How to never lose a fish, even a very large one, through line or shaft barb breakage? The spearfishing Vice World Champion, Luigi Puretti, reveals important tricks for connecting sling spearguns shaft.

If we follow all the tips on sling spearguns shaft linkage provided by Puretti, it is almost assured that once we shoot a fish, we are talking about Mediterranean fish, it is virtually impossible for the prey to exert a force that goes beyond the minimum breaking strength of the line we use. Indeed, in the water, with the ability to cushion sudden pulls and escapes of the fish, we can use all our strength to try to thwart, for example, an amberjack that wants to go break on the rocks or a large grouper. As forabrasion, it obviously depends on the area, where areas with mussels or sharp elements, for example artificial wrecks, can create problems. But for this very reason Luigi will advise us on the best choice for monofilament and line.

The importance of sling spearguns shaft connection

Luigi Puretti checks the integrity of the Dyneema line

“I consider this article very important. Let’s talk about a part of our equipment that is often underestimated by underwater fishermen. In fact, what we are going to talk about plays a crucial role, especially when dealing with important preys. Unfortunately, or fortunately, in our discipline one must always be ready for the encounter of a lifetime. You spend a lot of money to have the top sling spearguns and then you get lost in details that maybe are quite simple, but make a difference. We will then talk about the sling spearguns shaft connection, thanks in part to my experience with fishing rods where we play on much finer details.

Why breakups happen

Why do ruptures occur? The line can break by tensile stress, that is when the tensile strength of the material is exceeded. The same can also be broken by abrasion.

Tensile fracture

Regarding tensile strength, each line we use has its own tensile strength that indicates the maximum strength to which this material yields. Generally, breaking loads are indicated on the packaging in kilograms or lb. The relationship between thickness and breaking load has a trend that increases with the square of the diameter.

We have to imagine that we are connecting the line to a weight, and the breaking load will correspond fairly closely to the maximum weight we can lift without breaking the line.

In a fishing complex composed of several lines and materials, the breaking load will be that of the part having the lowest breaking load.

Luigi Puretti makes the knot with the Dyneema to connect it to monofilament locked with sleeves

Abrasion fracture

Regarding abrasion failure, this refers to failure due to the rubbing of the line against a harder or sharper material. The harder the line, the harder it is to abrade it. For example, in angling, fluorocarbon is used in the last section where the hooks are connected, which has a lower breaking strength than Nylon but a higher hardness. This decreases the possibility of the fish breaking the terminal by rubbing on the rocks. In the case of abrasion resistance, theincrease in diameter results in even more crucial strength growth than tensile strength. A monofilament in 100 or 120 nylon, in fact, as it touches the rocks it breaks, instead with a 160 160 it is very difficult for a fish to break the line by rubbing on the rocks.

Thicknesses and loads at break

Dyneema for spearfishing

Dyneema line is almost exclusively used in spearfishing reels. The most commonly used diameter is 1.5 mm, which is an innerDyneema with a coating of an outer polyester braid. A fairly inexpensive product today. This has a real tensile strength around 70 kg. There are more expensive solutions and 1.5 mm Dyneema without coating that reach loads as high as 300 kg .

Nylon Monofilament

In the reel to shaft connection, Nylon monofilament is used instead. And it is in the choice of monofilament that the game is often played with large preys. The most commonly used diameters are from 120 to 180. For the cheaper Nylons, with the 120 we are talking about 50 kg real breaking strength, to over 100 kg for a 180 Nylon. Then there are better quality Nylons, but the differences are not as important as for Dyneema. Of course, we are talking about new monofilaments in perfect condition.

The pulling power of fish

The experience with the fishing rods

The accumulated experience of rod fishing helps a lot because the reel clutch is calibrated very very carefully. In fact, one has to deal with tunas and amberjacks using 0.50 to 0.70 mm Nylon. It must be said that thanks to the bending of the rod and the precisely calibrated clutch, one is able to finish fights with very large fish. Even in spearfishing, of course, the weight of the fish is reduced because of buoyancy, and we can cushion the pull with our arm and by going down a little below the water surface while working the fish.

In rod fishing, for example, a 30Kg amberjack, with a clutch closed at 12-15 kg, will not be able to catch more than a few tens of centimeters from the reel. With tunas of 50 kg it is very difficult for the fish to slip a clutch set on 20-25 kg. In fact, with such calibration, 300-400-500 kg tunas are fought in the ocean. In such situations, you have to be harnessed or held by other people otherwise you will be catapulted overboard.

Breakage in spearfishing

It will have happened to everyone to break with a nice fish with a rigging that in theory should maintain those breaking loads. One of the first reasons is Nylon wear. Those breaking strengths, for example Nylon 120 for 50Kg, apply when the monofilament is new. Instead, using it at sea, Nylon is subject to sunlight, salt, minor wear and tear due to the line release, the turn the Nylon makes around the jumper at the header, and of course the joining of the monofilament with the rod.

Nylon and Dyneema passages on the muzzle where unbeveled steel components can wear out the lines

Nylon shaft connection

The most common reason and the main error is often in the joint, that is, the connection between Nylon and shaft. This is less keenly felt in pneumatic spearguns where a slider is present.

Wear and sharp edges

In the sling spearguns, on the other hand, Nylon should be inserted into the shaft hole, the bridge, or the holes that are in the shark fins . Being steel with often somewhat rough machining, meticulous polishing and beveling of the above parts should be done. I personally use steel wire from bicycle brakes by running it through the holes. I then use a piece of thin sandpaper to polish to a mirror-like shine and finish the areas where the wire passes through.

Line side release lever beveled and polished to a mirror finish by Luigi Puretti

In addition, a protective stocking should be put on , for example, polyester stocking of 1.5 mm or 2 mm Dyneema. Just cut it off and remove the Dyneema core.

Knot or rivets

There is always the diatribe of whether to use on Nylon a knot or rivets. There is absolutely no history here. On the Nylon with the thicknesses we use in spearfishing the sleeve should be used. This manages to maintain almost 100% of the breaking strength. As for the knot, each one reduces the breaking strengthof Nylon by 20 to 40 percent . For example, with very stiff Nylons, the knot becomes a very very weak point.

Luigi Puretti tightens the sleeves on the monofilament using the appropriate pliers

Then, absolutely use rivets, of the best quality, preferably the binocular ones made of steel, not aluminum, and tightened with the appropriate pliers.

Sleeves properly tightened on the monofilament
Nylon monofilament reinforced with polyester sock. Above sleeve tightened correctly, below incorrectly
Nylon monofilament reinforced with polyester sock. Left sleeve tightened correctly, right incorrectly

Monofilament thickness

In the reel, I would recommend a very good quality pure Dyneema with a diameter of 1.5 mm. As for the Nylon, there are those who use a fairly thin monofilament to make the shaft faster (greater penetration into the water of the monofilament). In fact, the difference is really minimal. My advice, therefore, is to use a 160 Nylon, partly because 120, precisely because of what was explained above, is very poorly resistant to abrasion. I have often had the breaking of the 120 Nylon while with the 160, I’ve never had breaking, even with large groupers going to rub against the rocks.

Dyneema wire connection notch with Nylon monofilament locked by a sleeve

The shaft

The weak points of the shafts are the notches, which are used less today and were a point of failure, or the barb. The latter is often not very good. In my opinion, companies often use poor-quality barbs, although some shafts have well made barbs. I tend to change the barb on large sling spearguns and put in a longer, thicker one and a larger pin size.