Posted By RichC on June 19, 2016
Unknown to many sailors, the halyard knot is nonetheless an elegant compact knot that is particularly handy to know about if you need to bend a line on to some sort of shackle or clip (a halyard shackle being the eponymous example) on a more-or-less permanent basis, but are too lazy (or ignorant) to be bothered with actually splicing the line on to said bit of hardware. (see SAILfeed)
The knot most people use in these situations is, of course, the perennial and ubiquitous bowline, which is not quite ideal in this application, as it is bulkier than it needs to be (a drawback, for instance, when you have to hoist a halyard shackle up close to masthead sheave) and involves a fixed bight or loop of line that necessarily must be larger than necessary.
The halyard knot is very easy to tie. Pass a line through the shackle in question, take two full turns around the standing part, then slip the bitter end up through the turns alongside the standing part. The result is a low-profile slip knot that will snug down tight and neatly against the shackle.
The halyard knot is very secure and is very unlikely to come undone after it has been loaded up. Unlike a bowline, however, it is not that easy to untie once it has been in service for a while. In the end, when you want to get your shackle back, you may have to cut it off. At a minimum you’ll need a nice marlinspike to pick it apart.