This is obvious, but in both pre-starts it was clear that these boats don't turn too well.
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I wonder if you could build a cat sort of like USA-17, with the same total beam but just no center hull.
Peter Raymond
It not obvious to me that "these boats don't turn too well". Please expand on this and say by what measure they don't turn well in your estimation.
USA certainly turns quite well as the video footage of her sailing in San Diego shows. Alinghi cannot turn with USA for a very good reason.
When looked at from the standpoint of how many boat lengths are needed to turn, I would agree, a 8 knot boat turns a tighter radius than a 20 knot boat.
When looked at as time through a tack or time from speed before a tack to speed after a tack, the stopwatch shows USA to be the equal of the boats used in AC32.
It is possible that dropping to 10-12 knots through the tack from 20+ means a tack is more expensive in terms of boat lengths to windward.
It appears that both boats have issues when tacking down speed. Part of that is lack of practice and part design.
IMO the key to USA's superiority tacking is the big reason that you would NOT want to build a boat like USA with no centre hull. The centre hull is the key to the whole deal.
Alinghi is dead slow in tacks because she is a 75 foot beam catamaran. USA does not have both amas in the water through a tack except for a very short time. For must of the time she tacks like a catamaran with a 45 foot beam, then sails with the RM of a 90 foot beam. Without the centre hull USA would lose this advantage.
The centre hull has other advantages that are not readily apparent.
Alinghi must duplicate sail controls on each hull. Half of the hardware is sitting as dead weight when sailing. USA need only one set of sail controls because they run the boat from the centre hull.
The major masses in Alinghi are in the hulls, far from the CG. For turning and yaw control whilst sailing, weight far from the centre requires greater force from the foils to counter = extra drag.
The centre hull allows the placement of the cross beams to be independent of the mast step location.
The centre hull has lower drag aerodynamically than the struts and wires the catamaran uses to handle loads.
When sailing on one hull USA's centre hull is only 45 feet from the leeward ama. Alinghi's windward hull is 75 feet away. In a lull both boats roll upright at about the same speed, but Alinghi's hull hits the water with much higher velocity than USA's to the the distance from the roll axis.
When the windward hull of Alinghi slams down (repeatedly in Race 1) the inertia is high and boat is upset. Alinghi slams down on a large relatively flat hull area. Compare to USA ... the centre hull is has very little beam, it has no flat surface to slam into the water. When USA's centre hull drops it seems to kiss the water and not upset the boat as much as Alinghi.
Going back to the 45 foot effective beam vs the 75 foot beam, USA's amas don't need much rocker to help them turn. The runs for and aft are much fatter for that reason.
So IMO what we saw is almost a complete miss on the design side from Alinghi. Their boat was at the least 5% slower than USA.
This was going to be the case as soon as they decided to stay with a 75 foot beam knowing they would face a 90 foot beam. Alinghi never had a chance.
R