Keels Again...

Keels are once again the hot topic in America's Cup medialand...

The non-deflecting-keel-gate rumbles on in the media surrounding the America’s Cup – although I’m not sure it’s to any great purpose. But keels have been a sensitive issue in the Cup ever since Alan Bond first covered his up in 1983, and then took the trophy home with a revolutionary winged keel. So I suppose it makes sense that now (with the new rules) the keels can’t be screened, the interest has shifted to the engineering inside the boats, which is still hidden.

Tim Jeffries chucked in his two cents worth in the Telegraph, where he comments, ‘What has been going [sic] is far more subtle and is a continuous thread of development through the last three or four Cups. Just as the sail designers know how advantageous it is to let the mast twist to match the curvature in the wind, so hull designers know that keel fins work much more effectively if some of the efficiency losses caused when they sag to leeward as the boat heels can be clawed back.

‘Precisely because the designers would love to make the mast and keel fin do things, the rules prevent them from using complex mechanisms to make this happen. What teams can do is use controls to limit or harness what happens when normal sailing forces are applied.

‘Any piece of smart, agile engineering that harnesses natural forces acting on the rig and fin keel is beneficial.

‘What is noticeable about the SUI 100 is that its keel fin shape varies over its four-metre depth. This suggests it will react differently as it 'flies' through the water. But Alinghi are not alone among teams in trying this idea.’

This is far from my area of expertise, but I thought the difference in fin shape from top to bottom was usually due to either weight optimisation – as the lower part of the fin carries less load – or down to varying the lift distribution over the fin. More lift at the root of the keel will be worse for wave drag, and more lift at the bottom will be worse for induced drag. The designers are playing these elements off to look for the most efficient solution. Using this shape to somehow alleviate the fin deflection sounds like the kind of free lunch that just doesn’t exist in sailboats.

Meanwhile, the NZ Herald is chasing the idea that… ‘Devices that move the keel are not permitted, but it is understood a number of teams have been looking at a way of linking the fin to the rig so that when the boat heels over, the pressure comes on the fin via the rig, which may reduce the deflection on the keel.’

This sounds like some seriously complex, and therefore, heavy, engineering, particularly as the rig loads enter the hull in a different place to the keel loads – and surely they’d have to line up, otherwise you’d be twisting the keel, not stiffening it? On balance, I’m still inclined to think that this whole thing blowing up at the start of the Louis Vuitton, and in an NZ newspaper, was too much of a coincidence - someone is just trying to pull our chains. Fortunately, with no racing for a couple of days and not much else to talk about than which supermodel Oracle have on the back of the boat, we’ve got plenty of time for such diversions…

Louis Vuitton and America's Cup Live Race Commentary at:

Mark Chisnell ©