Dyneema Splicing

Why Dyneema Requires a Different Splice

Dyneema single braid is a hollow braid — there is no core. The structure is a single braided tube, and the technique for splicing it is completely different from both three-strand and double braid methods.

The three-strand technique relies on friction between twisted strands. The double braid bury relies on the core and cover interlocking. Neither applies to a hollow single braid. Dyneema splicing uses a Brummel technique, named for the interlocked tuck that locks the splice against pull-out.

Additionally, Dyneema's low-friction surface means that a simple bury without the Brummel interlock would slip. The interlocking tuck is the mechanical feature that makes the splice hold — not friction alone. Understanding this helps you understand why bury length matters: the Brummel interlock itself is the primary holding mechanism, and the bury behind it provides redundancy.

Two forms are used in practice: the simple Brummel (for low-to-moderate loads) and the locked Brummel (for high-load running rigging and soft shackle terminations). The locked version adds one additional tuck that prevents the interlock from working loose under repeated loading cycles.

Locked Brummel Splice — Tools and Setup

The locked Brummel requires minimal tools but benefits from the right setup:

Tools:

- Splicing needle or hollow tubular fid — for threading the working end through the braid structure

- Pull wire — a stiff wire with a bent hook end, used to draw the rope tail through the hollow interior

- Permanent marker — for measuring and marking bury length

- Whipping twine and needle — for finishing without heat

- Tape — for the rope end before threading

Setup:

1. Decide on eye size. Add the bury length (20–40 times the rope diameter depending on application — use 32x for running rigging, 40x for safety-critical applications) plus 5cm working tail.

2. Mark the bury length on the standing part, starting from where the eye throat will be. On 6mm Dyneema with a 32x bury, that's 192mm — call it 20cm.

3. Mark the center of the eye with a second mark — you'll need to access both the standing part and working end at the throat point.

The Locked Brummel — Step by Step

Step 1 — Form the eye:

Fold the working end back to create the desired eye. The throat of the eye is at the throat mark on the standing part.

Step 2 — First pass (working through standing):

At the throat, open a gap in the standing part braid using your splicing needle. Thread the working end through this gap — the working end should pass completely through the standing part from one side to the other.

Step 3 — Second pass (standing through working):

Now open a gap in the working end braid (the part that just passed through the standing part). Thread the standing part tail through this gap, in the opposite direction. The two have now passed through each other — this is the Brummel interlock.

Pull the eye open and the standing part in the other direction to firm up the interlock. It should not slip — you should feel the two parts grip each other as you pull.

Step 4 — Bury the working tail:

Using the pull wire, thread the working tail into the hollow interior of the standing part at the throat. Push it down inside the rope for the full bury length — 20cm for our 6mm example. Exit the tail through the rope body at the end of the bury zone.

Step 5 — Locked tuck (the 'lock'):

Pass the pull wire back from the exit point to a point 2–3 rope diameters short of the bury exit. Draw a small bight of the working tail back out through the rope body at this intermediate point, then thread the tail end back through this bight. This locks the bury against pullout — the 'locked' Brummel.

Step 6 — Milk and trim:

Grip the rope on either side of the throat and milk toward the splice to compact the bury. The exterior should look smooth with no lumps. Trim the tail exit and whip or stitch the exit point.

Soft Shackle Splicing

A soft shackle is made from a single length of Dyneema single braid with a Brummel eye splice at one end and a diamond knot (or sewn button) at the other. The loop of the eye passes through the attachment point, and the button catches to close.

Making a basic soft shackle:

1. Cut a length of 6mm Dyneema — approximately 45cm for a working soft shackle with a 10–15cm loop.

2. Splice a Brummel eye at one end. Eye size should be just large enough to pass the other end's button through when the shackle is being 'opened' — too large and the button falls through during use.

3. At the other end, form a diamond knot (also called a lanyard knot or Josephine knot): the knot that forms the button stopper. This knot is tied around a bight of the same line and tightened to form a compact, hard ball.

4. Test by closing the shackle (passing the button through the eye) and loading it progressively. The button should not deform or pass back through the eye under load.

Soft shackle breaking strengths vary by line diameter and construction. A 6mm SK75 Dyneema soft shackle typically has a breaking strength of 2,500–3,500kg — comparable to a 6mm stainless shackle at roughly 10% of the weight.