Please select your home edition
Edition
Cyclops Marine 2023 November - LEADERBOARD

America's Cup- Steve Clark on Bows, Stress and Weight

by Richard Gladwell on 8 Jul 2009
BMW ORACLE Racing’s BOR90 suffered noticeable platform wracking at times, which will also be a challenge for Alinghi 5. BMW Oracle Racing Photo Gilles Martin-Raget http://www.bmworacleracing.com

Over the past two days, the sailing world has glimpsed some of the most advanced sailing technology ever seen.

Last Monday BMW Oracle Racing relaunched their trimaran, BOR90 after a period of substantial modification following several session sailing trials off Anacortes and San Diego.

Like Alinghi 5 revealed the day before in Villeneuve, Switzerland, BOR90 featured the wave piercer bow - one of several modifications from her previous mode.

Sail-World asked multihull and high performance sailing guru, Steve Clark how these bows work and that the designers are trying to achieve with this style.

Clark's pedigree goes way back into the early days of C-class catamarans, in fact his father Van Allen Clark sailed the US C-class cat Beverley against Hellcat (GBR) in 1962. Since then Steve has been involved in the development of C-Class catamarans culminating in the superb Cogito which won back the Little America's Cup in 1996. The C-Class catamaran have been the pioneers of much of the technology seen in these two America's Cup 'supermultis'. Wing masts for instance first appeared on C-cats over 40 years ago and the hard wingsail first appeared 35 years ago in 1974.

It's familiar technology for Clark, and the issues are well known.

'The raked back bows get called 'wave piercers' but that really is a misnomer,' he explains. 'The idea is to have the hull go right through the wave instead of rising over it.


'The notion is that you don't waste the energy making the boat go up and down ( heaving), and you don't incur pitching. The result is supposed to result net reduction in energy expended on sea-keeping thus making the vessel more efficient.

'If you look at the INCAT fast ferries, these are true wave piercing bows, and they make the ride more comfortable for the passengers.

'In sailing catamarans, the tendency has been toward wider waterlines and fuller bows and sterns. The NA (naval architecture) term for what you achieve with this is higher 'waterplane inertia (which means that the hull is less susceptible to trim changes.) That is to say it is harder to push the bow down.

'As a result, there is less need for reserve buoyancy forward, so freeboard can be cut down. Further you do not require as much or indeed any flare in the above water sections, so you can reduce surface area by pulling the deck beam in. As you do this, the stem starts to rake aft at the top, giving the Dreadnought profile.

'There is a further benefit of reducing the skin area forward, and the effect of that is that the wetted surface can't grow by as much, so the cat is slowed less if it is trimmed bow down for a short period. This makes it less likely to 'trip' over itself.'

In summary, the benefits of the so-called 'Dreadnought' bows are a reduction in pitching, and reduction in surface area of the bow, giving less is less drag.


Turning to Alinghi 5, one of the features which created considerable comment was the lack of visible support for the bows - as her design team had opted for a two beam (main and aft beam) configuration rather than the more conservative approach which has been to add a third beam forward to tie the platform (hulls and structure) together

Steve Clark explains: 'The big structural problem with these big multis is the torsional stiffness of the platform. That is to say making it so that the bows rise and fall together. Photos of BOR90 show there can be quite a bit of wracking between the weather ama and the leeward ama.

'We solved this in the C Class by using a four stay shroud system. This, essentially, turns the mast into a king post truss and relieves the beams from providing much in the way of platform rigidity. But if you are setting jibs and big asymmetrics, you can't have the four stay layout. So the usual response has been to add a third beam, such that the bows and sterns are linked solidly together.'


Alinghi doesn't have a third, forward beam.

'Jo Richard's innovation on Le Black (the 41 ft catamaran on which Alinghi 5 is said to be based) was to use a matrix of dolphin strikers and dolphin striker straps under the platform to achieve this torsional rigidity', explains Clark

' Essentially this system makes a tension structure under the trampoline do what the four shrouds on a C Class do above the trampoline. But on these America's Cup multihulls, there is more to it than just that, because there is also a honking great bowsprit to support, so 'web central' is quite a big deal.'

'The concept has been pretty well tested on Le Black, so the question is how well can it be scaled up to jumbo size?'


Clark has long advocated that the America's Cup should be sailed in the ultimate sailing craft, and looks set to see his dream realised.

'Alinghi is a pretty striking beast.' he says. 'I hope we actually get to see both these boats sailed hard.'

'Of course the most important thing will not how up in photos. HOW MUCH DOES IT WEIGH?'

'The same question has to be asked of BMW Oracle Racing's BOR90 before we can start to figure who has what kind of advantage here.

'It may be simplistic, but in the C Cats the heavier boat rarely won a series, and on th eodd occasion when they did, that was usually because the lighter boat broke too often. The scales were the best predictor of the outcome,' he concludes.

