In marine use it is vitally important that the right knot (or hitch or bend) be used for the job in hand, so we need to know what knots should be used and how to tie them correctly.
One thing stands out when we talk about marine knots as opposed to other purposes. When a rope with a marine knot in it has been placed under strain and pulled tight, it must be able to be undone without having to resort to use of a knife. All good marine knots have this characteristic - they can be undone after strain.
There are nine marine knots that are useful and regularly used. That's all you really need to know for good rope work, plus one splice called the eye splice. This is a method of making a permanent eye in the end of a rope in such a way that it will not undo and will retain 90% of the strength of the rope.

The nine essential marine knots:

Figure of eight	Double sheet bend
Sheet bend	Clove hitch
Round turn and two half hitches	Rolling hitch
Reef knot	Bowline
Overhand knot