America's Cup 33

Ian Campbell of the University of Southampton’s (UK) venerable Wolfson Test Unit takes data provided to him by SAIL and runs it through their velocity prediction programs and the WinDesign VPP developed in conjunction with Clay Oliver’s Yacht Research International. His detailed analysis, which begins on page 14 of SAIL’s February issue, suggests that
Author:
Publish date:
Updated on
USA_sails





Ian Campbell of the University of Southampton’s (UK) venerable Wolfson Test Unit takes data provided to him by SAIL and runs it through their velocity prediction programs and the WinDesign VPP developed in conjunction with Clay Oliver’s Yacht Research International. His detailed analysis, which begins on page 14 of SAIL’s February issue, suggests that BMW Oracle’s trimaran, USA, can fly a hull in just 8 knots of true windspeed, can sail to windward at twice the true wind speed (TWS) and can reach VMG speeds about 50 percent higher than true wind speed.

Campbell uses estimated weights and sail areas for both boats and also scales a C-Class catamaran, another class with no weight restrictions, up to 90ft. The estimated data for Alinghi’s catamaran, A5, and BMW Oracle’s USA, compare favourably with the scaled up C-Class cat.

Because these boats are so fast, apparent wind speed and wind angle will hardly change when these boats bear away on a downwind course. That means, says Campbell, that achieving maximum speed is really going to depend on how well each team knows their boat’s optimum sailing angle for any given wind strength. Both crews will try to foot fast rather than point higher and go slower.

Alinghi_sails

Downwind, Vmg speeds with a Code 0 headsail can produce apparent wind angles of just 22–28 degrees. But because of more sail area and the ability to carry water ballast effectively, USA could be 20 seconds/mile faster than A5 in 8 knots of wind. In fact anytime the boats are flying a hull, says Campbell, the data shows that USA is the faster boat.

Because USA’s wing mast can quickly produce camber coming out of a tack, that will help it to fly a hull more quickly. And even though large Code 0 headsails on A5 could reduce slightly the speed advantage downwind, any time the boats are flying a hull USA should be faster. Of course with large and staggeringly powerful boats like these, anything might happen. But if the engineers and builders have done their job, and the USA crew can avoid breakdowns, they should prevail over A5, in the 33rd America’s Cup Match, and possibly by a considerable margin.

For an in-depth analysis of both boats, including polar diagrams and estimated speed differences over a full range of windspeeds go to page 14 of SAIL’s February issue.

Related

FamilyCruise

Bareboating on Puget Sound

Depending on where you are, Puget Sound can look no bigger than a mountainous version of the Intracoastal Waterway. That’s what I thought when I first laid eyes on it from the lighthouse at Mukilteo Park on a sunny day last July. Then I went to the top of the iconic Space Needle ...read more

Bali4point1

Boat Review: Bali 4.1

Coming fast on the heels of its predecessor, the Bali 4.0, the Bali 4.1 adds a number of improvements, many of them inspired by feedback from owners and charterers. She’s an evolution of a concept that has already proven popular and very many benefits from its builder’s ...read more

Headsail

Ask Sail: Silencing A Rattling Headsail

Q: Our Pearson 26 has a 110-percent jib that tends to rattle very noisily at the top hank. We only bought the old boat recently, but it must have been happening for a long time, since there’s a deep groove worn inside that bronze hank. The jib has an unusually large and wide ...read more

Alerion2048x

Alerion Yachts 33, the 90 Minute Get Away

Easy to sail, luxurious, and swift; the Alerion 33 is the solution to your busy life. The intuitive, simple rig design, easy set-up, and put-away mean there’s no need to wait for crew to enjoy a weekend, a day, or an hour out sailing. Her beauty and comfort are evident in the ...read more

anchor

Know how: Ground Tackle

Your ground tackle is like a relationship—the more you care for it, the longer it will last. So, how do you enhance the relationship? First up, think of the accommodations—a damp, salt-rich, often warm environment, just the kind of thing to encourage corrosion. What can be done? ...read more

DSC_7522

Boat Review: Beneteau Oceanis 46.1

The Beneteau sailboat line has long represented a kind of continuum, both in terms of the many models the company is offering at any given moment and over time. This does not, however, in any way diminish the quality of its individual boats. Just the opposite. Case in point: the ...read more

shutterstock_1016585167

Cruising: Memories Made by People You Meet

Steve greeted my boyfriend, Phillip, and me as soon as we tied Plaintiff’s Rest, our 1985 Niagara 35, up to his dock on one of the Berry Islands in the Bahamas. He was tall, cheerful and clad in a hodge-podge of clothes one might wear to paint a house: oversized, grungy and old. ...read more