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America's Cup Rialto: August 1 - what we've seen in the first week in Auckland

by Richard Gladwell/ 1 Aug 04:28 PDT 30 July 2020
American Magic - Waitemata Harbour - Auckland - America's Cup 36 - July 28, 2020 © Richard Gladwell, / nz

America's Cup Rialto is a new series for the 36th America's Cup, and will publish each day an Americas's Cup boat sails - with images of the day. Usually there will be a morning report (NZT) based on when the boats have passed North Head - when there is usually the best photo opportunity.

Strong winds are lashing the Auckland area, and there was no sailing Friday, Saturday and Sunday.

Monday to Friday of the coming week should be moderate to fresh winds - all from an easterly direction.

American Magic sailed their AC75, Defiant, on three days of the four available, last week. Emirates Team New Zealand, with a choice of an AC75 or a test boat opted to sail only their 12 metre long test boat Te Kahu. We have not yet had the opportunity to see boat AC75's side by side. However we can now go back through previous images in similar locations of the two AC75's and get some idea of their relative strengths and issues.

Te Aihe has a skiff concept complete with a centreline bustle. Defiant is at the other extreme with a scow type hull notable for its shallow underbody, with no bustle. In fact Defiant is now the only AC75 without a bustle - now that the British have retrofitted a similar device within the limitations of the 12.5% hull surface area modification permitted by the AC75 class rule. Luna Rossa launched with a bustle, as did ETNZ's Te Aihe.

Both teams, in Auckland, have perfected the technique of being able to sail to windward with the hulls very close to the water without making contact with the surface. (We presume this is also the case with other teams.) The bow-on view of Defiant is notable for both the low flight height, and what happens when the underside of the hull does appear to make contact with the water. Generally contact appears to be very minimal, causes no spray to be flicked up, unless it is a serious closure with the surface, in which case the displaced water appears to shoot sideways, and gets picked up in the foil spray.

At times, Defiant seems to be throwing a lot of water from her immersed (leeward) foil in winds at the lighter end of the scale. It appears that her ability to foil at the lower end of the wind range is not as good as we have seen on Te Aihe.

Further up the wind scale, there appears to be little difference in this regard between the two AC75's (Te Aihe and Defiant). We can't estimate speed from the shore, and speed guns are not reliable at more than 500metres distant.

In foiling conditions (winds above 7kts) Te Aihe is quick to foil - taking less than a couple of seconds to get foil borne. From what we have seen of Defiant she appears to take five seconds or more to get on her foils, and usually does this by starting very bow up, and with a lot of water being thrown about in the area of the foil arms.

Once she is foil borne Defiant doesn't appear to have too many issues staying in the air, and presents what appears to be a very efficient aerodynamic profile - bow down and slightly heeled to windward. She seems to be able to carry this stance up and downwind.

It is not clear why Defiant appears to be bow-up, when she exits from a tack that is not a dry tack. In the AC75 Class rule the rudder is permitted under control to move fore and aft (rake) and sideways (yaw)

It also must be remembered that in all these images and tests, they are just that - images from test programs. They are not a definitive record of whether one boat will always be slower or faster than the other. Plus one of the test practices is to test a configuration which may be optimal in heavy air, for instance, and would be expected to exhibit some serious downsides in light air. And then of course, as we saw with ETNZ's light air daggerboards in the last Cup, the trick is to extend the range of the preferred board beyond its optimum.

For the 36th America's Cup the competitors are only permitted to use one set of foils per round, which must be declared two days before the start of that round. In the last Cup they could be changed daily - depending on the forecast. As a consequence "All Purpose" wings and flap systems must be used

Of course, Defiant has not sailed for five months and it would be expected that her performance would not be as slick, as had they been sailing solidly (five weeks of lockdown aside) as the Kiwis.

From the amount of time taken during the time outs which have punctuated Defiant's test sessions, our guess is that they have proceeded to try new developments/gear - instead of just sailing the boat in the same design configuration as she was in Florida.

The occasion of Te Aihe and Defiant being on the same patch of water will be of great interest, and the comparison will be continued.

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