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How to Make a PolySail Spritsail

Dave Gray, Principal Partner, HR Solutions/PolySail International

All Rights Reserved

(For links to other instruction pages on making polytarp sails, see the links at the end of this article.)

Polytarp sails, or polysails, are a simple, inexpensive solution to the problem of getting your newly constructed sailboat onto the water quickly. Unfortunately, most would-be amateur sail makers are forced to use blue or silver sail-making materials that look more at home covering farm machinery than powering a newly launched craft nimbly across the water. With our White Polysail Kit and simple ten-step construction process, however, you can create a polysail that is nearly indistinguishable from traditional sails. Make your sail in the morning and be on the water by afternoon--usually for under $100.

To make a white PolySail, you will need your sail plan and the following materials, space, and attitude:

In sailmaking, there are two ways to create the depth of curvature needed for the sail to work. Professional sailmaking lofts create this curvature by cutting and shaping panels of cloth or synthetic material and then sewing these panels together. This method is usually labor intensive and expensive.

A second, more traditional method for cutting sails, is simply to create shape in the sail by cutting the edges in a curve. This second method, called the edgecut method, has been used by small boat sailors for centuries and is a far easier, faster, and less expensive method of constructing a sail. We use this method in constructing all PolySails. As you construct your PolySail, remember that by putting curve into the side of a sail as you construct it, you create "belly" in the sail when that side of the sail is straightened under tension against a mast or boom.

Like many small boat builders, once you get "hooked" on PolySails, you will probably build a number of experimental sails improving your technique and the appearance of your finished product each time. One kit is usually enough to construct two triangular, or jib-cut sails.


 The following instructions are for creating a simple jib-cut spritsail for a mast without a track, but these directions can easily be adapted for many types of sails or a mast with a track. The illustrations are not to scale.


Unfold the polytarp material and stake the corners and edges. Stretching the polytarp in the warm sun will help remove the wrinkles and provide a better surface for laying out the sail plan.

Very lightly mark the dimensions of the sail on the polytarp material. (You will want to be able to remove all trace of these marks later, so make some test marks first.) Mark the luff length first (the side that is next to the mast), placing a series of small dots about 5" inches in from the edge of the polytarp. Note that the edges of the polytarp material are not always straight. If your unstayed mast curves, this line of dots should follow the curvature of your mast. If you have a small, easily handled mast, lay the mast itself on the polytarp and mark along the inner side of the mast. If the mast is too heavy, use the steel measuring tape to make a line of dots approximating the curve of your mast. In the illustration, I have used the mast, sprit boom, a batten, and a tape measure to create my base lines of dots.


After you have lightly marked the foot measurement, lay a batten or your tape measure along the line you have made. To create "belly" in your sail, curve the batten or tape outward about 1 1/2"-2" from the base line you drew in Step 1. At either end of the line, the batten or tape should be touching the base lines. The greatest distance between the base line and the new curved line should fall between the lower end and middle of the line as shown on the diagram below. In fact, the curve can be slightly reversed near the clew, the corner of the sail furthest from the mast. (Note: the base lines, or original lines in the diagram below, were computer enhanced so that they would show on the diagram. Mark your base lines lightly or the ink might show through the completed sail.

Follow the same procedure to mark the luff line, the edge next to the mast. However, you will want even greater curvature in the luff of the sail than for the foot; so increase the distance from your base line to the new curved line to 3 1/2"-5". Again, the greatest distance between the base line and new curved line should fall between the middle of the luff line and the lower corner or tack of the sail. For sails with a luff of over 14', increase this curvature by 1/2" for each additional 3' of luff length. Before marking the new curved line, sight along the batten or tape measure to see if you've created a "fair curve."

Next, mark the leech, the longest edge of the sail. The leech line should have little curvature compared to the luff line. In fact, a slightly hollow leech will help prevent a fluttering leech that could quickly wear out your sail .


