The Irish Lashing is for fixing two poles (spars) together. For best results these poles should cross at an angle between 40 and 90 degrees to each other.
The Irish Lashing was invented in the late 80's as an alternative to the square lashing. It has two main advantages over the square lashing, (a) it uses less rope and (b) because of the interlocking rope at the back it will stop unraveling if rope snaps, more on this later
Step 1: Starting Clove Hitch
To start the rope work, you must tie a clove hitch.
To tie a clove hitch, take the rope around one of the outside poles (pic 1). Then wrap the rope around the second time, crossing over the first wrap, making a 'X' (pic 2). Finish the clove hitch by threading the rope through the 'X', passing the working end under the cross-over from the previous wraps (pic 3). When you pull both ends of the rope it will tighten on itself and hold.
Step 2: Wrapping
Once you have your clove hitch tied on the top pole you can start the wrapping.
Bring the rope from the top right, under both poles to the bottom left corner (pic 2-3).
From the bottom left corner, over the top pole and down the top left corner (pic 3).
Under the bottom pole, diagonally to the bottom right corner (pic 4)
The top should look like you are about to tie a Square Lashing and you should have a cross or a 'X' on the back.
Continue these wraps until you have four or five complete wraps. Keep these wraps as tight and as neat as possible.
Step 3: Frapping
Once you have made the required wraps its time to really tighten the lashing by adding the frapping. To do this you pass the rope around one pole and then completely round between the two poles, pull tightly and repeat four or five times.
Step 4: Finishing Clove Hitch
When you are finished the frapping, hold the tension by pressing with your thumb and finish with a clove hitch. With the working end make a 'X' with the rope then pass the working end through the center of the 'X' and pull tight.
Now when you look at the back, the rope should be interlocking (one over the other). If the rope snaps during use the lashing will only unravel some of the way, as the friction from the overlapping should hold the rope.
These lashings are used for attaching cross-beams and braces for tripods - https://www.instructables.com/id/Figure-of-8-Lashin... and many other projects.