Australia II Wing Keel Controversy – Part 2

Peter van Oossanen

On the morning of August 6, 1981, Peter van Oossanen, left, and two technicians at the Netherlands Ship Model Basin (NSMB) carried out tests of the final hull, keel, winglets, trim tab, and rudder configuration of Australia II, the Australian challenger for the 1983 America’s Cup.

We pick up Peter van Oossanen’s account in Part 1 of his team’s involvement in developing Australia II.

On April 9, 1981, I sent a telex to designer Ben Lexcen, asking him what changes he wanted to make to the Australia model after it had been tested. We had discussed this in Sydney on March 13, but that hadn’t led to a firm plan. He replied that he wanted to change the sweepback angle of the keel and, afterward, test a thicker version. I was surprised he was thinking of such small changes, suspecting they wouldn’t be sufficient. We had earlier discussed major modifications such as those relating to shortening the waterline length, reducing displacement, and testing widely differing keels for Australia II.

More than a year prior, I had met Joop Slooff, an aerodynamicist employed by the National Aerospace Laboratory (NLR) in Amsterdam. We had been seconded to a Royal Netherlands Navy working group studying the merits of employing advanced marine vehicles for specific naval tasks. We discovered we had similar interests, one of which was sailing. I called Slooff on April 13 to ask about the possibility of performing calculations to determine the merits, in terms of lift and drag, of widely differing keel shapes. He was enthusiastic and agreed to perform the study. After he’d informed me of the approximate cost, I sent a telex to Warren Jones, executive director of Alan Bond’s America’s Cup Challenge, and Lexcen on April 15: “A new computer program has become available at the aerospace laboratory in Amsterdam with which a study can be carried out to determine the optimum shape of the keel for maximizing side force and minimizing the associated (induced) drag. I strongly recommend that this program be used to arrive at one of the alternatives to be tank-tested. Please forward your agreement, or otherwise, by return telex. The results of the calculations would be available in time for incorporation into the test program in May. The additional costs involved are in the order of . . .”

Guy Gurney

Fitted with the controversial wing keel, the 12-Meter Australia II, left, defeated defender Liberty, right, ending U.S. domination of America’s Cup competition since 1851.

Slooff was unfamiliar with the America’s Cup and the type of yacht used for the event, so I decided to visit him to inform him of the format of the race, about 12-Meter class yachts, and that any work he was to do was to be kept strictly secret. When he confirmed that condition would not be a problem, we discussed the next steps. He and his colleagues offered to carry out the calculations for as many as five keels of drastically varying aspect ratios and sweepback angles, all at a minor cost. Slooff’s superior sent me a formal proposal by letter. Since I still hadn’t received a reply to my April telex, I called Jones. He wanted Lexcen to decide on the study, so I called directly. Lexcen was lukewarm to the idea but agreed to have it done when I told him that I didn’t believe his modifications of the existing keel would offer enough potential performance improvement. A colleague and I visited Slooff in Amsterdam that same afternoon. We finalized the scope and details of the work and the shape of the four keels to be studied, with the fifth keel reserved for the best of the four fitted with winglets. (Slooff had convinced me to look at the merits of winglets.) He estimated he could complete calculations for the first four keels by May 19, 1981.

Lexcen and his wife, Yvonne, had arrived on April 28. I met with Slooff and Lexcen at the Netherlands Ship Model Basin (NSMB) on May 4. We discussed the keel configurations for which Slooff would perform calculations, and Lexcen told us about the two keel modifications he wanted to have tested. We set him up in an office close to the testing site, and NSMB staff prepared drawings of the two keel modifications and had them built such that when the base keel was removed from the model, these new variations could be fitted.

Lexcen said he wanted to work on the design of a laminated composite construction he envisioned adopting for the new boat. As far as I’m aware, this was the first time anyone considered composite construction for a 12-Meter, with New Zealand being the first to actually do it, in the 1987 Cup. He told me that while he was with us, he would visit Lloyd’s Register in London to seek approval of his construction plan before returning to Australia.

