America's Cup: Understanding technology 3: Hydraulic drive and car steering wheels

A modern AC catamaran is traditionally steered using the rudders. These are connected to the steering wheel. However, in addition to the direction, the helmsman must also regulate the altitude, attitude and stability of the catamaran. This is done by pressing a button or using other input options on the wheel. These send signals to the control valves of the hydraulics, which then adjust the foils accordingly (see article Foil mechanics).

For example, it is possible to set that pressing once means an angle change of half a degree. This signal is transmitted to the valve and electronically controls how long it has to be open until half a degree is reached. The vertical control of the catalytic converter is therefore digital for some teams.

Various teams have reported 120 to 200 entries per minute by the helmsman, Team Land Rover BAR reports 1200 during a 20-minute race. This gradual adjustment is a simplification for the helmsman. If it were analogue, i.e. the angle of attack changed as long as the helmsman held down the button, he would have to visually check via displays when the desired position was reached. This would distract him, especially as the speed of the adjustment also depends on how fast the cat is, i.e. how much pressure there is on the foils and how much pressure is in the hydraulic system.

With this "jerk method", on the other hand, he can count the inputs and draw conclusions about the angle of attack. Oracle Racing introduced this system at the last Cup and thus secured a major advantage.

Story about the creation of the Land Rover BAR wheel

However, Oracle Team USA has now published pictures and videos of its bike, which has two twist grips like those on motorbikes. According to his own statements, helmsman Spithill is able to steer in an analogue way. As long as he turns the handle forwards, the cat sinks; if he turns it backwards, it rises. However, this variant could also be a "jerking method", except that Spithill does not have to press any buttons, but instead turns the foils to a certain degree.

Helmsman Jimmy Spithill, Oracle Team USA, explains his steering wheel with motorbike handles

Land Rover BAR has also integrated gearshift paddles borrowed from the automotive sector into the wheel, which can even be operated when the driver's grip changes.

How exactly the signals are transmitted to the foil valves in each team is kept strictly secret.

However, computerised steering and electronic feedback to the helmsman about the foil position are not permitted.

Hydraulics - power from arms or legs

All energy for the mechanical systems on board must also be generated on board. These systems are operated using hydraulics. With the exception of the New Zealanders, all teams use two grinders each, which are cranked by up to four men. The New Zealanders, on the other hand, have four pedal systems integrated into each hull. Instead of using their arms, they crank with their legs.

In both systems, the rotation from grinders or pedals drives hydraulic pumps that provide the necessary pressure to hydraulic cylinders distributed everywhere. These cylinders adjust the individual components either directly or via line connections.

Only three energy accumulators for hydraulic pressure are permitted: one each for the blade angle of attack and one to move the blades up or down. These accumulators are a concession to the dynamics of the competition. Maximum hydraulic pressure is required in the manoeuvres in particular, because most of the adjustments are made. However, as the crew has to change hull sides and cannot crank at times, there would not be enough pressure available in these important phases, and power turns completely on foils would hardly be possible.

Fighting words: Fitness expert Ross Edgley vs Land Rover BAR sailor Neil Hunter

Each team would then have to consider whether it can afford a turnaround or not. Partially stored energy, on the other hand, alleviates this problem. Nevertheless, the energy stores must be replenished after every manoeuvre.

Depending on how much energy the team can generate and how much energy the adjustment systems require, this is a limiting factor for manoeuvring behaviour. For example, how many turns can be made in succession or how often the foils can be fine-tuned.

With their leg-powered pedal system, the New Zealanders can generate around 40 per cent more energy than the other teams with their arms. In addition, the position of the crew members is supposedly more aerodynamically favourable than with standing grinders.

Impressions of the brutal training with Emirates Team New Zealand

On the other hand, it takes a little longer to adopt this position or to change it, which means the crew is less agile. However, this disadvantage was hardly noticeable during the first training runs off Bermuda. During manoeuvres, only two "cyclists" change position to the other side of the hull at the same time. The other two remain seated and can thus generate as much power during the manoeuvre as three men on the grinders of the other teams.

With these, three men often change sides at the same time. Although they are back in position more quickly than if they had to get on and off the bikes, one more man remains seated on the New Zealanders. The advantage of the New Zealanders is that they ensure permanent pressure generation. In return, they have one more man sitting downwind for longer after the manoeuvre.

Two days ago, a new installation was discovered on the defender, a bicycle behind the helmsman. This means that the New Zealanders are no longer the only ones to rely on wheel drive. However, this change at Oracle Team USA probably has a different background to that of the New Zealanders.

However, the higher energy supply is only one reason why the New Zealanders rely on bicycles. With them, the helmsman and foil trimmer functions are shared, at least some of the time. While in all other teams the helmsman also adjusts the direction of the cat as well as the flight attitude using different control systems on the bike, in the New Zealand team helmsman Peter Burling is primarily only responsible for steering. His former 49er foresailor Blair Tuke, who sits on the front wheel, directly above the foil, is responsible for adjusting the foil for long stretches. As he needs free hands for this, which he would not have on a grinder, this was another reason for the New Zealanders to put the crew on wheels. However, this division of tasks requires extremely good coordination between the two active players, which is only possible with Burling/Tuke due to their 49er years together.

For the defender Oracle Team USA, helmsman Jimmy Spithill is responsible for both course and attitude. But a bicycle was also recently spotted on this cat, behind the helmsman. It is apparently mainly used for weight trimming on downwind stretches. There it is important to have the weight aft. This trim can also be achieved by adjusting the T-foils on the rudder, but this creates more resistance on the foil.

Tactician Tom Slingsby sits on the wheel aft, but on upwind courses he is in fourth position on the grinder from the front as usual, because on this course it is better to have the crew weight a little further forward.

The fact that Slingsby sits aft on a wheel probably has less to do with the increased power he can generate by pedalling and more to do with the limited space available there. A grinder would take up more space than a wheel.

Oracle Team USA does not appear to be copying the New Zealanders' pedal drive, but simply testing a new trim variant.

The big Cup guide: In the America's Cup special in YACHT 12/2017 you will find all the information and background to the sailing event of the year. From 24 May at the kiosk or digital here.