Water knot (tape knot)

The water knot is an overhand knot tied double. The first end of webbing lays out the knot, and the second follows it exactly in the opposite direction, layer by layer. At the end, two layers of webbing lie flat on top of each other everywhere, and a standing part and a tail come out on each side.

Flat webbing has a much larger contact area than round rope. Where the layers touch, friction arises, and that friction holds the knot together. Every twist in the webbing reduces this area. At the same time webbing is often slick and somewhat stiff – which is why the tails can work through the knot bit by bit under changing loads.

In a good water knot, both bands lie flat and parallel on each other throughout, without twists and without any place where they cross over each other. The second band follows the first so exactly that you might almost think it was a single, thicker band. A standing part and a tail come out on each side of the knot.

It is set firmly: pull on all four strands, in pairs, until the knot is compact and tight. A water knot that is only lightly set creeps more easily. Leave the tails clearly longer than with many rope knots – generously long tails give you a reserve if they creep in a little, and you notice a change sooner.

Typical mistakes are twisted webbing in the knot, tails that are too short, and a knot that is only lightly set. The most important failure mode is tail creep: with each loading and unloading, a tiny bit of tail can slip into the knot. Over many repetitions the tail can disappear completely, and then the knot comes undone.

That is why the fourth mistake is perhaps the most dangerous: tying the knot once and never looking at it again. A water knot that stays in use for a long time must be checked regularly. If the tails get shorter, retie it. For round rope there are better bends.

The knot is the obvious solution when you want to join two ends of webbing or close a piece of webbing into a loop – for example for an improvised carry strap or a tie-down band for luggage. Such improvised straps are not meant for people.

In mountaineering it is taught together with a warning about tail creep, and sewn slings have largely replaced it there. A self-tied webbing loop is not a substitute for a sewn, certified sling. Life-safety use only after proper training with certified equipment.

Make it a habit to take a quick look before every use: are the bands still lying flat? Are both tails still as long as when you tied it? It helps to note the tail length when tying, so that you notice any change.

Also look at the webbing itself: frayed edges, hard, shiny spots or discolouration point to abrasion, heat or ageing. Synthetic webbing also ages in sunlight. Webbing that looks like that should be retired, however good the knot is.