We have a battle on our hands!

Last weekend, during races one to four, we were treated to a dominant performance by Emirates Team New Zealand. Quite simply, they were faster than Oracle Team USA.

Speed always makes you look smart - it makes decision-making on the race course easier. You can make mistakes and not have them cost you a race.

Day three of the America's Cup match and we have a different scenario than the first two days. Oracle Team USA have closed the gap speed-wise, especially upwind, and with more even boat-speed, two things become more critical.

Firstly, the start. Secondly, mistakes.

In today's racing, Spithill and Oracle Team USA managed their starts very well. They got the favoured windward position on both occasions and while they blew that favoured position by starting too early in the first race, they nailed the second one.

Burling was far more assertive in both starts, but in the second, he was scrambling to avoid being hooked and then was just fighting for an even start from there. He minimised the damage, but still lost the start and trailed around mark one for the first time.

The closer the boats are in speed, the more critical it is to hit the line with speed and lead around mark one. Team Oracle USA did that job better today.

The speed issue is interesting. I certainly did not think Oracle Team USA had the ability to close the gap over the five-day period, as they appear to have done. We need to consider the context, though.

The wind range for racing today was higher than expected at 11-12 knots. Both yachts were at the top end of the wind range for their lighter wind set ups.

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In these same conditions, in the challenger finals, Emirates Team New Zealand and Artemis were relatively even in speed, whereas ETNZ has had the edge is in the 7-10 knot wind range, which is the forecast for tomorrow.

The interesting question to consider is what have Team Oracle USA done to improve their boat speed? To my eye, they have focused on two areas - upwind boat speed and turn-rate, and acceleration out of the tacks.

This has led them to make the following changes:

1. They have changed the tips of their main foils (dagger-boards). They have added more area and a noticeable kink - similar to, but not as dramatic as ETNZ's.

The additional area gives more lift, but the kink has made them less stable, so the trade-off they have made is to be faster upwind, they are a little slower downwind and reaching, and they are less stable in the turns.

2. They have changed their elevators (the winglets on the bottom of the rudder) to make them larger and provide more "bite" into the water. This allows them to apply more rake to their rudders and "pull" the windward hull down, allowing them to keep more power in their wing upwind.

Emirates Team New Zealand have been sailing in this mode for quite some time - the bow-down and windward heel mode they sail in is fast and Oracle is now copying them.

3. They are trimming their wing (the main sail) more like Emirates Team New Zealand, using more flap adjustment and twist than in and out sheet adjustment. Glen Ashby, trimming the wing on ETNZ, adjusts the flaps continuously, especially the top two flaps (these yachts have three flaps to adjust), but he does not adjust the bottom flap and angle of attack of the entire wing much.

This has been a major advantage for ETNZ. Oracle understand this and are now copying it.

4. Tacking turn-rate. Emirates Team New Zealand use a faster turn-rate than any other team. This means the yacht loses less speed through the turns and thus makes gains on an opponent.

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The problem with turning the yacht so fast is that you run the risk of stalling the foils and the wing, which will result in a crash down off the foils ... which is very slow. With the change to their foil tips, new elevators and lighter boat, Oracle are now getting closer to ETNZ's turn-rate.

5. Oracle Team USA have taken weight out of their boat - they have removed the retro-fitted bike on the back and have taken as much non-essential gear off the yacht as possible. A reduction in weight, especially in the ends of the yacht, helps with acceleration and turning.

Those are all very smart moves from Oracle Team USA and they have certainly improved their upwind speed, but have traded off some stability and some downwind speed.

In 11-12 knots of wind speed, they have shown they are fast enough to be competitive and win races. However, there are still question marks about how competitive they will be in marginal (say, 6-8 knots of wind) and lighter (8-10 knots of wind) foiling conditions.

What is clear is that we have a much tighter battle on now.

The attitude that Peter Burling showed in the after-race comments and press conference was spot on. He expressed that he was enjoying the fight, was glad Oracle were more competitive and was looking forward to the battle.

Great stuff.

Emirates Team NZ always expected this to be tough and it is. Take that on, relish the challenge, enjoy being tested, welcome the opportunity to fight with all you have.

It makes a victory even more satisfying.

By Mark Orams, The Sailing Professor
School of Sport and Recreation, Auckland University of Technology