Streamlining and availability are key factors
Many divers carry dive knives. In many ways, a knife is probably the one piece of gear that most people associate with diving, perhaps thanks to films which feature dive knives so prominently dating back to 1963’s James Bond film “Thunderball.”
Dive knives are useful — though maybe not as important as many novices think — especially in case of entanglement. If you find yourself caught in a bit of fishing net or kelp, cutting yourself out of it is a quick way to free yourself. And while a pair of trauma shears could actually do the job equally well, or maybe even better, many divers still chose to carry a knife.
However, considering how rarely this scenario occurs — I’ve been diving for nearly 20 years and it hasn’t happened to me yet, knock on wood — we have to accept that our dive knives spend most of their time idly strapped to our person. So what, then, is the best way to store it?
Most importantly when diving with a knife is to make sure it doesn’t jut out too far, but that it sits streamlined along your person. If it does jut out, it ironically increases the risk of entanglement, as it makes for an excellent place for nets, lines, and kelp to get tangled. Secondly, you must be able to reach it easily whenever you need it, even from awkward situations. So where to put your knife?
The knife’s classic position is strapped to the ankle; this is one of the quintessential images of the diver, geared up with a large dive knife on his or her leg. However, this placement is largely based on tradition — again, largely thanks to James Bond and other action films. Back in the early years of scuba diving, this was where you put your knife, partially because the knives of the time were quite large so the leg was the only place it would fit.
However, the leg isn’t an optimal place for a dive knife. It’s more likely to get tangled up in stuff when it’s on the leg, and it can be hard to reach in cramped spaces. Also, as most modern divers today carry much smaller knives since large knives aren’t really necessary, putting them on the leg isn’t required.
Wearing a knife on your leg can still make sense if you’re snorkeling, as it is then the only place you can put it (for lack of a BCD, etc.).
If you do prefer putting your knife on your leg while diving, put it on the inside of your ankle, as it is less likely to become entangled when placed here.
BCD low-pressure inflator
This is also a very popular placement. The knife is attached with either cable ties or some other method in an upside-down fashion to the BCD’s low-pressure inflator hose. This method allows the diver to reach the knife with both hands, and it’s easy to reach in cramped quarters. There is still a small entanglement risk, and putting the knife back in its sheath can be tricky as it can be hard to see what you’re doing.
Some divers prefer a very no-frills method of simply putting a small knife into their BCD pocket. The risk of entanglement is near zero here, but reaching the knife can be tricky if you’re under pressure due to the stress of an entanglement situation.
Attached to BCD
A number of BCDs feature attachment points for knives, and many divers using a wing-and-backplate BCD wear their knives on the waist belt, like you would any knife. Depending on where you attach your knife (if using a jacket BCD with prefabricated attachment points, you’re a little bit at the mercy of the manufacturer), the knife can be reached with both hands, risk of entanglement is generally very low, and putting the knife back in its sheath isn’t too difficult.
Ultimately, picking a placement is a matter of both personal choice and the kind of environment you dive in. But remember the two most important factors: low risk of entanglement and ease of access.