Something is clearly going on with the jib systems on both Emirates Team New Zealand and Luna Rossa, and neither camp is in a hurry to explain what.
Over the past two days, both teams have lost training time to issues centred on the jib. In Auckland, Taihoro was sidelined for around 40 minutes yesterday, compounding a 15-minute stoppage the day before that halted sailing almost as soon as it had begun. The Recon Team following Luna Rossa, meanwhile, reported that the boat suddenly stopped, with crew gathering around the jib track to investigate inside the soft fairing.
Ask the sailors directly and you get very little back. They duck and dive around it, as sailors tend to when something sensitive is at play. Talking to technicians and shore crew from the last America's Cup in Barcelona in 2024, one thing is clear: the jib traveller has long been an area of development on the AC75.
The AC75 uses what's known as a 3D traveller system, built to manage the huge loads and twist profile of the jib. It allows load to be exerted on the sail at the clew in three dimensions, something no other boat does.
Athwartships movement, inboard and outboard, changes the jib's sheeting angle. That adjusts how tightly the sail sheets towards the centreline, which affects pointing ability, the slot between jib and mainsail, and aerodynamic drag.
Fore and aft movement changes the effective jib-sheet lead angle. This influences the balance between foot tension and leech tension, helping control how camber and twist are distributed through the sail.
Vertical movement, up and down, changes the vertical component of sheet tension. Raise or lower the effective lead and you alter leech tension, twist, and the aerodynamic loading higher up the sail.
It's a genuinely complex piece of engineering. The traveller system is linked to hydraulic controls, which are tied into the Programmable Logic Controller onboard the AC75. Every team is chasing the same thing: the optimum sail shape for every condition and every phase of the boat's performance, pre-foiling, mid take-off, and at full target speed.
Adding another layer, the traveller systems sit in grooves below deck level to cut aerodynamic drag. They're covered by combings made from all sorts of materials, rubber, neoprene and carbon sheeting among them.
With so much adjustment happening constantly, both from the trimmers and from pre-set controls, those fairings take a hiding. Technicians from the last Cup cycle reported them wearing badly, and in the worst cases shearing off entirely during nosedives. They remain vital to the aero efficiency of the whole platform.
Whether Luna Rossa and ETNZ are wrestling with fairing wear or something deeper in the 3D traveller itself is being kept firmly under wraps. But when technicians start jumping onboard mid-session, as has happened with both boats, it's a fair guess the issue runs deeper than a simple aerodynamic cover.
Recon teams around the world will be watching this area of development closely. Expect more technicians climbing aboard as both the 3D system and its covering get refined to the nth degree.
