Hi,
Loren is right on about getting measurements and working closely with your sail maker. As I've been working through sail upgrades on Emerald, I've found it hasn't been as straight forward with the cutter rig, especially when shopping used sails. Most of what you find used, and what my local sail maker seems to have experience with, is a low clew that is standard on the sloop genoa, but not a short leech and high clew like you find on a classic cutter yankee. That's why I was leading into what your wind conditions are like, because I'm not doing what seems to be typical for a cutter for most of my sailing. We get a lot of light air on the Chesapeake, like it seems you do also. I was given a "yankee" in nice shape that is really a traditional genoa, and I have found I do gain significant light air performance over the original sail with the high foot. I have experimented switching sails back to back, but there are tradeoffs. When pointing as high as possible, the lower foot blankets the staysail somewhat and I'll gain performance almost always when pointing higher than 45 degrees to furl up the staysail. That said, I'd say I feel I get more power this way than with the traditional setup going upwind, and as soon as I am reaching, the staysail doesn't have the same interference problems. However, when the wind starts hitting mid to high teens, I would go for the more traditional setup with the higher cut foot, and in fall and spring when the winds tend to be higher, I'll often leave the traditional yankee on the foil, but right now, and for all summer, I've had the larger sail with the lower foot. I've attached several pictures of the two yankees hoisted togeher (I was doing this anyway as part of doing a new staysail right now) and also a shot with both yankees and the staysail. You can see the angle of the leech is about identical on the two headsails, but where the clew lands and how it impacts the staysail is very different. Also note I don't like the sheeting angle on the original staysail, and part of what I am looking at with the sailmaker (back to what Loren said
) is what changes to make to improve this sheeting angle and to build a sail with better pointing performance. I find when it's blowing into the 20's the staysail and main work very nicely with good balance. Just for grins so you have an idea of fit as you look at used sails, the dimensions on the original yankee are luff 36' 3", leech 29' 8", foot 18' 7". The larger yankee is luff 36' 5", leech 35' 1", foot 20'.
So, hope all this ramble is helpful, and honestly, if I was building a yankee from scratch, I'd go with the more traditional sail shape with the high clew, but if I was shopping used sails as part of the mix, I'd certainly give a hard look at a nice sail that was more like a sloop's genoa if the price were right.