When lashing something down it can be difficult to get the securing rope sufficiently tight.
The answer is the Trucker’s Hitch.
We must all have seen a lorry driver or farmer using this knot to secure a load. It works because it creates a 3 part tackle to give a mechanical advantage when tightening, although there is of course lots of friction. However the original version of this only works safely with a stranded natural fibre rope and
can collapse if made using a slippery synthetic or braided rope. Pass the rope over the object to be secured and make a loop some way above the ring-bolt
or whatever you are securing to. The loop can be almost anything depending on your fluency with knots [a lever hitch (the right way round), a middleman’s knot or a bowline-on-the-bight would all do well], but despite its relative inelegance a Figure-of-Eight loop is a good choice.

It is easy to see if you’ve made it wrongly and it can always be undone easily.

It won’t come undone by itself but it is easily undone when needed, even if it’s been in place for a long time.

Robin Hunt