How to sew slugs back onto a mainsail |

How to Sew Slugs on a Mainsail

One day when we were out sailing, the mainsail separated from the mast like a zipper. Luckily, the wind wasn’t too strong and the sail remained attached to the mast at the top and bottom by a few slugs. We quickly brought the sail down and that was the end of our sailing for the day.

When we got back to the marina and inspected the sail, we could see that the webbing that attached the slugs to the sail had rotted through from UV exposure. This never should have happened and made us realize that we needed to establish a new maintenance schedule for the boat. When we lived aboard, we were always checking  this and that and were on top of repairs before they failed.

We had a couple of different repair options to consider – use shackles to reattach the slugs to the sail or sew on the slugs. The people that we bought our boat from had sailed to the South Pacific and New Zealand and used the sewn-on method of attaching the slugs to the sail. I thought if hand-sewing could withstand offshore cruising, than this method would work for me too. The slugs themselves were in good shape, it was just the webbing that needed replacing.

I searched online for information about how to sew slugs on a sail and found bits and pieces but not complete instructions. I do not profess to be an expert at this, but I thought I would share what I did.

First, assemble your supplies:

How to sew slugs back onto a mainsail |
Assemble your materials
  • Rot-resistant webbing
  • BBQ lighter to seal the ends of the webbing
  • Waxed thread and strong needle
  • Scissors
  • Measuring tape
  • Sailmaker’s palm.

Although only eight slugs broke off on our mainsail, I replaced all of the slugs.  I wanted each slug to be identical once they were fastened to the sail so that the sail would sit properly once hoisted.  I left one slug attached to the sail temporarily as a prototype while I did the repair.

I spent quite a bit of time trying to figure out how I would wrap the webbing through the slug. Once I was clear about how I was going to do this, I started by cutting 7 3/4″ lengths of webbing and sealing the edges with a BBQ lighter. If you have a hot edge knife, this would work well too. If you singe off a lot of the webbing while sealing the ends, you might have to start with a slightly longer piece of webbing.

How to sew slugs back onto a mainsail |
Cut all your pieces of webbing

I then marked the webbing with a pen where my fold line would be. For me this was 1 1/16″. This was a very helpful step to insure that each of the slugs would sit the same distance away from the sail.

How to sew slugs back onto a mainsail |
You can see where I lined up where I folded the end of the webbing inside to protect it from fraying

I wasn’t sure if there was a difference between the ends of the slugs, so I made sure that they would be similar to the one that I had left on the sail.  I put the webbing through the opening in the slug once and tucked one end inside using my 1 1/16″ line as a reference point.  I sewed the webbing in place tightly around the slug sewing three wraps on each edge using the waxed thread.

How to sew slugs back onto a mainsail |
Here is a side view. Continue sewing each slug onto a piece of webbing.

Double-check the length and reseal the edge of webbing if you need to shorten.  I then attached the slug to the sail and sewed the remaining edge of the webbing in place. Double-check that the slug is the correct distance from the sail.  Finish off your thread by looping three times.

How to sew slugs back onto a mainsail |
Insert the end of the webbing through the grommet and through the slug for a second time. Tuck the end of the webbing inside before sewing in place. Double-check as you are sewing that the slug is sitting the same distance away from the bolt rope. For me, this was 1/2 inch.

Once I had a system for this, the repair job went quickly.


  1.  Leave one slug on the sail as a prototype so that you can double-check your measurements.
  2.   Measure and measure again.
  3.  Once you are confident that you have the correct measurements, cut all pieces of webbing and seal them.
  4.  Take your time figuring out how to do this and then once you have a system, attach each slug to a piece of webbing. Continue until you have attached all the slugs.
  5.  Sew the slugs to the sail.  Keep checking that the slug is the same distance away from the sail.
  6.  Make one extra slug attachment as a prototype for future repairs.

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