Peter van Oossanen

The top figure shows the original Australia fitted with the base keel (model reference: Keel I), and alternative keels—one possessing less sweep (Keel II), the thicker keel (Keel III), and the first “inverted” keel (Keel IV), and with crude winglets (Winglets I). The middle figure shows the original Australia hull fitted with the smaller inverted keel with more refined winglets (Keel V with Winglets II). At bottom, the 44′ (13.41m) hull is fitted with the final inverted keel and winglets (Keel V A and Winglets II A), and new rudder.

The extensive series of tests with the base model, which included fine-tuning the towing arrangement, finished on May 6. We spent two days analyzing the results and discussed our findings with Lexcen on May 11.

Four days later, Lexcen returned to NSMB with Jones as we performed the tests with the Australia hull fitted with Keel II (the leading edge of which had less sweepback but was otherwise the same as the base keel—Keel I). We tested the thicker version (Keel III) the next day. The three of us spent time on the towing carriage on both days, discussing the project and the results thus far.

Meanwhile, Slooff had completed the calculations for the four “planar” keels. He called me on May 12 to say that the “inverted” keel (possessing zero sweepback and a taper ratio equal to 2.0) was marginally better, leading to approximately a 1% increase in velocity made good to windward in 8 knots of true wind.

By today’s standards, the subject calculations were crude, the hull, keel, and rudder having been primitively modeled by relatively large flat surface panels and, in adhering to zero heel for these calculations, not addressing the physics properly. I figured that the error in the subject calculations would probably be the same in all four cases, however, leading to the conclusion that the inverted keel was not inferior to the base keel. I remember thinking that the advantage of adopting the inverted keel lay in the possibility of fitting the required lead ballast lower in the keel—precisely the characteristic required of the 44 (13.41 m) waterline length concept.

Before Jones returned to Australia, I proposed redesigning the hull to test the 44 concept in the tank with the inverted keel. After considerable discussion, we agreed to first test the inverted concept on the existing Australia hull to check Slooff’s calculations. We referred to that model as Keel IV.

In a meeting with Lexcen on May 19, Slooff expanded on what he had told me over the phone. We agreed with his suggestion to add winglets to the panel model of the inverted keel and to repeat the calculations. We discussed the design of these winglets in terms of location, span, chord length, and dihedral angle. The resulting configuration constituted the fifth and final model to be analyzed by NLR.

We had another long discussion with Lexcen about the results of the model tests with the base keel (Keel I) and Keels II and III. The results in terms of the speed made good to windward (VMG) at discrete true wind speeds were as listed in Table 1.

These results reveal that Keel II possesses lower VMG values at true wind speeds up to 8 knots and small increases at higher true wind speeds. And Keel III yields lower speed made good to windward values at true wind speeds up to 9 knots and somewhat greater improvements at higher wind speeds. Lexcen wasn’t unhappy with these results, but he realized that they were not going to win the America’s Cup for Australia.

The drawings required for the manufacture of Keel IV (with and without winglets) were prepared between May 20 and 22. I had instructed Henk van Amersfoort, the draftsman seconded to me for the project, to adopt the same lateral area as the base keel, the same foil shape, for the quarter-chord distribution across the span to possess zero sweepback, and to adopt a taper ratio of 2.0. The two of us designed that first keel with and without winglets, with input from Slooff.

Peter van Oossanen

In the top drawing, the continuous line is the contour of the original Australia keel (with Keel I). The dash-dotted contours are the thicker keel (Keel III); and the dashed line is the more upright profile (Keel II). The contours in the middle figure are the first inverted keel (Keel IV) on the original Australia hull fitted with (crude) winglets (Winglets I). The continuous line in the bottom figure is the refined inverted keel on the
Australia hull (Keel V and Winglets II); and the dashed line is the final keel (Keel V A) and winglets (Winglets II A) and trim tab on the 44′ hull (note the vertical trim tab stock)

Testing the Winglets

On June 5 Slooff told me that his calculations indicated the winglets reduced the drag due to lift (the induced drag) by as much as 35%. I was relieved; we had already prepared drawings of the winglets as an add-on to the inverted keel, and the manufacture had commenced. Lexcen was in London to discuss the yacht’s construction with Lloyd’s Register.