Next, outline the sail shape you have created with the double-faced tape, except for the tack and head corners. The double-faced tape should end about 3" short of the corners at the tack and head. Place your strips of tape just outside the newly-marked curved lines but leave the protective coating on the top side of the tape. When you are finished taping, check to see that you have created "fair" curves in the foot and luff, and a straight or slightly hollow line in the leech.

To create even more belly in the sail, you can place "pleats" in the tack and head of the sail. I call these pleats V-Darts. To make V-Dart, make about a 1" fold or V in the edge of the material at the tack and head. This will create a slight wrinkle in the material that angles toward the middle of the sail. This wrinkle should be largely covered over when the corners are taped, but its effect is to create more "belly" or camber in the chord of the sail. If you want even more draft for light airs, you can add V-Darts along the edges of the sail before the protective covering is removed from the double faced tape. For detailed instructions on V-Darts, click this link:

If your eye tells you all is well, begin cutting out the sail shape. Use the outside edges of the carpet tape as a guide for cutting! CAUTION: Allow plenty of extra material at each corner of your sail! Leave at least an 8"x 8" tab at each corner. Notice how extra material has been allowed at each corner in cutting out the sail shape in the illustration above.


Once the sail shape has been cut out, you can fold up the excess material and remove it. Make certain that you have a clean place to work, then stretch out and stake the sail shape, by putting a nail through the corners about where the corner grommets will be placed. Remove the protective covering from the top of the double-faced tape. Beginning at the tack, lay rope on the inner side of the carpet tape all the way up the luff to the top corner, or head. Check to make certain the rope is stuck to the double-faced tape in a fair curve. Do not cut the rope! After taping the luff rope down, check the dimensions of the foot, the luff, and the leech.  

Following the procedure you used to create the luff line, continue to lay out the rope in a fair curve for the leech and foot creating a nicely curved "belly" for your sail. (Note: The leech rope can be left out or reduced in diameter if you prefer a finer edge at the leech.) If you want, you can make a small loop in the rope at the head and clew of the sail for adjustments (See the previous illustration). At the tack, however, the loose ends of the rope will meet and extend out from the sail material about 18" before being cut.

STEP 5 (OPTIONAL): Before the polytarp is folded over the rope and taped, each corner can be reinforced with additional material. These pieces are not necessary for lighter duty sails, but are needed for heavy air and higher performance sailing. Because of the extra thickness of the material, special grommets which are not supplied might be needed at reinforced corners.

Using the utility knife provided with the kit, cut out pieces from 1/16" to 1/8"-thick scrap plastic, or some other waterproof, fairly rigid material. Sand the edges smooth, and wrap the plastic with vinyl tape. Place these pieces inside the corners and tape the rope to them as shown. Additional reinforcement panels can be added wherever extreme stress might be placed on the sail, e.g., at reef clew and tack points.

Plastic or anodized aluminum dinghy headboard sets are also available from marine stores and sailmaking suppliers. Normally, these plastic headboards are 4" or 4 1/2" x 5". Anodized aluminum headboard sets are available in sizes up to 7 1/4" x 9". If you plan to use these on your sail, purchase these headboards first, then cut the head of your sail to fit the headboard. The headboard set can be added when your sail is completed by pop riveting the set together. (HR Solutions/PolySails has the plastic headboards available as a kit accessory.)

(ALSO OPTIONAL): If you want to include additional adjustment in the leech of your sail, you can make an adjustable leech line in your sail. To make this adjustable leech line, you will need to encase a line (from 1/8" to 3/16") in a flexible plastic sheath before going on to the next step (taping the edges). The idea is to have this line slide inside its sheath once the sail is taped. One option is to use a series of plastic soda straws to encase smaller diameter lines. Thread your leech line through the straws leaving a small gap between each straw. The leech line must be secured around the grommet or sewn in at the head of the sail. The line should exit at a reinforced opening just above the clew in order to work. The leech line is cleated tight to a boom for light airs and loosened to flatten the sail in heavy air.


Smooth out all wrinkles of material along the edges of the sail as well as possible. Invariably, there will be wrinkles in the body and edges of your polytarp sail--it is the nature of the material. But few people will notice these wrinkles in the material once you are on the water and the sail is filled.


