a scuba diver with a knife

Do Scuba Divers Need a Dive Knife?

Fans of classic James Bond movies will be quite familiar with dive knives. This is the iconic weapon that the superspy used in underwater battles. However, modern dive knives are quite a bit different from those on the silver screen.

Within the diving community, there is a bit of a difference of opinion regarding the utility of dive knives. Many divers carry a knife while other seasoned divers never strap one on. So the question remains: Do scuba divers need a dive knife?

For most divers, dive knives are an important safety tool to carry with them. They can be used to get free from entanglements in fishing line, kelp, and other things underwater. Thus, having a dive knife is recommended.

Let’s take a further look at this topic by examining a bit about the history of dive knives, their purpose, and the different things a diver wants to consider when selecting a knife.

A scuba diver exploring a cave

History of Dive Knives

The dive knife became notable as an important tool used by commando swimmers and frogmen during World War II. They kept large blades strapped to their calves. These military-issued blades served a variety of purposes.

They were used to navigate difficulties in underwater terrain such as slicing through nets. However, they also had the added importance of being able to be used as a weapon in hand-to-hand combat. 

Thus, these original dive knives were quite large and very sharp.

Over the years, dive knives have found their way into pop culture through various movies. There are several underwater fight scenes in the James Bond franchise with Thunderball perhaps having the most memorable. 

Dive knives can also be seen in various movies as far back as the 1940s with divers fighting giant octopuses or sharks with the tool.

However, the modern dive knife takes many forms, is typically more compact, and is largely used as an important part of a diver’s overall safety kit.

scuba diving environment

What Do You Use a Dive Knife For?

There are many different uses for dive knives. The most common use is to simply free one’s self from entanglement. 

Do you need a dive knife to free yourself? 

Not necessarily. 

In fact, most times you can move very slowly and carefully with the help of a dive buddy to free yourself without one. During my first ever dive, my tank got caught on a guide wire in a quarry. My dive buddy was able to free me in less than a minute.

However, dive knives are quite useful for the fact that it makes it much easier and quicker to free yourself from an entanglement. Monofilament fishing line is very strong and quite difficult to cut through. 

Dive knives are specially designed to be able to cut through line with relatively minimal effort.

Kelp is also a major hazard for divers, particularly those in environments like the large kelp forests off the shores of California. 

Giant kelp can be as strong as rope, requiring significant effort to get free. Many divers in these areas carry larger dive knives for the added strength.

Additionally, dive knives have other uses. One of the most common uses is to use it to get the attention of your dive buddy or other divers. Be banging a dive knife against the metal of your tank, you can easily get the attention of people around you.

One of the more surprising uses of dive knives are as protection during an unexpected difficult current. Knives can be used to anchor into the sea bed to prevent drifting away when your hands can’t get a good grip on rocks. 

This is a rarely used purpose, but can be incredibly important if needed.

Finally, a dive knife can be used to help rescue marine life that is trapped in stray fishing lines or nets. As always, when interacting with marine life, be observant and ensure that you neither harm the wildlife nor put yourself at risk.

kelp with a scuba diver

Are Dive Knives Good for Self-Defense?

As we noted, dive knives originated as both a tool and a weapon for soldiers. So are modern dive knives good for self-defense? 

The reality is that they are not. 

This is a myth that pervades a bit from television and movies, where divers can be seen using knives as defense against marine life.

First, let’s consider the fact that dive knives typically have rounded tips, meaning they aren’t good for stabbing something. 

This is due to the fact that a sharp tip would be quite dangerous for a diver. A puncture of a wet suit would ruin it and potentially cut the diver. A puncture of a dry suit could result in an emergency situation.

Additionally, let’s consider the source of encounters with marine life. Most attacks are due to divers accidentally spooking the animal or not understanding the animal’s behavior. 

These are known as provoked attacks. Unprovoked attacks are extremely rare and typically a case of mistaken identity from a few species of sharks.

If a diver does find themselves amidst an attack, it is likely that they would find it difficult to quickly and easily reach their dive knife. Additionally, it would be much easier to simply use their hands to defend themselves (such as poking a shark in the sensitive gills). 

Thus, while the movies make knives look impressive, they aren’t likely to be useful as a defensive device.

2 scuba divers exploring a wreck

What Should You Consider When Buying a Knife?

When looking at purchasing a dive knife, there are a number of things that divers should consider. Let’s take a look at some of the major differences.

Metal Type

Dive knives are generally made from either titanium or stainless steel. Titanium is more lightweight and also quite strong. It is typically preferred by most divers. They also better resist corrosion. The one benefit of stainless steel knives is that they are easy to sharpen; however, they require more maintenance.

Blade Structure

Blades can be either straight or folding. A straight blade is typically stored in a protective sheath to prevent accidentally cutting anything. The benefit of a blade that folds is that it is more compact, easier to carry, and safer; however, it may be difficult to open with one hand.

Tips

Blade tips are sharp, blunt, or tanto. (A tanto blade is one with a sharply angled tip that looks almost like a chisel.) Blunt tips are safe as they prevent accidental punctures and probably best for most divers. 

Sharp tips are often preferred for spearfishing. Tanto tips are probably the strongest option; however, most divers will not use the tip as much as the edges.

Edges

There are two major options when it comes to dive knife edges: straight and serrated. Straight blades are used with a slicing motion while serrated blades are used to saw. 

Straight blades are good for cutting plastics and nylon while serrated blades are best for natural fibers and kelp. 

Many divers will opt for a knife with one edge on each side. Whatever you do, ensure that you find one with a notch (typically near the base) designed to cut fishing line.

Size

Most dive knives are compact, and this is the preferred size for modern divers. Knives of a minimum of 7 centimeters will be long enough to cut through netting. Smaller knives are also easier to wear and wield. Really the only reason to get a large knife is if you are diving in kelp forests of spearfishing.

Comfort

This is much more of an individual decision. Hold dive knives before buying them. Make sure your hand feels comfortable in the grip. Consider holding it while wearing gloves too. This will help you determine the best knife to use.

fish part in an arch as a scuba diver goes through

Final Thoughts

Dive knives are an important tool for scuba divers as they can be used to easily free yourself from entanglements with fishing line, nets, and other hazards. Dive knives have come a long way over time with many options for divers.

When buying a knife, a diver should carefully try out its grip. New divers should also practice sheathing and unsheathing their knives. When it comes time to have to use it, you need to be comfortable being able to use it.

There are many options available. For most divers, a small titanium knife with a dull point is ideal. 

The knife should also be specifically designed to cut through fishing line. Whether you opt for a straight or serrated edge, make sure the knife has a notch for cutting fishing line.

Mike Seals
Chief Crisp Eater at Guiness Brewey | + posts

Mike resides in landlocked Indiana but takes every opportunity to travel to warm waters for diving. When in his home state, he typically dives quarries. His favorite place to dive is the reef off of Ambergris Caye, Belize. When not diving, he works as a researcher, runs marathons, and spends time with his three kids.

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