Please select your home edition
Edition
Auckland On Water Boat Show

America's Cup- Predictwind - Lighter winds initially for Day 13

by Richard Gladwell on 24 Sep 2013
The America’s Cup Race Course, framed by the Golden Gate Bridge - today the wind blows from right to left, and the ebbing tide flows from left to right against the windflow. The blue sea that can be seen behind the City to the right, is not ocean but the greater expanse of the San Francisco Bay - which exits through the relatively narrow channel under the Bridge. © Richard Gladwell www.photosport.co.nz

The regular San Fransisco breeze is expected again on Day 13 of the 34th America's Cup, for Monday and Races 16 and 17 of the 2013 America's Cup. The first race is due to start at 1.15pm on Sunday, local time with the second race scheduled for 1415hrs.

Towards the bottom of this story we feature Predictwind's course routing optimised for wind and tide on the AC race course, and using an AC72 performance profile. It is included to show that the effect of the tide on the race course and race strategies. See bottom of story for the course variations.

For the official line on how the current factor is determined click here Today the tide is flooding (coming in through the Golden Gate) and will negate the previous advantage that exists with an ebbing tide.

With the first race of the day set for its regular start time of 1315hrs the wind feeds produced by Predictwind indicate that winds will be around 12kts. Both feeds produced by Predictwind are in agreement on the strength at the race start time, however the significant feature of the forecast is that just 90 minutes before the start the winds will be near calm.

The minimum breeze required to complete the course within the 40 minute time limit is 10kts (although the specified minimum breeze is 5kts), and the time limit could be an issue in the first race of the day, but for the second race, the wind should be very adequate without exceeding the maximum of 23kts plus tidal effect.

The breeze is expected to quickly build in the late morning and early afternoon to reach a strength of 15-18kts for the second scheduled race of the day.

The forecast does not take account of the influence of fog, which can have several effects on the race course winds.


The above image shows the wind speed and direction 1300hrs with breezes expected to be 12kts at the start of Race 16 - these are only average speeds and gusts will be higher.


The second image (above) shows a graphic representation of the wind build - confirming the numbers for the prognosis. The significant feature is the feed are very similar for the 90 minutes before the start of the first race of the day. They vary, but not too significantly for the second race.


The above image shows the wind speed and direction at 1400hrs still with a small increase in the breeze in the middle of the course indicated by the yellow wind arrows.


The second image (above) shows a graphic representation of the wind build - confirming the numbers for the prognosis. Reading the top line we can see the wind direction, the wind strength with winds forecast to be 15-18kts and from the SW.

The third chart (below) shows the wind expectations for Monday and Tuesday. Typically the forecast for Tuiesday is revised upwards closer to the time of the race start. Note that sea conditions described in this chart are based on open water and are not descriptive of an enclosed harbour


The courses optimised by Predictwind for an AC72 show that the optimum course only has no real variation between races. The faint purple line shows the recommended course for Race 16 and the red dotted line shows the course recommended for Race 17. The mark positions used in this projection are only very approximate - and will vary on the course set for the day. At the bottom of the upwind leg the model shows that the boats cannot use full width of the course because on the adverse, incoming tide.

The point here is that downwind is there is little variation in the options, aside from the recommendation to gybe early and get into the incoming tide. And upwind in both models the fastest course is to the south, or cityside shore, aside from allowing a short leg to Alcatraz in the first race before heading for shore. The tide is expected to be in flood (incoming) for this race, and boats will need to avoid its effects upwind by taking the city shore.



Two weather feeds are used by Predictwind, the key to the accuracy of the forecast lies with the graphs, as when the two lines for the two feeds are quite close together and following each other in the trend, then the likelihood of the forecast is high. If there is separation to any marked degree, then there still some issues to be resolved but usually 24 hours from the race they are well aligned.

The Predictwind model takes various weather feeds and then polishes these, part of this process is factoring in the effect of local topography on the breeze - well demonstrated by the images with the funneling of the breeze.

Developed by former Olympian, Jon Bilger (470, 1992), www.predictwind.com!PredictWind application was used by the Swiss team Alinghi to win the 2003 and 2007 America's Cups, and has become the leading wind system used by racing and recreational sailors around the world. It is available on a subscription basis and also with a free forecast option.

A mobile app for Android and iPhone is available and www.predictwind.com!PredictWind is probably the most used app on the Sail-World iPhone.

Real time local wind observations have been added as further functionality.

You can check the weather anywhere in the world, and get a five day forecast, plus a variety of other features and functions of www.predictwind.com!PredictWind. The app is synchronised with your PC, so that your latest set of locations are always available without resetting each time you change a device.

