SailGP: Understanding the funky breeze on Guanabara Bay

Race Day 1 of the ENEL Rio Sail Grand Prix - Rio de Janeiro, Brazil. Day 1 - 11 April . Rolex SailGP Championship Event 4 Season 6 © Ricardo Pinto/SailGP

These images, shot during the 2016 Olympics, give some idea of why the breeze on Guanabara Bay is highly variable in pressure and direction.

Adding to the challenges is the tidal influence of the rock which was converted into a fortress - Forte da Laje in the 15th Century to augment defensive on either side of the entrance. The fortification was converted to a prison, which closed in 1997.

On the other side of the visible landmass lies the Atlantic Ocean - providing a steady breeze which tumbles through the spiky and substantial landmass before reaching Guanabara Bay - and tormenting the sailors.

Course location for Race Day 1 of the ENEL Rio Sail Grand Prix. The Atlantic Ocean is visible is the other side of the Rio landmass - Rio de Janeiro, Brazil - Day 1 - 11 April . Rolex SailGP Championship Event 4 Season 6 - photo © Ricardo Pinto/SailGP

Breeze and course graphic of the ENEL Rio Sail Grand Prix - Rio de Janeiro, Brazil. Day 1 - 11 April . Rolex SailGP Championship Event 4 Season 6 - photo © SailGP

Race Day 1 of the ENEL Rio Sail Grand Prix - Rio de Janeiro, Brazil. Day 1 - 11 April. Rolex SailGP Championship Event 4 Season 6 - photo © Ricardo Pinto/SailGP

Race Day 1 of the ENEL Rio Sail Grand Prix - Rio de Janeiro, Brazil. Day 1 - 11 April. Rolex SailGP Championship Event 4 Season 6 - photo © Jason Ludlow/SailGP

Race Day 1 of the ENEL Rio Sail Grand Prix - Rio de Janeiro, Brazil. Day 1 - 11 April. Rolex SailGP Championship Event 4 Season 6 - photo © Ricardo Pinto/SailGP

The areas shaded green are high hilly ground - white is lowland containing apartments, houses and office buildings. The grandstand for spectators is marked with the red pin, the airport can be further down the coast - April 2026 - photo © SailGP

Race area at Botafogo Bay. The grandstand is marked by the red pin. The Sugarloaf is opposite Forte da Large is just visible in the entrance to Guanabara Bay - photo © SailGP

Forte da Laje is a prison (closed in 1997) on a rock at the entrance to Guanabara Bay, adding tricky current flows to the funky breeze - July 2016 - photo © Richard Gladwell - Sail-World.com/nz

Viewed from the Atlantic Ocean the size of the landforms influencing Guanabara Bay. Christ the Redeemer is in the centre of the image - Rio 2016 - July 2016 - photo © Richard Gladwell - Sail-World.com/nz

The size of the Sugar Loaf and surrounding landforms has a significant impact on sailing - Rio 2016 - July 2016 - photo © Richard Gladwell - Sail-World.com/nz

Forte da Laje with Christ the Redeemer in left background - Rio 2016 - July 2016 - photo © Richard Gladwell - Sail-World.com/nz

Christ the Redeemer is surprisingly small in the context of the other landforms - Rio 2016 - July 2016 - photo © Richard Gladwell - Sail-World.com/nz

Gintare Scheidt (LTU) tunes up in a 35kt squall before racing was abandoned. 10 minutes earlier it had been a glassy calm - Rio Olympics - photo © Richard Gladwell