Let’s cut straight to the chase… having worked for three years to perfect his DeckSweeper rig and sails, in a fleet of 118 boats Mischa Heemskerk (left) won all seven races at this year’s A-Class Worlds in Medemblik (he stayed ashore for the eighth and final race). Second overall was former Tornado king and multiple world champion Darren Bundock of Australia
both more driving force and less drag. In other words, an aerodynamicist’s dream. I
started trialling the first prototype
DeckSweeper sail in 2013, sailing on my local lake to see if I could make the profile perform and identify what the effects would be – good and bad. Initially I cut down an existing mast to drop the tack of the sail closer to the deck and then added a modified windsurfer boom to control the clew.
With relatively simple refinements – including a new custom spar and boom – I began preparing for the next A-Class Worlds in Takapuna in New Zealand. At the same time as getting to grips with this new rig I was also trying to learn how to foil properly with the latest J-boards – control was a big challenge and the rudders of the time were an obvious weak point in trying to keep control when flying. With limited time before the worlds I
had to make a choice and decided to park the idea of the DeckSweeper. However, in Takapuna it was still cool to see a not dissimilar DeckSweeper concept, designed by Jay Glaser, being tried by Pete Melvin but compromised by not using lift-foils. However, watching Pete sail I immediately saw the enormous potential of this concept but also some potential weaknesses.
ing me to calculate for myself the forces involved and how to resolve them. My introduction to the A-Class cat followed an invitation from my friend Pieter Jan Dwarshuis (from the DNA Performance Sailing division of Holland Composites) to race the A-cat Worlds in Denmark in 2011. I was given a boat along with instructions about how to sail it… ‘The Aussies are trapezing downwind to use the power of the new C-foils – you’d better learn to do the same.’
Man, did I have a lot of crashes with those C-foils, powered up downwind and trapezing hard with the boat constantly leaping out of the water.
In 1956 the ‘A-Division Catamaran Class’ was originally created in England by the former International Yacht Racing Union as a restricted development class. Sixty years on and the class is still going strong – perhaps stronger than ever – and now stands proud as one of the oldest and most
active world. Being a development class, access to the catamaran classes in the
countless improvements over the years in hydro and aerodynamics, plus better construction and materials, have led to the A-Class now being among the purest and most refined of today’s high-tech perfor- mance boats.
The A-Class has been able to push the boundaries because it has so few design limitations. Only the basics of maximum hull length, maximum beam, maximum sail area and minimum weight must be adhered to. Pretty much everything else is left to you.
And so, in the search for more power to exploit the increased righting moment from foils and with today’s more aggressive sailing techniques, we come to the DeckSweeper rig.
The DeckSweeper
The concept of the DeckSweeper is not driven by the need to clean up the plat- form, though a clean platform does help, it is about the fundamental aero advantages that are readily available. And those aero advantages are significant – delivering
Why a DeckSweeper sail? A sail, just like any other wing, has a high- pressure side and a low-pressure side. The air wants to flow from high pressure to low pressure around the ends and this air leaking around the tips, the head and the foot of the sail, causes a reduction in pressure difference. Besides this loss in pressure difference, and therefore of lift, it is also causing vortices, turbulent air, which add to drag.
The pressure loss can be seen as pump- ing air into a tyre with a hole in it: you keep pushing air but you never get pres- sure. If the foot of the sail is not sweeping (touching) the deck you have a leaky tyre. Pressure is what is giving you your driving force so the loss of pressure is a direct hit to performance.
Another consideration is that a conven- tial sail foot, set in the air above the deck, will be designed with less camber in the bottom of the sail in order to reduce the vortices flowing from windward to lee- ward beneath the sail foot. You might have noticed that having a very loose out- haul on most boats is not fast and makes the boat staggery (draggy) to steer. But I wanted maximum shape and driving force in the bottom of my sail. The lower the centre of effort in the sail the
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