ship yard practices

                                   

DESCRIPTION OF CONSTRUCTION STAGE IN SHIPBUILDING

•      Treatment of steel in a shipyard

•      In the shipyard corrosion protection is of prime importance.

•      Pre-Heating

•      The plates & profiles first pass through a pre-heater, this raises the temperature of the metal ready for blasting & removes any surface moisture.

•      Blast Cleaning

•      Sheets & profiles are thoroughly blast cleaned.The blast chamber removes rust and mill scale  and provides a finish to internationally recognised preparation grades

•      Rust grades

•      Four rust grades are specified. These are defined by precise written descriptions

•      and photographic examples in ISO 8501-1documentation. They vary from A: mill scale,to D: where the mill scale has rusted away and general pitting is visible.

•      Preparation grades

•      Surface preparation by blast cleaning is designated by the international standard ISO8501. Four grades are specified, ranging from Sa 1: light blast cleaning, to Sa 3: blast cleaning to visually clean steel.

•      Paint spray chamber, voc-system and filter

•      The various plate and profile widths are automatically identified and are coated in a continuous process with a weld-primer coating

•      thickness of approximately 15 - 25μm.

•      Paint dust and solvents (if no water based paint is used) are treated according to the local requirements in an automatic filter unit and aVOC-treatment plant.

•      Drying chamber & slat conveyor

•      This chamber can be heated by the exhausted air from the pre-heater . Additional circulation of high quantities of air accelerates the drying process.

•      Lying on the support points of the conveyor cross slats the wet primer remains undamaged as the plates pass through the drying chamber.

•      Marking

•      Each sheet has its own unique identification to allow subsequent allocation and control. The mark is spray painted by computer controlled nozzles.

•      Edge cleaning

•      To ensure optimum weld quality, the edges of the profiles are blasted to remove paint from the weld area .

•      Airblast units for this operation are suitable for smaller profiles and often precede a gas-cutting machine.

•      Conveying

•      The plates are now conveyed to be fabricated into ship segments

•      Building and repair activity has changed considerably over the years not least with the introduction of prefabrication techniques.

•      New technology providing exact measurement has allowed the larger and heavier section to become the norm rather than the exception

COMPUTER AIDED DESIGN / ENGINEERING / MANUFACTURE

Since the late 1970s, developments in computer hardware based on microchip technology have made available to industry very powerful computer systems at moderate cost. This technology has led to a significant advance in the capability of systems for computer aided design, computer aided engineering and computer aided manufacture (CAD/CAE/CAM) which are commonly available to industry. Such systems have steadily replaced manual draughting and numerically controlled parts programming in many shipyards. Computer based shipbuilding systems developed during the late 1960s and early 1970s and used for numerically controlled production machines and loftwork , have now been enhanced to extend their scope to the design and drawing office functions and provide interfaces with a comprehensive

range of other shipyard systems.

The CAD/CAE/CAM systems are based on a 3D Ship Product Model in

which the geometry and the attributes of all elements of the ship, derived from the contract design and classification society structural Requirements are stored.

This model can be visualized at all stages and can be exploited to

obtain information for production of the ship.

It has been common practice for the drawing office to contain a material

ordering department, which was able to lift the necessary requirements

from the drawings and process them. Also, the office worked in close conjunction with the loft and planning production office. With the introduction of CAD/CAE/CAM systems to the drawing office these functions have been increased and improved. From the 3D ship product model, the precision of the structural drawings generated enables them to be used with greater confidence than was possible with manual drawings and the requisitioning information can be stored on the computer to be interfaced with the shipyards commercial systems for purchasing and material control. Subassembly, assembly and block drawings can be created in 2-dimensional and 3-dimensional form and a library of standard production sequences and production facilities can be called up so that the draughtsman can ensure the structural design uses the yards resources efficiently and follows established and cost effective practices. Weld lengths and types, steel weights and detailed parts lists can be processed from the information on the drawing and passed to the production control systems. A 3-dimensional steel assembly can be rotated by a draughtsman on screen to assess the best orientation for maximum downhand welding. The use of 3-dimensional drawings is particularly valuable in the area of outfit drawings where items

like pipework and trunking can be ‘sighted’ in the 3-dimensional mode and more accurately measured before being created in the 2-dimensional drawing.

Today CAD/CAM software programs for ship construction are available which can be run on ordinary PCs having sufficient memory. These programs can be used to design a ship according to one’s own requirements. Besides hull design and production of plans it is also possible to calculate hydrostatics and stability, internal structural design, Strength, wind and sea resistance and power requirements.