A-Class: Pete Melvin on new Sail / Tramp designs

Images: Pete Melvin Takpuna Worlds 2014 by Richard Gladwell sail-world.com , Mischa Heemskerk Punta Ala Worlds 2015 , Landenberger new tramp by Felix Egner Oct 2015.–
While past years developments in the A-Class were focused mainly on foils Pete Melvin tried a new sail design solution back in January 2014. Mischa also took a similar rig to Takapuna Worlds but it wasn´t actually used for the event. Thus Pete was the first to give the soon to be standard A-Class rig, a good racing test.

In 2015 Mischa Heemskerk developed the concept a step further for Punta Ala combined with a sealed tramp (check his interview for more details) while Glenn Ashby adopted the concept two weeks before the Worlds with feedback shared by Mischa.

Now Felix Egner from Landenberger sails has launched a membrane trampolin that looks super stylish (photo above) along its functional design. Felix also has been working on the loft new sail, the prototype was sailed by Jacek Noetzel past week. More info at facebook.com/OneDesignSails/?fref=ts
In the US they are also working on new booms, visit USACA Fb for pics.

To know more about the working concept behind the proven superiority at Punta Ala of the new sail & tramp design combo I contacted Pete Melvin, who is a former A-Cat World Champ, AC level designer & Rules maker along his partner Gino Morelli  at MorrelliMelvin , two of the most renown and respected Multihull specialists Worldwide.
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Pete Melvin on Decksweepers & Aero Tramps

CSN: You sailed a Mischa Heemskerk like setup rig already at Takapuna Worlds in 2014. Which were Pros and drawbacks of that sail, as the rig didn´t catch up further at that moment, and why in your view the solution working now.

Pete Melvin: When I tried it, I learned that I had too much hollow in the leach of my sail which flattened the sail too much when I sheeted in for power downwind. The setup was very fast upwind especially in breeze.

I was first to the windward mark several times at the 2014 World’s in Takapuna but could not hang on downwind. I developed the sail, boom, and mainsheet system with Glaser Sails but sold my boat after Takapuna and have not had time to sail A Cats since then. I firmly believe in the concept and would like to design a new boat that would take better advantage of the end-plate effect.

It looks like he is using the same boom, mainsheet, and sail foot geometry as we developed in 2014 but has improved the shape of the sail in the middle and top so that it develops better power downwind.

Deck-sweeper mainsails have been tried on catamarans in the past but what makes them more viable now is pairing them with a sealed trampoline. Not only do you get the benefit of a longer luff for lower induced drag and lower center of effort, but you can lower the center of effort further still with a sealed trampoline. This allows you to develop more power and forward thrust without the healing moment of a higher center of effort.

On a conventional sail with no foot sealing, you generate a large draggy vortex off of the foot. If you try and make the foot fuller and flatten or twist the top of the sail in order to move the center of effort lower, I think what happens is that you generate too large a vortex and associated induced drag at the bottom of the sail.

I noticed while using my deck sweeper sail with endplate fairing at the Takapuna Worlds last year, I could really ease the outhaul and power up the bottom of the sail when it got windy and would go faster and faster. I had to be careful because the center of effort was so low that I could develop more side force and the boat would leap out of the water due to the vertical component of the foil lift I was generating.

I had an airfoil-shaped main beam fairing with trampoline behind it. When I saw Peter Burlings’ fully sealed trampoline I immediately had “tramp envy”. What Mischa has done is combine the deck sweeper sail with a fully sealed trampoline and I think this is a good way to go.

Congratulations to Mischa for taking it to the next step.”
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