America's Cup: Emirates Team NZ close up - Day 3
by Richard Gladwell Sail-World NZ 18 Sep 2019 23:24 PDT
19 September 2019
Emirates Team New Zealand foiling under a fast tow in light winds on the Waitemata Harbour - September 19 © Richard Gladwell
With multi-directional, light winds prevailing on the Waitemata Harbour, and Hauraki Gulf, Emirates Team New Zealand were unable to sail their AC75 on its third day on the water after launching.
The silver lining in this particular cloud, was that the AC75 was slow moving, particularly as she near-drifted down the Waitemata Harbour offering plenty of opportunity for those with a long lens, in their photography kit, to check out the AC75's rig and other features.
As with the first two days, there were issues again with the head of the mainsail, however close up shots revealed that this is quite a complex piece of kit, coming square off the very top of the D-Section mast and supporting two mainsail skins.
Today the mainsail was at the very top of the mast, not short of full hoist as it was on Day 1, and the crew member's stay almost 30 metres above the Waitemata, today was less than half that of yesterday - so maybe progress is being made.
One of the points of interest today was Te Aihe's deck sweeper mainsail and how her mainsail support strut and mainsheet system actually works.
Close up shots of the boom end show a support strut poking out of the clew end of the double skinned mainsail, which sweeps the cockpit deck at its after end.
The loose footed sail is slightly above the support strut for much of its length, with the clew controlled with hydraulics, including a hydraulic ram effectively acting as a mainsheet and providing vertical tension on the leech. The ram locks into a slider on a track, but it is not clear how the angle of the mainsail is controlled.
In several of the beam-on shots the efficiency of the deck sweeper main and jib can be seen as they sit tight on deck with little opportunity for turbulent air to flow under the sails disrupting airflows, sail efficiency, and ultimately power.
A significant feature of the AC75 class is the size of the foretriangle - needed to set the big Code Zero and Working jib. While the ratio between the tack of the jib and mast, to the mast and transom is reasonably conventional proportions, when the distance from the mast to the tip of the bowsprit (tack of Code Zero) is taken into account the distance is almost 60% of the AC75's length.
One of the features of the AC75 class is their ability to be towed, on their foils at relatively high speed, making a spectacular sight, particularly with all sails set. For the America's Cup racing the transition between Courses A (off Takapuna), Course C (off North Head) and Course B in the Rangitoto Channel (between A and C) should be very fast.