Baltic Yachts and Farr Yacht Design, naval architects for this highly innovative new superyacht, have made a significant and positive statement by committing to using DSS at this size and displacement; previous larger DSS applications have been limited to lighter and very much less powerful 100-foot maxi racers. Working with a 9m lateral sliding foil on a boat of this size demands great precision while operating at a very large scale – every model maker will understand why Baltic Yachts first trial-fitted a dummy DSS foil (left) before touching the precious real thing which took Isotop a year to finish


With the decision made to proceed with


the DSS foil, the project shifted to a new level, requiring the entire team to develop a detailed understanding of the implications of DSS on the design. The presence of the DSS has a profound effect on the naval architecture of the yacht, influencing every- thing from the hull shape and interior arrangement to the sizing of the ballast package, specification of structural, rig and rigging loads, and the sizing of the sailplan. Detailed studies of foil shaping, foil posi-


tion, tip detailing, actuation systems and performance and handling were required, and the hull shape was carefully optimised in terms of its trim response with speed and heel in both conventional and DSS mode. With the position of the foil established


conventional wisdom of canting-keel performance advantage becomes


As yacht size increases much of the less


certain. With limited draft relative to yacht size (even with lifting/telescopic keels), lower ballast ratios and proportionally heavier canting components, the available righting moment boost from the canting keel is less marked than might initially be expected. Lifting or telescoping keels pro- vide a means of increasing the effective righting moment from the ballast package while still permitting reduced draft access to port. Compared with a canting-keel alterna- tive the requirements for the lifting systems are lighter and more compact, having less impact on the interior arrangements. Over recent years FYD has been


researching foil-assisted sailing solutions and sees some significant performance advantages available from the Dynamic Stability Systems (DSS) approach. From a performance perspective the positive feed- back loop introduced by DSS offers some significant benefits. The vertical force pro- vided by the foil acts to reduce the effective displacement, while providing dynamic righting moment. As the drag reduces, the speed increases and the foil provides more righting moment. At higher speeds, as the foil begins to approach the free surface, the foil lift begins to reduce, creating a soft, automatic ride-regulation system. However, while for smaller boats at


high speed the foil can be carrying 50 per cent or more of the boat’s weight, how well do these advantages translate to a much larger and heavier yacht?


FYD undertook a significant amount of


computational simulation to explore the proper sizing, angle of attack and position- ing of the foil to verify the validity of the concept at this much greater scale. The 9m foil’s span is largely driven by


the beam of the boat and this drives the amount of lift and righting moment that can be generated from the foil. Unlike the existing DSS raceboats, it is anticipated that the effective maximum displacement ‘reduction’ from the foil would only be in the order of 15-20 per cent (still 40,000kg+) but still sufficient to allow a reasonable boat speed increase. It is important to remember at this point


that one of the primary reasons for consid- ering DSS in this application was for the significant reduction in operating heel angles and the substantial reduction in pitching motions and, as such, these speed improvements are a notable added benefit. From a risk assessment viewpoint, the


DSS systems have been in use for some time and their performance and reliability are established. Real-life testing of the foils and actuation systems has been verified, albeit at smaller scale, and the use of a single sliding foil minimises additional weight and complexity, allowing the foil to be completely retracted into the hull. In con- junction with FYD’s development work, the client’s team and Baltic Yachts spent extensive time and resources performing due diligence on this decision – sailing on existing yachts with DSS and undertaking additional technical studies before com- mitting to move ahead late in 2016.


in terms of the naval architecture, the engi- neering team within Gurit then set about a preliminary structural study for the complete yacht, to define the structural arrangement, typical laminates and carry out an assessment of the global stiffness and strength requirements. It was also crit- ical at this stage to invest time in a design loop for the DSS foil and supporting struc- ture, to assess the feasibility of the pro- posed arrangements and ensure that any necessary changes were put forward as early in the project as possible. The reduced displacement that the


adoption of DSS allows creates some challenges structurally when the vessel in question is a cruising yacht, where there is a need for a minimum level of internal volume for a comfortable interior. If displaced volume is to be reduced without compromising the vessel’s beam, then the result is a reduction in draught or fullness of section. Overleaf (page 42) is shown a hull


section of the Baltic 142 compared with a slightly smaller, non-DSS but still high- performance superyacht. It can be seen that the smaller hull has an underwater section that requires more fullness due to its higher displacement:length ratio. This has a knock-on effect of reducing


the available space within which to house the DSS and its supporting structure, which of course needs to be below the waterline and any accommodation fit-out. A co-ordinated preliminary structural


design of the DSS system was carried out to evaluate both the foil section and the feasibility of supporting the bearings in the limited space available. Initial findings 


SEAHORSE 41


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