GENNAKERS, CODES ZERO, ASYMMETRIC SPINNAKERS & STAYSAILS
Built by Oceantec, the Aquatich 40 is the Humphreys design office’s first serious flirtation with the ORC system; it is also one of still surprisingly few attempts to create an ORC-competitive racer-cruiser slippery enough that it should also be competitive racing offshore in the big IRC events. This was borne out by the fact that while the crew struggled to get the boat ready for the narrow-groove upwind/downwind inshore courses she did show some encouraging flashes of real speed during the coastal stage
in IRC and in many box rule classes, where the simplified nature of these formats affords the designer much more freedom to simply draw fast shapes.
Obviously the ORC VPP attempts to pick up the enhanced performance that these more contemporary shapes can generate. However, based on our own CFD/VPP studies using the 2017 version of the rule the increase in rating is not currently matched by the increase in performance, particularly given the heavy bias towards windward-leeward performance at championship events. The result is that more classic hull shapes with relatively fine fore-and-aft sections remain strongly favoured within ORC, certainly among the mid-sized light to moderate-displacement designs, and this very much fed into the hull form we developed for the Aquatich 40. This is characterised by a modest ratio of beam to canoe body draft, with a fairly evenly distributed rocker profile (certainly more so than we would introduce for IRC where the aft overhang is more heavily factored in the rating), as well as relatively narrow, symmetric heeled waterlines making for an efficient upwind shape – and with an impressive high mode.
One further factor contributing to this is the current ORC treatment of rated righting moment, which is calculated as two-thirds measured (by inclining test) righting moment and one third default righting moment. This dilutes the rated righting moment for higher stability designs or amplifies the rated righting moment for low stability designs; it was introduced to encourage typeforming towards higher stability with more lead in the keel as opposed to in the bilges. For a new design, employing well-refined engineering, materials and build processes, as has very much been the case on the Aquatich 40, this was an obvious avenue to exploit. The resulting high mechanical stability that is achievable for a given displacement once again tends to favour an approach towards relatively lower form stability, slender-section hull forms.
While this approach towards delivering relatively high mechanical stability is certainly beneficial when the boat starts to power up upwind in above 8-9 TWS, which is well in line with our optimisation targets for the client’s home waters in the Baltic, this is less the case in the really light winds as experienced at the last worlds in Croatia, where the ORC VPP tends to over-rate high stability at very low wind speeds.
Given the proximity of the last worlds and Europeans, there was no opportunity to re-mode the boat specifically for the different events following the light conditions anticipated for the worlds in Trieste, but there are several configuration changes that could be implemented to better suit very light-air Mediterranean venues. Aquatich hull number two is now in build at Oceantec in Slovenia and could be available early in the New Year, allowing plenty of preparation time ahead of what promises to be another fascinating season, particularly given the highly anticipated combined IRC/ORCi world championships to be held in The Hague in July. Tom Humphreys, Humphreys Yacht Design
SEAHORSE 31
EASY TO FIT AESTHETIC LIGHT
Photo : © E. Beaugé / Facnor /Carac
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