Clockwise from top left: the owner’s cabin is sited well forward as can also be seen in the launch photo; there are plenty of other areas of great complexity in what, seen externally, is a fairly straightforward – large – yacht. This is the three-stage keel lift assembly with a couple of humans included for scale; the yacht is launched with the keel in the midway position; the port topside is carefully inched into position; FEA plot of the sacrificial grounding block at the aft end of the keel slot – which is engineered to 1,300 tonnes


did not play a structural role and hence were allowed to be comparatively small. A global finite element (FE) model was


created to evaluate the vessel deflections and laminate strains with the doors open and closed, combined with multiple load- cases to reflect sail configurations, sea states, rig loads and events such as ground- ing. It was also used to extract the loads imparted on the door hinge and locking mechanisms to feed into the mechanical design and sizing of metal components. This model, together with various sub-


models, was used to help design the keel trunk, keel and mast support structure, and reinforcements surrounding openings and the complex geometries, since the very large loads observed in vessels of this size may initiate failure modes that would not be commonly seen in smaller vessels. The result is a unique and simply


stunning feature for an owner’s cabin in a sailing yacht. A genuine first, in fact.


54 SEAHORSE


Supporting the keel The design and engineering of the carbon- fibre trunk that houses the 71-tonne lifting keel was also undertaken within this project, which represents another signifi- cant challenge. The keel can be locked into one of three vertical positions, allowing a range of draught of 4.5-7m. The size of the keel fabrication and enor-


mity of the loads meant that close collabo- ration between ourselves and keel suppliers APM was essential to establish a keel head and fin geometry that would load the inter- nal surface of the composite trunk and the hull shell in a manner that could be accom- modated. Once more, with such large loads being applied, it was critical that the full thickness of the keel trunk laminate was built up in the right way to avoid any lami- nate imbalance, which could see laminates failing in through-thickness shear or out- of-plane bending when loaded in tension. All of these global as well as local


considerations were investigated using solid and shell element FE models to verify a very detailed final laminate specification. Again the scope of Gurit’s engineering


for the keel trunk was not restricted to the composite parts but also included the design of a machined sacrificial Super Duplex stainless steel grounding block at the trailing edge of the fin in the region of the hull. The purpose of the grounding block was to transfer the grounding loads (over 1,300 tonnes) from the keel fin into the heavily reinforced lower perimeter of the keel trunk, such that the loads can then be dissipated evenly into the hull shell and surrounding structure. This area was designed and then


extensively optimised for weight saving using FEA while applying geometry constraints to ensure the finished geometry could be practically machined. Baltic Yachts were then provided with a 3D file for machining.


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