Constructing My Favorite PolySails: The 59 Square Foot Bolger Leg o’ Mutton Sail

The 59 sq. ft. Bolger Leg o’ Mutton is a fine little multipurpose sail. Designer Philip Bolger specifies this sail for a number of his designs, including: Brick, Cartopper, Elegant Punt, Gypsy, June Bug, Ruben’s Nymph, Surf, Sweet Pea, and Teal. Many other builders use this sail on smaller craft because of its efficiency and simplicity. I personally have used the sail on a Cartopper and on a PDRacer as well as a 16’ sharpie of my own design. The sail pulls well, dumps air in a gust, and requires only a single line for handling and shape control. The sprit-type boom rides well overhead and poses no danger to the crew in an unexpected jibe. In addition, the sail stores easily by wrapping it around its mast.

Constructing this sail from one of our 12’ x 16’ or 10’ x 20’ PolySail Kits is a simple three to six hour project, depending upon whether one chooses to stitch up the sail before use or simply use the taped up sail. The following photos outline the steps I use in constructing one of these sails.

Step 1  Mark Out the Sail Dimensions

For this sail project, you will need a 10’ x 20’ Dinghy Kit or a 12’ x 16’ Skiff Kit to accommodate the 14’ 3” luff, 13’ 7” leech and 9’0” foot of the Bolger Leg o’ Mutton Sail. Unfold the white tarp and stretch it out as flat as possible. On a concrete or other flat surface, use weights at the corners. I use one-gallon paint cans. On dry grass, use tent stakes or long spikes to spread out the tarp. Next, mark out the sail dimensions. Allow a 2” gap at the head and clew and a 3” gap at the tack. Use an erasable marker to mark the corners and at each foot along the luff, leech, and foot. I find it helpful to tape down the tape measure in two or three places so that the edge doesn’t move much while marking these straight reference lines.

Using an erasable marker allows you to make reference marks directly on the sail surface and then erase them by rubbing them lightly with your finger.
**Novices sometimes ask why they can’t simply use the grommet-ed edges for a sail edge. The simple answer is that these tarp edges are straight, and straight edges aren’t appropriate for this sail—except for the leech where the edge grommets would disturb the air flow. Further explanation follows in Step 2.

Step 2 Taping the Edges

With the reference marks down, the next step is place the double-faced tape. Taping the leech is fairly straightforward. Place the tape along the leech just to the outside of the marks you’ve made defining the leech. There is no roach or rounding in the leech of this sail, so the big challenge is to make a straight run with the tape from the head to the clew. On the other hand, the tape in the luff and foot must be rounded correctly to help create camber (curvature) in the body of the sail and in order to create a proper foil shape.  I usually eyeball these curves with the maximum of 3” rounding in the luff falling at the 5’ mark up from the tack.. For the foot, I round the edge so that the inside of the tape is at its maximum of 2 ½” midway between the 3’ and 4’ marks, again measuring from the tack.


Step 3 Cutting Out the Sail Shape

Once the tape is in place, you can begin to cut out the sail shape. Using a sharp pair of scissors, begin at the head and cut along the outside edge of the tape along the luff. If your scissors are sharp, you should be able to run the scissors along the edge of the tape, slicing the material, without even closing the shears. Continue cutting counterclockwise around the sail until the sail outline is finished. Save the scrap. The edge material will be used later in the process for making corner reinforcing strips.

Step 4 Forming the V-Dart in the Tack

To add additional belly to the sail, I usually place a 1” x 12” V-Dart in the tack. First, I fold a V shape into the tack. Next, I add a triangle of double-faced tape to one side of the V. Finally, I remove the backing on the double-faced tape and close up the V-Dart. Darts must be placed into the sail before the reinforcing rope is added to the inside of the double-faced tape and the overlap folded back over over the line.

Step 5 Taping in the Rope Reinforcement

Lay out the reinforcing rope around the edges with one end protruding about three inches from the tack.  Peel back the paper backing from the fiberglass-reinforced tape at the tack and fold the overlap over the rope at the tack corner. Next, place a weight on the overlapped corner. Stretch out the rope and luff edge and place a similar weight on the rope and material at the head of the sail. Work up the luff, removing a few feet of tape backing at a time and folding over the overlap. As you work, remove the erasable markings by rubbing them with your finger. Try to achieve a fair curve in the luff as you tape down the overlap. Repeat this process for the leech and foot making certain that the leech is straight and that the foot has a fair curve. Once the overlaps are taped down, I pound down the overlaps with a rubber hammer—on the advice of an adhesives expert from 3M.

Step 6 Reinforcing the Corners

From the edge strip you removed in Step 3, cut out two similar edge strips for each corner of the sail. For the tack, the length should be adequate to cover the V-Dart or about 14”. For the head and clew, the pieces should be about 12”. Place double-faced tape on one side of each edge strip and trim up the edge material to the width of the tape, then trim the ends as shown. These strips will have the effect of distributing the strain on the corner grommets into the body of the sail. Once these strips are in place, add vinyl tape (shown in red in the pictures) to the corners for additional reinforcement. I use two strips of vinyl tape placed diagonally at each corner. Cut the tape so that it overlaps the edges and can be wrapped around to the opposite side. Cut the corners off the tape diagonally as shown below in the first picture on the second row. When you add tape on the reverse side, follow the same procedure in order to construct a finished corner.

Step 7 (Optional) Stitching the Perimeter

After the corners have been reinforced, you must decide whether you want to stitch up the perimeter of the sail. If you really can’t wait to get out on the water, you can skip sewing the sail and begin grommeting the corners and luff. If you decide to stitch up the perimeter, on the other hand, it helps to have a sewing machine with a walking foot and an edge guide like the one shown below. Use V-69 polyester sail thread or a similar thread for the seams. After stitching down the reinforcing strips and tape in the corners, I run a straight stitch around the perimeter of the sail about 1” in from the edges.

Step 8 Placing the grommets

In my custom-made sails larger than 50 sq. ft., I usually place a larger 7/16” brass spur grommet in each corner just to the inside of the reinforcing rope. I place slightly smaller 3/8” grommets evenly along the luff. The combination of vinyl tape, corner reinforcement strips, rope reinforcement, and stitching makes for exceptionally strong corners in this sail. To demonstrate this strength, I suspended the finished sail by its three corners and placed items weighing a total of 91 lb. in the center. The next picture shows the finished, and undamaged, sail. A final picture features a Bolger Leg o’ Mutton built earlier that has lawn cushions under the sail body near the luff to demonstrate the camber or “belly” of the sail.

When the sail is finished, it can be attached to the mast with the cable ties supplied with the kit or with rope or commercial mast hoops. Mast hoops can also be made by sawing ¾” strips from a large diameter piece of PVC water pipe. Make certain that you file down any sharp edges. One of the better sites for pictures showing how to rig the Leg o’ Mutton sail is at Michael Storer Boat Design. Michael, an Australian designer and racer, has created a photo essay showing how he rigs his PDRacer at this site:

The Bolger Leg o’ Mutton sail can be built in other configurations. I use what I call a “Reverse Bolger” sail on one of my PDRacers. This sail has the luff and leech dimensions reversed, lowering the clew by nearly 14” and the center of effort (CE) by nearly 8”. On my other PDRacer, I fly a biplane rig made up of twin 52 sq. ft. Bolger-type Leg o’ Mutton sails. A rope bridle on the front of the sprit booms helps keep their movements synchronized while allowing them to be sailed wing on wing downwind. Pictures of these boats appear below.

Overall, I think the Bolger Leg o’ Mutton  is one of the premier sails a sailor can use for optimum performance on a small boat.