The Cutting Edge

A realistic look at why most of us don’t really need or bother to carry a dive knife.

The origin of the dive knife

Back when intrepid men donned hard hats to plumb the depths, they didn’t leave the surface without a trusty sheath knife. Wood-handled beauties like the brass-encased Morse MK V are works of art, and they make a great collectors item. But I can’t imagine any reason why I’d take one underwater.

Ditto for those foot-long “Shamu Stickers” that you still see strapped to the legs of some divers. It’s hard to imagine why a recreational diver on a tropical reef could possibly need a weapon suitable for skinning a bear. And—news flash—attaching a heavy, extraneous object to your lower leg creates performance-robbing drag each time you kick, and can become a entanglement hazard itself. To be fair, I don’t consider a compact knife affixed to a BC to be much more practical. In fact, I’ll go so far as to say that most divers don’t even need a traditional dive knife. Period. If I were still writing for one of the glossy print dive magazines, I’d be censored by the sales team for making such a heretical statement.

But we’re not selling knives here, so the truth can be told. Training manuals correctly point out that a dive knife is not a weapon, but they do consider it to be an essential safety device, and a potentially useful tool for prying things and so forth. OK…maybe. But I’d argue that in there are better options for both safety and utility.

Let’s start with the safety question. Entanglement is usually cited as prime reason to carry a dive knife, which is apparently used to extricate oneself from snarled balls of monofilament, saw through entrapping anchor lines or slash enveloping strands of kelp. After 30 years of bottom time in a wide range of environments, I can’t recall any cases of entanglement that required extensive and aggressive hacking or slashing. Usually, a slow, methodical approach and a judicious snip or two does the trick.

But let’s assume you have somehow managed to seriously bind yourself in a web of fishing line or a trawler net. Waving a sharp object about while you are in a compromised position and potentially stressed state of mind might not be the smartest thing to do. So at the very least, knife enthusiasts should consider a blunt-ended blade. And that flat cutting surface? No matter how sharp, it’s still not the best choice for slicing through a free-floating bit of mono or rope—especially if you are working one-handed.

Serrated blades are better for making big cuts in tough lines, and if I were tasked specifically with sawing a fouled trap line out of a boat prop, that’s the tool I’d probably take down. But for making a quick cut through most any line this side of a ship’s mooring cable, I’d go with a line cutter. Many dive knifes incorporate some type of line cutter into the blade—it’s that little circular indention with a sharpened edge that’s usually set close to the handle. I consider this cutting notch to be the most useful feature of a dive knife, but there are better line cutters available that are smaller, safer and more cost effective.

Benchmade line cutter left, with a EEZYCUT line cutter right.
Benchmade line cutter left, with a EEZYCUT line cutter right.

For years cave divers have carried the same type of captive-blade line cutters used by skydivers. These compact cutting tools have no exposed sharp edges, and make short work of stray lines by guiding them into the cutting surface without requiring you to maintain tension against the blade. You can pick one up for under $10, while premium models such as the Benchmade Cutter Hook still run about $40 USD.

EEZYCUT line cutter for scuba diving.
An EEZYCUT line cutter going through a piece of 2-inch nylon webbing.

My personal favorite is the EEZYCUT, which comes in around $25 – $29. I’ve used this compact little cutter to slice through heavy monofilament, wire fishing leader, two-inch webbing and even an anchor line. By comparison, a low-end dive knife could easily run $40, while a fancy titanium model will set you back more than $100. So, for most any type of line-severing task, a cutter trumps a knife, both for price and function.

trauma shears

And for the few things that cutters can’t handle, a good complement is a pair of trauma shears, which will run you $10 to $15. Like a line cutter, trauma shears don’t have sharp points that could cause injury or put a hole in a BC, and the cutting process is far more controlled and contained that with a knife.

Moving on the supposed tool functions of a dive knife, why would you choose to use a sharp, expensive and somewhat fragile blade to pry or scrape things? Abalone divers use dedicated pry bars; working divers carry actual tools specific to the job, and hard-core wreck penetration specialists rely on side-cutters to deal with wire snags. The point is, for most any specialized type of diving that requires a cutting device or tool, there’s something better than a dive knife for the job.

Now that I’ve listed all the reasons why dive knife aren’t need, here are a couple of cases where they are. Underwater hunters need a sharp, stiletto-like knife to immobilize their quarry by pithing it between the eyes. And since spear fishermen do run the risk of getting tangled in their own lines, their knifes should ideally have a line cutter incorporated into the blade.

Another use for knives is clearing large ropes or masses of netting that can’t be snipped or sliced easily. As I said before, a sturdy blade with a serrated edge makes a good sawing tool. If you already have a dive knife, try a few sample cuts on monofilament or rope the next time you go diving. If the results are anything less than fast and easy, consider adding a line cutter to your dive kit. And if you still want to carry that knife—just in case—at least mount it on your BC rather than your calf.

The commando look may have worked for Mike Nelson in Sea Hunt or James Bond in Thunderball, but in real life, it’s a potential entanglement hazard that creates extra drag, and will likely draw veiled chuckles from divers in the know.