Matthew Sheahan considers whether a canting keel be Alinghi's secret weapon for the America's Cup?
Could a canting keel be the latest secret development aboard one of the Cup boats? On the face of it and according to the rules no. Of the two permitted movable appendages under version 5 of the ACC rule, neither, ‘shall increase the righting moment nor change the fore and aft trim.’
Yet there is growing speculation that the Defenders Alinghi might have been experimenting with a system that could move their keel in the lateral plane.
The conjecture comes following a number of public interpretations, (official and public answers from the measurement committee to specific but anonymous questions), that ask several detailed questions relating to the lateral deflection of a fixed appendage and whether any rule would be breached if lateral deflection was to be controlled by various methods.
In response, the public interpretation appears to state that rules would be breached in such a case. ‘Any means of inducing or altering deflection of a fixed appendage other than by; lift or drag generated by the motion of the appendage through the water, or loads due to self weight or other attached appendage(s), would contravene the deflection of “fixed” as used in rule 17.’
So why the speculation and why would a team wish to try and move a keel fin sideways?
America’s Cup fins are long, (4.1m), with very heavy bulbs, (20 tonnes), the current generation also sail at large heel angles, (around 35 degrees), in order to achieve as long a waterline length as they can even in the lightest breeze. At this angle of heel and with such a considerable weight on the end, the keel fin droops to leeward, reducing the available righting moment and therefore reducing the overall power that the sail plan can develop.
It seems unlikely that there is any scope in the rule to consider canting a fin to windward in the same way that say a Volvo 70 does, but even if it were possible simply to reduce the deflection there could be a potential advantage. At a typical upwind heel angle of 30 degrees, one degree of righting moment would be around 1,000kg.m, that’s three big crew on the rail, or around 3 percent of the total righting moment when fully powered up.
Setting aside the legality of such a feature, how might this be achieved? One possible answer may lie in a connection between the rig and the upper mounting of the keel. It’s not out of the question to think that a system that connected the shrouds or the under deck tie rods to the head of the keel could allow the rig to effectively pull the keel back up to weather by just enough to reduce the lateral deflection or droop.
One of the questions in particular from the Public Interpretation seems to elude to this when it asks, ‘Is it permitted by the Rule to deflect the internal structure of the yacht if it compensates the deflection of a fixed appendage thus bringing it back to the centre line plane?’
The answer was, ‘No, any induced deflection or alteration of the position of a fixed appendage would contravene the definition of “fixed”.
Given such apparent clarity in the official answers, under normal circumstances there would be little to suggest that a team had done any more than simply explore a wild ‘blue sky thinking’ idea. And yet during the unveiling day a few small details on one team’s boat seemed to provide a possible connection between the concept and the reality.
Instead of being a clean angular join between the underside of the hull and the keel fin, Alinghi’s latest boat SUI100 appeared to have some form of large radius filet in this area. While the white paint job on the fin appears to disguise this, when compared to the others in the fleet SUI100’s configuration stands out. Could this be a flexible compound, a gap filler between the fin and hull?
Another detail, this time on deck, appeared unusual too. Instead of a more conventional pin style chain plates, SUI100’s vertical stays disappear through collar like arrangements in the gunwale.
Of course neither is firm evidence that Alinghi is either experimenting with moving the keel or connecting it to the rig other than in the normal way. Furthermore, given the anonymous nature of the public interpretations there is no connection between the team and the questions either.
Looking on the other side and taking a sceptical view, the questions could be anything from a simple exploration of the limits of the rule to a hoax or spoiler. The large radius filet could have some very simple explanation. But if the last America’s Cup taught us anything about technology and the AC rule, the Hula became a glaring example that there are still areas of the rule that could be ripe for exploitation.
With swinging keels being all the rage at present and their potential benefits clear to see, it’s hardly surprising that designers might be taking a closer look.
So as the dockside chit-chat starts to do the rounds, the first issue to sort out is whether you really can, or you cant.