Improve Sail Shape and Performance with a Leech Line

Before I dive in to the main topic of this post, I want to wish all you stingy sailors out there a Happy Thanksgiving Day. Even if you don’t live in the US or don’t normally celebrate this holiday, I hope you can take some time today to express your gratitude for the blessings in your life with those around you that you love. Whether it’s good health, a loving family, a job that pays the bills, or just fond memories, we can all find something to be thankful for.

Let’s face it, if you’re reading this blog and you either already own a sailboat or are just thinking about getting one, you’re more prosperous than most of the people on our planet. I urge you to look for ways to share your prosperity with those who are less fortunate. On to the project!

The current sail inventory on Summer Dance is a collection of mostly older, original sails. The mainsail, at least, is from a different C-22. That means, besides the fact that these sails are well-used and a bit stretched out by now, that they were made before leech lines became a standard feature on most sails.

The mainsail is still in fair condition, the jib and genoa are in good condition. So far, my efforts to get better performance and longer life out of these sails has been to improve their ability to be trimmed properly by adding control lines: boom downhaul, mainsail outhaul, boom vang, and headsail pendant. These have helped the shape of the sails a lot but they don’t do much to extend their life other than to prevent them from flogging around as before. Even when trimmed properly now, the leeches often chatter in a fresh breeze, which breaks down the fabric and, in the case of the mainsail, causes extra wear on the partial batten pockets from the battens vibrating.

A leech in time saves twine

If you’re unfamiliar with a leech line, it’s a small diameter cord that runs inside a narrow pocket along the length of the sail’s leech. The line is fastened permanently at the sail’s head. Its tension can be adjusted with small cleats sewn to  the sail above the clew and above the reef cringles, if any. Tension on the leech line supports the edge of the sail to keep it from fluttering. Tension can also be used to fine tune the shape of the sail at the leech. More about that later.

Most new sails today come with leech lines built-in, particularly on larger sailboats. A sail loft can add a leech line to almost any sail. Considering the age of my sails and the simplicity of this project, I decided to add leech lines myself to the mainsail and jib. The genoa gets used mostly in lighter air, which doesn’t produce much chatter, so I left it alone. I saw this as an opportunity to try my hand at moderate sail modification/repair and to get some experience using leech lines before my next set of sails, which I hope will be new. Who knows, maybe someday I’ll build an entire sail!

Materials list

I purchased the materials for each sail from Sailrite:

I already had enough V69 polyester thread and Seamstick basting tape left over from earlier projects. I used our home sewing machine with a #18 needle and adjusted for its longest and widest zig-zag stitch. I cranked the thread tension up to bury each stitch crossover in the material. It took some hand cranking to sew through the head and clew patches but the machine chugged along the rest of the way on its own.

I added a leech line to the jib first since it doesn’t have any battens to contend with. I watched the Sailrite video on leech line installation and then installed the leech line in about an hour. The mainsail took longer to loosen and reattach the batten pockets and to add a cleat at the reef cringle. The Gransegel cleats are an ingenious design that is easy to install, surrounds the line exit from the leech pocket, and doesn’t catch on the shrouds when tacking.

Installation step-by-step

Following is an overview of the installation steps:

  1. If thesail has batten pockets that extend to the edge of the leech, detach enough of the end of each pocket so that you can sew the new leech pocket underneath. For 1-1/2″ Dacron tape, remove about 1″ of stitchesinward from the edge (Picture 1). Wider tape willrequire removing more stitches; figure 1/2 the unfolded tape width plus 1/4″.

    BEFORE - Batten pocket before leech line installation
    Picture 1 – Batten pocket before leech line installation. Remove the stitches in red to install the leech pocket underneath.
  2. Apply Seamstick to one or both inside edges of the prefolded Dacron tape. Leave the release paper on the outside of the Seamstick until you are ready to apply the Dacron tape to the sail. I found that applying Seamstick to only one side of the Dacron tape was enough to hold it in place while sewing; the Dacron tape is fairly stiff when folded.
  3. Starting just below thesail head (Picture 2), stick the Dacron tape to the sail edge, being careful to push the sail edge completely into the Dacron tape fold and press down firmly over the Seamstick. I folded 3/8″-1/2″ of the Dacron tape under itself at each end of the tape to make a more durable edge. Work about a foot at a time, peeling the Seamstick release paper off as you go. Be sure you don’t make anypuckers in the sail edge that will add friction.

