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Race 8 - Land Rover BAR’s windward rudder clears the water and reduced the downward force of the foil by 600-700kgs, precipitating a massive nosedive - 35th America’s Cup - Bermuda May 27, 2017 © Richard Gladwell www.photosport.co.nz
Race 8 - Land Rover BAR’s windward rudder clears the water and reduced the downward force of the foil by 600-700kgs, precipitating a massive nosedive - 35th America’s Cup - Bermuda May 27, 2017 © Richard Gladwell www.photosport.co.nz

America’s Cup

Day 3 of the 35th America’s Cup has dawned bright and sunny with a fresher breeze than yesterday.

As is common practice all teams go out for a training and tune-up session on the Great Sound before returning to base for final adjustments and lunch before leaving for their racing.

One of the features of Bermuda’s Great Sound is that getting from the harbour and base area at the Royal Dockyard to the race area is only a few hundred metres, and slipping between racecourse and base is very easy, to say the least.

Three races will be sailed today, beginning at 2.00pm local time.

America’s Cup Defender, Oracle Team USA leads the series points table with five points – having only lost one race and carrying a bonus point as runner-up in the America’s Cup World Series. Land Rover BAR and Emirates Team New Zealand tied at three points, Artemis Racing in fourth with two points, and SoftBank Team Japan and Groupama with one point.

The Race Schedule is:

RR 1 R13: Land Rover BAR v. Groupama Team France (2:08 pm)
RR 1 R14: Artemis Racing v. Emirates Team New Zealand (2:37 pm)
RR 1 R15: Groupama Team France v. Softbank Team Japan (3:06 pm)

Groupama Team France is racing twice today (although all boats sail the same number of races in the Round Robin). Oracle Team USA is not racing at all having sailed three races yesterday.

The Match of the Day will be Race 14, with the two 49er World and Olympic Champions in Nathan Outteridge (Artemis Racing) and Peter Burling (Emirates Team New Zealand) competing.

Murray on foiling
At this morning’s Briefing with Regatta Director Iain Murray and Chief Umpire Richard Slater, there a number of interesting points and observations made.

First was that of the six teams, Emirates Team New Zealand has the highest ‘bottom’ speed during a foiling tack or gybe.

The ‘bottom’ speed being a carry-over from the 12 Metre days and IACC boats sailed for 50 years in the America’s Cup prior to the multihull era.

It is the speed which the crews train endlessly to keep as high as possible during a tack or gybe to minimise the speed loss and improve their acceleration out of a tack or gybe, minimising the time taken to get back up to target boat speed for the conditions.

For viewers without access to the data, it can be visibly seen in the AC50’s by watching the amount the catamaran sinks lower on her foils or if she touches the water – with either a soft kiss around the daggerboard area or with a speed-robbing nosedive.

A typical scenario for the AC50’s would be sailing at 23kts, bear off to build speed to 27kts before the tack – to the turn with speed dropping to 18kts (the ‘bottom’ speed) and then build back up to 23-24-25kts as they head off on the new tack or gybe.

The discussion then turned the the choices of daggerboards for the teams and where the cross-over lay for light air – high lift boards, and the moderate to heavy air daggerboards with less lift and less drag giving a higher overall speed.

Race 8 - Groupama Team France got the daggerboard call correct and won her race against Artemis racing - 35th America's Cup - Bermuda May 27, 2017 © Richard Gladwell www.photosport.co.nz

Race 8 – Groupama Team France got the daggerboard call correct and won her race against Artemis racing – 35th America’s Cup – Bermuda May 27, 2017 © Richard Gladwell www.photosport.co.nz

Yesterday this difficult decision was demonstrated by Artemis Racing, who were caught out in the first race of the day, when the Swedish Challenger fitted her All Purpose boards and then got caught when the wind reduced below the cross-over and trailed the Groupama Team France who had made the right call and opted for a set of light weather boards.

According to Murray, Artemis Racing returned the favour later in the day, when the wind picked up to 11kts, and she scored a win against Oracle Team USA after the wind increased above the cross-over for her AP daggerboards and she had the right boards for the increased wind strength. Oracle Team USA probably had their light air boards fitted – which would have been OK in the increased breeze, had all teams used the same configuration, but unfortunately for her, Artemis Racing had chosen the correct option for the conditions.

Murray, a noted yacht designer as well as former Olympic and America’s Cup skipper and seven times world champion in the 18ft skiffs, commented that while he did not have the time to pay close attention to the foils used by the teams, he had not noticed any teams using two different styles of foils in this series – as is commonplace in testing.

At the bottom end of the wind scale, Murray noted that the speed difference for the AC50s filing and not foiling was huge – with the boats taking double the time to complete the course sailing in displacement (non-foiling mode). Of course, that then opened the possibility of one AC50 being able to foil in the minimum windspeed and her opponent not being capable – and if that happens, the gap will be huge.

Turning to the spectacular splashdown by Land Rover BAR – triggered by her windward rudder lifting clear of the water just moments before the nosedive, Murray comments that the lifting of the rudder and its end-foil clear of the water would suddenly reduce the downward pull on the aft end of the AC50 by 600-700kgs – accounting for causing the spectacular crash.

By comparison the crew weight of AC50 is 525kgs – so the effect of the rudder tip losing grip and clearing the water is massive.

Staying with foiling, and foiling heights Murray noted that there was a tradeoff between the AC50’s foiling high and with reduced drag, and the boats losing grip and sliding sideways, or making leeway. Clearly, there is a balance between the two – which applies in both sailings up and downwind, and also in tacks and gybes – where the AC50 will slide sideways if she is too high in the turn, and will lose speed if too low and makes contact with the water. A fine balance is required on foiling height.

Chief Umpire Richard Slater confirmed that Emirates Team New Zealand had been penalised for early entry in her match against Land Rover BAR the New Zealand boat entered the starting box 0.7secs ahead of the official time and was penalised.

The boat and mark positioning systems used in the America’s Cup is accurate to 2cm measured ten times per second, of all key boats and marks and timing.

Emirates Team NZ’s early entry was not the narrowest margin seen by the ‘booth’ umpire team. One AC50 had been judged in a Practice Session to be early by just 4cms.

by Richard Gladwell

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