Smaller non-DSS design – higher DSPL/L
Baltic 142 DSS – lower DSPL/L
suggested it was going to be very difficult to support the required foil span within the space available for supporting bearings. The shallow sloping shape of the hull in
way of the foil exit (see above) exacerbated this by requiring the outer bearing to be installed a long way inboard to fit within the physical envelope of the hull. With this arrangement the two supporting bearings were too close to one another and needed to be pushed further apart to reduce both the shear force and bending moment in the foil, and the loads in the bearings, which would need to be supported by structure concealed beneath the owner’s cabin. In developing a solution to distance the
bearings from one another, Gurit engi- neers collaborated closely with Baltic Yachts to make small adjustments to the accommodation layout and with the Farr office to locally alter the hull shape, devel- oping a subtle blister around the foil exit capable of housing the outer bearing. Incorporating this discrete blister into
the hull shape not only achieved greater bearing separation, and thus more man- ageable bearing loads, but it also enabled an increase in exposed span by moving the whole assembly slightly further outboard. Further to this, by changing the hull-to-foil interface shape the foil’s lift characteristics were also improved. The end result was not only a more effi-
cient structure, but it also led to added righting moment and an improvement in
42 SEAHORSE
Left: the midships section of the hull of the Baltic 142 DSS shown with (inside) the hull of a smaller non-DSS design but of relatively heavier displacement. While the hull of the bigger yacht curves up steadily from close to the keel line, the relatively heavier smaller boat carries its fullness out further with a flatter floor to increase immersed volume to support the greater displacement. The knock-on implication for the lighter DSS design is that the shallower angle at the level where the DSS foil exits the hull necessitated some clever engineering to support the foil sufficiently while ensuring easy movement. Top: this graphic nicely illustrates the aft position and pitch of the DSS foil as well as the size of the two carbon under-deck drums on which luff-furled headsails are stored
performance, all confirmed through CFD studies carried out by Farr Yacht Design. Furthermore, through close collabora-
tion between Gurit and Farr, the foil sec- tion shape was optimised to minimise the weight of the internal spar while not having a detrimental effect on performance. The importance of this early work was
clearly demonstrable and was also essen- tial when the loads reach this order of magnitude. With a maximum steady state lift of 40 tonnes and an estimated peak dynamic lift of over 60 tonnes, the structure supporting the bearings needed to withstand up to 140 tonnes and 200 tonnes at the inboard and outboard bear- ings respectively. The resulting foil, weighing 1,125kg, with a complex pre-preg carbon lay-up
was meticulously constructed over the course of 12 months by Isotop in France, easily the most intricate and complex pro- ject the company had undertaken to date. The carbon inner mandrel, weighing
340kg, was made from six hollow profiles, all made in female moulds and cured in an autoclave. The outer pre-preg laminates, 200 layers in total, which are up to 80.6mm thick at the hull exit, the most highly loaded area, were also optimised in their distribution to ensure failure points are located outside the hull envelope. Lift isn’t the only load case that needed
careful consideration. Risk of impact with or fouling by a UFO is a scenario that can- not be ignored and such load cases would also be significant and potentially quite different in nature. So the challenge was to
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