We tested the model fitted with the inverted keel on Monday, June 9, and added the winglets late that evening for tank-testing the next day. Lexcen was present both days, and I invited Slooff to witness the tests with the winglets fitted. Our eyes were glued to the raw data the computer on the towing carriage spat out after each run. That information told us that the generated lift (side force) of the hull fitted with Keel IV and Winglets I was significantly higher, as was the drag. The winglets had added wetted surface area, leading to higher friction drag. It became obvious to all of us that afternoon that the keel needed to be considerably smaller, retaining its depth but decreasing chord length. My graph of measured side force versus leeway angle led me to propose a reduction of 25%. When that was decided, my draftsman was given instructions on how the keel and winglets needed to be modified. Lexcen prepared a sketch of the way the keel would look, a sketch I released to journalists after the Cup competition was over.

Peter van Oossanen

Van Oossanen, left, and Australian designer Ben Lexcen watch as the inverted keel with the first crude winglets fitted to the base Australia model was readied for tank-testing at NSMB.

To determine the required twist along the span of the winglets, I arranged to segment them, allowing each of the five segments to rotate about an axis that passed through the quarter-chord location. A force transducer in each segment allowed us to measure the lift, drag, and pitching moment acting on that segment. After finding the angle-of-attack setting each of these segments required to minimize drag sailing downwind, it was relatively simple to determine the twist along the span. This twist was adhered to in the design of the smaller winglets and in all subsequent winglets.

The results in terms of the speed made good to windward, available the following day, were disappointing, as shown in Table 2. These results indicated that the inverted keel possessed an edge over the base keel, except at true wind speeds of around 6 and 7 knots. The improvement of between 0.04 knots and 0.09 knots in VMG upward of some 7.5 knots of true wind was beginning to look promising. The velocity made good to windward for the case with winglets, however, was everywhere considerably less. When I showed these results to Lexcen, he too was disappointed—a letdown after seeing the high side-force values the keel with winglets was developing the previous day.

The project had by now considerably increased in scope and budget. I sent Jones a telex after he visited NSMB on May 16 and 17, and he agreed to increase the budget, allowing us to test Keel IV with and without winglets. When Lexcen and I discussed the state of our research on June 11, we decided that we needed to test the downsized keel with the more refined winglets as well. Jones again agreed to cover the cost. In his telex dated June 9, he informed me: “I am today arranging to forward … dollars, as this is the sum already granted by Australian government reserve bank controls. I am now applying for permission to remit the balance of the estimated sum, which should be cleared within 14 days. I agree that Lexcen must remain [at NSMB] until final configuration is agreed upon, thus leaving you to complete your formal report, which is required by Alan Bond by the earliest possible date. We are becoming concerned that our total program is already six weeks behind our original schedule.”

In this telex, Jones alluded to the importance of Lexcen’s attendance at NSMB for the duration of the project. I had informed him before that the naval architect was “sick of cheese” and wanted to return to Australia as soon as possible. It was the first time in all our discussions and correspondence that Jones and I hinted at the Dutch influence on the design of the yacht and its possible consequences. This was later to become an issue, leading the NYYC to consider abandoning the 1983 America’s Cup. Lexcen didn’t heed Jones’s instruction and, after providing him with copies of our drawings, calculations, and test results, he left NSMB on June 17. According to telexes I have copies of between Jones and Lexcen, the latter flew to Australia on June 20. He did not return until much later that year, to discuss other matters.

We performed the tests with the smaller inverted keel and more refined winglets on July 2 and 3, with Slooff in attendance to witness some runs on the second day. As I expected, the results in terms of the speed made good to windward remained disappointing. As shown in Table 3, the base model with Keel I was still the best in true wind speeds of up to about 7.5 knots.

