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SailGP F50 v America’s Cup AC50 catamarans

SailGP F50 v America's Cup AC50 catamarans.

To the casual observer the F50 foiling catamarans that will be used in next year’s inaugural SailGP professional circuit will look pretty much identical to the America’s Cup AC50s boats introduced to the sailing world at the 36th Cup in Bermuda in 2016.

Both designs are about the same length and width, are powered by giant wingsails, and fly above the water on retractable adjustable foil daggerboards.

In reality though the SailGP F50s are a much more advanced version of their America’s Cup predecessors, having been almost entirely re-imagined and re-built over the past year by a team of around 100 people at the specialist Core Builders Composites facility in New Zealand.

Three of the six boats for the 2019 season have been built from components originating in the previous AC50 models, while the other three boats have been built from scratch.

Let’s take a look at what the main differences are between the America’s Cup AC50s and the SailGP F50 catamarans.

Performance

Both classes are blisteringly fast of course, but the new F50s are expected to be significantly faster than their predecessors with the SailGP promoters claiming they will capable they say of speeds around 54 knots or almost 62 miles per hour/100 kilometres per hour.

The fastest recorded speed for an AC50 was 47.2 knots (54 mph/87 kph) achieved by the Swedish team Artemis Racing.

New advance foil package

The F50’s additional speed compared with the AC50 comes predominantly from the development of a new highly-advanced hydrofoil package.

The new foils have been built from a higher modulus (in layman’s terms: stiffer) carbon than previously. This means the F50 foils are thinner and so produce less aerodynamic and hydrodynamic resistance, allowing the boat to go faster.

The shape of the new foils has been designed to project outside the maximum beam (width) of the boat. According to the respective published specs of the two boats, the F50 is already more than a foot wider with a max beam is 8.8 metres (28 feet 11 inches), compared with the AC50 max beam of 8.47 m (27 feet nine inches).

The extra width of the F50 produces significantly more righting moment which directly translates into more power and more boat speed.

SailGP designers also believe that the shape of the new foils will result in the boats achieving higher speeds before cavitation (a phenomenon where the pressure on one side of the foil decreases to a point that the water begins to boil) occurs and slows the boat down.

Flight control enhancements

Put simply the designers have made the F50 catamarans significantly easier to get airborne and maintain stable flight.

Gone is the need for the teams to manually generate the hydraulic pressure required to run the flight control systems. The F50 flight control system runs on battery power, meaning no “heads down, bums up” cycling teams will be needed on the SailGP circuit.

The other big difference between the F50 flight control set up compared to the AC50 is that the F50s will have active control of the rudder pitch (the angle at which it is raked fore and aft which determines the angle of attack of the horizontal foil on the bottom of the rudder blades).

In the America’s Cup the teams were required to set and lock off the rudder pitch prior to the start of each race, making for some ragged edge of control scenarios for the helmsmen on more than one occasion when the conditions changed mid-race.

According to the SailGP website:

“The flight of the boat can be controlled from the twist grips on the steering wheel or from a joystick controlled by the crew member sitting in position 3 (flight controller). The ride height of the boat can be adjusted independent of the fore and aft bow down pitch.

“What seems like miles of hydraulic lines stitched inside the hulls and under the floorboards are used to distribute power to cant the boards to the most efficient angle and activate the rudder pitch control system.

“The helmsman can control the ride height, the jib sheet, and the rudder differential from push buttons on the steering wheel. The helmsman can also adjust the speed at which those functions are adjusted by adjusting a dial in the centre of the steering wheel.”

Crew roles

As well as reducing the number of sailors down from six in the America’s Cup to five in SailGP, the addition of battery power for the flight control systems means the sailors will have more time for sailing the boat rather than grinding to produce oil pressure.

In the America’s Cup in Bermuda we saw Emirates Team New Zealand sailor Blair Tuke controlling the boat’s flight via a handheld controller, leaving helmsman Peter Burling free to concentrate on sailing the boat fast and able to look around to assess the team’s position on the racecourse.

The SailGP boats have been set up similarly with one crew member designated as “flight controller”, freeing up the helmsman to “just” drive, while the wing trimmer will be responsible for maximising the boat’s straight line speed.
With batteries connected to a new hydraulic accumulator to power the foil and rudder pitch controls, the jib sheet, and the wing twist control, the two grinders are there to provide power for the wing trimmer to operate the wing sheet.

Manoeuvrability

The introduction of battery powered flight control means that rather than having to wait for sufficient oil pressure to be generated by the grinders before a tack or gybe can be undertaken, the teams will be able to carry out any manoeuvre at will.

In theory at least this should keep the racing close and make for some thrilling boat on boat action when the teams converge.

Design evolution

In a similar way to how Volvo Ocean Race was able to tightly control the evolution of the one-design VO65 between the 2014-15 and 2017-18 editions to introduce improvements across the fleet, SailGP is committed to the continual evolution of the F50s.

A central design team headed by Mike Drummond has been set up to ensure the F50 class remains at the cutting edge. The hydraulic and electrical control systems and software are being developed and improved at Artemis Technologies a company led by British America’s Cup skipper and Olympic medalist Iain Percy.

Planned development areas include new wing sail designs based on a modular system to allow teams to use a range of rig sizes – 18m, 24m and 28m – in different wind strengths.

The first heavy-weather wings could be ready for testing as early as the event in Cowes in August 2019 and if successful could be used at 2019 season finale in Marseille.

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