I go in to quite a bit of detail about the gear required for SCUBA diving.
Breathing Gas
Note — this is a gas mix, not “oxygen”. You can call it “air” and be right some times. “Air” is 21% Oxygen, 79% Nitrogen. Other mixes include Nitrox (air + extra oxygen), Trimix (air + helium), both at various levels of supplementation. Two common Nitrox blends are 32% and 36%. That means you end up with 32/36% oxygen instead of 21%. Some tech divers take down small bottles of 100% oxygen for doing decompression stops.
Cylinders
There are many kinds of cylinders, “tanks”, “water heaters”, and what have you. The “standard” is the aluminum 80 (A80). This is a rather large tank that holds 77.4 cubic feet of the gas of your choice when at 3,000 psi. It’s buoyancy characteristics suck: it goes from negatively buoyant (“negative” — sinky) when full of gas to positively buoyant (“positive” — floaty) when nearing empty. That means you have to wear extra weight to compensate for your “floatiness” at the end of your dive. Yuck.
Luckily, you can buy cylinders made of steel! The first tank I bought was a low-pressure steel 80/85 (LP 80). It’s “low pressure” because it’s got it’s 80 cubic feet of gas at 2,640 PSI. Since it’s made out of steel it starts out pretty negative at the beginning of the dive, and ends up neutrally buoyant (“neutral”) at the end of the dive. Sweet! That’s a few pounds of weight you don’t have to wear!
I happen to have a high-pressure steel 80 (HP 80). This tank is significantly smaller, and holds more air. It’s “high pressure” because it holds 80 cubic feet of gas at 3,500 psi. To accommodate such pressures without exploding, it’s made of very thick steel. As anybody on the Titanic could have told you: steel likes to sink. The amount of steel is so high that this tank goes from very negative when full to slightly negative when empty. If you want to have a fun descent, wear the same amount of weight for an A80 when diving this tank. You’ll sink faster than a rock. The size also means you’re less likely to hit your butt on the cylinder. Plus they’re cute.
Regulators
There are two classes of regulators: balanced, and unbalanced. A balanced regulator will adjust it’s sensitivity with depth to keep ease of breathing constant. An unbalanced regulator will not.
Either way, there are still three kinds of regulators: first stage, second stage, safe second.
The first stage attaches directly to the tank and releases gas from the tank at a lower (though still high!) pressure than in the tank. There tend to be two sets of ports: high pressure, and low pressure. The high pressure port(s) tend to have a pressure gauge, dive computer, or similar attached to them. These bits tell you how much air you’ve got left in the cylinder, in terms of PSI. The low pressure ports are used to supply air to the rest of your gear at a pressure it can use. The standard dive kit makes use of three of these ports: one to your second stage regulator, one to your safe second, and one to your BC’s power inflator.
The second stage regulator is the one you put in your mouth. It releases gas at ambient pressure (in a balanced regulator) to your mouth. There are different styles but most modern second stages are of equivalent quality within a given price range. You tend to get what you pay for here: more expensive regulators tend to “breathe easier” than less expensive regulators.
The “safe second” is a backup second stage regulator, usually clipped off to your BC. In most set-ups, if you buddy runs out of air this is the regulator you’ll give them. A considerate buddy will not drag this thing through the sand and leave it nasty. A more recent alternative is a combination BC inflator and safe second. In this set up the power inflator also has a regulator built in to it. When your buddy runs out of air you give them the regulator you’re currently breathing off, and use your inflator to breathe. This is the set up Jessica and I use. I think it’s got a few benefits. First of all, it’s one less hose coming off your first stage. Second, it means your buddy can come up and tear the reg out of your mouth when they run out of air. Apparently that’s what they’ll do anyway, since they know it works. Finally, it makes you a more considerate diver: since I know I may have to breathe off my safe second, it’s in my best interests to keep it clean and functioning.
Masks
Our eyes are designed to work in air, not water. To get our eyes to work correctly underwater we take a pocket of air in with us, in the form of a mask.