Knowing that wind speeds of less than 7.5 knots were common in the summer off Newport, Rhode Island, I felt justified in now pushing to have Lexcen and Jones embrace the 44 concept we had spoken about together several times before. The short telex I sent to Lexcen on July 1 was to the point: “Subject tests are to be carried out on Friday, July 3. Will telex results on Monday, July 6, 1981. The wetted surface of the hull with Keel V is still 5% higher than the hull with Keel I. We are drawing a new aft-body-rudder configuration for your consideration. Will send drawings early next week. We hope you have recovered from our climate, etc., and travel back to Sydney.”

The 44 Concept

Wednesday, July 1 through Friday, July 10 was the high point of the project for me. Upon considering the results obtained to date and knowing that the wetted surface area of the hull fitted with Keel V and Winglets II (the smaller inverted keel and more refined winglets) was still about 5% greater than that of the hull with Keel I, I believed that we needed to address design changes required to implement the 44 concept. I sat down with my draftsman and redesigned the aft 40% of the hull, reducing the displacement to correlate to the flotation waterline length (on the MWL plane) of 44. It entailed a considerable modification to remove the pronounced bustle that all previous 12-Meters possessed since Intrepid and move the rudderstock forward by 0.3m (11.8). I increased the thickness of the winglets (to accommodate more lead ballast) and reduced the height of the keel to that required by the 12-Meter Rule when length is lessened. Furthermore, I took the liberty of changing the design of the rudder and trim tab as well. I sent Jones a long letter on July 2 explaining what we were doing. I called Lexcen on July 4 to update him on the test results and two days later in a long telex explained that what we were doing was necessary to improve light-air performance. In the letter to Jones, I addressed the cost and time issues. Knowing that I needed to explain my reasoning in detail, I decided to travel to Australia to discuss everything and answer questions.

When I visited Lexcen at his office at home in Seaforth on July 16, I showed him the results of the last set of tests, calling his attention to the upright drag tests (representing downwind conditions), which revealed the boat was slower than the base boat in light conditions. I showed him the speed-made-good plots and compared them to those of the earlier models. We also compared the values for the center of side force of all the models and the results of turning tests indicating that the model with the smaller keel and winglets required a turning force about 25% less than that of the base model for a rudder angle of 30°. We realized that pre-start maneuvers would greatly benefit from adopting the smaller keel.

I showed him the drawings we prepared for the 44 concept, and we discussed the proposed changes to the keel, winglets, trim tab, and rudder I had prepared drawings for. We focused on the resulting values of the prismatic coefficient because we knew that with decreasing length, we would incur additional wave drag at high speeds—such as on the reaching legs of the Olympic triangle used for the America’s Cup. Some two hours later, Lexcen agreed to all proposed changes subject to wanting to make a small modification to the waterlines immediately in front of the rudderstock.

Guy Gurney

Helmsman John Bertrand, left foreground, and head of the challenge syndicate, Alan Bond, right, are dockside on Australia II between races in Newport, September, 1983

He asked me to return on July 19 to pick up the table of offsets for the change to the waterlines and to answer any questions he might then have. I knew he would want to think further about what we talked about and that he might need to call Jones to discuss this radical development. On the 19th he asked me to implement everything I had proposed. He had prepared the table of offsets for me to send to NSMB the following day to allow model manufacture to get under way.

I returned to my office on Monday, July 27 and was surprised by a message from Jones about wanting to visit us with Alan Bond and helmsman-elect John Bertrand and that they would arrive within the hour. He said they were sailing the Admiral’s Cup and that today was a lay day. They had traveled to Wageningen by helicopter and wanted to see the latest model and talk about its performance.

I asked Slooff to attend and decided to chair the meeting, present them with an agenda, and run things very formally. Slooff and I explained in detail, step by step, the work we did. It soon became apparent that Bertrand was hesitant to build and campaign a yacht that was as radical as the proposed Australia II. Bond and Jones were enthusiastic, however, and before they left to return to their waiting helicopter, Jones told me that they had decided to build two boats—the conventional hull with Keel III, and the design with the 44 hull and the final inverted keel with winglets. Both boats were to be built in Fremantle at Steve Ward’s boatyard. And both would be aluminum, as there was insufficient time left to work with Lloyd’s Register on the composites option. It was my turn to be elated. Jones thanked me by telex when he returned to Perth: “Peter, thank you for receiving Alan, John, and me. We were delighted with the trip, and they certainly left your premises enthusiastic about the approach which had been adopted.”

