For construction we optimised the materials as the principal place to save weight, and utilised NEB’s strong expertise in building lightweight pre-preg carbon-Nomex structures and components. We iterated between compliance requirements (in this case CE) and FEA to optimise the construction; the FEA was kept particularly busy on detail items. For racing we turbo-ed the sail plan, with a big 105% jib led to fore-and-aft tracks and an inhauler, and a square-top mainsail. However, for day sailing we went with a self-tacking jib and a pinhead main – so no runners. This aligned well with the respective stability requirements – there are no hikers day sailing – and the resulting sail plan is easy to handle. Under IRC the boat would be likely to fair better in non-turbo mode, but be less dynamic and fun to sail. We knew already that we would have a furling boom with a furling foil on the headstay. A bit of weight, a bit of windage, but these systems allow such a powerful boat to get sailing quickly and easily. On a separate design spiral, we evaluated sailing systems for weight and usefulness. In the end we split the power requirements between hydraulics for a mainsheet MagicTrim, allowing super-easy mainsheet trimming for day sailing, and electric power for the winches to make sure that we didn’t have speed losses when racing on account of needing high hydraulic flow to multiple winches simultaneously. We worked with Mike Toppa and Chris Williams to optimise the sails and the balance of the boat using their yaw VPP. Working with NEB, we decided upon an electric bow thruster. We were also able to ditch the generator and use two engine- driven alternators to charge the lithium-ion house batteries that drive everything. Smooth and silent, as instructed.
The result We designed to and achieved a boat weighing 15,500kg that was both wider and with a heavier bulb than we initially thought. The boat is equipped with a lifting keel and twin rudders – driven by the shoal-draft requirement We chose a Hall Spars deck-stepped, swept-spreader rig for simplicity and location (the rig sits above the lifting keel box, which offers a nice structural solution) With only 75HP (the biggest Yanmar engine with a saildrive) the boat makes 10.5kt with a Gori three-blade folding prop (which is surprisingly low drag when folded) The boat has a Cariboni MagicTrim mainsheet, Harken electric winches, a Reckmann recessed furler headstay, a removable furling staysail, a self-tacking jib, a Hall furling boom and a square-top main plus runners for racing Power consumption is well within comfortable limits (in our early trials we completed a full day under sail including numerous manoeuvres and drew only 15% of the yacht’s available battery power) Chessie is easy to steer and has good stability. We comfortably carry one jib (J1) up to about 20kt of true wind The boat powers up quickly, the crew hiking downwind from 6 to 7kt TWS. We used exactly the same tools and technology to ‘predict outcome’ on both the state-of-the-art carbon 62ft Chessie Racing and the groundbreaking steel/aluminium 282ft Aquijo. The modern tools that have become de rigueur in the global design arena are CFD and FEA – both can accurately predict the outcome when used correctly. That said, they won’t design the boat. It is still up to the human
brain to read the physics, see the vectors and visualise triangula- tions or projections as necessary. The tools themselves can’t look or see into the future, but the
proper use of new tools does move design forward, just as new technology keeps opening up further opportunities. The next state of the art is always out there if we look. A big thanks to the teams at NEB, North Sails, Hall Spars and
Harken, and to my colleagues David Egan, Stephane Leveel and Nate Yeater for all the help in looking. Bill Tripp, Norwalk, Connecticut
CARIBBEAN SAILING AT ITS FINEST.
racing in paradise since 1972
24-26 MARCH 2017 SEAHORSE 59
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