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Magical mystery tour. Before the defender ‘eased’ themselves into the challenger trials – ie in 2017 – relative performance stayed largely unknown until the Cup itself began. If Ted Turner and Dennis Conner (left) knew ahead of time that their 12 Metre Mariner was barely fast enough for a 6 Metre regatta they could have done something else for the summer of 1974. (Alright, DC did then join Courageous and Ted Hood to win his first America’s Cup…)


more than 5° from the water plane. The rudder must draw no less than 2.1m but not exceed the AC50’s maximum draft limit of 2.4m.


For the daggerboards themselves the rules are more prolific. The boards:  must be positioned in the hull 7.3- 8.05m forward of the stern plane, and laterally within 0.150m of the centre plane of each hull.  must be within the boat’s 2.4m maximum draft.  can have a maximum straight-line dimension between any of their extremities of 4.2m.  when


fully retracted they must


protrude no deeper than 0.4m beneath the water plane.  can only be used fully deployed or fully retracted.  cannot exceed Bmax below the


waterline, but can by up to 0.5m within a line extending diagonally out and up from a point 1m above the water plane at maximum beam.  can be raised or lowered and are permitted two further axes of rotation: <15° cant and <12° rake (cant being the lateral rotation of the board about its bottom bearing and rake being the equivalent fore and aft rotation). Added to the complications are that Bermuda’s Great Sound is effectively a lake in the middle of the Atlantic. Its average wind speed for June is 11kt which is substantially less than the 20kt+ sea breeze that you could set your watch by in San Francisco. However, while this is the average, the teams can expect not only a much broader range of conditions in gen- eral, but also a broader range of conditions each day compared to the 34th AC. Then there are the limitations to the number of daggerboards that can be built – six for test purposes on the teams’ test boats, plus four race boards (ie four in total, not four pairs) for the AC50 itself. Com- petitors can change <30% (by weight) of their race boards four times, but can change <10% an unlimited number of times. These changes can be reversed without it being counted as an extra modification. Nonetheless, beyond these rules there remains considerable freedom for design teams to work magic on the overall shape of the boards, their section shape and how this varies along the length of the board. Then there is the monumental engineer- ing challenge to ensure the foils can not only withstand carrying almost the entire weight of the boat, along with the impres- sive dynamic loads as the whole package moves


through the water at speeds


approaching 50kt, but also will deform in a way that the designers intended throughout the range of conditions.


Given the enormity of this challenge, all of the teams have thrown huge resources into this area and, if the pre-race hype is to be believed, with extraordinary results. This is perhaps best demonstrated by the fact that following the numerous months spent carrying out R&D and recording data from their 45ft test boats, some if not all the teams can now very precisely model the boards. As a result they have been able to confidently pare away safety margins to next to nothing – mightily impressive given the complexity of the AC50 daggerboards with their massive array of variables.


As Artemis Racing’s French foil guru Michel Kermarec confirms: ‘There has been a lot of progress in terms of building and understanding the loads and under- standing the boat. Everything gets more accurate, which of course also means you can get closer to the limits…’


Daggerboard strategy


Given that, following an 11th-hour change to the Protocol, they are now permitted to replace boards if they destroy them, teams are perhaps now more inclined to have strong wind and light wind pairs of race boards, rather than the safer option of one set and a spare. Compared to their light wind equivalents, the strong wind boards will have a (significantly) smaller area and a flatter section shape, better suited to operating at higher speeds. However, given the breadth of conditions they can expect to experience during a day of racing in Bermuda, the operating range of each pair will be wide, with a large crossover area where the two options meet. Another significant issue in this equa-


tion is that it takes around three months to fabricate a pair of AC50 daggerboards from scratch. Thus the latest a team can leave starting the build of their race boards is the last week in February (although boards can subsequently be modified as per the rules above). In light of this, it is possible teams will choose to have a set of Mk1 race boards ready for the launch of their AC50s and will then wait for the last possible moment, in other words after all the other AC50 raceboats have been launched and opposing team spies have gained enough intel on them, to start construction of their Mk2 boards. Though the wind range in which racing is permitted has yet to be finalised, it is expected to be 6-25kt. These limits are likely to throw up problems. At the light end, which is still expected to be ‘marginal foiling conditions’ even for the nimble AC50s, the team with the largest foils may be fastest as they should fly more readily. But the drag from applying too much rake to the foils in these conditions can also mean there are moments when it is faster to ‘low ride’.


Performance in light winds will also come down to crew positioning: will the AC50 cockpits be configured so that the grinders can man the pumps to leeward, enabling the weather hull to pop up, to gain enough speed to get up on the foils? Given this, it seems that moments when the AC50 will be low riding will be rare – in light conditions upwind or if there is


SEAHORSE 33





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