We performed tests with the final hull fitted with the final keel and winglets and the new trim tab and rudder on August 6 and 7. I called Lexcen about the results. I told him that we now had the performance needed to win the America’s Cup.

The Final Design

The speed made good to windward of the original Australia, the Australia hull with the inverted keel reduced in size (Keel V) and modified winglets (Winglets II), and the 44 hull with modified keel (Keel VA) and winglets (Winglets IIA) were as given in Table 4. They reveal the significant improvement in the speed made good to windward. The right-hand column in Table 4 presents the results for the final configuration with the 44 flotation waterline. We also performed so-called tuft tests to determine the nature of the flow on the keel and the hull in way of the keel.

Guy Gurney

Australia II’s winged keel was hidden from public view when the boat hung in slings between races, and its deceptive paint scheme disguised its shape while under way. The keel was revealed to curious crowds after the last race.

Knowing that these tests represented the final step in the design, Lexcen requested that I send a full set of hydrostatic and stability calculations and a full set of test results. A table of offsets for building the yacht, the required position of the mast, a lines plan on a 1:10 scale, a copy of all drawings prepared for the project, a complete set of all photographs taken, the location of the required lead ballast, and the resulting center of gravity—I sent most of this information to him on August 14 together with a cover letter in which I provided the information for rating the yacht. This included a table defining the rated length of the original Australia and the 44 yacht, the LWL value, the displacement in racing trim and when floating on the MWL waterline, the weight of crew and sails, the wetted surface area, the maximum draft, and the rated sail area.

I informed him of the necessity to move the rudderstock aft by 7cm (2.76) and the keel forward by 210mm (8.27). The hydrostatics of the new hull, keel, and winglets revealed that the yacht’s center of gravity needed to shift forward by 187mm (7.36) to accommodate the new location of the center of buoyancy, and that the resulting flotation waterline would then have a length of 14.03m (46.03 ) instead of the desired 14.1m (46.26 ). I reminded him of these changes when, at his request, I sent him tracings on Mylar of the lines of the hull, keel, and winglets on September 10.

Jones had requested an update on project costs. I sent those in a long letter dated August 13, enclosing an invoice for the remaining costs and the Table, which I also sent to Lexcen.

In late August I embarked on a much-needed holiday with my family and upon returning to NSMB was faced with extensive travel for other projects—Leningrad, Newcastle (England), Seattle, Washington, D.C., New York, Hamburg, Boston, London, Sydney, Hoboken, and Brussels—before I was able to start writing the final report.

Guy Gurney

Bertrand and Bond on the winner’s podium with the America’s Cup.

Lexcen visited me at NSMB in late October mainly on matters not related to the 12-Meter project, and we stopped by NLR to see Slooff. I visited Lexcen in Sydney when I was there for a week on November 14.

I finished my final report in December 1981. It included details of our tank-testing process and results.

Australia II went on to win the America’s Cup after eliminating contenders from Britain, Canada, France, Italy, and two other Australian yachts. It was the first time the United States lost the competition in 132 years. Soon after the yacht reached Newport, Rhode Island, controversy raged about the Dutch involvement in the design of the keel and hull. I have provided an accurate account of the Dutch team’s work with the Australian challenger in Chapter 16, Volume 5 of my work The Science of Sailing (www.vanoossanen Professional BoatBuilder will be publishing more details of the testing and design work along with my account of some particulars of the protracted controversy over the wing keel online in coming months.

About the Author: Naval architect Peter van Oossanen was a principal scientist at the Maritime Research Institute Netherlands (MARIN) in 1969–1991. He wrote the definitive text on the resistance and propulsion of ships in 1988 and founded the Van Oossanen Group in 1992. Since retiring in 2013, he has written five books about the science of sailing.