A friend in need--the dive knife
The world's waterways have provided mankind with food and transportation since time immemorial. The oceans in particular have been the subject of sea stories, books and movies. One thing the oceans are not, however, is safe. Having the proper equipment along while out on the water can be the difference between having an exciting story to tell and resting in a watery grave.
One such item is the dive knife. While it is not a weapon, it can be more valuable than a spear gun when a diver is tangled in ship lines, seaweed, or some other natural or manmade hazard. A sharp knife can let a diver get back to the safety of the surface.
Having the right knife is important. A knife should be sharp at all times, so a material that tends to lose its edge is not ideal. A knife that will stay sharp may cost more, but the edge in performance is worth any extra cost. Titanium is a good example of a very expensive knife that is well worth the price.
Even a sharp knife won't do you any good if you can't draw it when you need it. That's why you should consider a fixed-blade knife, carried in a sheath. The sheath should allow you to draw the knife with one hand and without any struggle; remember that panic tends to affect fine motor skills, so it should be easy to draw the knife under pressure. Sheaths can be worn on the hip or around the leg, depending on your needs and preference. If you wear gloves while diving, practice drawing the knife while wearing gloves.
A knife's edge can be smooth or serrated. Depending on the situation, you may need either to slice or saw, so your knife should be able to handle both tasks, unless you prefer to carry different knives for different tasks. If you take that option, be aware of the extra weight you'll be taking with you under the water. Keep in mind as well that some states regulate the size that a knife can be. If you are going to be diving in one of those places, be sure of the legal size of your knife. If you can't carry your favorite knife there, have a substitute ready.
Whether you get a basic knife or one with extra features, such as a large handle or, in the case of some folding knifes, multiple blades, keep in mind that your knife is a valuable tool that will do its job as long as you take care of it. No particular knife works for every diver, so take your time selecting what knife or knives you want to take along. Your life could depend on it.