of a ship having a welding-purpose bottom work space in accordance with the present invention will be described with reference to the accompanying drawings.

[18] The present invention is applicable to ultra large ships which are too large to be built in a single dock, e.g., heavy lift vessels, ultra large crude oil carriers, floating production storage and offloading units and floating barges. The heavy lift vessels refers to ships equipped with a large-capacity crane and specially designed to transport large-sized and heavy cargos that cannot be transported by a typical cargo ships.

[19] Fig. 3 is a front view showing a ship having a welding-purpose bottom work space in accordance with the present invention. Fig. 4 is a top plan view of the ship having a welding-purpose bottom work space shown in Fig. 3.

[20] Referring to Figs. 3 and 4, the ship of the present invention is built by independently constructing left and right hull parts 1 and 2 and then welding joint portions C2 of the left and right hull parts 1 and 2 together. The ship has a bottom work space 10 formed below the joint portions C2 of the hull parts 1 and 2. The bottom work space 10 allows a welder to gain access to the bottom ends of the joint portions C2. Owing to the presence of the bottom work space 10, the joint portions C2 to be welded are positioned above a water line (WL). This makes it possible to avoid any underwater welding work when welding the bottom ends of the joint portions C2. The hull parts 1 and 2 are of a structure suitable for a ship including building heavy lift vessels, ultra

large crude oil carriers, floating production storage and offloading units and floating barges.

[21] As can be seen in Fig. 3, the bottom work space 10 has a planar ceiling surface 10a that allows a welder to weld the bottom ends of the joint portions C2 with ease. The bottom work space 10 has a height H great enough to secure a water-free welding space with an effective height AH when the hull parts 1 and 2 are launched into water. The height H of the bottom work space 10 may vary with the size and use of a ship to be built. Referring to Fig. 4, the bottom work space 10 has a length L decided by the length of the joint portions C2 which would be welded together by an underwater welding work if the bottom work space 10 is absent.

[22] The bottom work space 10 has a substantially trapezoidal cross-sectional shape in the illustrated embodiment. As long as the water-free welding space with an effective height AH is secured, the bottom work space 10 may have other cross-sectional shapes depending on the use of a ship and required speed thereof. Reduction in transverse strength caused by formation of the bottom work space 10 can be overcome by reinforcing transverse web frames and transverse bulkheads.

[23] As described above, the ship having a welding-purpose bottom work space in accordance with the present invention ensures that the joint portions of the hull parts 1 and 2 lie above a water level when welding the hull parts 1 and 2 together. This eliminates the need to perform an underwater welding work, thereby enhancing the welding quality and the welder's safety while reducing the welding cost.