Calculation of breaking strain

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Calculation of breaking strain

Post by Blr243 » 13 Sep 2019, 8:15 pm

Fishing line can be purchased in several different strengths. If an object weighing 8 kg is attached to a long Line with a breaking strain of ten kilos and the object is travelling at 40 kph obviously the line is going to snap when the object reaches the end of the line ( assuming no stretch) ..... I’m curious. How does one go about calculating the force applied to a line when a fast moving object reaches the end of its line ? Ie , 8 kilos travelling at 40 kph ....this question I raise in the interests of purchaseing a product with an adequate breaking strain to ensure the line does not snap .......is there a simple mathematical formula ?
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Re: Calculation of breaking strain

Post by Stix » 13 Sep 2019, 8:32 pm

Mathmatical formula(s)...yes...!!

Simple...No...well not really...unless you're a physicist...

Mass, inertia, the elasticity/tensile strength of the line, along with the length of the line, density of the atmosphere (whether in water/air/vaccuum) im sure would all come into play there...
Meaning if its a 15lb fish in water moving at 10ft/sec, the result/point of failure would be different if it was in our atmosphere at sea level...

The idea is to have enough line on the reel, & thus a reel with enough space on the spool so as to not run out of line/or not hit the end of the line....

Otherwise its like bungee jumping a 100m drop without shortening the 110m bungee cord... :shock:

If wanting to get fussy, just set the drag with a spring scale to your desired percenatge of the breaking strain of (correctly) chosen line... :thumbsup:
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Re: Calculation of breaking strain

Post by Die Judicii » 13 Sep 2019, 10:30 pm

Jeff, I presume your not actually talking "fishing" in the problem you've put forward, however,,,,
Braided line as opposed to mono filament has a huge difference in characteristics,
In the case of mono filament,, the longer the line,, the more stretch,, therefore less likelihood of snapping,
The same applies to braided, but with very minimal stretch which is the main purpose of braid.

Most line failures are usually at a knot, specially so if it is an unsuitable type of knot.
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Re: Calculation of breaking strain

Post by Baronvonrort » 14 Sep 2019, 12:36 am

Blr243 wrote:Fishing line can be purchased in several different strengths. If an object weighing 8 kg is attached to a long Line with a breaking strain of ten kilos and the object is travelling at 40 kph obviously the line is going to snap when the object reaches the end of the line ( assuming no stretch) ..... I’m curious. How does one go about calculating the force applied to a line when a fast moving object reaches the end of its line ? Ie , 8 kilos travelling at 40 kph ....this question I raise in the interests of purchaseing a product with an adequate breaking strain to ensure the line does not snap .......is there a simple mathematical formula ?


You need to understand stress and strain before attempting any maths on this subject.

Fishing line is rated to breaking load which is really ultimate tensile strength (stress) therefore with 10 kg breaking load it's about 98 Newtons. ( 10 kg x 9.81)

When a material is loaded with a force, it produces a stress, which then causes a material to deform. Engineering strain is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material.

The youngs modulus of a material will tell you how much you can apply so it will deform and spring back to its original length, exceed the youngs modulus then it goes through inelastic deformation. Therefore before it breaks it will go through inelastic stretch how much depends on the material line is made from. A 10kg line might start going through inelastic deformation around 8kg as youngs modulus is lower than breaking load (ultimate tensile stress)

Lots of variables here because 10 kg breaking load is what we call a static load which greatly differs from a dynamic load of 8 kg fish travelling at 40 kph.

You can try looking at this link if you want to learn how to calculate dynamic loads which can also be called suddenly applied loads in this case.

https://www.google.com.au/search?source=hp&ei=2qJ7XeOdF-PA3LUPkJ2ZMA&q=suddenly+applied+load&oq=suddenly+applied+&gs_l=psy-ab.1.0.0l3j0i22i30l7.1120.6588..8770...0.0..1.742.3488.0j16j6-1......0....1..gws-wiz.......0i131j0i10.QwsKBcWpfz0

If that starts getting too complicated for you then just let the line run when a fish bites and don't try to slow it down too quickly when hooked which is how people land bigger fish than what line is rated for on breaking load.

If you give a man a fish you feed him for a day, if you teach a man to fish he will sit in a boat all day drinking beer with his mates while trying to catch fish. :drinks:
Last edited by Baronvonrort on 14 Sep 2019, 12:53 am, edited 1 time in total.
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Re: Calculation of breaking strain

Post by Baronvonrort » 14 Sep 2019, 12:51 am

I should have added if you catch a 12kg fish on a 10 kg line you will need a hook or net to bring fish in as the water supports a lot of the the weight of the fish while its in the water. When you lift it out of the water it will exceed the ultimate tensile strength of the line and it will break.

The other comment about knots is also relevant as this could reduce breaking load
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Re: Calculation of breaking strain

Post by Blr243 » 14 Sep 2019, 2:18 pm

Thanks for the replies men, Baron , do u mind doing the maths for me please? Based on zero stretch. 35 kilo object moving at 40 kph. I’m looking for a suggested breaking strain to be safe and of course I will allow a margin to be even more safe
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Re: Calculation of breaking strain

Post by duncan61 » 14 Sep 2019, 6:21 pm

I have set my trolling game stick at 3 kg drag and have 80 kg braid.I let macks and tuna burn off then crank them in with a bit of grunt.When you hook that big one it feels good to know you have some horsepower they can be landed on 10kg gear but it will take a while and 90% of the time sharks will destroy it.Hope that helps you are not fishing for whiting
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