Out of many thousands of knots that have been developed over the years, a basic selection is all you should need for most of your narrowboating requirements.  Many rope manufacturers print booklets with drawings of simple knots, which you will find useful to help you to practice tying knots.

Round Turn and Two Half Hitches

The simplest and most useful knot in all mooring situations is the round turn and two half hitches.  This can be used to make fast to a bollard or ring and for attaching fenders.  It is a simple knot easy to tie and easy to undo and can be used at either end of the rope, see how to make this know below:

round turn and two half hitches knot

The important thing to remember is that the rope must go round the bollard or ring twice and it is essential that you apply both the half hitches for a secure mooring as only one will slip.  However for temporary applications the second half hitch can be omitted and for quick release the hitch can be made with a loop.

The Bowline Knot

The second essential knot is the bowline.  This knot is used to make a loop or eye that will not slip but is easy to untie.  However much load is put on it the loop will not close but is easily released when the load is taken off.  This is why it is the only knot used by climbers for tying a rope around themselves.  On boats it can be used for putting an eye in a mooring rope so that it can be quickly put over a cleat or bollard on board, or it can be used for joining two ropes securely; a bowline is tied in the end of each, the second one through the first.  This is useful if you need to tow someone, the mooring lines can be used to make a longer line.  This knot needs lots of practice as its not the easiest to tie.  See how to make this knot below:

 Clove Hitches and Reef Knots

Other common knots are the clove hitch and reef knot, but they need using with caution. The clove hitch is used for mooring round a post sometimes, but it can slip or unwind and is not the best knot to use for mooring. The reef knot can be used for joining two ropes together but should only be used for light loads when the ropes are the same size and structure.

clove hitch and reef knot

Splicing Rope

Splicing is the technique of joining two lengths of rope together without a knot by unlaying the rope ends, then laying them back round each other.  Its can be used to put a smooth eye in the end of a rope, such as on the end of a mooring line where it attaches to the boat, making a smooth neat loop to attach to the boat.  See how to make an eye splice in the picture below:

making an eye splice

Please note this is only a guide, for more information get yourself a book.

Reference: BARRELL; E., 2003. The Inland Waterways Manual. 2nd Edition. Adlard Coles Nautical