By the early 1980s model yacht designers were rapidly tempering beam to reduce heeled drag, but for IOR offshore racers many top designers were going in the opposite direction. This is the 1983 Half Ton Cup winner, Denis Peres’s Freelance, a very pretty boat designed by Philippe Briand that made maximum use of crew weight with these flared upper sections. A 40ft Briand development of this boat would win the 1984 One Ton Cup a year later and the same concept characterised some of the best boats at the subsequent 1985 Admiral’s Cup in Cowes. However, by 1986 Bruce Farr had started to look at more vertical topsides on his IOR designs and this approach would soon dominate, as upwind rather than offshore reaching speed became a new priority for all-round competitiveness
By the time that the first new boats
began construction to the all-new IACC rule, after a short period of unemployment I was lucky enough to join the Swedish America’s Cup Challenge. However, not being possessed of a Swedish passport, I could not be directly involved with the design of the boat and so assumed more of an advisory position, which was interest- ing to say the least… Our team’s technical director was Ib
Ussing Andersen, who ran the Danish North loft, and the Swedish designers were Peter Norlin, he of Scampi fame, Hakan Södergren and Prof Sven-Olof Ridder. (Incidentally, along with Lars Bergstrom, both Ridder and Södergren became, I believe, quite rich on the royalties they claimed from their patent of the Windex). Once our group assembled it quickly
became apparent to me that the only one of them who really understood yacht design was Peter Norlin, though to be fair I did learn a lot, particularly about junction drag, from Sven, then professor of aero - dynamics at Stockholm University. But the trouble with yacht designers,
particularly in that era, was that they were very much influenced by the type of boat they had been currently designing, even though this new IACC rule required a totally different concept. The IOR rule, the major rule at the time,
relied very much on crew weight on the rail to provide righting moment and thus sail power and very little from keel weight which was sometimes even negative, some
56 SEAHORSE
of the keel fin often being built out of wood which tended to float and thus reduced measured righting moment, as well as improving the yacht’s pitch gyradius. The legacy of this thinking would infect
the early generations of yachts built to this new America’s Cup rule, so that beam on deck was very often at the maximum to maximise crew righting moment, while the waterline beam was narrow to reduce drag. This produced boats with sometimes
dramatically flared topsides, which is fine if the boat is sailed upright, or somewhere near, but once the boat heels those flared topsides add wetted area and volume near the water surface, both of which are draggy. In 1990 computer design was rather less
good than today, when a design can auto- matically heave, sink and trim when heeled. Back then we started from the position that the yacht would heel axially, which of course it did not, and the resulting approximations meant that the so-called in-wedge (the wedge of sectional area that went into the water when the boat heeled axially) was considerably greater than the so-called out-wedge (the wedge of sectional area that was removed from below the water when the boat heeled axially) so that, for equilibrium to be maintained, the boat would have to float higher in the water (it heaved or jacked upwards) which meant that it would use less of its overhangs, and its sailing length would thus be shorter than if it hadn’t heaved or heaved less to maintain equilibrium. Furthermore, crew weight compared to
overall weight was small in the new class so the crew contribution to righting moment was also small. Bulbs were a fairly new concept at full size, but in this new class it was immediately obvious that bulbs were the way to go; weight so low down pro- duced so much righting moment that crew weight on the rail was trivial by compari- son – and should therefore not have been a factor in deciding maximum beam. Looked at this way, the logical shape
for a boat built to this rule would therefore be narrow with vertical or near-vertical topsides or even tumblehome if it was allowed (which it wasn’t), so that when the boat heeled it heaved or jacked out of the water as little as possible so that as much of the length beyond the waterline endings was used and sailing length maximised and heeled wetted area minimised. In essence this was the path taken in
designing radio sailing yachts which, because there is no crew to provide move- able ballast, was very akin to this new design problem… and this was an area in which I had a lot of design experience. (Incidentally, radio sailing yachts had been using bulbs since the mid-1950s so in that respect were 30 years ahead of their full- sized counterparts). This suggestion as to the direction IACC design should take was, however, not heeded and, like all of the challengers, to a greater or lesser extent, the Swedish boat had flared top- sides. The only boat to conform to the alternative, more slender design path was America3
. Predictably she walked it.
AJAX/ALAMY
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 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114
