Trans RINA, Vol 154, Part C1, Intl J Marine Design, Jan - Jun 2012
floating correctly, and that any discrepancies from the original weight study could be accommodated where possible in the ongoing construction. Although it is possible to adjust the amount of ballast in the keel to compensate for minor discrepancies, it is essential to get the weight study as accurate as possible before the final design of the hull is committed to building, as increasing any weights would likely result in a drop in stability and have a negative impact on performance and handling characteristics.
Fore and aft balance had to be considered in relation to beam, ballast, crew placement,
righting moment,
displacement–length ratio and the conditions for which the boat is to be optimised This is ultimately determined by evaluating the fore and aft symmetry of the hull, expressed by the diagonals, while considering these other factors in the context of the boat’s concept.
Waterline angle of entry is a critical component
contributing to resistance. Every effort was taken to minimise this angle while maintaining the fore and aft balance of the boat. A slight hollow is acceptable in the first 5% of the waterline length but any more than this can have negative effects on resistance and handling characteristics. The result of my design research was a waterline entry which has a slight hollow in the first 200mm, fairing into a straight line aft to station 3.5, then into a curve which runs through the mid-section of the hull.
I chose not to complete the analysis of the draft hull lines and reach the final model until the construction of the deck was complete and the weight study updated and finalised. For this process, I transferred my hand-drawn lines plans to the computer and proceeded using a CAD (computer-aided drafting) model, supplementing the CAD image by plotting out many scale drawings for ease of viewing.
With the design transferred into a CAD program, I was able to move from the art-based approach of the early concept design to a more scientific one, analysing the design’s key characteristics such as stability and balance from an engineering standpoint, and refining details. I used this methodology because I wanted to be confident in the concept design before working on the detailing; I believe if the basic (art-based) concept is flawed, science cannot be deployed to “fix” it.
Having gone through a thorough process of determining both the desired numerical attributes for the final draft and its form characteristics, the development of this final model was a straightforward process. This enabled me to concentrate on achieving a perfectly fair and accurate model, blending together the optimum numerical and form
characteristics identified through the iterative
design process. The experience of creating this model was quite a
Construction of the Shaw 9m Karma Police was completed and the boat launched in May 2009. A sister ship, Deep Throttle, was launched in February 2009. On- the-water testing, trialling and racing of these two boats was then carried out to assess the performance of the design and investigate how the action spiral process resulted in its success.
As stated earlier, the process of designing the Shaw 9m combined aspects of “art”, or using intuition and the “designer’s eye” to generate ideas and concepts, with the “science” of using computer evaluation tools
and
engineering disciplines to develop and refine the design. As above, the three key considerations in the design of the yacht were:
Accessibility (in terms of cost and ease of construction, and transportability)
Performance (including quantifiable elements such as speed)
Handling characteristics/feel (user experience and ease of sailing and crewing).
As well as my self-evaluation of the concept, since its launch the boat
has been reviewed by independent
authors and featured in a number of published articles and website reviews. It has also generated a strong race record, both short-handed and fully crewed.
4.1 ACCESSIBLITY
A key driver was for the boat to be accessible, keeping the cost of construction and running to a reasonable level while still producing a yacht which would offer high performance and ease of sailing. This was done through the considered design of hull, deck and rig, in terms of specification of construction materials, rigging and deck gear.
The design resulted in the production of a 9 metre boat for around $285,000, comparable to other boats of this size, and considerably less expensive than other boats offering a similar performance, which are larger. Using the action research spiral to investigate and refine aspects of the construction process as outlined earlier made a major contribution to keeping the boat affordable. This in turn made the boat appealing to a wider market sector.
contrast to the previous stages of design development. Whereas in earlier iterations I frequently experienced a sense of surprise or intrigue as the model was developed, this time it was more of a feeling of familiarity, as the model was the development result of maturing objectives. This indicated the success of the action research spiral model, as observation and reflection at each stage of the design development enabled a clear, well-considered and logical design to emerge.
4. DESIGN EVALUATION
©2012: The Royal Institution of Naval Architects
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