Home' Work Boat World : June 2010 Contents Developments in NAVAL ARCHITECTURE and CAD/CAM
A recent study by the US Government
found that US shipyards often take
longer to build ships than their European
and Asian counterparts.
The report concluded that processes and
practices that employed pre-production
were a key reason for the difference. It was
observed that US shipyards put less
emphasis on Design for Production (DFP)
principles in engineering which resulted in
significantly higher man-hours per
Compensated Gross Tonnage. To rectify
this problem, the US Navy-funded National
Shipbuilding Research Program (NSRP)
instituted projects to apply DFP principles
It was found that junior designers in
shipyards often lack knowledge of production
processes and facility constraints which can
lead to inefficiencies in production designs.
Fortunately, this challenge can be partially
overcome by incorporating DFP principles
into software tools.
US shipyards felt they could benefit by
incorporating the following DFP principles
into their CAD/CAM applications:
Minimisation of total piece parts
and welding, minimisation of
fabrication /assembly complexity, and the
standardisation of parts. American
yards predominantly use a production
detailing software suite made by
ShipConstructor Software so the company
agreed to develop new modules which
enhanced those DFP principles.
It was found that by minimising the
overall complexity and number of parts in
a single commonly used sub-assembly,
shipyards could save over 120 man-hours
per vessel. Thus, once a DFP-optimised
design for a sub-assembly was generated,
it was important to be able to re-use
Taking note of this fact, ShipConstructor
created a module called "Standard
Assemblies". A Standard Assembly is
defined as a part, or set of parts, including
Structure, Pipe, HVAC and Equipment
components defined once and used
repeatedly throughout the detail design of
a vessel. The definition includes both the
3D model of the assembly as well as the
specific assembly sequence to be used each
time the assembly is used in the 3D
product model of the ship.
This module allows experienced designers
to build a library of commonly used parts,
assemblies, and components that can be
consumed by less experienced designers.
These assemblies can be moved between one
vessel and the next, allowing for significant
reuse of this captured knowledge.
Reusing portions of the detail design
across shipbuilding programs increases the
degree of repeatability during the build
process of vessels which reduces the
amount of training required in production
across vessels and once again, lessens hours
spent in production. When used correctly,
this process creates significant cost savings
due to reduced production labour and time
required to model the portions of the vessel
where these Standard Assemblies are used.
Furthermore, if the definition of a
Standard Assembly is changed, all instances
of it are automatically updated via
ShipConstructor's Associative DWG
technology which significantly reduces errors.
Improved Pipe Supports
Shipyards identified another area where
an extremely low degree of standardisation,
little use of documented shipyard preferences
and a high degree of assembly complexity
was causing unnecessary production work.
The culprit was complex supports for piping
systems throughout the vessel.
Each situation where a pipe support is
required is slightly different, which results
in different support arrangements.
Different material types are used for the
doublers, legs and cross tiers for each
support. Different end-cut and cutout
standards are applied to each of the
elements in the support depending on the
preferences of the designer.
Upon insertion into the 3D model, the
pipe support, derived from the selected
template, has the required cutouts,
end-cuts, trims and materials required
to produce each one of the components
needed. In addition, each of the
components can be included in
ShipConstructor's usual array of production
output including plate and profile nesting,
profile plots, assembly drawings and more.
To ensure that the standardisation
added to the design of pipe supports was
correctly leveraged by the shipyard, a final
requirement of the new software was the
addition of functionality to generate
template-driven construction drawings for
the supports. The drawings needed to be
automatically dimensioned and annotated
based on the shipyard's requirements.
Complete bills of materials on each
drawing were required that would facilitate
the fabrication of the support.
For further information contact:
Practical applications of design for production make big savings
Improved pipe supports in a ShipConstructor model
June 2010 WORK BOAT WORLD
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