Knives and cutting devices
While most recreational divers who dive in groups will most likely not need a knife, divers who frequently visit wrecks or perform technical dives will certainly want a quality knife in their kit. Just make sure the knife is readily available in a sheath and strapped to your arm, dive belt or BCD so you can easily reach it if and when the need arises.
Consider the following points to choose the right knife for your kit:
Relevant- Stainless steel knives are strong, but need to be washed after each use to prevent rust. Titanium is another option that is almost completely rustproof, has a sharp edge and is corrosion resistant; however, for these reasons, it also comes with a higher price tag.
Size- You really don't need a big knife, and the more compact it is, the less hassle it will be. Opt for either a small 2-3 inch blade that will be easy to fit in your kit and light to travel with - or a medium 4-5 inch blade which may prove to be the most practical option for cutting thicker lines. . Whichever you choose, just be sure that you can get a firm grip on the handle even if you're wearing thick gloves.
Fixation- a device such as a scabbard can help mount the knife to your equipment, such as your BCD, waistband, or even wrist.
shape- Look for a knife that has both a serrated edge that will cut both plastic and natural fibers straight. You will also have to consider the type that will work best - a rounded tip is the safest option as it will prevent you from accidentally poking holes in hoses or show clothes. Scissors, unlike a knife, are safer and can quickly cut a line. Consider getting a knife and scissors if you intend to dive in areas known to have fishing nets or tangles.
A cutting device is essential if you plan to dive in areas where fishing nets are a hazard.
A good cutting device is an essential part of your kit, but you may find that what works well for someone else doesn't work for the type of diving you do.