Waterline Systems




Keel and rudder fairing is substantially more complicated than bottom fairing is.  Foils need to be a very precise shape, and they need to be in exactly the right place. Subtle differences in these factors have a huge effect on a boat’s performance around the race course.

Foil placement affects the balance of a boat. If the center of lateral resistance is too far aft, you get lee helm; if it too far forward, you have too much weather helm.

Foil shape is flat-out tough science and hard compromise. Foils need to generate a certain amount of lift or the boat isn’t going to go well upwind. But pesky physics dictate that when lift goes up, drag goes up too.

Sometimes, such as on the starting line, you want lots and lots of lift. Easy. You can make a fatter keel that will be hard to stall, will have tons of lift, and will enable you to keep off the leeward boat without a problem. Sounds good, right? Not entirely. With that keel you’ll feel like a horse and buggy on the freeway downwind.

So you think, “I’m getting great starts, but bad results. We’re poky downwind, so let’s make our keel really skinny to fix that.” Now you’re smoking fast on the run, but suddenly your starts suck and you can’t hold a lane to save your life.

In a perfect world you would have a different foil shape for each different condition. Much like sails; you make your sails full when the breeze is light and flat when it’s heavy, and you sheet them in and out all the time. But most of us can’t do that with foil shape. We don’t have trim tabs, and there’s no such thing as a keel cunningham!

The science of Waterline Systems’ foil program lies in making good compromises. We need to find one foil shape and placement that will give the best “around-the-course” performance in a wide range of conditions. It’s important that the boat gets off the line and can hold lanes, but doesn’t kill VMG upwind and speed downwind.

So how do we find this ideal compromise given that very subtle changes in foil shape and placement can create huge differences in lift, drag, stall, and pressure distribution? Waterline Systems works closely with some of the world’s foremost hydrodynamic engineers and naval architects to help us arrive at the best foil shape and placement possible. These people have the brains, experience, and computer power to solve the problem and to stay within class rules.

Our team at Waterline Systems has been with us for years. We fair more keels in any given year than most yards will do in a lifetime. All these hours of experience are another reason for our success.