There are a few variations between masks, mostly shape, but there are a few features to look for. First you want it to be low volume. It’ll take less air to pressurize the mask as you descend and it won’t burp as violently on the way up. You obviously want a good fit: put the mask on your face and inhale through your nose. It should stick for a second or two when you do that, then fall.
I dive with a color tinted mask. As light tries to penetrate water shorter wavelengths drop out, starting with red at 30 ft. These tinted masks try to compensate for that with a funny tinting. I like it. Clear masks are available as well, and really it’s up to you.
There’s really only two kinds of silicone skirts: black and clear. Everybody I’ve spoken with says that the black skirts are made of higher quality silicone and won’t degrade as quickly. Obviously this isn’t something I really want to test.
In my experience the tinted, black skirted masks are the highest quality. Get whatever shape makes you the most comfortable and work with it. If you can’t see anything, why are you diving?!
Fins
Our feet make terrible paddles: they don’t move us through the water very well. Using your arms works, but not for very long. To solve this problem we wear fins (NOT “flippers”!)
There are two kinds of fin: “paddle” and “split”. The traditional fins you see on at least the macho guys are the ScubaPro Jet Fins. They apparently are the best fins on the planet, and are relatively inexpensive. Also in the “paddle” category are the Force Fins that my local dive shop tries to push. Force Fins are very expensive, and shaped in a very strange way. They’re supposed to work really well and if I ever have money again I might give them a shot.
The other kind of fins are split most of the way down the middle. This apparently makes some awesome propeller like action when you kick. I don’t really know that much about hydrodynamics, so why not? I’ve got a pair of Atomic Splitfins and they work just fine. My only complaint with them is that the foot pocket is very stiff, so on longer dives I get the very beginnings of a blister. It also seems impossible to perform alternative kicks (like the frog kick) with split fins, they don’t “grip” very well.
Pros and cons of each type. Split fins apparently let you move faster, with less effort. You know, for chasing Manta Rays and Blue Whales and all that. Paddle fins apparently give you more control and make you more nimble. Split fins tend to cost more, and are longer. Split fins get tangled in kelp very easily. Paddle fins tend to be negatively bouyant. That’s handy if you’ve got “floaty feet.”
Thermal Protection
Thermal protection is always a concern, the question is only ever how big. In the tropics where the water is ~ 80° F all the way down to 120 ft. your choice in thermal protection is more about style than anything. In California where the water on the surface can be ≤ 50° F in the winter (when the visibility is the best) it’s a major concern. You really have two options: diving wet or diving dry.
Wet suits are great: they’re relatively streamlined, they’re not as expensive, they come in lots of nice colors, and there are lots of brands. You can get lots of options like integrated hoods or extra zippers around the feet to make don/doffing your booties easier. They work by keeping a layer of air bubbles (trapped in the neoprene) between you and the rest of the ocean. They do NOT work by keeping water against your skin which your body warms. That is complete myth. In Basic Open Water training we learn that water conducts heat away from the body forty times faster than air. The downside to wetsuits is that you end up getting wet all over. This isn’t a problem in 70° F water, or even in the mid 60′s, but after a while it’s just too cold for too long. I’ve got an 8-7-6 mil XCEL wet suit right now. The core area (chest, torso, etc.) has 8 mm thick neoprene. The hood, shoulders and arms have 7mm thick neoprene. The legs have 6mm neoprene. The legs are the thinnest because all that kicking you do generates heat, so your legs end up the warmest part of your body while diving in colder water. I really like the integrated hood and front entry design: it’s handy.
Dry suits are great: you stay nice and try, you can wear whatever you want under them, they’re incredibly customizable, you can dive year-round in one. Of course good ones (like from DUI) are very expensive: spending about $3,000 would get you a very nice dry suit. Surprisingly, dry suits work on the same principle as wet suits: keeping a layer of air between you and the rest of the ocean. The difference is that dry suits don’t let in much water at all: just a few drops at worst. This is accomplished with a series of latex or neoprene seals around the neck, wrists, and sometimes ankles. Under the suit you can wear shorts and a t-shirt if the water is warm, or special undergarments that wick away moisture and keep you warm and comfy. A dry suit is a great investment for a moderate water diver, I plan to buy one in the winter.
