I would like to try to put to rest this notion that a big knife is only for divers with inferiority complexes abut their manhood. Somewhere along the way thiis myth about large knives came into being. Probably from the DIR divers, who dive caves and adhere to a different overall philosophy, which meets their particular needs.
I mentioned in an earlier entry that I am a northeast wreck diver. I don't dive warm water or caves and know little or nothing about that particular type of diving. I suspect that since most divers are vacation divers diving in warm water, they do not feel the need for a big knife since they are not wearing gloves. Same for cave divers. And that's fine.
However, if you must wear gloves to protect against the cold and rusty projections, etc. as cold water wreck divers do, a large knife and at least one backup plus a shears is a necessity. We generally carry a pry bar, a 2-3 lb. hammer and a chisel. But, if you need to cut yourself loose from netting that somehow found its way around your ankle while you were busy, you need a serious, very sharp knife with a decent size handle. Not only would a little baby knife be frustrating, you're already dead.
Now then, if you are on a dive in the islands and you want to impress someone, pull out that brand new expensive titanium, light weight, unsharpenable, ugly-ass dive knife. The captain will, of course, recognize that you are a vacation twice a year diver with too much money to burn. Pull out a decent size, used-looking, steel knife (and maybe a sharpening stone for effect) and the captain will say, "Ah, now there is a guy who obviously dives cold water, knows what the f he's doing. I don't have to keep an eye on him."
What if something stupid happens and you get the guide line caught and you are near the end of your downtime. Are you gonna have time to open that penknife assuming you can even get to it?
Years ago, I got my ankle caught in heavy twine we were using as an upline. I was a new diver. I lucked out as I was able to get loose with the help of my buddy who just happened to look over. I will never forget the feeling of panic I had to overcome. I could never have cut that rope with a small knife, which I probably would have dropped. More recently, I was on a dive with a fellow diver who related the story of how only a week earlier he saw a paniced, distressed diver slashing away at eighth inch line that had wrapped around his ankles. The other diver started cutting the stuck diver out and found himself becoming entangled. They finally got free. The point being that maybe a small knife will cut eighth inch line as well as a large knife but what about say a dozen or more eighth inch cords wrapped around your ankle. Me thinks I'll take the big knife over a small one any day thank you very much.