The half blood knot
I haven't yet taught Karen to build leaders. We made mention of the fact that the recommended minimum length of leader (fly to flyline) is one and a half times the length of the rod. And this is as far as we have taken things.
Karen: Could you please refresh the reason why one and a half times the length.
Paul: Certainly. As the loop unfurls it is important that it looses energy, so that the fly lands gently and not with a dramatic spash. With regards to common fishing situations this leader length should be one and a half times the rod length. With regards to saltwater fly and heavy hooks this leader length can be shortened slightly.
We have however discussed the half blood knot. Karen being a 'line-fisherwoman' of notoriety does indeed already know the knot.
However there is a trick.
Before we go into details, let me first discuss the properties of leader materials, since they are rather different to those of rope. The knots you learned as a Boy Scout (Girl Guide - Karen) and shoe wearer are unsuitable for sticking bits of leader material together. This is party because leader material (which includes monofilament, copolymer and fluorocarbon) is slippy and partly because it deforms under pressure.
A good example is the old faithful overhand/granny/wind knot. This sort of knot can be rather useful in string. The same knot in your leader can weaken it by 50% one to avoid then.
So let's tie the half blood.
First poke the tippet (the end section of the leader) through the eye of the hook. Now you want to twist the 'tag end' (the end bit of the line) around the main line about 5 times. The hard way to do this is to conscientiously twist turn the tag end around and around; it's all fingers and thumbs. The easy way (the 'trick') is to turn the fly. It can be even easier if you stick the tag end between your teeth. You may only have one set of hands, especially if you're a guy, but you probably have a mouth.
Poke the tag end between the loop you created at the eye (my, I'm pleased that I can draw, as this scanning from my book will no doubt demonstrate) and stick the tag end back in your mouth, hold the fly and pull the main line tight.
It is very important that you tighten this knot by pulling the main line and not the tag end. If you were to pull the tag end you would create a little pigtail just before the hook. In terms of interest this ranks highly, in terms of presentation it sucks.
A variation of the half blood knot is the tucked half blood knot. The difference here is that the tag end is taken through another loop. I only bother tucking the tag end back through with large hooks. Size 8 and above gets the tucked treatment by me. I've hardly ever had the knot slip below this hook size.
Do check the knot before by giving a bit of a tug. Then you simply clip the tag end leaving approx 1/8th (couple of mm) spare.
Karen will be getting the full leader treatment in lesson 4.