America's Cup Rialto: July 30 - A revealing day for Defiant
by Richard Gladwell/Sail-World.com/NZ 29 Jul 2020 22:49 PDT
30 July 2020
American Magic's Defiant closes fast on a racing mark dropped by the team - 30 July 2020 - Waitemata Harbour © Richard Gladwell / Sail-World.com
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.
New York Yacht Club's American Magic looks to have dropped into a solid training routine, necessary to catchup the five months that the team has been unable to sail their AC75, Defiant.
The AC75 was out of the shed about 8.00am, in the water an hour later, and towed out for a five hour training session in the Course C and D area between North Head and Motuihe Island to the east. It is mid-winter in New Zealand, with grey overcast skies today, and an easterly breeze, which is a warmer direction than most.
The session was punctuated with long breaks - presumably to make adjustments, rather than repairs.
The breeze was being recorded as being as low as 8kts from an easterly direction, meaning it was blowing straight down the course. When Defiant started sailing and exiting the inner Waitemata Harbour the breeze was up and faded around noon before building back at the end of the session.
Another factor which will challenge all teams in the Prada Cup and America's Cup on this course is the influence of Rangitoto, the youngest of approximately 50 volcanoes in Auckland. The 640 year old cone is 260 m (850 ft) high and always plays a role in breeze strength and direction in winds from NE to SE direction.
During the three hours of the five hour session that we observed from the base of North Head, the breeze appeared quite patchy. There was only a slight slop, however fast ferries frequently cross through the sailing area, and the wake does seem to affect foilers in a spectacular way at times, and came close to breaking over our camera position with the incoming tide.
It is obviously quite impossible to estimate wind shear from our viewing point, and one suspects from the wind patterns on the water, that what was happening at sea level was quite different from higher up.
Like her last sail on Tuesday in fresher breezes Defiant looked to be quite "sticky" and having struggling to get onto her foils, and exhibiting noticeably different behaviour than ETNZ's Te Aihe in a similar situation and wind strength.
Exiting the inner harbour (seen in the shots with the waterfront drive in the background), Defiant looked a lot more comfortable and did at least one dry tack.
When the racing mark was dropped almost at our feet on North Head, she looked OK reaching into the mark with maybe an inconsequential touch down during the rounding.
But after an extended adjustment break, a chaseboat crew picked the mark up, and relaid it 200 metres closer to Rangitoto Island - in a position of what could have been more wind influence - and some of the images, comments and conclusions must be seen in that light.
Defiant appeared to be not generating sufficient lift from her rudder foil when she was attempting to get foiling, and when the wind softened, lost lift very quickly when tacking and gybing. Consequently she had a very bow up attitude until she got into level flight.
Her issues seemed to be exacerbated by the amount of spray being generated by the foil arms at low speed and turns, and the speed build looked to be tortuous at times in a softer breeze. Obviously from the image above in level flight, in a stronger puff, the spray looks minimal and her flight height and trim looks similar to what we have seen on Te Aihe.
These impressions are surprising given what has been seen on video, with Defiant doing dry laps. As she left the inner Waitemata Harbour, with the breeze slightly stronger she did several a dry tacks, performing as seen on previously released video. Her ability to fly so close to the water surface, in a slightly stronger breeze was quite remarkable. Her normal sailing attitude seems to be stern high, bow down, which appears to be at variance with the lack of lift seen from the rudder wing in lighter airs.
The underlying message may well be that the conditions on Course C are a lot more variable than the designers realised, and achievement of foiling may not be quite as achievable as in other locations.
Of course, American Magic, rather than picking up from where they left off in Florida, may have made wing/foil/flap modifications and these are still being worked through - indicated by the long time-outs. We have seen the same happen with Te Aihe, and over a week the downtime reduces, and the performance improves. It will be interesting to see if this is the same with Defiant. A couple of crew did spend some time out on a wing, presumably adjusting errant wing flaps.
It is impossible to estimate the speed of an AC75, even off a camera due to issues such as parallax, and the only real estimate is from a pacing chase boat.
As on Tuesday, Defiant's sails, particularly the jib looked to be set up with a lot more twist than Te Aihe, and overall concept of the Kiwi rig is that it is a lot harder in its set up - maybe through the way they use battening in the unrestricted part of the mainsail. Quite who is correct will be revealed later in the year.
During the packup to leave North Head, Defiant looked to have having "Minties Moment", appearing to go out of control sailing downwind, and gybed, coming to rest at what appears to be an alarming angle. However without generating lift from the leeward foil, this is not an unusual angle and has been seen before on Te Aihe going to windward in strong breeze in displacement mode.
The forecast from tomorrow Friday is for freshening winds and the same for Saturday and Sunday, before better sailing conditions return on Monday.
Emirates Team New Zealand's Te Kahu didn't sail today, but was out yesterday, and the brief period we observed had several long periods of down time, indicating that new development are being tested. There is no indication as to when Te Aihe will come back out of the shed.