ORC
Newbie
Among 120 or so boats at the ORC Worlds in Trieste this month will be at least one welcome ‘new face’ in the shape of the brand new Humphreys-designed Aquatich 40. In the past some have criticised the ORC rule for not inspiring new designs; the counter argument being that the rule works well enough that with careful tweaks many well-proven (and well-sailed) existing designs remain competitive. There has certainly been some clever – and sometimes aggressive
– playing around with ORC optimisations in the past few years, perhaps getting too clever at times as we saw with the Scugnizza episode last year. However, the new Aquatich 40 was drawn very much with ORC competition in mind and it will be interesting to watch her at this regatta (but keep in mind that in Trieste she is among a minority of Corinthian entries in the largely pro-crewed Class B). This year’s host venue at Porto San Rocco in Muggia, just south
of Trieste, is expected to have conditions typical of many ORC championship events: light to moderate thermal breezes and flat water. As is normal at major ORC regattas the regatta will consist predominantly of windward/leeward races, plus a coastal race or two depending on weather conditions. As always with windward/ - leeward courses, particularly in light airs, getting and holding a lane off the start in clear air will be vitally important, so most recent designs and optimisations have focused on these parameters. Lymington-based Humphreys Yacht Design were approached by
Norway-based Bjørn Erik Bjørnsen for a new ORCi-optimised design of around 40ft that would be fun to sail but also comfortable enough to be suitable for the rather long commutes Bjørnsen must make from his base in Stavanger to other racing venues in the region. With this mandate Tom Humphreys was able to take a fresh look at ORCi and develop the design for the Aquatich 40 racer-cruiser starting from the office’s good understanding of the wheels and levers that optimise performance and rating in IRC.
26 SEAHORSE Humphreys reviewed all the principal parameters, focusing initially
on beam, draft, displacement, VCG sensitivity, rig height and appendages, working with Roland Kleiter at KND-SailingPerformance who supplied DasBoot CFD and yaw-balanced VPP data. This process turned into a thorough analysis involving considerable back- ground research on the ORC system itself and so Tom’s comments in comparing IRC and ORC influence on design are interesting. Having established the parameters for a base design, Humphreys
graphed the base boat to demonstrate the effect of displacement variations from 600kg lighter to 400kg heavier. This displacement range of 1,000kg was what they identified as achievable for a design of this size, given the relatively production-oriented build materials and processes used – ie infused vinylester/foam/E-glass sandwich with a gelcoat finish (the intention is that Ocean Tech in Slovenia will produce the boat as a series-build). ‘Graph 1 (overleaf) shows the time difference in going lighter or
heavier than the base boat,’ says Humphreys. ‘For this example I’ve assumed we’re looking at 12kt TWS so have used the ORC Medium (wind strength) Triple Number time-on-time scoring for wind- ward/leeward racing [typical for an ORC championship]. The ratings are compared in terms of time differences (seconds per hour) to the base boat. Negative values represent a lower/slower rating. ‘As you can see, the ORC rating increases significantly for
displacements lighter than the base boat compared to IRC, while going heavier shows a similar rating reduction under both systems. ‘Graph 2 displays corrected time deltas (sec/nm) compared to
the base boat on a 12kt TWS windward/leeward course. Negative values represent a slower corrected time than for the base boat. As on Graph 1, the same ORC Medium Triple Number windward/ - leeward ToT scoring is used. ‘For the ORC studies we used the ORC VPP,’ says Humphreys,
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96
