Brett Bakewell-White comments on new America's Cup class rule

by Richard Gladwell, Sail-World on 5 Feb 2009
Team Alinghi consultant Tom Schnackenberg and Team Origin's Andy Claughton will explain the new America's Cup Class rule to a media conference tomorrow morning in Auckland.

The new rule was announced on 31 January 2009, and calls for a yacht of similar dimensions to that currently used for the America's Cup, known as ACC Version 5.

However while the new yacht is smaller than the two previous editions of the 33rd America's Cupper, it is similar in concept. The significant difference being the reduction in displacement from 24 tonnes to 17.5 tonnes, but carrying a similar sail area.

Sail-World.com asked Brett Bakewell-White of leading marine design firm www.bakewell-white.com!Bakewell-White_Yacht_Design to comment:

'The main change over the old IACC boats is that the Meter style rule has been abandoned for a simple box rule with defined dimensional limits,' Bakewell-White explained.

'This means that the designers efforts will be focused on creating a faster hull form rather than fooling the rule measurement methods.

'The sailplan is clearly defined and essentially one design and so the designers will be concentrating on the best hull form and the best appendage configuration but the boats are likely to be very similar in a short space of time with the biggest dilemma for designers being Righting Moment vs. Drag – how wide do we make the boat?

'As the boats get lighter, crew weight becomes more relevant. As usual the engineers will be trying to optimize structural weight as much as possible to maximize the ballast weight.'

'The most obvious change to the casual observer is that the Americas Cup will be raced in yachts that look very much like and have more relevance to your typical Grand Prix race yacht racing IRC or a TP52, rather than some odd looking drunken canoe that is optimized to a rather complex length measurement process.'

In that last comment Bakewell-White is referring to the icebreaker bow developed by Team New Zealand designer, Laurie Davidson to maximise the effective sailing length permitted under the ACC rule at that time and since copied by other designers in 2003 and 2007.

The longer length bow also allowed more volume in the ends of the canoe body of the hull.

Bakewell-White expects that the designers will trade-off righting moment from use of wider hulls against drag, and flared hulls may come back into vogue as designers use crew weight to add righting moment compensating from the reduction in ballast.

He expects the new class to be about 5kts or more faster downwind than the current class type, adding that for their length the new class is lighter than the familiar TP52 type.

'This rule will produce yachts that are considerably lighter for their length and much faster downwind – maybe twice as fast at times? They will struggle to be as effective upwind and I would expect they will be more demanding on the crew to maximize performance.

'But the design development will have more relevance to the wider yachting community. A new rule offers greater opportunities for new teams and designers to become involved and to be successful as they will not have the same degree of catch-up to the established teams', he adds.

The media release issued by AC Management announcing the new design on 31 January is republished as follows:

The AC33 has been designed through consultation between the Defender, the Challenger of Record and the 17 other entered teams and the process was headed by Tom Schnackenberg as the class rule and competition regulations consultant for AC Management.

Designers and team managers from the 19 America’s Cup syndicates met regularly in Geneva, Switzerland, and Valencia, Spain, since the design process began in early November 2008.

This group agreed to develop a boat similar in cost to the America’s Cup Class Version 5.0 boat, but with a more exciting performance. The AC33 Rule evolved to a race yacht of 26m maximum length overall, with 5m of draft and a displacement of 17.5tonnes.

The sail plan area is greater than with the ACC Version 5.0 but without overlapping headsails, and as with the AC90 Rule contemplated in 2007, the boat has a bowsprit and the spinnaker area is limited only by sheeting constraints, not by measurement of dimensions. Given the lighter displacement, the AC33 will be more demanding to sail upwind, and will provide sparkling performance on the runs. Maximum beam is 4.8m, which will seem wide to people used to the appearance of the Version 5.0 yachts, where the last generation of yachts had a beam not much more than 3m in many cases.

Key dimension differences between an ACC Version 5.0 and the new 33rd America’s Cup Class Rule, the AC33:

ACC Version 5.033rd America’s Cup

Class AC33
Length overall: 24.5m typical26m maximum
Length waterline: 18-20m26m maximum
Beam3.3m typical: 4.8m maximum
Draft: 4.1m5.0m
Weight in measurement condition: 24T17.5T
Mast height from sheerline: 32.5m33.6m
Spinnaker area: 512sqm maximum unlimited
Mainsail area: 214sqm typical 225sqm maximum
I from sheerline: 26.1m28.5m
J: 8.3m10m
Spinnaker tack from mast: 11.6m (pole)13.65m (to end of bowsprit)
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Tom Schnackenberg, class rule and competition regulations consultant for ACM, on how the process worked and what to expect of the new class: 'We have had a very active 10 weeks pursuing this new AC33 Class Rule. The process was very similar to that of the initial AC90, and we deliberately used many of the clauses already developed for it 12 months ago. Because of our previous experience, this process seemed familiar and ran smoothly, in spite of the interruption caused by the Christmas holidays.

'The boat was originally suggested as one with overhangs, and girth restrictions, (a sort of mini J-class) but as different designers got into the act, it quickly evolved into a boat defined only by the length overall, weight, max beam and draft. This allows simple measurement processes for the hull itself, and each change seemed to make the boat go faster!

'As it turned out, the boat is slightly longer than the ACC Version 5.0 boats and several tonnes lighter, with similar sail area and righting moment. It promises to have similar upwind speed and to have sparkling downwind performance.

'We think it will be a boat which the America's Cup community will really enjoy; a worthy successor to all the wonderful boats that have gone before.'

America’s Cup Defender Alinghi’s principal designer Rolf Vrolijk on the new class: 'For designers it is always more exciting to be involved in a new class or with a new type of boat than the highly evolved existing class where we can only focus on very detailed optimisation . It is quite challenging because it means starting from zero and this is a class like nothing we have seen before so if you do your homework right, you would be competitive. Some teams might be very competitive in some corners of the rule, so that will be very interesting.'

John Cutler, technical director for the Challenger of Record, Desafío Español, on how the new class can level the playing field: 'It is a clean sheet of paper and therefore everybody has a good opportunity to come up with and design a fast boat or possibly the fastest boat, so we think that this is a good opportunity for all challengers and it will work well for Desafío Español.'

Andy Claughton, design team coordinator for TeamOrigin, the British challenger, says: 'Creating the new AC33 Class Rule has been a terrific combined effort from Alinghi and the challengers. The vision of the boat was clearly established; it had to be fast, up to date and challenging to sail, whilst not being prohibitively expensive to build and campaign.

'The rule