Gear breakage fears remain in high in America's Cup winds - Sailing Prof Mark Orams

Team BAR crew members look at the breakage following today's retirement. Photo / Ricardo Pinto

Ben Ainslie Racing is now racing all right, to get their boat ready for tomorrow's two semifinal races against Team New Zealand.

BAR's dramatic gear breakage today was always on the cards. It is surprising the regatta had got this far without serious breakages. The AC50s are high end machines making their debut - reliability was always likely to influence the outcome.

Emirates Team New Zealand and their supporters may be happy to take the points, but an easy sweep of the series would not be in their best interests.

Decision making in tight races is their weak point, as revealed in two losses to Oracle Team USA. TNZ need hard racing, under pressure. It is worth remembering that the challenger finals series involves three races per day. Reliability is a major priority.

The loads these AC50s generate, as they approach speeds of 50 knots (80 km per hour), are huge. The highest risk comes when the boats turn around the bottom gate to go back upwind.

The load cells which measure the pressure on the main foils during these turns spike through the roof, as the design engineers close their eyes and pray. When the boffins start praying to a higher power, you know the pressure is on.

All teams will have practiced above the maximum allowable 26 knots but actual racing is a different matter. Was it a coincidence that Team BAR broke an internal component of their wing for the first time after the most aggressive, high-speed pre-start manoeuvres so far? And the forecast wind speeds tomorrow are 20-25 knots, which would be the highest in the regatta to date.

The shore teams will be checking and re-checking every component. They will look for hairline cracks, loose connections, frayed lines, joins that might have opened up, anything that does not look solid. Spares will be ready to go. But the teams will remain nervous about the potential for breakages, no matter what they find and repair.

The Artemis v Japan semifinal is shaping as a beauty. Team Japan definitely stepped up today. Their upwind speed was impressive and quicker than that of Artemis, the previous front runner in the higher wind-speed range.

At times they were doing 30 knots upwind - wow! How have they achieved this improvement? Probably through small changes to their foils but these are hard to identify from television coverage.

Significantly, they were flying a little higher above the water surface, meaning less drag. The trade-off is stability - they were a little 'skittish' and had a few crashes off their foils in both races.

Artemis did a great job of staying close in the second race. When the breeze got unstable and dropped they split and got what opposing skipper Dean Barker called "the shift from God" (quote of the day for me). As the breeze dropped a few knots, the speed between the boats seemed to even up.

Can't wait for the battles to start again!