Emirates Team NZ’s AC75 up close after two weeks off the water ~ America’s Cup
After a couple of weeks off the water, during the Hyundai 49er Worlds, Emirates Team NZ’s AC75 was back on the water in a fresh offshore breeze on Monday for a four-hour session.
The breeze wasn’t quite so co-operative the next day, and the team set up at the entrance to the Waitemata Harbour before being towed further offshore into the Hauraki Gulf for another four-hour session in light winds.
Yesterday was an early morning start for what proved to be a nine hour on the water session in fresh breezes.
There are no obvious differences from the previous edition of Te Aihe, given that above deck the AC75 is deceptively simple in appearance, and the “engine room” and control systems are largely below deck. This simplicity is evidenced to some extent by the fact that it takes the team around 30 minutes to step the mast and set up/connect up the boat after the hull is wheeled out of the shed.
1. A close look at the deck-hugging double-skinned mainsail on Emirates Team New Zealand’s Te Aihe. Main boom/struct is visible between the two mainsail skins connected to the mainsheet ram attached to the traveller. The mainsail skins only come close together around the first contour stripe – photo © Richard Gladwell / Sail-World.com
It seems that most of the changes have been refinements and enhancements as to what has been seen before, rather than taking the design and systems in a new direction.
Not apparent in these shots are changes that seem to have been made to the top of the mainsail. The head of sail now appears to be pre-loaded on the dock, and a new system may be in place both making the sail easier to hoist, but also give greater control over the head of the sail.
The endplate area – or where the sails meet the deck appears to have been tidied up to make a cleaner sail to hull join.
There may be new wings fitted; however, these are harder to track, as these are not always visible when the AC75 is towed – trifoiling (with all three foils underwater). The Challenger spy boats can track this very accurately through beam-on camera/video shots when the windward wing raised clear of the water.
2. The flush fitting mainsail foot is clearly visible – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
What is obvious is that Emirates Team NZ has chosen to stay with the longer wing, no ballast fuselage, adopted by the other teams, who all seem to have less length in their wings/thinner wings to reduce drag. The others have offset the lack of weight in the wings with a centre ballast torpedo or fuselage to bring the weight of the wings, and righting moment, up to the maximum weight allowed under the AC75 rule.
It is also likely that the Kiwi team is running the same practice as followed in the AC50 with running different wing shapes and designs on different sides of the boat. This allows better comparative testing of foils to be undertaken – as the two designs are being tested in the same conditions. It also allows the teams to test more wings – a maximum of six (three sets) are permitted per AC75. Up to 20 foil flaps are allowed (which are control surfaces separate from the wing). For wings and flaps, the item may be altered in any way except that alteration may not exceed 20% of the weight of the wing (184kg maximum alteration).
3. The complete end plate effect on the main and jib is evident in this image – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
Yesterday (Wednesday) ETNZ conducted one of their longest sessions to date with nine hours on the water, in fresh breezes of 15-20kts. There were plenty of stoppages indicating adjustments were being made regularly either as part of a test script for the day or to resolve software and hardware issues. The sailing including a lot of reaching runs, without crew training exercises – indicating that the team is in a substantial testing phase of the changes to lock down design options for the second AC75 – expected to be the team’s race boat.
In almost exactly 12 months the first racing will be underway for the Christmas Cup – the preliminary regatta ahead of the start of the Prada Cup or Challenger Selection Series. It is not known whether the Defender will race their first or second AC75 in that series. If it is the first built AC75, Te Aihe, then the team will effectively have another couple of months design/build/test time over the Challengers, with the America’s Cup match not starting until March 6, 2021.
4. In low wind speeds the AC75 is very draggy and slow even with the sails grunted up- Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
5. As with all deck sweeper jibs part of the sail sits on the deck raised only at the tack and clew to permit sail trim adjustment – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
6. Te Aihe with eased sheets and very grunty rounded jib shape to generate maximum power to get foiling – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
7. Te Aihe as her sailinging angle tightens, sails still sheeted wide trying to come up to foiling speed. Once foiling the AC75 will increase in boat speed from 5-6 kts to 25kts or sail at four times wind speed. The sails must be effective and able to be trimmed across 10kts apparent windspeed to 30kts apparent windspeed – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
8. A different angle on crew position and sail setup and trim – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
9. AC75 slows dramatically as the foil drag kicks in when the wind strength lightens slightly – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
10. Back in speed build, reaching mode with sails eased – maybe out of sync given the back winding in the mainsail. The gap between the skins is more visible, being close together at the first contour stripe- Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
11. Close up of jib controls on sheet and tack, still with the leeward foil exit generating a fuss and drag – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
12. Always present is the windward foil clear of the water, when the boat is heeled, but still adding expensive aero-drag – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
13. The complete rig package with the contour stripes showing plenty of twist at the head of the jib while the foot of the sail appears to be very flat. Similarly, but less so for the mainsail as the rig is powered up. The windward foil is still clear of the water given the boat is relatively upright – Te Aihe – Waitemata Harbour – December 10, 2019 – photo © Richard Gladwell / Sail-World.com
by Richard Gladwell/Sail-World.com/nz