The luff is where a headsail either fits the boat or does not. This page covers the two systems in full, and the one dimension that decides whether the sail can be hoisted at all.
The furling system
A roller furler is three things working together: a drum at the bottom that turns the assembly, a foil that runs the length of the forestay and carries the sail’s luff, and a top swivel that lets the halyard stay still while the sail turns.
The sail interacts with exactly one of them. The foil has a groove running its length, and the sail’s luff runs inside it.
The groove is the whole question
The groove has a specific size and profile, and the sail’s luff tape has to match it.
Too small and the tape will not run — the sail jams part way up, usually with someone on the foredeck and the halyard already tensioned. Too large and it will not stay put: under load the tape can pull out of the groove, which fails at the worst possible moment.
The tolerance is not generous, and the profiles are not standardised across manufacturers. This is why the furler’s make and model is the single most important piece of information about a furling headsail — knowing the model tells us the groove.
Luff tape
The sail’s luff carries a rope core inside a tape, sewn into the leading edge. The rope’s diameter sets the finished size, and it is specified in steps.
Three things follow from getting it right. The sail runs freely up and down. It stays in the groove under load. And the leading edge is clean — a tape that is loose in its groove lets the sail move around the foil, and that shows up as a soft, unstable entry.
The feeder
Where the sail enters the foil at the bottom, a feeder guides the tape into the groove. It is on the boat rather than on the sail, but it is worth checking: a missing or damaged feeder makes hoisting difficult regardless of how well the tape is matched.
Twin grooves
Some foils have two grooves. That allows a second sail to be hoisted before the first is dropped, which matters when racing, and it provides a place for a storm jib on a furling boat.
Hanks
A hanked sail carries a row of hanks along its luff, each clipping around the forestay.
What matters about them
The size, relative to the stay. The hank has to close around the forestay with enough clearance to run and not so much that it can twist or jam. Wire and rod stays of the same nominal size are not the same diameter.
The material. Bronze hanks are traditional and durable and are heavier. Stainless is stronger for its size. Plastic hanks are light and kind to the stay, and less tolerant of heavy loads.
The spacing. Hanks closer together hold the luff more evenly to the stay and share the load between more points, which matters more on bigger sails and heavy-weather sails. Too far apart and the luff scallops between them.
The count. Taken off the existing sail, this is the reliable number.
Hank models in the builder
The builder uses the current hank catalogue. The reference families are:
- Plastic Jib Hanks — A038 and A039, for small forestays up to 4–5 mm.
- Stainless Steel Piston Hanks — HK01 through HK05, for 9–20 mm maximum forestay.
- Bronze Piston Hanks — HKB00 and HKB03, for 6–15 mm maximum forestay.
- Wichard Hanks — HKG01, HKG02 and HKG05, for 9–15 mm maximum forestay.
The exact part number is more reliable than a generic description such as “stainless hank”. Match the existing sail whenever possible; if the part number is unknown, a close-up photograph of the hank around the forestay is the safest way to identify it.
What hanks are good at
There is nothing mechanical to fail. A hanked sail can be dropped on deck and secured in any conditions, and it can be exchanged for a different sail. If the halyard fails, the sail stays attached to the stay.
These are the reasons boats set up for offshore sailing still use them, and the reason a storm jib is almost always hanked to something.
The tack fitting
At the bottom, the sail’s tack attaches to the boat, and there are several families of arrangement rather than one.
A webbing loop — simple, light, low, nothing to break. Fine where the tack fitting is straightforward.
A ring — takes a shackle, spreads load into a metal fitting.
A shackle, fixed or free-hanging. Free-hanging allows the sail to align itself with the load rather than being held at one angle, which reduces distortion at the tack.
A hook — quick to attach and detach with one hand, which matters on a sail that is changed.
A soft shackle — light, strong, quiet, nothing metallic to swing about.
The right one follows from what is on the boat, how often the sail is set and struck, and how much height is needed under the tack. On a furling boat the height above the drum is often the deciding constraint, and it is smaller than it looks.
Tack height and the pennant
The sail does not always attach directly to the fitting. A pennant — a short strop between the tack and the boat — raises the tack.
Raising the tack lifts the whole sail, which lifts the foot clear of the deck and the guardrails and improves the view underneath. It also loses area and moves the sheet lead. On a storm jib a pennant is normally required, to get the foot clear of water coming over the bow.
Configuring this at SurgeSails
Has Furling sets the path. With a furler, Furler Model identifies the system and Luff Tape Size is matched to its groove. Without one, Luff Type offers hanks and Hank Model identifies them, with the count available in the Pro view.
Tack Corner and Tack Type select the tack arrangement, with the specific fitting following from the type. Tack Cut Back and Luff Tape Tack Cut Up position the tack clear of the drum and the fitting.
Where the furler cannot be identified from a model number, it is identified from photographs. The groove dimension is not something to enter.