36th America’s Cup – Auckland tidal currents
Blog, Recreational, Sailing 1 min read 10/12/2020 
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Tidal currents: the hidden factor in America’s Cup racing
Like many sailing fans, we can’t wait for the action to begin in the 36th America’s Cup in Auckland. Wind speed and direction, as you’d expect, will be the main factor that determines sail and foil choices, and of course, tactics on the course. What about tidal currents? With the speeds that these boats go, you’d be forgiven for thinking that current will be irrelevant. That’s not the case though. Here’s why:
Tidal current changes the true wind that the boats ‘feel’. So if the current is ‘lee bow’ i.e. running at 2kts from the start line towards the top mark on an upwind leg, it will result in an increase in true wind speed of 2kts – which will result in a substantial difference in boat speed – perhaps the difference between foiling and non-foiling in light winds?
The reverse is true with current behind the boats on a downwind leg – it will reduce the true wind speed.
At some states of the tide, there is a differential in tide between different sides of the course, so picking the right side for tide could become very important. Watch our for courses B and C, where the strongest tides are to be found.
The teams are using tidal current to calculate their water speed, as they have no way of using a conventional doppler log, since very little of the boat is in the water most of the time. GPS COG and SOG are recorded continuously and calculations are made using our current model to remove set and drift from the equation.
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