Dive Knife Handle Material for Buoyancy?

I think it would be difficult to find a material that would remain buoyant at all depths. Even a hollow handle (or helium, as was mentioned) would eventually compress at some depth and sink, just as the air in your tank and BCD does. I wouldn't personally recommend a lanyard as I wouldn't want to get caught in a swell of current and have a sharp object dangling around uncontrollably. I've never lost my dive knife but then I've never had to use it either. As dive knives are rarely ever really used except in spearfishing to dispatch fish, even the cheapest 300 series stainless knives, which isn't really a knife grade, are accepatable. Just buy cheap and if you lose it, oh well. Just my thoughts.
 
That was always my theory as well.

My knife is the one part of my kit that is disposable.

That being said, I did spend a tank searching for one I dropped, found it too...
 
You can make something with an incompressible void - that what those glass bubbles are for, or just a big hollow inside a cast handle. It's just a question of material strength. That's how submarines work, some of which are plastic.

I can't imagine a porous material like cork or neoprene working, though. However, a piece of foam could be used as a core that is coated in something pressure tight.
 
RX-79G said:
You can make something with an incompressible void - that what those glass bubbles are for, or just a big hollow inside a cast handle. It's just a question of material strength. That's how submarines work, some of which are plastic.

I can't imagine a porous material like cork or neoprene working, though. However, a piece of foam could be used as a core that is coated in something pressure tight.
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When I mentioned that the hollow handle would compress, I should have worded it a bit differently. I meant that the gas(air) inside would densify, not the handle itself would crush.
 
I loved diving in Guam. Went from Guam to San Diego, CA. The difference in water temperature, and visibility was an eye opening experience.
 
RX-79G said:
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There is a material I'ver heard of which consists of tiny glass spheres full of air or vacuum. They can be cast into a resin to form fairly strong, depth resistant material of excellent buoyancy. I don't know how big a handle it would take, but making a minimalist blade would also help.
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Ideally, something approaching neutral buoyancy would be ideal - it wouldn't rocket away from you up or down if dropped.
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I suspect you're thinking of "microballons" - RC airplane types use these to thicken epoxy and/or superglue to fill gaps without adding much weight.
hobby stores (especially RC stores) sell them by the pint tub, which weighs not much of anything. you might be able to make a handle scale mold, mix up some epoxy and add the microballons to it at 1 part epoxy and 2 or 3 parts balloons then rivet or epoxy this to your knife blank.
another thing, I'd go with a fairly thin steel for the knife itself or skeletonize the blade for weight savings.
 
mlewright said:
When I mentioned that the hollow handle would compress, I should have worded it a bit differently. I meant that the gas(air) inside would densify, not the handle itself would crush.
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You can't have one without the other. If the airtight canister doesn't crush, then the air inside is not being compressed. If the air is getting denser, it's because the handle is getting smaller.

But I think we have our best answer - Microballoons!

I would make a wide, flat blade with a wide, skeletonized blade. Then I'd just try making a mold out of clay and just cast a premix of microballoons and resin.
 
You guys need to go take a physics lesson. RX-79G is correct.

Add to that that the buoyancy would have to be greater than the mass minus the volume of water displaced, which would mean either a super light knife, or a super size handle. Ships float because they displace a LOT of water - more than they weigh. Cork floats because it has little weight compared to volume ( lower density than water). Knives sink because they don't have either attribute.

I can't understand why anyone would try and make a floating dive knife, anyway. If you are worried about loosing it, put a LED strobe in the handle. One AA battery will run it for days.
 
You could put an acoustic beacon in it, too. That way the FAA could find it.

Actually, I think I'd just buy something from Bud K and leave it on the bottom.


But seriously, I think it is a neat idea. There might be some combination of thin, whippy blade and "hand filling" handle that might be moderately useful for the job. It might look a Ginsu sticking out of a cantaloupe, though.

Okay, had to do the math. 2 oz. of blade and handle would require 2 fluid oz. of displacement. That's about 60 cubic centimeters, or a cylinder of air that's 8 cm long and 3 cm in diameter. Since a whole Mora, with sheath, weighs 2.5 oz, it really wouldn't be hard to get a blade and resin down to 1.5 oz., making the hollow even smaller. This is entirely do-able, with balloons or just a sealed tube handle. I'm pretty sure it could even look pretty decent.
 
Emphasiski said:
A lanyard isn't always feasible. Dive knives are normally held on or near the ankle for comfort and "out of the way" convenience. I've made hundreds of paracord bracelets, lanyards etc, and for the life of me can't think of one worth tying on a dive knife.
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How about this:
You have the knive in its sheath on your right lower arm with a lanyard around your wrist.
You pull the knive with your left hand, placing it in your right.

