The follow video is a break test of a used 5/8" solid braid polypropylene rope that many in house and road riggers favor to
use as a drop line with a bowline knot at the end. A new rope without a knot would have a breaking strength of 5,300 Lbs.
Putting a bowline knot in a rope will decrease the breaking strength by at least 50%. The rope we broke was quite used and
broke at more than 50% of it's tensile strength when a knot was used. Please note that you should never use a rope at it's tensile
strength without a knot in the rope or with a bowline knot in the rope. Always use a working load limit when using a rope with
any type of knot of at least 5 to 1. This means that, when a rope has a breaking strength of 5,300 Lbs., you should subtract 50%
of that number when a knot is used. ( 5,300 - 50% = 2,650 lbs. working load limit without a knot ) Now this is specific to the 5/8"
rope that I am talking about here. It is common practice to use the same design factor of 5 to 1 for other types and size ropes as well.
This part is very important now, we always use a knot in a rope when using it as a drop line don't we. So in reality we must
recalculate our working load limit, W.L.L., when using the rope with a bowline in it. Take your braeking strength of 5,300 lbs. and
subtract 50% because of having a knot in the rope which would = 2,650 lbs. and then divide that number by 5 and your new working
load limit, W.L.L., of the rope with a bowline knot in it will be 530 lbs. My rule of thumb is, what ever rope you use and what ever
type of knot you tie into the rope you can take 10% of the tensile strength of the rope and it will give you a 5 to 1 working load
limit when using a knot. Example: 10% of 5,300 = 530 lbs. W.L.L. This is simple and easy to remember. Because of the compression
of the rope compressing against itself under tension, causing the fibers not to take equal loading and a heat build up within the knot
itself causing a break down of strength within the rope is why you should alway use a good design factor of at least 5 to 1.

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