Design
Bigger, faster
Ed Dubois is right in the thick of creating a new 58m sloop with the Royal Huisman Shipyard in the Netherlands. And as is being seen elsewhere in the superyacht market, outright performance is steadily making its way ever higher up the scale of owner priorities…
Design 405 – 58m sloop
Dubois Naval Architects are delighted to be designing this exciting new yacht for a highly experienced owner who has com- peted at the highest level in offshore and inshore yacht racing. It was clear from the outset that his priorities were exciting in so far as he wanted to combine high perfor- mance with completely reliable and also comfortable world cruising ability, and for the yacht to be capable of remaining inde- pendent for long periods of time. From the outset Royal Huisman Shipyard were chosen and we, as design- ers, saw this as a great opportunity to fur- ther cement a relationship with this most prestigious and exceptional yacht builder. The design has drawn on our high level of experience over many years, beginning with racing yacht design success and carry- ing on with the emergent, and then boom- ing, superyacht design era through the 1990s and 2000s. In particular, our expe- rience with such yachts as the 66m Aglaia and more recently the 46m Ganesha
42 SEAHORSE
(launched in 2011 and 2013 respectively) has proved a secure benchmark. As is becoming increasingly the case with modern performance superyacht design, we duly embarked on a research programme including Computer Fluid Dynamics (CFD) analysis and the tank test- ing of a large-scale (1:10) model, using the Wolfson Unit at Southampton University. The details of this research remain confi- dential; however, the aim centred on devel- oping and refining the various areas of 1) hull form (the best balance of reduced wet- ted surface versus stability), 2) performance in waves and 3) refinement of keel and bulb shapes. A fourth area of research was to investigate the comparative benefits of single and twin rudders. Structural analysis was a fifth focus for attention, including longitudinal strength and bending. On this latest design an interesting chal- lenge is posed by the relatively shallow hull, high mast compression loads and a deep (lifting) keel. When these factors are com- pounded by the effective removal of useful deck material (because of large hatches) the load conditions become quite severe. As always, yacht design is a question of balance. In the case of structural consider- ations, the designer’s job is to understand the primary function of the yacht as a whole. In this case, the owner wanted per- formance which means an efficient hull, low windage, as high a strength-to-weight ratio as possible within these constraints and, as always, beauty of line.
Reduced freeboard reduces windage and therefore can improve upwind speed. However, the structural problems increase as freeboard is reduced because the moment of inertia of the hull as a whole is also diminished. Headroom restraints and other considerations also impact on the overall
‘equation’. Interestingly, we found that a convex sheer (the first time this configura- tion has been used in a Dubois-designed sailing yacht) delivered a significant impact in improving the longitudinal bending characteristics of the yacht and therefore allowed some useful weight saving. As mentioned above, longitudinal stiffness is further affected by typical superyacht-scale large deck hatches – to house the tender and downwind sails – thereby making the convex sheer in the forward area that much more effective. The increased freeboard in the forebody also improves dryness in heavier seas and, we believe (and as so often in nature and in physics), the advantage that this form brings for both strength and seaworthiness – and therefore to speed – sits well from an aesthetics’ point of view; in a nutshell, it just looks right…
The rounded stemhead – again an inno- vation on this type of yacht – was added after CFD work on the rig showed a useful reduction in turbulence over the lower part of the headsail and therefore improved aero efficiency.
Good stability is provided by the lifting keel, which drops to 8.3m when lowered and produces an efficient keel form as well as lowering the 72 tonnes of ballast. When raised, the yacht will be able to access all desirable harbours and anchor- ages while at the same time the keel mechanism does not intrude into the 360- degree visibility range from the saloon – something that is not always possible on lifting-keel designs.
The layout of saloon and aft area has been carefully thought through to give as much visual connection with the sea as possible with the extensive use of glass. It is one of the driving forces with all
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