Ancasta Ker 33 660x82Southern Spars - 100Zhik Isotak Ocean 660x82

Related Articles

Rio 2016 - America's Cup champ says Paralympic racing is closest ever
Twice America’s Cup champion, Rick Dodson is extremely impressed with the standard of racing in the three man Sonar Twice America’s Cup champion, Rick Dodson is extremely impressed with the standard of racing in the three man Sonar keelboat class at the 2016 Paralympics in Rio de Janeiro. The regatta is being held in Guanabara Bay on three of the courses used for the Olympic Sailing Regatta in August.
Posted on 13 Sep
Debriefing the Rio 2016 Olympics with Team USA’s Helena Scutt
I talked with Team USA’s Helena Scutt to hear about her Olympic experience, and to learn more about her post-Rio plans. The 49erFX was introduced to Olympic circles when it replaced the Women’s Match Racing event following the 2012 Games. Not surprisingly, it drew high-performance sailors for the Rio 2016 Olympics, including Team USA’s Paris Henken and Helena Scutt. While Henken and Scutt were Olympic first-timers, they put on a strong show. I caught up with Scutt to hear more about her Olympic experience.
Posted on 8 Sep
A Q&A with Peter Bresnan ONE Palma’s founder and director
Sail-World interviewed ONE Palma’s founder Peter Bresnan to learn about the company’s partnership with McConaghy Boats For the past eight years, ONE Palma (formerly OneSails Spain) has been building a strong name, first as a sailmaker and later with refit work. Recently, ONE Palma and McConaghy Boats-legendary boatbuilders who have crafted some of the planet’s fastest sailboats-entered a business partnership. I caught up with Peter Bresnan, ONE Palma’s founder and director, to learn more about this new direction.
Posted on 2 Sep
America's Cup - Emirates Team NZ train late on the Waitemata Harbour
Emirates Team NZ were out for a training session that ran into the early Thursday evening. Emirates Team NZ were out for a training session that ran into the early Thursday evening. The team were sailing their recently launched AC45 Surrogate test boat which features an articulated rudder gantry - taking the AC45 close to the geometry of the AC50 to be used in the 2017 America's Cup.
Posted on 1 Sep
Dateline Rio - Sailing Olympics review - as good as it gets?
The Rio Sailing Olympics was widely judged to have been the best of recent times. The Rio Sailing Olympics was widely judged to have been the best of recent times. The weather was better than Weymouth and Qingdao, the courses more varied, but from a working media perspective, it was the people running the Rio regatta who really made the difference.
Posted on 26 Aug
Rio 2016 - Plain speaking by triple-medalist on Olympic sailing moves
Triple Olympic medalist, Santiago Lange has been on the sharp end of changes made to Olympic classes and formats Santiago Lange, a six-time Olympian and Bronze medallist in the 2004 and 2008 Olympics, won his third medal – Gold sailing in the Nacra 17 class. With that length of experience at an Olympic level, having sailed the Laser, Tornado and now Nacra 17 classes his comments on the future shape of the Olympic regatta was one of the highlights of the Medallists Media Conferences.
Posted on 25 Aug
An Q&A with Steve and Heidi Benjamin about the NYYC’s 2016 Queen’s Cup
Sail-World caught up with Steve and Heidi Benjamin to learn more about Heidi’s historic win in the NYYC’s Queen’s Cup. When it comes to U.S. Grand Prix sailing, it’s hard not to encounter the names of Steve and Heidi Benjamin. The two highly polished sailors have been successfully campaigning their series of yachts, named SPOOKIE, for years, starting first with a Carkeek 40 and progressing to their TP52. I caught up with Steve and Heidi to learn more about Heidi’s historic win in the NYYC’s Queen’s Cup
Posted on 19 Aug
Rio 2016 - Images of the penultimate race in the Finns - Scott wins
Sail-World's Richard Gladwell was on the water for the final race of the Qualifying Series of the Mens Finn Sail-World's Richard Gladwell was on the water for the final race of the Qualifying Series of the Mens Finn, in what potentially could have been Giles Scott's (GBR) Gold medal winning race. In the end, the current world champion won in style.
Posted on 15 Aug
Rio 2016 - Images from the Mens RS:X Medal Race
Sail-World's NZ Editor, Richard Gladwell, was on the water at the Medal Race for the RS:X class Sail-World's NZ Editor, Richard Gladwell, was on the water at the Medal Race for the RS:X class won before the race by Dorian van Rijsselberghe (NED) without needing points from the Medal Race. Nick Dempsey (GBR) was second on a similar basis.
Posted on 15 Aug
Rio 2016 - Sailors talk of Life at the Extreme on the Atlantic Ocean
Certainly the Volvo Ocean Race catchcry of Life at the Extreme is not a phrase associated with the Sailing Olympics. The 470 crews were suffering the mixed emotions of survival of an extreme test by nature, the cold, and for some elation at their placings, after Thursday's battle for survival. In conditions that looked more out of the Volvo Ocean Race, than an Olympic sailing regatta, crews battled 20kt plus winds and Atlantic Ocean rollers that towered up to four metres.
Posted on 13 Aug