(presuming you are right handed)
 
mlewright said:
I think it would be difficult to find a material that would remain buoyant at all depths. Even a hollow handle (or helium, as was mentioned) would eventually compress at some depth and sink, just as the air in your tank and BCD does. I wouldn't personally recommend a lanyard as I wouldn't want to get caught in a swell of current and have a sharp object dangling around uncontrollably. I've never lost my dive knife but then I've never had to use it either. As dive knives are rarely ever really used except in spearfishing to dispatch fish, even the cheapest 300 series stainless knives, which isn't really a knife grade, are accepatable. Just buy cheap and if you lose it, oh well. Just my thoughts.
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I've never used my knife to kill, injure or otherwise harm any kind of water life. It is simply a tool that I use as often as I get a chance to. At 70+ feet I prefer not to use my fingers to pry up a chunk of coral or rock to get underneath it.

bladsmth said:
You guys need to go take a physics lesson. RX-79G is correct.

Add to that that the buoyancy would have to be greater than the mass minus the volume of water displaced, which would mean either a super light knife, or a super size handle. Ships float because they displace a LOT of water - more than they weigh. Cork floats because it has little weight compared to volume ( lower density than water). Knives sink because they don't have either attribute.

I can't understand why anyone would try and make a floating dive knife, anyway. If you are worried about loosing it, put a LED strobe in the handle. One AA battery will run it for days.
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I don't need it to float, like I said before, I'd be fine with it sinking slower so I have time to grab it before it hits the mud.

Hengelo_77 said:
How about this:
You have the knive in its sheath on your right lower arm with a lanyard around your wrist.
You pull the knive with your left hand, placing it in your right.

(presuming you are right handed)
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I've tried it on my arm, both arms. If I lose my reg or goggles for whatever reason I really don't want a knife dangling from my wrist, and I'd prefer not risking the possibility of slicing a hose while reaching for a regulator or goggle. Also, I just don't like the idea of a knife on my arm that moves so closely to my chest (BCD) and hoses...I don't care what kind of sheath it has.

These are all good ideas guys, but I wrapped some neoprene around a blank, and I really like the idea of a neoprene covered handled...it was comfortable to say the least (on a blank). Not sure what the internal handle will look like yet though.
 
titanium would cut your weight and make the buoyancy issue easier.Edge retention wouldn't be much of an issue since you are prying with it anyway. Then try a sealed hollow handle to make it buoyant. No need to use helium or exotic gas just make sure it don't leak. I still use a blunt tip dive knife. Your target is probably neutral buoyancy, I can see positive buoyancy being problematic. I think your goal is on target I think the best you are likely to get is less negatively buoyant than a standard dive knife.
You could try getting an empty 12gr CO2 cartridge sealing it up then zip strapping it to something already skeletonized like a Kershaw Amphibian. As a test.
 
Was thinking if you had a handle with a screw on end cap that could be some type of light bulb with a clear or colored lens, you could turn it on when using or diving so there would at least be a light for you to look for if misplaced. Would need an easy on switch and inexpensive batteries AA?

Something you could drop a mini-mag into the handle?
 
Several years ago I made a filet knife and wanted it to float if dropped overboard. It took a huge handle of cork to float it and it was a very thin blade. It wasn't practical at all. I can't imagine a knife that is stiff enough to use as an underwater tool for prying and having a handle that would float it.

About the best we could do with the filet knife that was practical, was to make one that sank blade first with the handle up. It was at least safer to grab as it went down.
 
putting lots of holes in the blade and tang will greatly reduce the necessary buoyancy
C10TRW_L.jpg
 
mlewright said:
I've never lost my dive knife but then I've never had to use it either. As dive knives are rarely ever really used except in spearfishing to dispatch fish, even the cheapest 300 series stainless knives, which isn't really a knife grade, are accepatable. Just buy cheap and if you lose it, oh well. Just my thoughts.
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+1!

Just buy several cheap dive knives...
 
I don't mean to be a naysayer, but I don't think you are going to be extremely pleased with any of the materials you are going to be able to pair with your blade at a reasonable expense, or measure of practicality.

I know it's not what you want to hear, but your best bet is really a lanyard or something like that going to a clip on your BC (not your arm). this is really just to catch the knife in the event that you drop it right?

As for some of your specific concerns of not wanting a knife near your arm/hoses/bc.

Seems like it would be way more dangerous to try to grasp at a falling blade (even a slow falling blade) due to water movement and vision distortion due to light refraction, than to just let your tether catch it for you.

It is pretty darn tough to cut through a scuba hose (HP or LP) on purpose let alone on accident. I have cut through many doing reg repairs and other stuff when I worked for a shop.

Many BC manufacturers equip their BC's with mounting grommets specifically designed for storing dive knives within your gear triangle (where your regs, gauges etc should be anyway). You aren't likely at all to puncture your BC with a knife dangling from it or you.

I'm all for the experimentation, but I don't think buoyancy (positive or neutral) is the answer. Don't mean to be a downer, just adding some points that you may want to consider.
 
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