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KA

Diagram

Reef Knot

Square knot · Reef

Binding two ends of the same line around a sail or bundle. Animated Knots warns against using it to join two ropes or for critical loads.

Binding · Beginner · Polyester / Nylon rope / Polypropylene / Natural fibre · 4 steps

ApplicationsHow to tie it

Finished structure

No drawing of this exact knot yet. The written steps are the reference.

  1. Step 01

    Pass both ends around the sail or bundle, cross the left end over the right, and tuck it under and up.

    No drawing of this exact knot yet. The written steps are the reference.

    You should now see

    One half knot snug against the bundle, with an end coming up on each side.

    If it goes wrong

    Starting a reef knot to join two ropes that will each take load. Pulled end to end it can capsize and come apart.

    Fix: To join two ropes, tie a bend such as a sheet bend instead, and keep the reef knot for binding.

    Why: Either end can go over first. What matters is that the second half knot is the reverse of this one.

  2. Step 02

    Cross the end now on the right over the left end and tuck it under and up. It is the same rope that went on top in the first half knot.

    No drawing of this exact knot yet. The written steps are the reference.

    You should now see

    Each rope's end lying alongside its own standing part, forming two collars that nest together.

    If it goes wrong

    Crossing the same way twice, left over right again. That makes a granny knot, and its ends come out across the standing parts instead of alongside them.

    Fix: Undo the second half knot and cross the other way.

    Why: Animated Knots notes the granny is often tied by mistake and holds even worse than the reef knot.

  3. Step 03

    Pull both ends evenly to draw the knot down flat on the bundle.

    No drawing of this exact knot yet. The written steps are the reference.

    You should now see

    A flat, symmetrical knot lying on the bundle, with each end and its standing part still side by side.

    If it goes wrong

    Pulling on one end only, or tying ropes of different thickness. One rope pulls straight and the other slides along it as a loop, which means the knot has capsized.

    Fix: Work the knot back into two flat loops and pull both ends evenly. If the ropes differ in size, tie a different knot.

    Why: The two half knots hold by pressing on each other against the bundle. Once one rope pulls straight, nothing locks the other.

  4. Step 04

    Leave the ends long enough to grip, and put the load on the bundle the knot binds rather than on the two ropes pulling against each other.

    No drawing of this exact knot yet. The written steps are the reference.

    You should now see

    The knot stays flat and unchanged when the bundle shifts, with the ends still alongside their standing parts.

    If it goes wrong

    Relying on it where a slip would drop a load or put someone at risk. Animated Knots warns against using the reef knot for critical loads.

    Fix: Keep it for sail ties and bundles. Where the load matters, tie a knot made for that job.

Failure modes

When this family fails, it fails as these. The recovered end still outranks the name.

Bind / drag family

A binding that holds two parts, or a hitch that tightens as you drag.

  • !Reef knot used as a bend — it spills
  • !Granny form (both tucks the same way)
  • !Timber hitch with too few wraps on the object, so it walks
Fails when
  • !The two ropes are pulled end to end as a join, so the knot capsizes and comes apart
  • !One end is pulled harder than the other, so one rope pulls straight and the other slides along it as a loop
  • !The two ropes differ in thickness, which lets the knot capsize
  • !Both half knots cross the same way, making a granny knot, which Animated Knots says holds even worse
Geometry

  • Used as a rope-to-rope join

    Capsizes and slips under standing load

    Animated Knots: always a binding knot at sea — never a bend · step 01

  • Granny — same hand twice

    Will slip as soon as the reef takes strain

    Second half-knot must reverse the first · step 02

  • Capsized or unequal-diameter bind

    Already failing as a reef

    The knot must sit flat on similar ends · step 03

If you saw this

  • Knot capsizes and slips under standing load

    Check

    • ?Flat nested half-knots
    • ?Binding a reef or bundle, not joining two ropes

    Then

    • →If you needed a join, retie a sheet bend or Zeppelin
    • →If you needed a bind, retie left-right then right-left

  • Used as a rope-to-rope join

    Check

    • ?Capsizes and slips under standing load
    • ?Inspect step 01

    Then

    • →Retie. Do not dress a defective structure and call it seated.

  • Granny — same hand twice

    Check

    • ?Will slip as soon as the reef takes strain
    • ?Inspect step 02

    Then

    • →Retie. Do not dress a defective structure and call it seated.

  • Capsized or unequal-diameter bind

    Check

    • ?Already failing as a reef
    • ?Inspect step 03

    Then

    • →Retie. Do not dress a defective structure and call it seated.
Same family

Same failure class, different geometry. Open the plates — Diagnose still starts from the symptom.

This failed — start Diagnose

Not ideal for

  • ×Joining two ropes (it slips as a join)
  • ×Unequal diameters
  • ×Any life-critical or standing load

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