Dirk Kramers on foiling and AC72 design

Chris Cameron / Emirates Team New Zealand
Oracle Team USA's engineering guru tells us all he can
Should we be surprised that the AC72s are fully foiling? On the one hand no – the logical conclusion of the lifting foils fitted to the ORMA 60s to the MOD70s and on Oracle’s 33rd America’s Cup winning trimaran USA 17, is getting the leeward hull consistently clear of the water. But on the other hand the writers of the AC72 rule took some steps (but clearly not enough) to try and make sure that the new breed of America’s Cup catamarans wouldn’t fly. As a result the AC72s are in the difficult situation of foiling, only not terribly well. “There are a number of features in the Rule that discourage flying, but clearly that didn’t quite work,” muses leading America’s Cup engineer Dirk Kramers, now part of Oracle Team USA’s Design Executive. “This is the trouble with rules always. Now we are flying and we are flying in a very difficult way and probably in a more expensive way than if there had been no rule.” Under the AC72 rule daggerboards are allowed to be moved pretty much how you like – in addition to being dropped or raised they can be canted, their pitch altered, etc. However the rule states the windward board is not allowed to contribute to righting moment, trim tabs and moveable winglets are prohibited and the boards cannot protrude outboard beyond BMax. There is no such flexibility for the rudder - it can only rotate about a single axis up to 10° off vertical and again, trim tabs or moveable winglets are verboten. “Pretty much as soon as the rule was issued it became apparent that things were available in the appendage part of the rule, that quite a lot was possible there,” continues Kramers. “It was obvious then that getting some degree of lift was going to