Next, fold the polytarp material back over the rope and secure the material against the carpet tape. Because this step gives you the final shape of your sail, make certain that all curves are fair and the sail shape is what you expected before you tape down the overlap. Fold the tabs of material at the corners over the reinforcement panels and/or corners, tape securely, and trim off the excess material.

You might have to snip the outside edges of the polytarp where it does not fit down snugly against the double-faced tape. You can identify where to snip because there will be "bumps" of material after you have completed the taping process. CAUTION: Snip only the material on the edge as shown in the picture. Do not make any cuts in the tape or on the opposite side of the sail or the sail will be substantially weakened.


After the rope and reinforcement panels are covered, you can begin to tape the sail edges with vinyl tape, if you so choose. The sail will hold together fairly well just with the carpet tape alone. However, the vinyl tape can help create a more finished look to your sail. If you choose to use vinyl tape on the edges, it's nice to have an assistant help you with this task.

Unroll about an 18" strip of vinyl tape (adhesive side face down) from the roll and begin taping from the top of the luff. Carefully lay the tape along the edge of the sail so that about 3/4" of the adhesive surface of the tape extends beyond the sail material. To avoid having this adhesive stick to something over the sail edge, place scrap wood or polytarp material under the sail edge. With the heel of your hand on the tape that has been laid, continue feeding out 18" strips of tape, allowing the tape to return to its natural length before applying it to the polytarp material. As you apply tape to the polytarp material, smooth the tape from the center out to the edge to avoid having the tape wrinkle.

Continue this procedure for the full length of the luff. Be careful not to let the tape fold over on itself and try not to backtrack (pulling up tape that has been firmly applied already). When you have finished taping one side of the luff, roll the overlapped tape around to the reverse side of the sail, smooth out any wrinkles, and apply firmly on both sides. Repeat this procedure for the foot and leech of the sail.

After one side is taped, the sail is turned over and the overlap is smoothed down. Then another strip of tape is applied to the other side of the sail using the same amount of overlap. Finish the corners as illustrated above by adding diagonal strips of tape to each corner for appearance and reinforcement. At this point your sail should look much like the illustration.


In order to attach the sail to a mast or boom, place grommets into the tape at intervals along each side of the sail that is to be attached. These grommets have other functions, as well. They help hold the tape firmly in place, help hold the internal sail rope in place, and provide a means of varying the "belly" of the sail. Grommets should be spaced no more than 18" apart on a PolySail to avoid overstressing the material. Separate instructions for attaching the grommets to the sail are included with the grommet kit that is a part of the PolySail kit. The optional corner rope loops are secured to the corner grommets for added strength. Use twine or heavy fishing line to seize and lash the rope loops to the corner grommets for added strength.

NOTE: If time is not a factor and you want to give your finished product more durability, I recommend stitching or sewing all taped edges. Eventually, the effects of sun and water will cause both vinyl and carpet tape to stiffen and lose adhesion. However, if you are eager to try out your sail, go ahead and skip this step. You can always do the stitching at a later time--or make another sail. If you do stitch up the edges, use a heavy-duty needle and thread. Lubricate the needle with Vasoline or silicon spray when sewing through tape with a sewing machine. Test sew through some double thicknesses of tape on a scrap piece of polytarp material until your stitches are smooth and tight. For a truly strong sail, we urge you to stitch the tape in place. It's not as hard as it might seem; and it's about the only way that you can put in reef points in polytarp.

STEP 10:

Once the grommets are installed, you can either attach wood or rope mast hoops to the sail or use a spiral lacing technique to attach the sail to the mast. Attach the sail to the boom with the same spiral lacing technique or by individual rope hoops attached with a square knot under the boom. (See the knot-tying guide enclosed with your poly rope.) Here's your final product ready for testing:



Happy PolySailing!

 For questions about this kit product or suggestions for improvements to the kit or directions, call Dave Gray at 317 842-8106 or write to HR Solutions, 7404 Madden Drive, Fishers, IN 46038-1366.

1999, HR Solutions-PolySails


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