Flood tide for first eight races of America's Cup means higher wind limit

When the 34th America’s Cup begins on Saturday it will do so in a flood tide. In fact, the first eight races are likely to be held in a flood tide (flowing into San Francisco Bay), which will then turn to an ebb tide (flowing out of the Bay) beginning on the second weekend.

“Two years ago we started looking at the currents for the race days of the America’s Cup and how that affects the tactics,” said ORACLE TEAM USA tactician John Kostecki. “Basically, the current affects the windspeed and it’ll play a major factor.”

A flood tide is favorable because it means the current is moving the same direction as the prevailing west/west-southwesterly wind and increases the wind limit for racing, which in the America’s Cup is set at a base of 23 knots. The limit will increase or decrease daily based on the strength and direction of the tide. A flood tide means less chop and flatter water, while the ebb churns up the water, as the wind is against the current.

In the Louis Vuitton Cup the crews sought relief from the flood tide in the lee of Alcatraz Island on the bottom of the windward leg.

“It is quite interesting having Alcatraz as part of the race track,” said Kostecki, who says he has sailed on the Bay for more than 45 years. “It really comes into play because on flood tides you can use the cone of Alcatraz as relief. You can get about 3 to 4 knots difference in tide just from behind the island.

“The speed of the tide on the racecourse can vary a fair amount,” Kostecki continued. “I have seen up to 4.5 to 5 knots in strength in the middle of the Golden Gate Bridge. On the race track it will be a little bit less, but you could see 3 to 3.5 knots on the racecourse in a really strong tide, and that really makes it interesting for us tacticians as to where we place the boat to take advantage of the strength of the tide.”

The strength of the tide is particularly important downwind, especially with the advent of hydrofoiling. Normally, a tactician would look for slack water sailing downwind in an adverse current. But with the AC72’s ability to hydrofoil, tacticians are now looking for more adverse current.

“It’s completely contrary to everything they’ve done in their sailing careers,” said ACTV commentator Ken Read, a veteran of two Volvo Ocean Races and countless grand-prix regattas. “Adverse current is helping downwind because the conveyer belt is moving against the wind and increasing the apparent windspeed the boat feels. Windspeed is king in the AC72. Increasing the windspeed makes up for the adverse current.”

If one of the crews wants to hydrofoil upwind they’ll be looking to avoid adverse current because it slows the apparent windspeed. The jury’s still out as to the benefits up upwind hydrofoiling, but Emirates Team New Zealand tactician Ray Davies thinks it will occur.

“It’s almost routine now,” said Davies. “I’d expect it to play a role in the Cup.”

- AC Media

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