A forecast tells you the breeze over a few kilometres of water. On the racecourse the wind squeezes between bridge towers, hides behind them, and bends along every bluff. Marena now shows you that wind, down to about 50 m, in 3D, and tells you what it means on the course.
Wind squeezed between two towers or two headlands speeds up, like water through a narrow pipe.
Behind a tower, pier or point the breeze drops and swings around. You can lose half your pressure in a few boat lengths.
Cliffs and bluffs steer the wind along them. That is a shift you can plan for before you see it on the water.
The forecast says WSW 240° at 18 kt across the whole bay mouth. Here is the idea, drawn by hand: the three effects the engine finds.
Arrow length shows speed. Arrows point where the wind is going.
Take the center spanThe middle of the bridge is a venturi: about 4 kt more breeze than the forecast. Cross there.
Don't hug the South TowerIts wake drops about 7 kt and the wind swings around 15°. Give it room.
Left shift by the Marin bluffsClearing toward the Marin Headlands the wind backs about 10°: a header on starboard. Tack on it.
Start from the WindBorne forecast for the area: wind speed and direction on a 2.5 km grid.
Add high-resolution terrain and the bridges, towers, piers and buildings that stand in the wind. Bridges get their real deck and towers.
A fluid simulation on a graphics processor works out how the air actually moves over and around all of it: about 50 m across the course, a few metres under bridges.
You spin the course in 3D, tap anywhere for wind and current at any height, and get the pressure and shift zones in plain sentences.
The live 3D fields use these sources. The Golden Gate example above is drawn by hand to show the idea; its numbers are not from a run.
Open 3D wind for your venue, or run it for any area you sail.