Diving Knife, Why Is It So Important?

If you are wondering what the diving knife is for and why it is so important, our HR and Course Director, Victor Cordoba, tells us in this article. Don’t miss it!

We have all seen in old movies the image of a diver with a huge knife attached to the calf, and all those who are not familiar with diving could think it is a weapon to defend against sea monsters and sharks.

I have been diving for more than 35 years and I have only had to use a diving knife once, and I assure you that it was not precisely to defend myself against any shark or sea monster. The real reason for the knife divers use is very different from this conception. In my case it was in a cave passing a restriction at a depth of 102 meters. This certainly isn’t the place one would choose to test if the knife works. Unfortunately, I was entangled on the line and there was zero visibility, but in about 15 seconds I was able to pull out the knife and cut the line to free myself.

The diving knife is just another diving equipment tool, that is mainly used to cut ropes or fishing nets in case of entanglement; We don´t attach it to the calf anymore and its size is much smaller than what we see in the films that I mentioned in the beginning.

Is A Diving Knife And A Line Cutter The Same Thing?

The line cutter was developed for cave diving mainly, where one of the most frequent dangers is getting entangled in the guideline with some piece of the equipment in conditions of zero visibility and not being able to free yourself.

For this situation, traditional knives are not very effective, since they are usually not too sharp and it is difficult to cut a 2- or 3-mm width nylon line with one hand in the difficult positions that sometimes you adopt in a cave or through some narrow passages.

For this reason, this tool was developed very sharp and with an indentation that can hook the line but is too narrow to accidentally cut a breathing hose, by mistake. Imagine a diver entangled in a cave and trying to cut the line behind his head but instead he catches a breathing hose and cuts off the air supply.

What Do Diving Knives Look Like?

Line cutters have much sharper blades but are not stainless steel, so they rust much more easily. Since the blades are very thin when rusted, they become brittle and lose their edge, making it impossible to cut with them. Diving knives are made of stainless steel, but in contact with seawater and if left in the sheaths without drying after each dive they can also rust and leave the edge unusable.

But what is the use of carrying a diving knife or line cutter if it doesn’t work when we need it?

Diving Knife Maintenance

The diving knife or line cutter is one more element of our diving equipment and, therefore, we have to keep it in the same conditions as any other element.

Bringing a diving knife that does not cut when needed, is as if we carry nothing. Therefore, one must ensure that the diving knife or line cutter is in perfect condition. It is important:

• to remove the knife from its sheath after each dive;
• to rinse it thoroughly with fresh water and then dry it carefully:
• some divers, once dry, apply a thin layer of Vaseline or silicone grease before putting it back in the sheath, which must also be dry inside.

As line cutters can easily suffer rusting and become useless, they need the same maintenance than the diving knife, but it is still inevitable that they rust, so the manufacturers of the best quality products provide replacement blades that can be changed when necessary. It is a good idea to carry some of these replacement blades in our small toolbox with basic accessories so that you can change them before a dive if needed. Some manufacturers make line cutters out of one piece of titanium that does not rust, but they are more expensive.

We already have the knife in perfect condition to use it, but where should I place it?

How To Carry The Diving Knife In A Proper Way?

Obviously and going back to the movies, it should not be attached to the calf. Carrying a perfectly sharp knife is not going to do any good if during the dive we cannot reach it by a quick hand movement and efficiently. As we have said before, the calf is not the recommended place because of the bodily contortions necessary in some situations to reach the diving knife.

Therefore, it is usually placed in a BCD pocket or fixed on a shoulder strap of the BCD. Some models have specific locations for the knife. Some divers use a technical diving harness, which is becoming more common, and they usually place the diving knife in a sheath on the harness waist strap. If a line cutter is used which is small and light, some divers place them on the strap or “bunggies” of the dive computer.

In any case, the most important thing is always to have easy access with both hands to be able to operate with the knife or line cutter.

If when I needed to use my diving knife it hadn’t been accessible and/or had not been sharp, someone else would probably be writing this article. And you, have you ever had to use your diving knife? Tell us on Facebook.