Underwater in recent years something new and positive has happened for sailboats. Compared to the hulls designed in the early 2000s, the most noticeable aspect we all notice is that edge that now characterizes many of the production boats as well, after its first appearance in the hulls of the Volvo Ocean Race, Open 60 and Class 40 classes. But it is not only this revolution in hulls that leads boats to sail faster today in both motor and sail with better performance and balance in both wide and upwind gaits.
The turning point in this positive evolution, which is, we repeat, also affecting production boats and not just racing prototypes, can be traced back to 2007. In that year, the America’s Cup having ended with Alinghi’s victory, a new regulation was set for 90-foot (28 m) boats that provided limits only for overall length, width and maximum draft, and minimum weight. Maximum freedom, then. Design teams went wild, free to conceive, the highest performing monohull boat in America’s Cup history. Then the Cup took another direction that we know well: that of multihulls, of rigid wings, of foils that make boats fly. Something that certainly has little to do with boats to cruise with. At least for now. But progress in monohulls had taken a new path.
We asked Claudio Maletto, a designer of world champion hulls who has worked for years on the America’s Cup design teams of Moro di Venezia and Luna Rossa, to explain this revolution. Claudio, bringing us as an example the evolution of the hulls of the most advanced and competitive class, the TP 52s, produced these sketches and technical notes, certainly not easy to understand, but interesting to understand what has been the evolution of hulls that, with transfer of technology from racing to mass production, is leading to this revolution in the performance and shape of contemporary boats.
CLICK ON THE DRAWING TO SEE HOW THE TRANSOM HAS CHANGED
“The sketches you see illustrate a comparison of the geometry of the stern mirrors of TP52-class boats. The comparison, based on direct or photographic observations, covers 10 years (2005-2015). For the comparison of hull shapes, the transom profile is used, which, being more readable than the hull volumes, makes the comparison more understandable. Further indications regarding the evolution of hull shapes are drawn from the plan view, particularly from the geometry of the deck and the course of the water lines, which at the bow tend to curve due to the need to increase bow volumes to balance, at heeled boat, stern volumes and increase, at upright boat, performance at carrying gaits. A key year for the evolution of the class is 2009, which sees the launch of ETNZ’s TP52 that will compete in the MedCup circuit in the 2009-2010 biennium.
In the same year, the hull shape refined over the years since the class debuted in 2005 reached its peak. A characteristic element of this evolution is the shape of the transom, which shows an increasingly pronounced “flare” involving the aft sections, given the general adoption of maximum width at the bridge, extended to the extreme aft to maximize the contribution of crew weight to stability and, at the same time, ensure longitudinal “trim” control.
THE WATERLINE PLANE RELATIVE TO THE DECK PLANE (CLICK)
Below the insell line we find, examining the boats in the fleet, a wide “range” of shape variations in an effort to balance shape stability and strength. The hull of ETNZ (2009) is very innovative compared to that of contemporary boats. The hull geometry has a rounded edge very high above the waterline and a second edge, also rounded, a short distance from the centerline of the hull with the obvious aim of acting on the values of hull hydrostatics and the distribution of volumes at heeled boat. How could it have come to be in 2009 to define this particular hull shape?
I am thinking of the experience conducted by the Botin Carkeek studio in the V70 class (“The Monster”) and perhaps some of the studies developed in the America’s Cup under the “America’s Cup 90 Class Rule,” a tonnage rule initially drafted for the 2009 33RD America’s Cup. It is again, as with the TP52 class, a “Box Rule” with control limited to overall length, width, maximum draft, minimum weight.
The boat that the regulations tend to configure corresponds to the largest and fastest monohull that can be built in accordance with the “Deed of Gift.” Interestingly, the 2009 ETNZ-type hull shape still finds confirmation in TP52s and is increasingly developed outside of competition and adopted by boats with “performance cruiser” characteristics. In the year 2015, all newly designed TP52 class boats feature a rounded edge, incorporated into the hull shape, which allows them to design sections that maximize shape stability for upwind sailing offer reduced waterline width in the straight hull condition. The hulls are characterized by a pronounced “corner” height at the transom with flaring of the stern sections above the “corner” to make the crew’s positioning in the stanchion more effective when the boat is heeled. The “edge” generally lowers as it moves toward the bow and disappears at the forward sections.“