Dive Knives vs. Line Cutters: What’s Best and Why?

“That’s not a knife… this is a knife.”
— Every diver in the 1980s, apparently.

Back in the day, divers strutted around with massive stainless steel blades strapped to their legs like underwater action heroes. Crocodile Dundee would’ve fit right in—minus the cowboy hat and Australian outback. These days? You’re more likely to see something that looks like a tiny letter opener or a futuristic can opener attached to a harness.

So, what happened? Did we just get less cool? Or smarter?

Let’s cut through the hype—pun intended—and take a look at the real pros and cons of dive knives, line cutters, and trauma shears so you can figure out what you actually need (and where to stash it).

Dive Knives: Classic, Bold… and Still Around

Pros:

• Versatile: Can cut thicker rope, kelp, or even pry or hammer in a pinch.
• Visual deterrent: Hey, if you’re diving with sharks or sea monsters, maybe looking like a knife-wielding lunatic helps.
• Tradition: For some, it’s just not a dive unless there’s a chunk of steel strapped to their leg.

Cons:

• Bulky: Most modern setups don’t have room for a 7-inch blade.
• Corrosion risk: Even "stainless" steel will rust without babying.
• Awkward deployment: Reaching for a leg knife while tangled can be a circus act.

Still Sold, Just Smaller Now
Dive knives are still sold today, but they’ve gotten a lot more compact. You’ll often see new divers buying one simply because that’s what they think divers are supposed to carry. Most haven’t heard of a Trilobite or trauma shears yet—and honestly, most instructors aren’t teaching much about tool selection at all.

Line Cutters: Compact, Purpose-Built, and Smart

Pros:

• Streamlined: Mounts cleanly on webbing, backplate harnesses, or even computer straps.
• Protected blade: Safer around drysuits, hoses, and teammates.
• One-handed use: Designed to slice through monofilament and braided line fast, even if you’re stressed or tangled.

Cons:

• Limited use: Not much good for anything other than cutting line or webbing.
• Can clog: If you don’t rinse it, it can jam up with salt or debris.
• False security: It won’t do much against thick rope or hard plastic.

Trauma Shears: The Underrated Workhorse

Pros:

• Cuts almost anything: Nylon, rubber, webbing, zip ties, heavy fishing line—no problem.
• Blunt tips: Won’t puncture your suit, wing, or your buddy’s bladder when you're working in tight spaces.
• One-handed use: Easy to grab, deploy, and cut with even under stress.
• Cheap and replaceable: You can get solid stainless shears for under $10. If they rust out, toss them and replace them.

Cons:

• A bit bulkier: Bigger than a line cutter and might need a pouch or dedicated mount.
• Requires some jaw pressure: Unlike a slicing motion with a knife or cutter, shears work by force—not finesse.
• Not flashy: No tactical dive ninja points here. Just practical utility.

Real-World Use Case:
“I’ve used trauma shears while laying line between attractions at Three Oaks Quarry. They made quick work of cutting buoy-style cord underwater—easier and safer than using a knife or line cutter. For dives like that, I thread the shears in a sheath on my right waist belt and keep my line cutter on the left.”

So What Should You Carry?

Honestly? Probably at least one—maybe two.

• Recreational divers: A Trilobite-style line cutter is usually enough. Mount it where either hand can grab it.
• Wreck, kelp, or entanglement-prone dives: Add a small knife or trauma shears. They give you a backup option for thicker materials or emergency use.
• Tech and overhead divers: Most carry both—one on each side of the harness, for access no matter your position.

Just don’t be that guy with a rusted machete on his leg and no clue how to deploy it underwater.

Final Thoughts: Carry What Works, Not What Looks Cool

Whether it’s a compact line cutter, a rugged pair of shears, or a modest knife, the best cutting tool is the one you can actually reach, deploy, and use under stress.

So test it. Practice with it. And rinse it when you're done.

Because at the end of the day, no one cares if it looks tactical. They care if it works when you're tangled at 60 feet.