Sail Design and Construction

Building good sails is a combination of technology, art, and most importantly, human interaction. Before we start any design process it is most important to spend time with the customer so that we can fully understand what his needs and expectations are.

We start with determining if the sail is for grand prix racing, club racing, racing and recreational sailing, recreational sailing, or offshore cruising? Then we need to know how long a customer expects a sail to last. This is a big factor in deciding what the best options of sail materials and cut are for a given customer.

Step two is proper measurement of the boat. In addition to actual sail dimensions, which may come from measurements or rating certificates, we also measure for sail construction details such as cutbacks, sail slide sizes, and luff type. For mainsails we measure mast rake, mast pre-bend, mast bend with different amounts of backstay and runner tensions, and backstay offsets. For genoas we measure the track locations and width for sheeting angles, spreader locations and lengths, and shroud and chainplate locations.

Once we have all the basic information the fun part starts! The design process is really four different steps; 2d measurements, 3d shapes, panel layout and calculation, and nesting for cutting. We start by inputting the 2 dimensional numbers. Luff, leech, and foot for mainsails; luff, leech, and foot or luff, lp, and clew positions for headsails. Then we add in the details for head width, roach, leech hollow, and foot round. The next step is developing the 3 dimensional profile or mold for the sail. Mast bend for mainsails is applied and headstay sag for headsails is calculated based on the size and geometry of the sail, apparent wind strength for the designed range of the sail, and headstay tension. Sail shape is defined for six different cross sections of the sail. At each section we have inputs for camber (the depth of the sail as a percent of the width), the distance from the leading edge to the point of maximum depth, rate of curve at any point in the cross section, entry angle, exit angle, and twist. Each of these functions are graphed and faired to insure a smooth continuous shape from top to bottom in the sail. At any point in the design process we can look at both numerical data for the sail and the actual 3d shape on computer screen. The sail can be rotated in any plane to give views of the sail from all directions. While shapes for types of sails will be very similar for similar boats, small differences have to be applied to fit their exact requirements. The sheeting angle, spreader length and spreader locations are added so that we can develop the proper twist distribution for the sail to insure it will sheet correctly around the individual rig.

The actual development of the shape is still a bit of the "art" of sailmaking. Sails are still very much "a development in progress". While we do use stress programs to calculate loads and distortions in a sail there are still no programs that really predict the final shape a sail needs to be for a given boat. That shape comes from years of experience and on the water testing. While a light #1 for similar boats such as a J29 and a Santana 30/30 may be very close in shape, a light #1 for a very light sport boat will be quite different from a light #1 for a heavy displacement 50 footer. And the differences between a great sail and a good sail for a given boat are very small. It comes down to designing in just the right amount of mast bend and headstay sag so that both main and genoa will be the right shape in a given wind strength when the backstay and runners are set; to having an entry angle that is just a few degrees different; to having just the right amount of curvature in the front 15% of the sail so that the sail has a wide enough "groove" but still points well; to having the proper twist distribution so that all the sections trim correctly around the rig while maintaining proper camber and entry angles.

Once the 3 dimensional mold is set the final profile can be calculated so that the sail will fit any girth and rule restrictions. Panels are then laid out over the mold in the computer memory to keep thread alignment in the material aligned with the load paths in the sail. Seam allowances, tablings, and details such as batten pockets, reef points, and draft stripes are added to the design and then the exact shape for each panel in the sail is calculated.

In our radial sails we don’t apply external corner patching. Instead each radial gore is flared back out as it approaches the corner to provide built in corner reinforcement. This gives us the lightest and strongest corners possible, and tapers the reinforcement well into the sail to alleviate any hard spots in the corners. Once this is done the panels are "nested" for cutting. This consists of laying out the individual panels in a computer file in just the order and position that they will be cut from the cloth. Panels can be rotated as needed to get the exact thread alignment in each panel to match it’s location in the sail. This file is then sent to the computer that controls the cutter.

Cloth is rolled out on our 60 foot table and vacuumed down to hold it in place. The cutting head makes two passes over the material. In the first pass all the seam lines are drawn, panels are numbered, and details are marked on such as draft stripes, reefs, windows, and numbers. On the second pass the panels are cut.

Batten pockets, reefs, numbers and draft stripes are applied to the cut panels and then panels are assembled using a variety of adhesive tapes so that each section can be put together and checked to insure it is smooth before being actually seamed together. The sections of the sails are then put together and final measuring and layout are done on the complete sail. The sail now has all the finish sewing done. Cross cut sails have the corner patching applied, tablings are applied to the edges, and leech lines, luff ropes, and foil tapes are installed.

The last step is "handwork". All the hardware is installed on the sail and the final check is done before being folded and bagged for delivery.