Know Your Knives: The Dive Knife

Image courtesy

Dive knifes have very different features from those intended to be used above the water because they serve very different purposes below. If you ever see a blunt-tipped knife with a line hook, one serrated edge, one plain edge and a rubberized grip, it’s definitely a dive knife. It gets bonus points if it’s garishly colored, too.

SCUBA diving isn’t the same as an underwater camping trip, and dive knives don’t get called on to prepare food, skin and chop up small animals, or baton firewood. Their main task is cutting lines and nets underwater, which could otherwise entangle a diver until his or her air supply runs out.

Extreme sharpness and hardness aren’t primary requirements for a dive knife: corrosion resistance is. The most expensive dive knives are made from Titanium, which is completely impervious to rust; others are made of reputedly excellent H-1 and N680 stainless, and many lower-priced models are made from 420-series stainless.

Copper Beryllium Knife

Copper Beryllium is a rarely-encountered blade material that you won’t find for sale at Blade HQ any time soon. It’s highly corrosion-resistant and nonmagnetic and it doesn’t spark. This makes it perfect for SEALS and underwater EOD specialists, but that lovely brown blade has a drawback for ordinary use: copper beryllium dust is toxic, and a known carcinogen.

Most sport-diving knives are blunted at the tip to reduce the risk of sticking yourself underwater.

Image courtesy KAI-USA

But not all of them: Kershaw has been making this dive-ready Amphibian with a (very) sharp tip for decades, and it must keep selling because they wouldn’t keep making it otherwise. The 420J2 Amphibian hasn’t even changed much in price since the mid-1980s: it was about $50 then, and it’s about $65 now.

Benchmade H20 courtesy

Folding dive knives like this Benchmade H20 are a relatively new development.

Image courtesy Spyderco

This Spyderco Atlantic Salt folder could be pressed into service as a dive knife, although like the Benchmade H20 it lacks a dedicated line cutting notch.

Folders like these aren’t as easy to deploy underwater as fixed-blade dive knives, especially with cold or gloved fingers, but they can be simpler to sport divers to travel with when going abroad.


  1. David says:

    Didn’t know they were scuba diving back in 1908 🙂

    I never understood why beryllium copper is used. Why not aluminum bronze? As hard (heat treatable in many cases) as B. copper & is slightly lighter to boot. It’s used in other marine applications for its extreme resistance to corrosion.

    1. knightofbob says:

      About one hundred years before that, depending on how you qualify the types of diving apparatus, but the weren’t carrying Kershaws back then.

    2. J- says:

      Some beryllium bronze alloys can be aged to a hardness of up to 44 HRC. Aluminum bronze peaks at 96-98 HRB, which is in the low 20’s of HRC. BeCu is also much more wear resistant, and has a much better spring temper.

  2. David says:

    Not sure if you got the joke or not but the reference was in regard to a typo that was made in paragraph 5. Which has been changed BTW.

  3. J- says:

    What you have to remember is: dive knives are crap. It’s true, sorry.

    When I did all my SCUBA certs, at least one person of every buddy team had to have a knife. The reason you carry it, 99% of the time is to untangle yourself from crap that can keep you from surfacing. Mostly old fishing line and fishing nets. Monofilament is damn near impossible to see underwater, and if you are in an area that is fished a lot, it’s easy to get snagged. I know, it’s happened to me. After that, it’s buoy line, dock line, rope, there is so much rope in the ocean.

    All you really need, then, is a knife capable of cutting through fishing line and rope so you don’t drown. That doesn’t take much, and most divers will never use their knife anyway. As long as they don’t rust up on you, they’ve done their job.

    If you think you are going to be using your knife underwater more than… never. There are many “land knives” that transition well to SCUBA use. The one I use is the SOG SEAL PUP (mostly because I owned it before I started diving). The full size SEAL it too big, but the pup works nicely. I’ve rinsed mine with fresh water after each dive, and have never had it rust on me.

    1. Matt in FL says:

      This is pretty much true. Dive knives are useful tools that are pretty mundane, and often quite crappy. But they don’t have to be exciting to do what they need to do. Mine is old, and ugly, and beat-up, and rusted, and still has an edge and will cut me out of a jam if I need it to. The rest of the time, I just ignore it.

    2. Kevin Snyder says:

      Great point, it has to be emphasized that dive knives are an emergency tool, not something to toy around with while underwater. I’m not so sure that I’d recommend deploying a folding knife for this purpose. Do you really want to count on being able to deploy such a knife in an emergency? I think that’s an unnecessary risk, really. Anyway, great post and thanks for sharing.

    3. CB says:

      I will second the SEAL Pup, much for the same reason, I had it and it just eats the abuse of diving without fail

  4. Tank Titan says:

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Know Your Knives: The Dive Knife

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