How to Tie a Reef Knot — and When Not to Use It

To tie a reef knot, cross the right end over the left and tuck it under, then cross the left end over the right and tuck it under: 'right over left, left over right'. Pull tight and the two ends lie flat alongside their own parts. On a boat it is used for tying reef points round a reefed sail and bundling sails or gear. It is not a safe knot for joining two ropes under load.

A mainsail stowed along a yacht's boom with ties — Sail ties and reef points are where the reef knot belongs. Photo: Craig Stanfill, CC BY-SA 2.0.

Step by step

Take one end in each hand. Cross the right end over the left end and tuck it under, as if starting to tie a shoelace.
Now cross the end that is in your left hand over the one in your right hand and tuck it under.
Pull both ends evenly. The finished knot is flat and symmetrical, with each end lying alongside its own standing part.

A reef knot with ends lying alongside their own parts compared with a granny knot — Right over left, left over right, or you get a granny.

If the ends stick out at an angle across the knot, you have tied a granny knot (right over left twice). It slips and jams. Untie it and repeat the second cross the other way.

What a reef knot is for

The name comes from reefing: when you reduce sail, the loose fold of sail along the boom is tied up with short lines called reef points, and each is tied with a reef knot. It lies flat against the sail, holds well when tied around something, and can be released quickly by pulling one end back over the knot, which 'capsizes' it.

Tying reef points or sail ties around a lowered or reefed sail.
Bundling a furled sail, cover or bag.
Tying a bandage or sling in first aid, where it lies flat against the body.

Slab reefing: the mainsail lowered to a reef cringle, with the reefed foot of the sail tied along the boom — In slab reefing, the loose sail along the boom is often tidied with reef points tied in reef knots.

Why not to join ropes with it

Reef knot vs sheet bend for joining ropes.
	Reef knot	Sheet bend
Ropes of different thickness	Slips	Holds; double it for big differences
Under shock load	Can capsize and pull apart	Secure
Purpose	Binding round an object	Joining two ropes

A reef knot only holds properly when it is pressed against something, such as a sail. Pulled from both ends in free air, particularly with ropes of different size or stiffness, it can capsize into two half hitches and slide off. Many accidents have come from reef knots used to join lines. Use a sheet bend or two bowlines instead.

Reef points today

Many modern yachts have slab reefing with a single line or two-line system and a lazy-jack stack pack, so reef points are less common than they were. You will still find them on traditional boats, dinghies and some cruising mainsails, and the reef knot remains useful for sail ties and bundles. Tie each reef point loosely enough that the sail is tidy but not strained, and untie every one before shaking out the reef. Forgetting a single tie when you hoist is a well-known way to rip a mainsail. A slipped reef knot, with one end doubled back as a bight, can be released with a single pull.

See all the core knots in essential sailing knots, and when to shorten sail in when to reef.

Related guides

Frequently asked questions

What is the difference between a reef knot and a granny knot?

A reef knot is right over left then left over right, and lies flat. A granny repeats the same cross twice; it sits crooked, slips under load and can jam.

Is a reef knot the same as a square knot?

Yes. 'Square knot' is the common American name for the reef knot.

Why is it called a reef knot?

Because it was used to tie reef points around a reefed sail, reducing the sail area in strong winds.

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