'Of course, the best way to mitigate the sailing loads on a catamaran is to be very aggressive about keeping the weight down. The lighter the boat, the less stability, the less stability, the lower the loads, the lower the loads, the lighter the structure and so forth....' says Clark expounding the self fulfilling prophecy of weight reduction in yachts of this type.

Against this backdrop of the pursuit of lightness and general weight reduction, the concept of using water ballast seems to be an anachronism. However Le Black, the seed for Alinghi 5, carried water ballast.

Clark admits to being a little perplexed on this point. 'I don't have a clear picture for the benefit of water ballast in these boats', he explains. 'Given the monstrous loads, why make it worse? Given the brute force required to sail a machine like this, why not just add crew?


'They move and can do more than just sit there, like water ballast. There is no requirement to sail with a fixed number of crew, so you can mode the boat for the day by adding monkeys.'

'It also occurred to me that at the speeds these boats are likely to sail, a 40 mile race isn't a particularly long event. The chances of getting caught out by a weather change are greatly minimized if the race takes 2-2.5 hours.'

The clear implication being that if you can predict the wind for the next three hours, then you should be able to mode the boat with the optimum crew weight to extract maximum performance for the expected wind condition. Which in turn points to the advantage/necessity of having venue which has steady and predicable winds.


Despite having his skipper and lead designer, Duncan MacLane, from the Cogito project, consulting to Alinghi, Clark can only guess at the development process the America's Cup Defenders have worked through with the multihull now known as Alinghi 5.

'I'm pretty sure that a bunch of the sailing Le Black did over the last year, was loaded to the gills with strain gauges as Dirk Kramers refined their understanding of how the various components of the struts and strings are loaded', Clark surmises.

'I also suspect they tried several different configurations of trussing to determine if there was a better plan. I have a great deal of admiration for Dirk and would hang my ass out a 10th story window on a piece he said was strong enough! So I would pr

C-Tech 2020 Tubes 728x90 BOTTOMSelden 2020 - FOOTERPredictWind - Offshore App 728x90 BOTTOM

Related Articles

Vendée Globe Thursday Morning Update
Escape from the Doldrums! The leaders of the Vendée Globe are just now releasing themselves from the grip of the Intertropical Convergence Zone, preparing themselves for the Equator and a ride down the South Atlantic.
Posted today at 7:12 am
Vendée Globe Race - Day 12 - Keel problems
Sam Goodchild continues to lead the Vendee Globe. Keel problems for Fabrice Amedeo Sam Goodchild continues to lead the Vendee Globe Race for the second successive day, as leaders clear the Doldrums. Race control has reported Keel problem for Fabrice Amedeo on Nexans - Wewise.
Posted today at 2:37 am
Eight teams jockey for 2024 44Cup podium in BVI
Racing sets sail Thursday out of Nanny Cay, Tortola in the British Virgin Islands Racing sets sail Thursday out of Nanny Cay, Tortola in the British Virgin Islands for the concluding event of the 2024 44Cup.
Posted today at 12:40 am
Star South Americans set to begin in Argentina
31 teams ready to compete on the Rio de Plata The 2024 South American Championship is set to kick off in Buenos Aires, Argentina, from November 20 to 23, bringing together 31 teams from around the world.
Posted today at 12:35 am
SiFi says the Doldrums could be messy
And look out for Dalin in the the Vendée Globe The Doldrums might cause a big shake-up at the front of the fleet and watch out for Charlie Dalin are two of the key messages from Simon Fisher as this fascinating Vendée Globe reaches the end of its 10th day.
Posted on 20 Nov
Vendée Globe Day 11
Richomme rockets to new 24 hour distance record One week on exactly since Nico Lunven (HOLCIM-PRB) set a new solo 24 hours monohull distance record, Paprec Arkéa solo skipper Yoann Richomme dramatically bettered that mark this morning on the Vendée Globe.
Posted on 20 Nov
iQFOiL International Games in Shenzhen day 1
A typhoon passing not too far from the coast created unstable wind and heavy rain The first day of racing at the iQFOiL Asian Championships and iQFOiL International Games faced challenging conditions, with only the Senior Men's fleet managing to complete a race.
Posted on 20 Nov
29er Eurocup Series 2025 official schedule
11 events across Europe at renowned sailing venues Following the incredible success of the 2024 edition, the Notice of Series (NOS) has officially been published, revealing the event schedule, rules, and essential details for competitors, coaches, and fans.
Posted on 20 Nov
America's Cup: Ben Ainslie reflects
Ben Ainslie's thoughts subsequent to his riposte to the Kiwi sport commentator Topics covered include his most memorable moment of the Cup, his thoughts subsequent to his riposte to the Kiwi sport commentator and much more in this frank review of the Brits performance in the 2024 America's Cup.
Posted on 20 Nov
Vendée Globe Race - Day 11 - Speed record
Sam Goodchild take over lead, Yoann Richomme sets a new single handed monohull speed record Sam Goodchild (Vulnerable) is the new Vendée Globe Race leader. Yoann Richomme sets a new 24hr distance record 551.84nm. Latest daily review/update video report.
Posted on 20 Nov