Please select your home edition
Edition
Bakewell-White Yacht Design

America's Cup- Predictwind - Marginal conditions for Day 5

by Richard Gladwell on 15 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

Predictwind indicates that fresh winds winds will again prevail for Saturday, Races 8 and 9 of the 2013 America's Cup. The first race starts at 1.15pm on Saturday, local time with the second race scheduled for 1415hrs. Racing has concluded in the 18fter International.

Today we show a new feature of Predictwind - course routing optimised for wind and tide on the AC race course. See bottom of story for the course vatiations.

Officially the breeze is being forecast at 19-23kts. Today is the first race day which will be held in an ebbing (outgoing tide) which will see a wind against tide condition in the main channel of the course - building standing waves which will require a more seamanlike approach to mark rounding at Mark 1 and Mark 3 in particular. At the bottom of the course there is minimal tidal effect on the sea condition.

With the racing at its regular start time of 1315hrs the two feeds produced by Predictwind indicate that winds will be averaging around 22kts, with the breeze having been up all night at around 15kts. The key point is that on the graph image the two weather feeds produced by Predictwind are very close together for the ten hours leading into the race start suggesting the the certainty of the prognosis is high. There is only a small amount of breeze build before the start, although for Race 2, winds are predicted to be over the limit of 23 kts with the feeds showing 23-24kts.

Today there was a heavy fog over San Francisco, which lifted as the morning progressed. However the City remains overcast - which may restrict the inland heating which drives the Frisco 'Doctor'. When there is fog, the cold air on the sea gets angrily sucked in by the hotter inland systems, increasing the strength of the breeze. Unfortunately the fog is not easy to predict or measure and so it is a random factor in the forecast.


The above image shows the wind speed and direction at 1300hrs with breezes expected to be 22kts at the start of Race 8 - these are only average speeds and gusts will be higher, but not enough to exceed the wind limit. There is a little variation in the forecast indicating a higher degree of certainty as to the outcome.

The key feature of the forecast is close agreement between the two feeds as to the rate of build of the breeze, and around race start they are consistent in their projection.

A feature of the wind image map for both 1300 and 1400hrs (above and below) is the intensity of the breeze in the actual race area - driven by the surrounding topography, which is factored into the detailed 1km forecast option used to compile these predictions. Surrounding the race area, winds are significantly lighter in strength at both times. The wind source, to the west of Golden Gate Bridge is also less strong than the strength to the east of the landmark - again a function of the wind being sucked between the two high headlands on which the Bridge is constructed, before fanning out into San Francisco Bay and losing intensity.

A similar but reverse effect happens with the tide flowing from east to west, against the wind, and with the massive body of water which forms San Francisco Bay trying to exit under the Golden Gate Bridge - a little like a bath draining down a plughole - with the plughole being the entrance to the Bay under the Golden Gate Bridge.


The second image (above) shows a graphic representation of the wind build - confirming the numbers for the prognosis. If the breeze builds later than predicted, then the light winds soon one the left of the graph will extend through to the race start time.


The top image shows the wind speed and direction at 1400hrs with breezes expected to rise to 23-24kts at the start of Race 9 - these are only average speeds and gusts will be higher, probably exceeding the wind limit of 23kts.

The key feature of the forecast is agreement between the two feeds as to the rate of build of the breeze, and again around race start they are consistent in their projection.


The second image (above) shows a graphic representation of the wind build - confirming the numbers for the prognosis.

The third chart (below) shows the wind expectations for Saturday and Sunday. Typically the forecast for Sunday 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 a small variation between the two races. The faint purple line shows the recommended course for Race 8 and the red dotted line shows the course recommended for Race 9. The mark positions used in this projection are only very approximate - and will vary on the course set for the day.





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 image 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.

Zhik Warehouse Sale 660x82upffront 660x82Barz Optics - Floaters

Related Articles

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
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
Rio Olympics - Fourth gallery of images the fearsome Niteroi course
Fourth image gallery from racing on Day 4 in the Mens and Womens 470 class on the Niteroi course in the Atlantic Ocean Fourth image gallery from racing on Day 4 in the Mens and Womens 470 class on the Niteroi course in the Atlantic Ocean - sailing in 3-4 metre swells and 20kt plus winds. believe it or not the sea conditions were worse inshore as the fleet encountered the backwashed Atlantic rollers
Posted on 12 Aug
Rio 2016 - Third image gallery of 470's braving the Atlantic Ocean
Third image gallery from racing on Day 4 in the Mens and Womens 470 class on the Niteroi course in the Atlantic Ocean Third image gallery from racing on Day 4 in the Mens and Womens 470 class on the Niteroi course in the Atlantic Ocean - sailing in 3-4 metre swells and 20kt plus winds
Posted on 12 Aug
Gladwell's Line - The challenges of Guanbara Bay
The decision to run Medal Racing on the Pao de Acucer course, probably won't be remembered as one of the brightest The decision to run Medal Racing on the Pao de Acucer, probably won't be remembered as one of the brightest of the 2016 Sailing Olympics. Over shadowed by a 1300ft tall granite and quartz mountain in the shape of a sugarloaf, the bay suffers from dramatic windshifts, and huge variance in wind pressure.
Posted on 11 Aug
Rio 2016 - Fresher breezes expected inside and outside on Day 3
Stronger winds are expected for the third day of racing in the 2016 Olympic Sailing Regatta in Rio de Janeiro. Stronger winds are expected for the third day of racing in the 2016 Olympic Sailing Regatta in Rio de Janeiro. Two of the fleet scheduled to race outside on the Atlantic Ocean course off Copacabana Beach, while the 470 Men and Women will race inside on Guananara Bay.
Posted on 10 Aug
Rio 2016 - Day 2 brings more tumult for some, salvation for others
The course area may have changed, but Brit, Nick Dempsey's performance early on stayed the same. The course area may have changed, but Brit, Nick Dempsey's performance early on stayed the same. He picked up where he left off on Day 1 in Race 4 of the Men's RS:X class on the Escola Naval race area to record his third win in four races. Poland's Piotr Myszka finished second with Brazil's Ricardo Santos third.
Posted on 10 Aug