Saturday, November 28, 2009

Tired of splicing? Substitue an 85% Strength Knot.

There are circumstances when a splice cannot be beat: chain to rope splice, spinnaker sheet to shackle or other snag-prone spot, or to the becket of a block where a knot would be too bulky. There are other times when a knot is a better choice: a dingy tackle that is easily tangled and frequently re-rove, a halyard that is prone to jamming in the head block, or a halyard that will be reversed or trimmed for wear. I like them on spinnaker halyards since they provide a big ball for me to hang on to (although I understand that on some rigs they can be snag prone at the mast head - it is all a mater of geometry). Many times a simple bowline will do the job; it is easily untied and compact. It is also a mere 45% strength knot and can come loose if tied loosely or with a too-short tail.

Standard figure-8
A common figure-8 is an 75% strength knot that is bulkier and more difficult to untie. It is, however, the gold-standard for mountaineers, and they stake their lives on its security and dependability. Even after a good hard fall it is not too difficult to untie, though saltwater and time do seem to make this more difficult.

Figure-8, Yosemite finish
The figure-8 can be improved upon; take the tail around the standing part again and feed it through the first turn. This increases the strength, makes it more secure against working loose, and makes it easier to untie. Three for one!

This has become my favorite mountaineering tie-in, and I have tested it through more than a few falls, as well as failure-testing it against both splices and standard figure-8s. It is less than line strength, but not by very much.

But what about chafe? A thimble won't work, but there is another solution, well proven on industrial lifting slings and used on my boat for 15 years: cover the wear area - the thimble location - with nylon or polyester tubular webbing. 1inch webbing for line up to 1/2-inch (12 mm) and 2-inch webbing for larger line; a 3-6-inch length will do. The webbing will move with the sharp spots and rope will only feel nylon sliding on nylon, it will protecting this critical area from sun, and eliminate all wear. I believe it out-performs a thimble in many applications and is certainly a safer choice for the beginning splicer, where the thimble many not be as securely positioned as needed and can shift. I have used tubular webbing "thimbles" on mooring lines and high-tec halyards, and the knot or thimble has never been the failure point.

1 comment:

  1. I use that knot all the time when I lead too. I find it less bulky and like you said, easier to untie after a big load.

    I dont mind splicing 3 strand rope, but braided rope is a pain.