Wednesday, March 7, 2012

The Clinch Knot Part 2

Finally found some time to do more line breaking tests this weekend. In The Clinch Knot Part 1 I discussed how to tie one of the most well known fishing knots, the clinch knot, aka the fisherman's knot. After teaching how to tie it, I explored various attributes of the knot that formed the strongest knot. The conclusion was that with light line (6lb Stren Original), the improved clinch knot with saliva lubrication applied formed the strongest knot with the least amount of twists in the knot, although more twists in any scenario resulted in a stronger knot. But this left me with the question. Would the same things hold true for a heavier line? That is what I'll be discussing in the post.

With the lighter line I used the method of attaching one end of the line in subject to a marine battery and the other end attached to a Rapala digital scale. I proceeded to slowly lift the scale, monitoring the weight, until the line broke. Although not perfectly accurate, as the scale does not update instantly, this method suited my needs with the lighter line. After trying this same method with a heavier line, 20lb Berkley Big Game, I decided to develop a new method to test the breaking strength of line that is more accurate and also easier on my arms. I attached one end of the line in subject to a small bucket, and the other end to a stationary object high enough to dangle the bucket from with enough room to allow for the monofilament line to stretch. In my case I used a treadmill. With this setup I can add weight to the bucket until the line breaks.
Bucket with sinkers and dumbbells
So there were 4 scenarios that I tested on the light line that I wanted to test on the heavier line. Normal clinch knot, improved clinch knot, normal clinch knot with lubrication, and improved clinch knot with lubrication. Which version of the knot would form the strongest knot with the least amount of twists?

From prior experience I knew that the breaking strength of the 20lb Berkley Big Game with a good knot was well over 20lbs and actually closer to 30lbs. With this In mind I decided to start each test by adding 2 10lb dumbbells. With my digital scale I found that the bucket and 2 dumbbells combined weight was 21lbs 14oz. With a 2oz sinker I would have an even 22lbs to start adding more sinkers and keep track of the total weight as I went.

In these tests I only did each knot once. Here were the results.
# of Twists Normal Improved Normal w/ Lube Improved w/ Lube
4 <22lbs <22lbs <22lbs <22lbs
6 <22lbs <22lbs <22lbs <22lbs
8 29.75lbs <22lbs <22lbs <22lbs
10 29.5lbs <22lbs <22lbs <22lbs

Only the normal clinch knot with 8 and 10 twists in the knot held the weight of the 2 dumbbells and the bucket, every other variation broke when the second dumbbell was added which would be less than 22lbs. It could have been slightly more than 22lbs due to the small bounce in the line when the second dumbbell was added in slowly. Not only did the normal clinch knot with 8 and 10 twists exceed the 22lbs that all other knots broke at, the line didn't fail at the knot effectively maxing out the breaking strength of the line at nearly 30lbs. But this didn't make much sense in comparison to the same tests with lighter line. So I reattempted the 8 and 10 twist normal clinch knots a second time to see if it was just a fluke. Wouldn't you know it, they both broke under 22lbs like all the other knots. This proved to me how variable and ineffective the clinch knot was with heavier line.

On a side note, these tests gave me the chance to measure how far a monofilament line like 20lb Berkley Big Game stretches under pressure. Here were the results.
Pounds of Force Length of Line
0lbs 10.25 inches
12lbs 11.625 inches
14lbs 11.75 inches
16lbs 12.125 inches
18lbs 12.375 inches
20lbs 12.625 inches

So the stretch of a 10.25 inch piece of line at 20lbs of force was nearly 2.5 inches. If you do the math (12.625 / 10.25) that is 123% stretch at the 20lbs that the line is rated for. A significant amount of stretch indeed. For example, say you cast a modest 30 yards, that would mean at 20lbs of force the line would stretch over 20ft.

That concludes my line experiments for now. Next time I'd like to examine another type of knot that may prove superior to the clinch knot.

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