The Real Test

What is the Real Test for a Boat Knife?

by David Boye


All sailors have heard some amount of boat lore. In that lore, most of us have heard stories of a knife that either did or didn't save a boat, or a life, or many lives.

A fouled prop is a classic nightmare, where many coils of tightly wound rope, line, net, or even seaweed must be cut - under water - usually cold water, with the boat bobbing up and down, maybe at night, and there could be sharks. Another sweaty situation is two sailboats with their collided rigging hopelessly tangled and to release them, tough rigging line must be cut aloft, maybe in a stiff wind, with choppy seas, with the two boats drifting, and maybe even with crew members ensnared, or overboard, or maybe a ship is approaching. I heard recently the story of a man who was caught and was hanging from his foot and swinging by a line that was too high to reach, so the knife had to be tied to a pole, and thus very little pressure could be applied to make the life-saving cut. Or a boat could be caught by a line, net, or object towed by an unawares other vessel. Maybe the rope that needs immediate cutting is large diameter. Have you ever tried to cut a real thick piece of line with a pocketknife? In a hurry?

My own father, Adolph "Whitey" Boye, had his leg severed from his body at the knee by a fast moving tow line on a tug boat, and lived to tell the tale. A good knife in the right place probably wouldn't have helped him, though, but who knows?

Someone may find themselves in a situation needing a blade day and night to survive, with perhaps no sharpening system available. How long will the edge hold?

I have been making knives for over 45 years. I have made in excess of 20,000 knives of many shapes and sizes and with a variety of metallurgies in my small factory, and I have conducted many cutting tests during that time. My criterion for a good performance test is this: does it tell me how a knife will actually perform in a real life situation?

The following is my critique of some knife tests that have been posted online ranking knife brands, styles, and metallurgies. Many of these tests, in my opinion, are deceptive as far as determining the actual ability of a knife to perform in real life. Most of these tests can be done in a few seconds and don't cost (much less prove) hardly anything. I include these for your information, but I do not recommend that you rely on these parameters for your own safety at sea:

  1. Does it shave hair?  I haven't heard of shaving hair in an emergency in any boat lore, even on a Saturday night. Furthermore, an ironic twist in metallurgy regarding "shaving sharpness" is that steels that are extremely fine-grained make excellent razor blades, but do not cut rope worth beans. It is the coarse-grained steels that excel at rope cutting. Certainly shaving hair is not a good performance test for a boat knife.
  2. Push-cutting one small diameter piece of rope by pressure only, without side to side (lateral, or sawing) movement and measuring the poundage of pressure necessary to part the line. This is unrealistic and not a very useful test. In reality virtually all rope is cut with lateral movement of the blade. Push-cutting is good for shaving hair or chopping vegies, but it doesn't cut rope without using a mallet. Also, only one cut?
  3. Pressing a knife into a phone book with a measured pressure and counting the cut pages. Again, much "accuracy," but very little relevance. No lateral movement. No wear on the blade. The thinner and sharper the blade, the deeper it pushes in. So what?
  4. Cutting one small diameter piece of rope, say 3/8", with lateral movement, and noting the number of strokes and how many pounds of pressure it takes to cut it. One cut? This doesn't tell you anything about edge holding at all. No repetition, no volume.
  5. Whittling a piece of wood, even hardwood, doesn't tell you much because it's more push-cutting - no lateral cutting action.

OK, so what's the real test?

How can you test your own knife to see how much cutting you can really do with it?

Ask yourself these questions: How much rope do you want your knife to be able cut in an emergency and still retain a useful edge? This is your call, sailor! How quickly do you imagine you will need to do it? How clean or full of sand or salt will the line likely be? How much time will you have to re-sharpen it? You might want to test cutting stamina and sharpen-ability on a variety of materials.

In my opinion, the only real way to find out the answers to these questions is to actually cut a quantity of marine grade rope with your knife non-stop and see how much you can cut without re-sharpening. There just isn't any cheap and easy way to do this kind of a test. I have used 1" clean hemp, 1" and 3/4" old (dirty) hemp, and the biggest diameter of new line of all grades I can get, including nylon, Spectra, Sta-Set, etc. (Don't forget to cut some of these hi-tech grades.) I realize that rope is expensive and/or a hassle to round up small snippets to practice on. But there just isn't any other way to face the music.

So here we go:

  1. After you have obtained a supply of test rope, sharpen your knife, if it isn't already sharp. How long did that take?
  2. On a clean table with a cutting board, start cutting. Hold the end of the rope bunched up with one hand, and cut with the other. (By the way, this is probably the best set-up for cutting you will every have, i.e. it's not in the dark, under the water, or up in the air.) As the test progresses, keep a record of how many cuts of which size and grade of rope you cut. Note the relative ease of cutting. How is your knife doing? Does it like to cut rope? Is it giving you confidence? How many cuts before you start to struggle or fray the line? Some serrations can cut aggressively at first but often don't hang in there and may start making a bird's nest instead of a clean cut. Herk up some adrenaline and see how much you can cut if you have to.
  3. When your knife just won't cut anymore, count up your score. Was this enough to deal with an emergency, in your opinion?
  4. Now, how quickly can you bring the edge back to a real working edge with the implement you will have on the boat? How long does it take? Could you realistically resharpen it in the midst of a white-knuckle situation?
  5. Then double check the sharpness by cutting a bunch more rope. Is it really as sharp as it was?

These are the real issues you need to consider to truly evaluate a boat knife. Unless you are a seasoned rigger you probably haven't cut a lot of line non-stop. And they probably won't have you do this in sailing school. Are you satisfied with the performance of your knife?

My point is this - if you don't practice cutting rope yourself, you don't know what you and your knife can or can't really do! Be creative. Have fun!

You can view the results of my cutting tests demonstrating the edge-holding and sharpening of Boye knives here. These tests were conducted in the presence of certifiable witnesses, using new hemp rope and synthetic deck and rigging line.