2021-02-19 17:09:39 | How do they work, what is foiling and how quick can they go?

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Story by: Tom Cary The Telegraph

Monohull

Had anyone but New Zealand won the 35th America’s Cup in Bermuda four years ago the boats for the 36th Cup would still have been catamarans. New Zealand, however, decided to revert to monohulls, which are more traditionally associated with the Cup, although they kept the foiling aspect of the racing. 

While they had to be 75-feet long and 16-feet wide, the hull shapes are strikingly different.

All the teams have ended up with some sort of ‘bustle’ on the bottom, with the intention to reduce drag of the hull as the boat starts to foil, to assist with the take-off in the lightest winds. And to have touchdowns which are “less draggy”.

Double skin mainsail

New for this America’s Cup cycle is the concept of a double-skinned soft mainsail. 

The idea was to create something which was like the rigid ‘wingsails’ of the last Cup cycle but which did not need to be taken on or off at the start and end of racing each day (a job which required around 40 people). 

These boats have a rig which can be left on the boat at all times.  But the sails still needed to generate huge amounts of power which could lift the boat out of the water. And they needed to be light. 

The designers came up with double-skinned mainsails, two sails separated by small carbon fibre components which can be manipulated and twisted by control systems to change their shape depending on the direction of travel. When going downwind you want more camber (shape) in the sail to give you power. If you’re going upwind you want most of your power low in the sail. Too much power up top can tip the boat over.

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Teams can choose from an unlimited number of different sized headsails – the smaller sail forward of the mast – depending on wind strength.

The foils 

Many people predicted these boats would be a complete disaster, that it would be impossible to get a huge monohull flying out of the water with two heavy arms sticking off the sides. 

But so far they have proved to be a real hit, with the boats well matched and capable of speeds in excess of 50 knots in the right conditions.

The boats were designed to ‘fly’ in a wind range of between 6.5 and 21 knots for the Prada Cup round robins and semi-finals. For the final the upper limit was due to be raised to 23 knots but organisers have now announced it will stay at 21 knots.

The arms, which are built by Italian Challenger of Record Luna Rossa, are a one-design part, with teams allowed to build their own ‘wings’ on the bottom, which span 4metres. 

Teams are allowed three sets of foils – ie 3 x 2 foils – to suit the conditions, and you can mix and match with different sized foils on either side of the boat if you like. 

The wing movements are programmed in a computer, which can change the angle of the wing flaps to alter the lift they produce to keep the boat flying at optimum height 

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Source References: The Telegraph

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