Tips for Spacing Slugs & Choosing Shackles for Your Mainsail

Item # X-HT-300209

Slugs and shackles are installed on a mainsail to make raising and lowering your sail easy and efficient. These small pieces of hardware are essential on every mainsail, and yet sailors who want to sew their own mainsail—or just replace broken pieces of hardware — are sometimes at a loss when it comes to installing slugs and choosing the shackle size appropriate for their sail. These short informational videos will tell you everything you need to know in order to make the right choice for your sailboat.

Tips for spacing slugs and shackles on your mainsail.

Spacing Slugs or Slides on Your Mainsail

For a professional-looking mainsail, you want to install your slugs or slides evenly spaced along the luff of your sail. Always install the first slug 1 inch down from the headboard (larger headboards have slots for the first slug attachment using webbing). Next, you’ll measure from that first slug down the luff of your sail to the tack corner and record this measurement. We suggest spacing slugs 24 to 26 inches apart along the luff of your mainsail. Take the length measurement you recorded and divide by 25. This is the number of additional slugs you will need (round down to the nearest whole number). Next, take this new number (the number of slugs) and divide from your original luff length measurement. This measurement indicates how far apart you will space each slug. For the most accurate and precise placement of your slugs, round this number to two decimal places. Then simply take this number and place slug location marks evenly spaced down from the first slug. If your slugs land on top of a reef cringle, then you will want to offset your measurements to avoid this. Here's an example equation for easy reference:

Use this equation to determine how far apart to space your slugs or slides.

For placing slugs along the foot of your mainsail, we recommend spacing them about 18 inches apart. The process for measuring slugs along the foot is exactly the same as for the luff of your mainsail, so simply follow the instructions in the paragraph above, but remember to divide by 18 instead of 25.

We’ve made a short video that explains everything you need to know about measuring and evenly spacing slugs or slides on your mainsail. We hope these instructions and video help you when installing slugs for a great-looking mainsail!

How to Select Shackles for Sail Slugs or Slides

Once you’ve measured and marked the placement of your slugs and have installed your grommets, the next step is choosing what kind of shackle to purchase and install. Make sure to select a shackle that fits through the slug or slide you’ve chosen. But what if you aren’t sewing a new sail and instead just need to replace a few pieces of old hardware? In that case, take your existing, broken shackle and measure the distance between the attachment point to the inside of the shackle.

Measure from attachment point to inside the shackle if replacing old shackles with new.

If this measurement is available in a shackle for purchase from Sailrite, you can go ahead and purchase as many as you need to replace the broken ones. However, if there is no equivalent size shackle available, it is best to replace all of your shackles even if they aren’t all broken. This is because your mainsail won’t function properly if there are different amounts of space between your hardware pieces and the sail.

Check out the video below for even more helpful information on selecting the right shackle for your sail.

Thanks for watching! And as always, Sailrite is here for all your sailing needs. We’re happy to help you regarding any questions you may have.