Page 131 - Ship Construction.DJ Eyres 6Ed

Ch12-H8070.fm Page 120 Wednesday, October 18, 2006 6:55 AM
120 Ship Construction
Computer Aided Design (CAD)/Computer Aided
Manufacturing (CAM)

The first use of computers in the shipbuilding industry probably occurred in
the 1960’s and because of the high costs involved were only used by the
largest shipbuilders running programs developed in-house on a mainframe
or mini computer for hull lines fairing, hydrostatics, powering calculations
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etc. The hull design would have been drawn by hand and stored on the com-
puter as tables of offsets.
In the late 1970’s the graphics terminal and the Engineering Workstation
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became readily available and could be linked to a mini computer. These
computers cost considerably less than the earlier mainframes and commer-
cial ship design and construction software became available for them. The
larger shipyards quickly adopted these systems. They developed further in
the following two decades to run on UNIX Workstations and Windows NT
machines and have expanded to cover virtually all the computing needs of a
large shipyard.
The early 1980’s saw the appearance of the Personal Computer (PC) and
several low cost software packages that performed simple hull design,
hydrostatics and powering estimate tasks. These were popular with small
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shipyards and also reportedly with some larger shipyards for preliminary
design work. They were however somewhat limited and incompatible so
that it was difficult to build a system that covered all the shipyards CAD/
CAM requirements. During the 1990’s the available PC software standard-
ised on hardware, operating systems, programming languages, data inter-
change file formats and hull geometry and are now widely used by naval
architects and the smaller ship and boat building industry in general.

SHIP PRODUCT MODEL Software systems for large shipbuilders is
based on the concept of the ‘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 infor-
mation for production of the ship. See Figure 12.3.
At the heart of the ‘Ship Product Model’ is the conceptual creation of the
hull form and its subsequent fairing for production purposes which is
accomplished without committing any plan to paper. This faired hull form
is generally held in the computer system as a ‘wire model’ which typically
defines the moulded lines of all structural items so that any structural sec-
tion of the ship can be generated automatically from the ‘wire model’. The
model can be worked on interactively with other stored shipyard standards
and practices to produce detailed arrangement and working drawings. The
precision of the structural drawings generated enables them to be used with
greater confidence than was possible with manual drawings and the materials