Opposite: a young Chris Dickson steers Kiwi Magic upwind in Fremantle with an equally youthful Brad Butterworth keeping an eye on the competition during the 1987 Louis Vuitton Cup. The New Zealanders’ Farr-designed Cup yachts – the only 12 Metres ever to be built in grp – after winning 37 of their 38 round-robin races would run eventual Cup winner Dennis Conner and Stars & Stripes closest in the Challenger series, KZ-7 going down 4-1 to Conner’s crew in a brutal final. KZ-7 was the faster yacht in light to moderate conditions and the Fremantle Doctor arrived only just in time for Conner’s last heavy, high-prismatic design. Left: 12 Metre Italia shows where all that displacement is hidden in this upwind monster… and what generates that big hole in the ocean once around the top mark. It’s worth recalling that 12 teams and 25 boats took part in the 1987 challenge eliminations
wind, because they can’t push past all the drag the ‘considerable’ underwater volume creates. With one quarter the displacement, the TP has much less drag and goes faster… but it points lower. Other differences are the genoas are long on the foot, 180 per
cent of the distance from the forestay to the mast, so the clew comes back to the jib trimmer. This makes tacking a 12 Metre much harder than a TP52. When tacking the timing of releasing the old jib sheet is critical,
held long enough to get the clew and its patching past the leeward shroud, but not so long, and aback, that the jib fills too early on the new side and has to be ground a long way to final trim in a low/slow gear (this greatly displeases the grinders). Steering the 12 Metre in the tack: the first part of the tack is actually
a long shoot, or coast to windward. The helmsman stands on the windward side, turns slowly up to sail higher and higher on the jib, and once the first metre of the jib is luffing you start the proper turn for the tack. Timing of the turn, and jib release, work together so the whole jib
16kt+ of wind downwind Because of the shape and weight of a 12 Metre it hits a wall at about 8.5kt of boat speed. The boat is too heavy to get on top of the water downwind like a TP52. The more wind the bigger the hole in the water as hull volume pushes the water in its path out of the way. Because the boat doesn’t go faster by reaching up once it has hit this wall, the fastest way to sail is straight to the mark, shortest distance.
Trim tab The purpose of the trim tab is to counter the side load that the sails produce. This allows the 12 Metre to progress straighter through the water, at only 1° of leeway, whereas the TP has 6°. Because the trim tab is an efficient way of doing this, using a trim tab the keel can be smaller with less drag. Simply put, it is just like an aeroplane wing flap on the back of the
keel. The more you put on the more lift and more drag the keel produces. Upwind there is a table we will use for how much tab is required. It’s based on boat speed and heel angle. The tab is a ‘set and forget’ thing. Once you have the right setting you don’t need to adjust it until you tack. When tacking the tab you go to 0° when head to wind, and the
upwind number as the jib fills on the new tack. Downwind you use no tab, to minimise the keel drag. Jib reaching,
if the boat is heeled (indicating side force of the sails) you would use about 70 per cent of the upwind number.
PART II – 12 METRE VS A TP52 A typical 12 Metre is 65ft long, 12ft wide and weighs a lot! So it is long, skinny and very heavy compared to a TP52. The crew does not hike because the windage loss is greater than the righting moment gain. 12 Metres are searching for power in light airs (anything below 10kt of wind) like a big truck with a tiny motor, then comfortable in 10-13kt and bleed off power in sail force in 15kt of wind; whereas the TP52 is comfortable to sail in 7kt and starting to de-power in 12kt. 12 Metres have a target speed of 8-8.1kt upwind, in moderate
foot goes from one side to the other in one flap. There is a tacking line, a rope from the middle of the foot to the bow. This gets pulled as the sail is released to aid the one- flap tack. All this time the helms- man stays on the old windward wheel (new leeward one) until the sail is filled and has been sheeted, and the boat is going straight through the water, then you switch sides to the new windward wheel. The turn is slow for the first third, a little faster for the middle and a little slower again for the last third.
A few tips 1. The first part of the turn, the coast, will be about 300mm on the rim of the wheel (say 3° of rudder).
2.Second part of the turn, the head to wind part, is two to three times that. 3. The last part of the turn is slow so the jib can be sheeted and the boat ‘falls onto it’ (careful here, because you need to end up lower than where the genoa first fills, so keep turning).
4.Starting and stopping the turn should always be smooth and never jerky with the rudder.
5.Acceleration angle is 3-5° below the target true wind angle. Depend- ing on the wind speed. 6. I look at the headstay and the horizon to make sure the boat is going straight before switching sides, because it makes it much easier to move across the boat and steer at the same time. 7. The trim tab goes from 6°, to 0, back to 6 on the new side as the boat tacks. But someone else should do that for you. It sounds difficult, but after a few practice tacks everyone gets
their timing right and tacking becomes a thing of beauty. How did the Sled team go? Pretty well considering being thrown
in the deep end. We didn’t hit anyone, got sails up and down at each of the marks, never leaving one in the water, and had some great races. Our bowman did a quick swim at the top mark once, but things happen with no practice. The highlight would be the three-boat tacking duel! Each boat tacked
18 times in the four-mile beat. Boats tacking as close to each other as the teams would dare. Ted Turner and Dennis Conner could not have stuck it in closer. It was real America’s Cup tacking duel stuff. Mr Okura was nailing the tacks better and better and became an absolute expert at tacking 12 Metres by the end of it. All good fun to take a step back to when the America’s Cup was all about boat-on-boat racing.
q SEAHORSE 31
GILLES MARTIN-RAGET
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