Originally Posted by Wouter
I was clearing out my archive of catamaran design topics and ran accross this paper. (BEWARE, it is a 13 MB download)

Paper on the non-foiling Alpha and foiling Rocker C-class cats when racing Patient lady 6 and Cogito

It is actually a good read and very insightful about foiling cats. I guess that this proofs Tim Bohans idea about lashing to Moths together and thus arrive at a full foiling cat with a leap in performance as outside of the realm of reality. Sorry Tim.

Basically the C-class contest tried to improve performance WITHIN a fixed rule base as indeed all the cats at the ISAD evaluation do. That Nacra 17 is pretty much a standard beach catamaran but fitted with partially lifting foils.

One of the more interesting questions is whether the Nacra 17 (or indeed nacra 20c) with curved foils is faster then the same designs with normal straight boards. Of course this question is not answered directlt by this paper, although both Cogito and Alpha used straight asymmetric daggers rather then curved foils as tried an earlier C-class competitor Patient lady ?? (I forgot which number this version had)

Most interesting fact in the paper was that Rocker proof just as competitive as Alpha ones the foils had been sawed off the boat. Auch ! That basically means that the performance of Rocker was actually held back by the lifting foils rather then being increased or stay the same.

I wonder what this says about (symmetrically) curved foiled cats. Afterall, Neither the Nacra 20C or the Nacra 17 has yet proven to perform beyond their Texel or ISAF handicap ratings. (i.e. Thai regatta and now the ISAF Olympic trials). Note that the Nacra 17 is rated the same as an F16 under SCHRS rating system (12 secs/hour quicker actually, but that is next to nothing)

Anyway, read the paper and make your own mind up.

Wouter



Nacra did extensive 2 boat testing during the F20c development and proved in-house that the curved foils were superior. Why else add an easy $1-$2K to the boat in a depressed economy? They are also here to stay in the A-Cat's. My general impression, from well outside both classes, is the curved foils aren't inherently faster upwind through beam reaching, but aren't slower on that point of sail. Downwind though they let the boat gybe through narrower angles, and if the sea state gets rough, make the boat easier to handle. There is still much to learn about there use and getting the maximum performance from a C-foil is more work than a straight board, that is inherent to the lifting nature of the design.

What I find interesting about these trials is the lack of Nacra F16 vs. Viper F16 data. Frankly, I don't believe a lick of information coming out of the event, it's all been spin doctored to death.

Last edited by samc99us; 03/26/12 10:37 PM.
Scorpion F18