The problem with doing only one vortex panel, or keel, and then trying to compare performance between tacks is that there are so many variables at play with a boat sailing to windward which makes it difficult to truly compare windward performance between tacks. You would almost need to be able to compare VMG via instruments and a computer program, something which tbe America Cup boys can probably do quite well but imagine the amount of money involved.
Then if you do fit one panel, trial it, and decide that it is a success? you would then be faced with another haulout and having to do the job all over again on the other hull. Far better to make up both panels and fit them while you have the momentum going. That is what I found building and fitting those Kim Keels on my catamaran, while I was doing one there really did not seem to be much extra work in doing the second keel. You are already engaged in the thinking and planning and with little jobs such fiberglassing the keels, once the cloth is rolled out on one keel then it is quick and easy to move right on to the second keel.
David
Bernd Kohler