Suits you, sir
Horses for courses or foils to taste, Andy Claughton looks at the increasingly varied range of flight choices appearing in 2019
Looking through the February Seahorse table of ‘Custom Builds’ nearly half the boats listed feature foils of some descrip- tion, from the 6.5m Mini Transat, through several new Imoca 60s to the Baltic 142 DSS. The list does not include the four America’s Cup Class yachts that are in build. Half the stories in the magazine also feature foiling boats, and tales of the travails involved in getting the best out of boats that fly. It’s quite a change – foils have moved
from a curiosity to mainstream in a decade. The stunning elegance and perfor- mance of the foiling Moths, the emergence of the Dynamic Stability System (DSS) boats and the shift of the America’s Cup to foils have generated this explosion of development. It’s no longer a binary choice, to foil or not to foil. There is a spectrum of operating modes from DSS through semi-foiling where the
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foil is job-sharing with Archimedes to support the boat weight, through to full foiling where the hull is clear of the water. How you use the foils depends on your
budget and type of boat: the Imoca 60s can fully foil, but once a boat gets over 20 tonnes it’s hard to go fast enough to gener- ate enough foil lift to get the boat out of the water. That’s not to say foils cannot be used to good effect in a semi-foiling mode to reduce hull drag and damp pitch and roll motions. Once you get above dinghy size you can
no longer use simple mechanical systems to control ride height. You are faced with either using naturally stable foil configura- tions, crew-controlled lift, or some form of electro-mechanical control using stored energy, as in autopilots. Two of the boats due for launch next
year are currently crammed into the same shed at Carrington Boats in Hythe, UK:
Hugo Boss 7 and the first Ineos Team UK America’s Cup AC75. These boats are good examples of the opportunities and challenges of foiling in boats that you can’t carry down to the water. The AC75 will be fully foiling once
there is enough breeze to ripple the water. Being a day racer with a large crew, stored energy and every driver aid known to man, it will be able to fly, and manoeuvre, without touching down. If it doesn’t the race will be lost. For the singlehanded Imoca skipper
their boat will sail most of the time in a semi-foiling mode. The class rule prohibits a horizontal foil on the rudders so full flight remains a party trick for flat water. When the wind is up, sailing downwind
an Imoca foil will be providing 6-8 tonnes of lift. This results in more righting moment (power) and less hull drag. As we saw in the Route du Rhum, getting the foil design and sailing modes correctly hooked up can give you gains of 15-20 miles a day. It does, however, add to the skipper’s stress and workload. At the very top end of the (current) size
range, with the soon-to-be-launched Baltic 142DSS, the foil will generate extra right- ing moment but the total vertical force is only a small fraction of the boat weight. That said, at this scale the engineering
JM LIOT/ARKEMA
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