Dive Knives & Cutting Tools
Purpose
A dive knife is really a tool, that you can use underwater in an emergency or at the surface. Underwater entanglement in fishing line, monofilament, kelp, or netting is one of the situations where having a cutting device can be critical. It's also useful for freeing a dive buddy who is entangled, removing debris from the seafloor responsibly, and general surface tasks like cutting reel line or tightening equipment. At the surface it doubles as a utility tool during surface intervals. The most important thing about a dive knife is that you have one that's accessible when you need it.
Features
Size
Smaller, compact dive knives are appropriate for warm-water diving where you won't be wearing thick gloves and a smaller one is easier to access from a BCD pocket or inflator mount. For cold-water diving in Canada, where you'll be wearing 5–7mm neoprene gloves, a larger dive knife with a more substantial handle is easier to grip and operate. Compact models and shears are now popular as backups even among cold-water divers.
Attachment
Smaller diveknives may be attached directly to your BCD, inflator hose, gauge hose, or stored in a pocket. A larger style will likely be attached with straps to your leg and may be too large or cumbersome to be attached to your scuba BCD.
Blunt vs. Pointed
A pointed tip may be helpful for those of you who spearfish or harvest (legally of course). Blunt tips can make a handy implement such as a screwdriver or a prying device. A serrated or partially serrated edge cuts through rope, monofilament, and kelp more effectively than a straight edge alone.
Metal Type
Stainless steel (400-grade or higher) holds a sharp edge well and is the most common material. It does require regular maintenance to prevent corrosion, particularly at the edge near the handle. Titanium is significantly more resistant to corrosion, is lighter, and requires almost no maintenance — but costs roughly 30–40% more than comparable stainless steel knives. Look for a full-tang blade (the metal extends through the entire handle) as it is stronger and allows the blade to be removed for thorough cleaning.
Alternative Tools
Line cutters and sea snips (blunt-nosed scissors) are excellent backup cutting tools and are particularly effective against monofilament fishing line, which can be tricky to cut with a standard dive knife blade. Many experienced divers carry both a knife and a small line cutter as a redundant system.
Care & Maintenance
After diving, always give your dive knife a good thorough rinse with fresh, clean water to remove any salt or chlorine. Stainless steel will rust over time if not properly taken care of. Some knives will allow you to remove the blade from the handle which allows for a much more thorough cleaning. Leave the blade to dry completely before placing it back into the sheath. Rub a little silicone or oil into the knife before storing for prolonged period of time. It may need to be sharpened before storage if you have been using it a lot.