    Leech line fastened at the sail head
    Picture 2 – Leech line (blue) running inside the leech pocket to a loop fastened at the sail head
  4. If the sail has reef cringles, stop the Dacron tape about 6″ above the cringle and start a new piece a couple of inches below the cringle (Picture 3). This will expose enough of the leech line above the cringle so that when you reef the sail, you can adjust it with the cleat that you will attach here later. Fold the cut ends under at each stop and start.

    Leech line passing a reef cringle
    Picture 3 – Leech line (blue) exits from the first Gransegel cleat, passes a reef cringle, and re-enters the leech pocket
  5. Continue sticking the Dacron tape down the sail edge to about 6″ above the clew and fold the cut end under like you did at the start (Picture 4).

    Leech line exits through a Gransegel cleat above the clew
    Picture 4 – Leech line exits through a Gransegel cleat above the clew
  6. Apply 3″-4″ of Seamstick to the sail edge under the open side of the Dacron tape at the sail’s head (Picture 2) and remove the exposed release paper.
  7. Double back one end of the Dacron leech line and press it firmly onto the Seamstick (Picture 2) to hold the leech line in place while you sew it down.
  8. Close the Dacron tape over the leech line and sew several passes over it with a zig-zag stitch to anchor it permanently.
  9. Sew a zig-zag stitch along the cut edge (not the folded edge) of the Dacron tape for its entire length. Reverse the stitches at least once for about an inch at each start and stop to lock the loose ends. Be careful to push the leech line as far into the leech pocket as it will go and avoid sewing over it. You want the line to slide inside the leech pocket when you adjust it. The sewing machine foot should push it out of the way as you sew. When you come to a batten pocket that you have loosened, fold the loose end of the pocket out of the away so that you can continue sewing.
  10. For each one of the batten pockets that you sewed the leech pocket under, sew the end of the pocket back down but sew only at the outer edge (Picture 5). Leave gaps between the new and old stitches so that the leech line can slide freely underneath and so that you can still insert the batten into the pocket. To keep the old stitches from pulling loose where you opened them, melt the thread ends into buttons with a hotknife and/or sew a small tack.

    AFTER - Batten pocket after leech line installation
    Picture 5 – Leech line (blue) passes inside the new leech pocket underneath a batten pocket. Sew the batten pocket back down (green) but leave gaps for the leech line to run freely.
  11. Cut the leech line about two feet longer than the overall leech pocket (Picture 4) so that you have enough slack to adjust it with and to tie the loose end to the sail clew. I recommend using a hotknife to cut the line and tying a figure 8 stopper knot.
  12. Pry open the sides of one Gransegel cleat enough to slide it over the leech pocket end above the clew. The V slot should point toward the clew. Position the cleat so that the end of the Dacron tape is in the middle of the cleat (Pictures 3 and 4). The leech line should pass through the widest part of the center slot in the cleat so that the line can run freely when it’s not cleated. You should be able to pull the leech line tight and set it in the V slot of the cleat without it binding at the end of the Dacron tape. For more help, see the Sailrite video on installing Gransegel cleats.
  13. If you bypassed a reef cringle in step 4, install another Gransegel cleat in the same way over the lower end of the upper piece of Dacron tape.
  14. Hand sew the cleats to the sail with waxed whipping twine and a large gauge needle through the holes in the cleats. Use an awl to punch holes through the sail and make this step easier.
  15. Melt the ends of the whipping twine into small buttons with a match, lighter, or hotknife.

Set the tension

The best time to trim a leech line is while under sail in a fresh breeze. Hoist the sail to its normal position and trim all control lines (halyard, boom downhaul, outhaul, vang) normally. The leech line should be released from its cleats. Pull the end of the leech line at the clew until the leech stops fluttering but not so much that the leech begins to cup to windward. Set the line in the cleat and secure the loose end so that it doesn’t catch on any rigging. The clew grommet is a good place to tie it off.

When you reef the mainsail, the leech line will go slack. Reset the tension with the cleat at the reef cringle. When you shake out the reef, release the leech line from the reef cleat as well. The line should come taut when the sail is fully hoisted again.

The Bottom Line

Suggested price: $125/sail
$tingy Sailor cost: $13.10/sail
Savings: $111.90/sail

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