WHY DO HOOKS BREAK?

Text: Alan Bulmer                        Lead image: Game Fishing Asia

One of the most frustrating things that an angler using lures can experience is losing a solid fish due to a hook breaking or pulling out. Why do hooks break and is there anything that can be done to reduce the likelihood of hooks breaking?

Aside from casting damage, the two most common reasons that hooks break are work hardening or stress corrosion cracking. To understand these terms and their importance it is important to first gain an appreciation of how hooks are made. Every hook manufacturer has its own proprietary production processes and these secrets are rarely disclosed however the basic process for manufacturing a hook is:-

Hook process 3

When hooks are formed the wire is deformed using stress and strain and the crystal structure of the metal altered to make it stronger. Once the hook is formed it is then heated (also called annealing), carefully cooled (also called quenching) and tempered to further strengthen it and make it more resistant to deformation.

hook tempering

Tempering is a controlled heating technique used after cooling to achieve greater toughness by decreasing the hardness of the alloy. The reduction in hardness is usually accompanied by a decrease in the brittleness of the metal.

Precise control of time and temperature during the tempering process is crucial to achieve the desired balance of physical properties. Low tempering temperatures may only relieve the internal stresses, decreasing brittleness while maintaining a majority of the hardness. Higher tempering temperatures tend to produce a greater reduction in the hardness, sacrificing some yield and tensile strength for an increase in elasticity (and plasticity). Each manufacturer has a set of criteria that determines the optimal hook characteristics and tightly controls the production process to achieve these consistently. If the process control is not tight enough then the hook can bend easily or be too brittle and snap under load.

Coatings are applied after cooling and the hook may also be sharpened chemically. Very occasionally the hooks can be weakened if they are cooled too quickly or too much heat is applied during the tempering (or coating) process. This is normally picked up in Quality Control checking as the hooks will be very brittle and snap readily when the hook point is bent outwards.

Once a hook has been formed, annealed and cooled the crystal structure is fixed. If a hook is then subject to further excessive work hardening then it will lead to crystal lattice realignment and eventually breakage. This happens when the hook point is repeatedly being forced away from the hook shank, either during the fight by a fish or when a lure is snagged and the angler is pulling the line to free it.

A graphic example of this is when you partially straighten a paper clip and work it from side to side where one of the bends was. As you do more work on the metal it becomes harder and more brittle. Eventually, it will become so brittle that it will snap. This generally happens to a hook well into a protracted fight but it also can happen suddenly if you’ve already hooked and landed several big fish in quick succession (or been repeatedly snagged).

I can still vividly remember a fishing session over 20 years ago where I hooked four large kahawai in just over an hour. The first was landed and released after a 15 minute tussle, complete with lots of searing runs, head shaking and aerial gyrations. The second was lost after 10 minutes when the tine on a body treble snapped off. I was not carrying any spare hooks so I kept on fishing with the successful lure. A third fish was hooked shortly after and again lost mid fight due to breakage of a treble tine. I’ll leave you to guess what happened to the final fish. This was classic work hardening failure in action.

Obviously it is necessary to reduce the amount of work hardening that a hook receives in order to stop it breaking. My advice is to always immediately replace hooks that are bent or damaged in any way. Resist the urge to bend hooks back into shape when they are deformed as this is tempting fate and should be avoided. More about this later.

Stress corrosion cracking is a term that describes the formation of microscopic cracks in a metal in a corrosive environment. Once the cracks form deterioration can progress rapidly and the environment only has to be mildly corrosive for the metal to eventually break under load. The scary thing about stress corrosion cracking is that the hook can appear shiny and bright yet still be filled with microscopic cracks.

Fortunately there are only three key factors involved in stress corrosion cracking namely:-

  1. A susceptible material
  2. Exposure to a corrosive environment
  3. Applying tensile stress above a minimum threshold

The good news is that if any one of these factors is eliminated then stress corrosion cracking becomes impossible.

One of the easiest things to do to reduce the chances of stress corrosion cracking is to thoroughly wash hooks in warm soapy water after each outing and dry them off before storing them. Don’t put them away damp, even if they have been used in fresh water. Obviously storing hooks or lures in a damp state is going to increase the likelihood of failure at a later date.

lure hook damage 3

The second thing to do is never use a hook that has been bent out of alignment. In the image above the bottom tine of the treble has been bend out of alignment. It is tempting to just straighten this tine back into shape and fish on but this is a mistake, especially if you store the lure after the session and continue to use it on subsequent trips. Enough tensile stress has been applied to bend it out of shape so microscopic cracks will likely have formed. When the hook is once again used in a corrosive environment it will eventually fail.

THINGS THAT CAN BE DONE TO REDUCE HOOK BREAKAGE

Hooks made with thinner gauge wire are more prone to work hardening so the logical thing to do to reduce breakage is to simply increase the wire gauge of the hook. However, this add to the hook weight and this can upset the balance of the lure so is not always possible. Another thing that has to be taken into consideration is that the thicker the wire gauge the harder it is for the hook to penetrate. In simple terms, if the wire diameter is doubled then it will require four times more force to get the same amount of point penetration. Thinking of this another way halving the wire diameter allows the point to penetrate to the same distance with only a quarter of the force.

One of the most common things done to reduce hook breakage on lures is to use two split rings to attach the hooks to the lure or to use a split ring in combination with a swivel. This is shown in the images below.

Attaching a hook to a lure via a split ring that is attached to another split ring effectively gives the hooks, especially trebles, a 360 degree turning radius which prevents the hook being jammed against the lure body. This reduces the amount of leverage the fish can place on the hooks when it is shaking its head or jumping and the amount of work hardening of the hook. The same principle applies when a swivel is used in combination with split ring. Not only will it protect the hook but it will reduce the likelihood of the hook points tearing out during the fight.

It is most common for twin split rings to be attached to the body loop and for the swivel and split ring combination to be attached to the tail. The ideal combination will be dictated by the lure action and type so it is best to determine what is most effective by experiment.

body double splits

lure swivels

When selecting split rings always be sure to use high quality, tensile rings that are made of the finest wire possible and rated to a breaking strain capable of handling  the fish that are likely to be encountered. See below.

Split rings

As I mentioned earlier, cleaning lures in warm soapy water and drying them thoroughly at the end of each fishing session in saltwater is very important to reduce the chances of stress corrosion cracking. I also tend to leave them out in a warm sunny spot for a couple of days to dry completely before putting the lures back in my tackle box. Use this opportunity to check for signs of damage and replace any hooks or split rings that have been bent during the session at this point. It makes sense to carry a few spare in line single or treble hooks with you when you are on the water to replace any hooks damaged during the session.

I always carry a zippered pouch made of fine nylon mesh to store damaged and used lures in so that they never end up being placed back in a tackle box with other lures while wet. This separation of used and unused lures is a really good habit to get into.

mesh-lure-bag.jpg

Storing lures in tackle boxes with Zerust dividers or adding a small wrap of Owner Rustop self adhesive tape can also potentially help limit stress corrosion cracking on high carbon steel hooks. Coating the hooks with mineral oil is another option.

 

rustop

 

 

Anything that reduces the stress and strain placed on the hook point by fish (or snags) will reduce the likelihood of breakage. Using longer shock traces, dropping the rod tip when a fish jumps and backing off the drag pressure will all help reduce the amount of hook point flexing and work hardening of the hook wire.

 

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