Friday, 23 November 2012

It is about all about design intent

There are more smililarties between designing an A-class like the DNA and AC 72 then one would imagine.
Ofcourse budgets are higher, tools are more refined but it remains the same art of designing, it is not math which will do the trick but building on what works and finding room for improvements.

In every design project you start which your intent: what do we want to build? You have to make choices as the possible design outcomes are infinite. Once you go into a certain direction, you create your own design philosophy. Some designers stick to the same philosophy for a whole career, the best ones will master new philosophies when needed.
The choice of a design philosophy is based on past experiences, looking at what works on other boats, feedback from sailors and gutfeeling.
This process is quite fascinating and also explains why the professors amongst the designers seldom come up with the winning boat.

The choice will be made early in the project and will position the team somewhere in the design box.
If we lookd ate the current AC designs we can speculate about the chosen philosophies and the consequent design choices. It is a good design if the outcome reflects the philosophy, but it is only a great design if it beats the other designs; the winner is always right.

Oracle has designed a boat with long slender hulls with little freeboard. The apparent philopsophy is low drag and low weight above all. Her design is defintely optimised for the lower and mid range windstrength.
The choice in low drag can be seen in the absence of backstays and  the low hulls. Idea is that the hulls can be smaller as the boards carry the boat as well. The choice for L-boards makes (theoretically) sense as the induced drag of L-boards is lower than that of comparable curved boards.
Is it a good design? yes it is executed extremely well. The wing is impressive and more refined than Team New Zealand's wing. The system with Jimmy can steer the boat (it is the railing on the rear beam, he can use to steer the boat if he walks to the other side) is smart and ingenious.
Is it a great design? Maybe not as it is my feeling that the choice of the design philosophy is made by the engineers and designers with not enough input of the sailors. It is the design you would come up with in a laboratorium enviroment, too much ivory tower here. The capsize of the Oracle is caused both by a design mistake and sailing mistake. The boat did fly where it shouldn't have flown, it did not have enough buoyancy when she digged in and the sailors reacted a little bit late as we could see in the video (realize that what looks for ages on the video is the blink of an eye for the crew).

The design of Team New Zealand is much more sailor driven as her hulls look more  like blown up A-cat or F18 hulls. No co-incidence with both Pete Melvin and Glenn Ashby aboard this team. The platform is conservative with higher freeboard and with both the front beam and rearbeam quite far above the water surface. The wing is pretty straight forward. The foils arrangement is really smart and we can see the hand of Luc Dubois here. It is self stabilizing system were the innerpart of the V will give less lift if the boat starts to slide sideways. With L-foils the boat will pop out the water once the speed is high enough or when the angle of attack increases. Prada has there fore made the angle between the vertical and horizontal part sharper to get closer to the ETNZ solution.
The philosophy here is to build a big small boat that is controllable (and can be pushed) in all circumstances and a decision to focus on the foil arangement. The experience of Pete Melvin with the Nacra 20 and the experience of Glenn, Luc and Dean with the curved boards on the A-class gave them a feel and idea were to look. The whole design process is driven by what they have found in on the water testing. (bottom up, inductive reasoning).
This team tried to tame the beast in the design process while still improving its top performance.
Is it a good design? yes. Is it great? It is definitely smart and intriguing, she is already shaping the future of  our sport.
There are 2 possible weak spots here. Light weather performance due to higher overall weight and less refined wing, and control issues over 25 knots of breeze. I do not feel  that the foil arrangement has that much more drag in lower wind speeds than the other teams. Control can become an issue if the wind picks up. The boat is sailing downwind with speeds of 1,6 -2,0 times windspeed. Over 25 knots of wind speeds cannot increase with that same ratio as cavitation of the boards will become an issue and the boat can get into an agressive nosedive. The problem that the boat wants to nose dive in the bear aways as told by Grant Dalton can be solved to accelerate around the topmark with the boat still in the water, The high volume hulls will do the rest. Once you are through the powerzone you get her up and going and just slow her down near the next mark.

In the Oracle design you stiil can see the trimaran experience, ETNZ is more a refined beach cat and in Artemis you see the background of Juan K in monohulls; e.g. both the daggerboard and the mainbeam are quite forward.
If the boat has really high buoyancy that position does not have to be a problem (similar too Marstrom A-class)  but is against the trend in A-class and F-18 to move the beam aft.
The first sails showed quite some wake and her nose was not gliding as well as that of the other three boats.
With the help of Loick Peyron, the man who introduced curved boards in multihulls they can fix that.
Once they add t-foil rudders and increase the rake of the daggerboards, the boat will go much smoother through (over) the water.
The wing of Artemis is interesting, as it is a three element wing. A solution sofar only seen in C-class. In C-class you need a three element wing downwind to maintain flow attachment. In the AC72 and AC 45 you do not need the three element solution as the jib and gennaker already help to improve flow attachement. (that's why sailing downwin in A-class is so difficult and such a good practice for the AC helmsmen and wingtrimmers).

We know from both A-class and F-18 that quite different designs can be competitive. It is a real possibility that all teams will make their philosophy work. That would be best outcome, because then the sailors will make the difference in the end. ETNZ has a huge advantage here as they are leading in the process of the taming the lady. Other teams can pickup though, never underestimate the quality of your opponents. There are so many topguys. Guys who know how to spell determination.

If we see ETNZ practizing we already forget how big the lady is. I do sincerely hope that this AC can draw more attention among the traditional sailors and the grand public. It is defintely more interesting to whatch than F1. Though we all have a car in our garage but not an A-class yet.

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