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America's Cup Rialto: August 17 - A day of two halves

by Richard Gladwell/Sail-World.com/NZ 18 Aug 2020 07:51 PDT 18 August 2020
No, not the first AC75 to sail in the Southern Ocean - American Magic - Defiant - Auckland - August 17, 2020 - Waitemata Harbour - 36th America's Cup © Richard Gladwell / Sail-World.com

Both America's Cup teams sailed Monday in Auckland in a fresh 15-20kts onshore breeze, and overcast skies. The weather dominated the day with rain squalls moving onto the course in the early afternoon with gusts of 25-27kts.

These fronts seem to be one of the hazards of winter sailing for the two AC teams. Last week American Magic left the training area off Eastern Beach earlier than expected - making it back to base ahead of a forecast SW rain squall. In hindsight a very wise call. It was a similar situation on Monday - except the US challenger stayed on the water.

Emirates Team New Zealand was first out of the dock, with a rapid foiling tow down the Waitemata Harbour into the white capped outer Waitemata and Motukorea Channel. This is America's Cup Course D area - which would probably be used for an easterly direction of wind. The area is ringed with islands, and the seas are generally flat - provided the channels with their strong tidal flows are avoided.

Half an hour later American Magic followed Te Aihe, except Defiant was sailing on her foils down the harbour and looked quite comfortable - if ever that word can be used in an AC75 context.

Both teams had timeouts in the lee of Motuihe Island team for reasons which were not obvious from our vantage point over 5nm away - and of which AC teams are generally reticent to elaborate.

Emirates Team New Zealand was first to get under way into the practice session - doing several runs in the shelter and flat water of Motuihe over a distance of around 1nm - and with helmsman Peter Burling throwing the AC75 into with a very tight high-speed gybe, or tack at the end of each run. Next came a longer run into Browns Island and then down the shore of Rangitoto Island, looking very fast and smooth, as she did last week - and with their short hoist #3 jib set. Te Aihe made just one minor splashdown on this run, trimmed down by the bow and with her stern flying higher.

The kiwis packed up ahead of the first of three rain squalls to hit the course area, and the AC75 did a fast tow on foils back to their base.

American Magic finished another lengthy timeout in the lee of Motuihe and followed a similar training pattern to Emirates Team NZ, with a mix of speed runs often ending with a high speed turn in the vicinity of one of their racing marks.

At the end of one downwind run, helmsman Dean Barker threw Defiant into a high speed gybe, emerging just above lay line for one of the team's racing marks. As the new windward foil was raised, Defiant appeared to load up and started to heel, while going into quite extreme bow-down trim, causing a shower of white water to fly high off the leeward foil - and with the windward foil arm and its attached wing quite clearly visible in the raised position.

What happened next will have provided some invaluable data for the simulator, as the jib sheet appeared to be eased by the trimmer, unloading the AC75, about the same time as a very solid rooster-tail was emitted from the rudder - perhaps indicative of ventilation causing the rudder to lose lift as the stern sank. The AC75 appeared to luff slightly - spilling more pressure - and now go bow up.

It is a similar routine to what was seen in the early stages video of Te Aihe's capsize in December 2019, except Defiant continued to move forward, generating uplift from her leeward foil combined with the righting moment from her 1385kg raised windward foil, helped the AC75 to get back on her feet. Eventually the AC75 physics all worked to pull the yacht back into level trim. They sailed on for a few hundred metres as the crew gathered their wits, and then got back into sailing at race pace, for a few more practice runs.

There seemed to be little point continuing to shoot with the advancing rain, and poor visibility, now a few hundred metres away and looking set to remain for the rest of the afternoon.

A couple of hours later, as so often happens, Auckland's weather had changed for the better, as the squalls passed and the skies brightened.

Defiant appeared to have changed for the better, too.

The dark blue hulled AC75 has always had a very distinctive downwind foiling profile - firing fine high-speed spray off her foil arms, while a substantial length of her 69ft long hull appears to be kept in suspended fine balance by the upward force from her foil arms and leeward wing, with trim controlled by the downward force from her rudder wing.

Upwind the profile changes with much less of her hull being so obviously clear of the water, and the spray off the foils looks to be a lot more solid. From study images at the same angle the spray appears to be coming from forward of the mast position - raising the question of whether it is generated from hull and surface contact - given that Defiant's scow-style hull has a lot more keel rocker than the flatter profile of Te Aihe.

Defiant is now the only one of the first generation AC75's not to feature a bustle or skeg down the centreline of her underbody.

However for any team, wringing performance improvements out of the first generation AC75 is now of limited use.

The teams will take delivery of their second generation and likely raceboats, next month and now it will only be worthwhile spending time on design and engineering aspects of the first AC75, if those developments can be transferred to the team's second AC75.

From what was seen at the end of Monday's session, on a long run downwind, Defiant looked very fast, with her hull well clear on just her rudder and leeward foil, with only fine high-speed spray being emitted from the foils.

After the session, Executive Director Terry Hutchinson felt god progress was now being made - after five months off sailing. "A big productive day on the water - and a bit tired at the end,"

Hutchinson was also dismissive of the "capsize" incident, saying the AC75 "heeled over a bit but did not feel risky".

Defiant rounded off a long day which ran until just before sunset, with a sail up the harbour - not quite to the harbour bridge and Cup Defenders, the Royal New Zealand Yacht Squadron.

Strong winds are forecast for much of the week and it is unlikely the teams will sail.

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