slightly more open than the VMG target (but much less so than we talked about previously), and is allowed to deviate from it by a few degrees on either side. Then an overlayer, a secondary suite of
parameters, called Supervision Mode, is placed on top of the VMG, expressed as a maximum angle of heel (for example, 22° for an Imoca). If the boat heels beyond this it gently luffs until the heel decreases and falls below the set threshold. Then heel is allowed to increase again up to that set point, but very gradually. And so the cycle is repeated, meaning that the boat is achiev- ing better performance as it responds efficiently to changes in windspeed. Sailing downwind, the Heel Supervision
Mode sets two stops: high and low. The ideal setting varies according to the boat, the most recent Imoca foilers hitting their target speed in downwind VMG sailing at around 10° of heel. Too much heel? Now the pilot bears away. Not enough? It luffs and accelerates again. And if you want to navigate downwind
in more aggressive mode activate the AWA Supervision Mode. The apparent wind pulls forward when the boat accelerates… the pilot bears away. The AWA shoots back after a surf, the pilot quickly luffs. The response rate and ranges are all pre-set by the skipper according to the conditions – and how aggressively he wants to sail at
48 SEAHORSE
‘In AWA mode you get scared so fast. We wouldn’t dare to attack like that at the helm, it’s demonic’ – Vincent Riou
the moment. ‘In AWA mode,’ says Riou, ‘you get
scared so fast. We wouldn’t dare to attack like that at the helm, it’s demonic. The pilot acts like us, minus the fear.’ The overheel function acts as a limit to
the potential excesses of the AWA world. Launched off a wave at 25kt with no limit to the heel, an Imoca can very quickly be laid on its side or, in the case of the new foilers, dangerously out of control. Yves Le Blevec, skipper of the trimaran
Ultim Actual Leader, explains that even on a direct course and with compass steering Heel Supervision remains relevant. ‘I leave the pilot 8° of travel on either side of the desired course, and the pilot follows the course in interaction with the wind, as we naturally do ourselves at the helm. ‘And I can choose the level of responsive-
ness, from a quiet to a hyper-aggressive ride. It’s like asking for one degree of deviation in the wind angle, you can ask for one degree of course change, or just half a degree, or conversely one and a half degrees.’
Upwind, multihulls adopt a slightly
different strategy from the Imoca 60s, this time with high and low-heel limits. ‘We know that at 10° of heel the trimaran develops her maximum righting moment, that at 8° the central hull is still in the water, and at 12° the main hull starts to lift out. We therefore use these two values, 8 and 12°. At 12° of heel the pilot will luff gently, at 8° it will quickly bear off again.’ Everything is adjustable – you play
freely with the multiple controls singly or in unison. Rather like sitting at a large mixing desk in a music studio! As an example, if you wish the range of
freedom around the main set point (‘the offset amplitude’ in MadBrain language) can be asymmetrical: the pilot is allowed to head 8° below the set point, but to luff only 5° above it. ‘We’re really becoming pilot adjusters…’ explains Riou. ‘Previously we knew that by hand-
steering we were going faster. It was the environment – the weather conditions – and the time we could devote to it given all the other tasks onboard that set the human limit. Now it would be counterproductive to spend time steering.’ With the latest systems the skipper only takes the helm very occasionally, mostly for the need to be at one with the boat for a moment, to check in with the boat’s behaviour and balance to make adjustments to trim.
JEAN-MARIE LIOT/ALEA
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