A dive knife is safety gear first and a tool second. Underwater its real job is cutting: freeing yourself or a buddy from monofilament fishing line, kelp, netting, or a stray anchor line. For recreational scuba divers the right blade is small, corrosion resistant, and mounted somewhere you can reach it with either hand. It is not about size or menace. It is about a reliable cut when your hands are cold and your visibility is poor.
The market splits along two decisions. The first is blade material: cheap, keen 420 stainless steel, rustproof beta titanium, or Spyderco's specialized H1 and H2 steels that resist corrosion like titanium while cutting like steel. Titanium never rusts and asks almost nothing of you, though it costs more and dulls a little faster under hard use. Stainless is inexpensive and takes a sharper edge, but it wants a fresh water rinse and an occasional drop of silicone. The second decision is tip shape: a blunt tip is safer around inflators and BCs and better for prying, while a pointed tip pierces. Most recreational divers are better served by a blunt tip.
This guide spans roughly $40 to $170. At the low end sits a compact stainless mini that clips onto a BC hose and vanishes until needed. At the high end is a full titanium blade with a positive locking sheath built to outlast the diver. We also include a guarded line cutter and a rustproof folder, because the best cutting tool is the one you will actually carry.
