Of all the sailing knots, the figure 8 is the simplest to learn.  That being said it is also one of the most important knots on a sailboat.  The figure 8 or “stopper knot” as many sailors refer to it, is used to prevent a line from slipping through a fairlead.  A stopper knot should be tied in the bitter end of any line that passes through a block, cleat, or pad eye.

To tie this knot you take the bitter end and pass over the standing line, then under the standing line (creating a figure eight), then pock it thru the top hole of the figure 8.  Tighten up the knot by grabbing hold of the standing line and sliding your hand down towards the knot.  This will create a balled up stopper knot preventing it from passing thru most blocks or fairleads onboard.

I have had sheet lines pass thru a jib fairlead, go overboard, wrap around the prop, and stall out an engine while passing under a bridge.  Catastrophes like this can be avoided.   A simple figure eight knot in the end of all your halyards and sheets can prevent a days worth of frustration, danger, and expense.