Trans RINA, Vol 154, Part C1, Intl J Marine Design, Jan - Jun 2012 performance or the boat inconvenient to sail well is uncomfortable and then the design cannot be


considered successful or to have fulfilled its purpose. 3.2 DESIGN DEVELOPMENT 3.2 (a) Principal Dimensions


The development of the concept first centred around the overall size of the boat. The main drivers here were cost and achievability issues, including time to design and build and the cost of design and construction. I settled on an overall length (LOA) of 9 metres for several reasons:


     


affordability compared to, say, a 12 metre or larger yacht


affordability of campaigning, marina storage and ongoing maintenance


established sailing divisions/records for yachts 30 feet/9 metres and under


ability for the boat to be transported in a 40 foot (12 metre) shipping container


suitable size for sailing with a crew of no more than six, and as few as two


large enough to safely compete in longer- distance and offshore events.


The second defining attribute was the boat’s maximum beam. I wanted the boat to have a generous beam to gain the righting moment required to be competitive and to enable short-handed sailing without the need for a high ballast ratio and increased displacement. However, as transportability by container was a key goal, this applied a restriction on the beam. I resolved that it would need to have the maximum beam possible which would still enable containerisation.


To ascertain this, I drew up a representation of the inside dimension of a container door in CAD and used this to experiment with various cross-sections through a draft yacht model. I found I could attain a maximum beam of 3 metres and fit the boat into the container by rotating the hull to approximately 50 degrees from horizontal.


After identifying these defining attributes of the boat, I began to build a visual image of what form the boat would take. This lead to a phase of problem shaping, identifying all the issues related to the development of a robust concept to meet the key criteria of accessibility, speed/performance and


handling. The process-based


challenge was to develop a complete concept with the flexibility for refinement through each iteration of the design spiral while maintaining a consistent vision of the outcome.


To achieve this I developed a set of fixed parameters which were essentially non-negotiable: the overall length of 9 metres, the ability for the boat to be transported by container (which defined a maximum beam of 3 metres), and the ability for it to be sailed by a crew of two to six


©2012: The Royal Institution of Naval Architects people. These factors were identified as elements of the concept design.


I also identified other elements as negotiable, to be developed through each iteration of the design, such as righting moment, displacement, construction materials, sail area (up- and downwind) and configuration, keel mechanism, other appendages and the deck plan. This enabled the ongoing development of the design and refinement of the concept once the project was underway, and provided a fertile environment for


flexibility in


ongoing concurrent design, as the development of these aspects was not limited to the initial design process.


The risk of


development was that resulting in


having


being overly reliant on this method of it could tempt poor planning, inferior


opportunities could be lost to fuse various design elements. To ensure


to adopt this


process was


solutions as successful


I


developed a clear concept and vision for the boat, accompanied by detailed plans of each iteration with areas for development and possible options for their final form clearly identified. Specific design aspects (as outlined below) were then approached using the action research spiral model.


3.2 (b) Hull and Deck Design


Within the parameters of maximum length and beam, section shape was primarily driven by the need to maximise form stability and


produce a hull that


maintains a high prismatic coefficient when heeled. Wetted surface area is a consideration in any yacht design but for this boat it was a secondary consideration to the more critical form resistance.


With the forward sections, my aim was to achieve a powerful shape that would provide good lift for reaching and running conditions, while not being so full that the boat would slam excessively when sailing upwind in a seaway. Based on my observations of other boats and previous design projects, I knew these attributes needed to be achieved while maintaining the chosen distribution of buoyancy.


These elements are intrinsically linked and variation to any of them could only be made with consideration of the effect the alteration would have on the other elements that define the hull form.


At this time I defined the elements that would determine the hull form. Given the desired characteristics I set the initial prismatic coefficient (Cp) at .557 and the centre of buoyancy at 55% aft. Next, I set


based on my personal defining


buoyancy using a personalised spreadsheet, based on the wave form theory developed by Colin Archer [18] developed


the distribution of and


experience and


feedback from other designers who have successfully applied the same principle.


C-31


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