America's Cup: Italian and British teams reveal first sailing AC75 images
by Richard Gladwell Sail-World NZ 19 Oct 2019 09:37 AEDT
19 October 2019
Luna Rossa Prada Pirelli sails their first AC75 off Sardinia, Italy © Luna Rossa
In the past day, two of the recently launched America's Cup teams have released images of their first AC75's sailing and foiling, and apparently doing it well in ideal sailing conditions.
With these shots sailing fans can get some idea of the merits and complete design packages, rather than just ruminating on the nuances and hull shape seen at the launches.
The four AC75's yachts now launched fall into two categories - the Skiffs and Scows.
The Italian Luna Rossa Pirelli have, along with with Emirates Team New Zealand gone for the skiff option, with both using a skeg in the Italian AC75, and a bustle with the Kiwi Defender to provide some low drag buoyancy to help get the AC75 foiling and then soften the touchdown.
As has been seen on the Kiwi boat the reverse bow and increased hull volume performs a vital function in a breeze in a splashdown situation, where the bow kicks in and lifts the boat back onto her foils without too much impact on speed. We haven't seen how the scow approach reacts in this situation, and whether the flat bottomed hull is as forgiving as the skiff.
In one of the images from the Italians, we can see their skeg coming into close proximity with the water, and we would expect to see the same reaction as the Kiwi boat showed in its first video in a similar "water closure" situation. The Italian skeg being more sharply defined than the Kiwi's more rounded bustle, may have to make a deeper intrusion into the water to give the same lift. Which is the better approach remains to be seen.
The scow designs would be expected to have an edge in the aerodynamic stakes, which results in lower aero drag. We saw a similar approach in the 2013 America's Cup with the more aerodynamically efficient Oracle Team USA having the edge over the Emirates Team New Zealand AC72 which had greater hull volume was designed to be able to cope with an upper wind limit of 33kts or more. That limit was dropped to 25kts, and the seaworthiness of the two designs was never really put to the test in racing after racing on several occasions never got under way due to the wind exceeding the variable wind limit of 19.9 to 25.4kts before the start, and on another occasion during the racing.
Wind limits are unlikely to be imposed in Auckland due to the issues that arrive when an absolute threshold is exceeded by just 0.1kt. There is the ability to shift one of five course options and to one less affected area for safety reasons, making wind limits redundant. This is the same approach adopted for the 2009 Louis Vuitton Pacific Trophy when racing was conducted on the final day in quite extreme conditions in the IACC monohulls.
Further the AC75's with their soft mainsail could either make that reef-able or have a heavy weather mainsail. Jibs also come in three sizes, so rig reduction at the top end of the wind range is possible in a way that was not with the hard wingsails of the AC50 and AC72 eras.
No wind limit assures the certainty of TV coverage starting on time, and avoids the crazy sight from the 2000 and 2003 America's Cup boats returning home without racing due to a wind limit being exceeded and ignominiously being towed past Optimist fleets quite happily racing in the "excessive" conditions.
Add in the fact that the Defender is led by two former Volvo Ocean Race skippers to whom heavy air sailing is just part of the game, and the chances of the Kiwis agreeing to a wind limit for the Match is very remote indeed. What the Challengers do for their selection series is their business to some extent. However they would normally sail in the same conditions as the Match.
New York Yacht Club's American Magic and Royal Yacht Squadron Ltd's INEOS Team UK are both in the scow corner of the AC75 rule, and with the video that has been released by the US team and the sill images from both, the show a very clean aerodynamic profile and in that respect, assuming that rigs and foils are equal, would be expected to have an advantage. However, that assumption is something that will never happen in real-life, and we won't know the answer to that question until the first America's Cup World Series event in Cagliari, Sardinia. However, by then the construction of the teams' second AC75's will be well under way.
A rule change allowing the teams to alter both AC75's by 12.5% of the hull surface area could well be significant if changes are to be made after Cagliari ACWS.
Interestingly, the old rule allowed a 25% hull surface area change to the first boat only. But even that degree of permitted change is not sufficient to turn a skiff into a scow, or vice versa. Now it is split evenly between the two boats built by the four Super Teams.
The conundrum for all teams is whether their second AC75 is a Skiff or a Scow - and that is a decision that can now only be made in the simulator. That process can only be done after the teams digitise what they believe are their opponents' designs and then undertake comparative sailing in the world of virtual reality.
The teams then have to make a decision as to whether to build one of each, and then do further testing with the possibility that their first boat could become their race boat.
Or if they opt the for a two skiffs, or two scows, approach. Then they are able to make incremental design changes to refine their race boat to be the best it can be.
Stars + Stripes USA, with one boat from a base Emirates Team New Zealand design is already committed to the Skiff or Scow camp - probably the former.