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