Feature 1 | Yacht Design anD construction
Weight management – a key element in
yacht design and construction
Peter Mitchell of renowned UK-based naval architects Burness Corlett Three
Quays (BCTQ) examines the part that weight management considerations
play on the design and construction of yacht newbuilds.
A
key part of the design development
process of a new one-off custom-
built yacht is an early assessment
of the lightship weight and centre of gravity
(with suitable margins), combined with
generating satisfactory loading conditions.
The lightship comprises the hull and
machinery, whereas deadweight is that of all
liquids onboard (fuel, water etc.), tenders and
water toys, stores, passengers/guests and crew
and their effects. The displacement or total
weight is the sum of these two groups. The
assumptions made now will have a lasting
impact on the final outcome, so it is essential
to make a good initial estimate of weight
and centre of gravity, and then to ensure
that these parameters are kept under firm
control throughout the remaining design
and build process through the application
of an effective weight management system. Design drawings are used as a basis for weight calculations (credit: Burness corlett three
Such a system will enable any undesirable Quays (southampton) Ltd).
trends in weight and centre of gravity to be
highlighted at the earliest possible stage so
that any corrective actions will have the best is exceeded, the deadweight will need to be all the technical requirements of the owner
chance of success. reduced. It is quite possible to design a yacht and regulatory authorities. Included in this
BCTQ stresses the potential consequences to need no ballast for stability reasons, and assessment would be verifying the lightship
of poor weight management, particularly in to be able to transfer fuel as it is consumed to weight and centre of gravity locations
the case of a single one-off design. The owner maintain trim, so any inclusion of ballast will against the large number of yachts in our
will want to be assured that his yacht will be imply a poor design. Corrective measures database, which would provide a high level
able to achieve the speed and range he asked to lightship weight and centre of gravity, if of confidence in the project’s viability. BCTQ
for, to be able to enter certain harbours or determined at a very early stage can include would then prepare a technical specification
restricted waters with minimal trim, and to increasing buoyancy forward or aft. Later on and assist the owner in the process of
have the capacity for a degree of future growth in the project when it is too late to change selecting a suitable shipyard to build the
in weight. If the lightship weight exceeds the the hull form it can be possible to substitute yacht. It will be at this point of awarding the
initial estimates, then the deadweight will some parts of the yacht by lightweight shipbuilding contract that responsibilities for
need to be reduced if the draught is to be components. Any of these options will of design are fully understood by all concerned.
maintained, with a consequent reduction course carry a price tag. The responsibility of ensuring that the yacht
in range – by far the largest component of A common process in arriving at a contract will meet all the technical requirements will
deadweight is fuel. with a shipbuilder will involve the above close be taken over from BCTQ as the consultant
If the longitudinal centre of gravity of liaison between designer and naval architect naval architect by the shipyard, so the
the lightship is much different from that consultant, and BCTQ has frequently taken shipyard must satisfy them, before signing
estimated, some form of ballast, whether the latter role combined with input from our the contract that they can indeed design and
permanent or not, will be needed to correct experienced marine engineers. We would build a yacht meeting all the requirements.
the trim, which will in turn increase the satisfy ourselves that a yacht as shown by the BCTQ would then take up the role of
displacement, or if the maximum draught designer’s arrangement drawings will meet providing technical assistance to the owner
Ship & Boat International March/April 2010 23
SBI_MarApr10_p23-24.indd 23 26/02/2010 12:21:42
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