foil flap which needs to fit within a very tight space. This is a special cylinder, along with the rudder rake cylinder which is also the most complex. These cylinders are square on the outside but round inside and have linear sensors inside so that a very precise amount of movement can be achieved and monitored. The sensor uses a magnet on the inside which means its position can be read on the outside of the cylinder. ‘The rudder rake control is also
complex because of the loads involved and the space that’s available,’ he continues. ‘The solution was to use a twin cylinder, but one of the most difficult parts is to machine two completely parallel and identical barrels. The assembly is also pretty tricky.’ But while the intricate double
cylinder is one of the most advanced products in the AC40’s hydraulic specification, the underlying concept is not new and was patented by Cariboni some years ago. ‘The idea originated from the
need to operate the jumper struts on the old monohull America’s Cup boats,’ says Cariboni. ‘They needed a double chamber to adjust the angle of the struts. Because of the loads involved and the difference small movements would make to the bend characteristics of the mast and hence the power in the sails, the adjustments had to be precise. A double cylinder was the solution. And while the item that the cylinder is adjusting today on the AC40 is a rudder and not the rig, the requirements and underlying principles are just the same.’ But the hydraulic story for the
AC40 doesn’t end there. Elsewhere
Right, top to bottom: the rudder rake control needs this intricate twin cylinder; rod terminal for the 2m- long main traveller cylinder; the mainsheet cylinder is also 2m long; the tiny foiil flap cylinder has to fit in a very tight space
within the design there have been further challenges. When it comes to the boat’s mainsheet and traveller controls the requirement is for a small-bore cylinder, but up to 2m long. This makes it very difficult to machine because you have to drill it in two parts due to the length. Clearly each operation has to be absolutely precise to achieve an accurate bore. Aside from building these special
cylinders, the speed at which they operate is also an area that is
pushing development. The mainsheet traveller is one of the best examples of this as trimming the mainsail while maintaining leach tension and a twist profile means operating at high speeds to maintain the careful balancing act. A balancing act that demands
precisemovements, executed at high speed. And it is this frenetic action under the skin of an AC40 that plays such a key part in creating the illusion of simple straight-line speed.
www.cariboni-italy.it
❑ SEAHORSE 61
MCONAGHY
CARIBONI
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