How to Flatten the Luff of that Baggy Old Sail

Do you have one or more old sails that, after you hoist them fully, have scallops and wrinkles along the luff like in the picture above? Or do you have to winch them flat or overtighten your backstay? Instead of a flat, smooth leading edge, those wrinkles disrupt airflow and rob your sail’s performance. If the sail has a polyester bolt rope in the luff and not wire rope, you can fix that yourself for almost no cost other than about an hour of your time. And you won’t have to take the sail to a sail loft, wait days or weeks to get it fixed, and drop a Benjamin or more out of your wallet.

Those sags in your sail are caused by two changes that have happened to your sail over the years. The first is the sailcloth has stretched slightly from use and abuse (kind of like what you see when you look in the mirror). There isn’t much you can do about that except have the sail recut back to its designed shape. But that’s expensive and it won’t prolong the life of your sail much relative to the cost. If your sail is that far gone, it probably needs other repairs too and possibly restitched entirely, which add more to the cost. With trailerable sailboats it’s more cost effective to replace a sail in that condition.

The second change is the polyester 3-strand rope that runs inside the luff of the sail has probably shrunk over the years. That can happen from changes in temperature and humidity and plain old age. With the sail cloth stretched in one direction and the luff rope shrunk in the opposite direction, you wind up with a wrinkly old sail that’s gathered along the luff and doesn’t work like it’s designed to.

Give your sail a facelift

The picture above is of the 150% genoa on Summer Dance. It’s probably the 34 year-old original and I use it a lot since the winds are usually light in summer where I cruise. Other than its bagginess, it’s still in pretty good condition. I probably won’t replace it anytime soon so like the leech flutter I fixed with the leech lines I added to my old mainsail and jib, I decided to see if I could improve its luff shape by what’s called raising the luff bolt rope.

The bolt rope runs inside the leading edge of the sail and is seized at the tack and at the head with hand-sewn whipping twine like in the following picture.

BEFORE - Original bolt rope whipping
BEFORE – Original bolt rope whipping

Raising the bolt rope involves removing the whipping from the bottom of the bolt rope, letting it ease up inside the luff pocket, which releases the gathering of the sail cloth, and then seizing it back onto the sailcloth in the right location. The big question to ask is, let it ease by how much? You don’t want to stretch the sail out completely along the bolt rope because the rope will stretch a bit when you hoist it. If your sail starts out at its full luff length and then you stretch it even more until the bolt rope is taught, the sailcloth could rip or the seams could come apart.

Instead, you want to raise the bolt rope just until the luff is back to its designed length (or a little more to compensate for sail cloth stretch) less what’s called preload. That’s the amount that you can expect the bolt rope to stretch at full hoist, typically 1″ for every 10′ of luff length in moderate (15-18 mph) winds. With proper preload built in, the sail will wind up at its ideal luff length right when the bolt rope is fully stretched.

The designed luff length for my C-22 genoa is 23′-6″. Before I raised the bolt rope, the luff was 22′-11″, a difference of 7″. For a preload of 2″, I raised the bolt rope 5″ for a relaxed luff length of 23′-4″. So in my case, the bolt rope had shrunken about 5″ over the years.

AFTER - One pass of whipping finished
AFTER – One pass of whipping finished. The pen is pointing at the start of the old whipping. The needle is pointing at the start of the new whipping raised 5″

Raising a bolt rope is easy and only takes about an hour the first time you do it.

Step by step

  1. Find the designed luff length for your particular sail type (main, jib, genoa) and sailboat model. One source of sail data online is the Sailrite Sailplan Database.
  2. Divide the luff length by 10 to find the amount of preload. Subtract the preload from the design length to find the relaxed length.
  3. Measure the actual luff of your sail with it pulled straight but not tight. Subtract this number from the relaxed length that you calculated above. The difference is the amount that you want to raise the bolt rope.
  4. Find the whipped end of the bolt rope above the tack of the sail. Measure up the luff from the end the amount you are going to raise the bolt rope and make a small mark.
  5. Remove the whipping above the tack of the sail. An Exacto knife and needle nose pliers or a hemostat work well for this.
  6. Have a helper hold the head of the sail while you slowly pull on the tack and let the bolt rope slide inside the luff pocket until it reaches your mark.
  7. Use waxed whipping twine and a large gauge needle to whip the sailcloth tightly to the bolt rope again with stitches similar to the original. For my sail, I started on one side of the bolt rope, made 8 whip stitches through the center of the bolt rope, made a lock stitch, then crossed over to the other side and whipped in the opposite direction back through the first set of holes to the beginning. I added a final lock stitch and then melted the ends of the twine with a lighter and pressed them flat.

Out on the water

As you can see from the following picture of the same sail, the luff now lays flat and almost wrinkle-free. Not a bad improvement for an hour’s worth of time! This sail still has some good life left in it now. The belly of the sail is still too far aft due to the stretched sailcloth but overall, it’s not bad and certainly good enough for cruising.

AFTER – A big improvement in luff shape

The Bottom Line

Suggested price: $125
$tingy Sailor cost: $0
Savings: $125


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2 Comments Add yours

  1. Sun says:

    Just out of curiosity did this project improve your pointing and or sailing performance with this older sail? I also have a C22 with the same issue.

    1. It undoubtedly improved the sail’s efficiency but not a noticeable amount. Trimming the sail well for the wind conditions is the biggest thing that you can do to improve pointing and performance. For tips on that, see Put That Lazy Sheet to Work and Point Higher, and How to Add a Draft Stripe to a Sail. For another baggy sail DIY fix, see Improve Sail Shape and Performance with a Leech Line.

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