Buoyancy Compensation
The buoyancy compensator (“BC”) attaches to the cylinder and has a few functions. First, it keeps the cylinder near you without occupying your hands or getting in your way. Having it on your back is actually pretty handy. Second, it’s got an air bladder to help you become neutrally buoyant (“neutral”) at a given depth. When you’re “neutral” you rise just a bit and sink just a bit as you breathe. This is a very Zen like state that can be hard to achieve.
At this point the BC stories diverge. Some people use a “back plate and wing”. This is a back plate for holding on to the cylinder(s), and a “wing” to hold air and balance you. The wing is screwed on to the back plate, and webbing is run though various cut outs on the back plate. Once the webbing is customized for a particular diver it’s supposed to be rather comfortable. Since it’s just a single piece of webbing it’s very failure resistant. It’s also got no pockets so it’s rather stream-lined. Finally, it’s infinitely customizable — you can add D-rings all you like, wherever you like, a crotch strap, whatever.
Others use the more familiar “jacket” style BC. This looks a lot like a life preserver because it wraps around you like a jacket and inflates around you as well. I call this style “the crusher” since it ends up compressing your ribs the more you inflate it. Some people find this pressure nice — I find it quite lame. These tend to have pockets for holding miscellaneous crap you don’t really need. They also tend to have weight pockets where you can put some lead. I’ll get to lead in a bit.
The third style is a hybrid — the back-inflate. This is the kind of BC I’ve got. It’s got the back plate and wing style inflation, but it’s also got weight pouches. I think this is the best of both worlds, and really like it.
Dive Lights
There are a wide variety of diving lights. There are large “canister” style lights that have a power generator that you wear on your hip, and a bulb that you bungee to your wrist. Those kind are insane: they’re heavy, create massive amounts of light, and are nuts.
The next step down are the high end HID lights. Jessica has a Light Cannon from Underwater Kinetics (UK). It takes 8 “C” cell batteries, 30 seconds to warm up, and you can’t use it on land because it’d melt it’s own casing. It is however, quite bright.
Another step down from that are the various incandescent lights, like I have. I bought a C8 from Underwater Kinetics (UK). It takes, surprisingly, 8 “C” cell batteries. It comes with two bulbs in the housing. This provides redundancy since they’re independent, and some control over the beam. One bulb is more of a spot and the other is more of a flood. Switching between the two just requires the flip of a switch. This light isn’t nearly as bright as Jessica’s, but it works well for my purposes.
There are also small backup lights that have a twist mechanism to active. These are OK as backup lights but that’s about all they’re good for in my opinion.
Dive Knife (a.k.a. Dive Tool)
Dive knifes have one very simple purpose: to get you untangled. They’re not for fighting off sharks or giant squid. As such you don’t need a four foot long sword attached to your leg.
For the most part, you also don’t want anything with a pointy tip. The best reason for that is that pointy tips don’t get along well with BC bladders. For that reason, most knives come in a blunted style.
From what I’ve read the most common need for a cutting instrument is to get yourself out of fishing line, kelp, a net, etc. In these circumstances a knife isn’t very effective and requires you to make big movements. Making big movements tends to get you tangled up even worse.
That’s why I carry inexpensive EMT shears. They can cut through a penny, have blunted tips, are bright colors, and easily cut through line or seaweed. You can find people selling these on eBay for a song. There are also multiple ways to attach them to yourself: keep them in a BC pocket, clip them to a D-ring, etc. Jess and I keep ours in a pocket. Jess also has a small dive knife that came with her light. It’s a backup cutter and makes a descent prying tool as well, should one be needed.
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