Sunday Morning Sailmaker
Radial vs. Cross-cut

Article by Brian Bissell

Not too long ago I was just like you. I knew how to sail and had learned how to race pretty well. I knew what my sail should look like up and downwind in various wind and sea conditions. I could tune my sail, trim my sail, take proper care of my sail, but if you asked me anything about how it was made, I’d shrug my shoulders. Now, after working for North Sails for three years, I can talk the talk when it comes to sail design. It wasn’t an easy learning process, however, because it seems like all sail designers speak a foreign language. Instead of trying to learn a new language at this point, let me try to be your translator.

If you called me tomorrow looking to buy a new sail, I would ask if you want a cross-cut or radial design. What’s the difference? Well, look at the drawings of the two designs. What do you notice right away? The cut out pieces of cloth, known as panels, are sewn together in different layouts. The radial sail panels radiate down from the peak and up from the clew. The cross-cut panels are sewn together horizontally. Now, count the number of seams (where panels are sewn together) in both sails. You should have counted 7 in the cross-cut and 13 in the radial. So, now that you’ve recognized the two biggest differences let’s explore what these differences mean in terms of performance in your sail.

We need to go over the stretch characteristics of sailcloth so that you will understand the next thing I’m about to tell you. Sailcloth is made up of tiny yarns woven together just like your t-shirt. If you have some free time, take a magnifying glass and hold it over your opti sail and hold it over your shirt. You should be able to see the individual yarns and how they are woven together.

Take a look at my drawing of a magnified piece of cloth. Warp, Fill, Bias??? We need a translator.

Cloth can be stretched from three general directions. It can be stretched vertically, horizontally, and diagonally. It is important to know in which direction cloth will stretch the most and why. Cloth is made by taking a bunch of straight parallel yarns and weaving other yarns, like a snake, in and out between the straight yarns. The vertical straight yarns, in sailmaker lingo, is called the Warp. The Warp yarns will stretch the least because they are already straight. The horizontal snake-like yarns are called the Fill. The Fill yarns will stretch more than the Warp yarns because they aren’t straight yet so they have room to stretch a little. The diagonal direction of the cloth is called the Bias. The cloth will stretch most in the Bias (diagonal) direction because it is not being pulled in the direction of either of the two yarns. A sail designer pays a lot of attention to this when he or she decides on the panel layout of a sail. Translation…..the way the cloth stretches in your sail really matters.

In a cross-cut sail the panels are laid out horizontally. This means that it will typically stretch most in the diagonal direction, the least in the vertical direction, and a little in the horizontal direction. In terms of the sail’s shape it will make the leach of the sail flexible. When a puff of wind hits a cross-cut sail, it will stretch in a way that will open the leach. Has your coach told you that you should ease out your mainsheet when a puff of wind hits you? Well, easing your mainsheet opens the leach of your sail too, spilling a little a wind out to help keep the boat flat. This is why cross-cut sails are better for beginner racers. They stretch more. If you don’t ease your mainsheet in a puff, the sail will stretch a little bit to open the leach for you.

The radial design is a lot less flexible. For one, the panels are laid out so that no two panels are going to want to stretch in the same direction. The stretching of one piece of cloth in the sail can be offset by its neighboring piece of cloth. The increased amount of seams in the sail will also prevent stretch in a small sail like for the Opti. A sail that doesn’t stretch much is really good if it is trimmed properly. The leach will not bend open in a puff. The mainsheet must be attended to constantly because that is the only thing that will open your leach and keep the sail from stalling out. The top kids in the country have been using the radial designs effectively. You will have an edge with a radial sail if you know how to trim it because you will be in more control of its shape since it will stretch a lot less.