There are many factors to consider when purchasing a snorkel: shape, mouthpiece, barrel type, valves, and even how well you like the look of it. One factor you may not consider is the length of the snorkel.

Some people might think a longer snorkel is always better. The longer it is, the less chance water will get in, right? While true, there are two other important considerations:

• Dead air space is a concept that comes up in many different areas of scuba. Dead air is the gas in airways left from the end of your last exhale. It consists of carbon dioxide, and is blocking the path for fresh air. This gas has to be inhaled first before new air can reach you, yet it is “dead” and thus worthless to your body. The space refers to where this dead air resides.

  For snorkels, the longer they are, the more dead air space they have. When you exhale through a snorkel, the carbon dioxide is trapped in the barrel. On your next inhale, you must first inhale all the carbon dioxide from the barrel before fresh air reaches your lungs. The longer the barrel, the more difficult it is to breath.

• Clearing gets harder with longer snorkels as well. When water gets trapped in the barrel you must clear it by forcefully blowing out any trapped water. Longer snorkels simply hold more water. Snorkels do have valves on the mouthpiece to force water out, but it will still take a little more effort for longer barrels.

These factors should figure in your purchase of a snorkel. Usually, a snorkel just long enough to clear the top of you head should suffice. These days they even have guards on the end of snorkels to prevent water getting in the top. You’ll pay extra for it, so it’s something to consider if you think you’ll often be snorkeling in choppy waters. Otherwise, you use a snorkel rarely enough to be worth the added expense.

Most divers never give much thought to what their air cylinder is made of. Even so, it can affect aspects of your dive. Besides, it never hurts to know a little about the equipment you’re diving with.

Material

Cylinders are made out of two types of material: steel and aluminum (actually an aluminum alloy). Each have different properties that make it appealing for different types of construction and use.

Steel cylinders are tough, making them resistant to damage. They also tend to support higher capacities, because of their increased strength. The downside to steel is that it can rust if not properly cared for.

Aluminum cylinders are softer than steel, so they’re not as tough, although they do just fine for general use. To compensate, the walls of aluminum cylinders are thicker than for steel. For this reason, an aluminum cylinder is larger and heavier than a similar capacity steel cylinder. They also don’t handle overfilling nearly as well.

Despite this, aluminum is the dominate choice of material for cylinders in many parts of the world. The upside is that aluminum tanks are far more tolerant of corrosion from salt water. As opposed to steel cylinders, when a layer of aluminum oxide, or “rust”, forms, it acts as a barrier to prevent further oxidation. 80 cubic feet aluminum cylinders are probably the most common type encountered in tropical dive destinations.

Identification

Unless you’re into metalworking, it can be hard to distinguish between steel and aluminum tanks. It’s even worse when the cylinders are painted for enriched air diving. Fortunately, manufacturers in North America are required to stamp certain information on tanks they produce, including the type of material used.

You can find this stamp at the top, rounded part of the cylinder. It is a sequence of letters and numbers stamped into the metal, arranged into two rows.

To determine the type of metal, look in the middle of the first row. These days, you will most likely see either “3AA” or “3AL”. “3AA” is the markings for chrome-molybdenum steel, which is practically all steel cylinders made today. “3AL” is the designation for the aluminum alloy used in cylinder manufacturing.

Buoyancy

The type of cylinder you use only has one major effect on your diving: your buoyancy. Aluminum tanks are more buoyant than steel, and thus you will require more weight when diving with them. It is worth knowing what you usually dive with in order to compensate one way or the other when diving with a different cylinder.

The usual recommendation is to add about 5 lbs / 2 kg to your base weighting you get from a weighting guide to compensate for an aluminum cylinder.

Aluminum has a particularly annoying characteristic. A full steel tank is negatively buoyant. An empty steel tank is also negatively buoyant, but less so. This is why during a proper buoyancy check it is recommended to use a near-empty cylinder, or add weight to compensate. Aluminum cylinders also become more buoyant as air is consumed, but they change from being negatively buoyant to positively buoyant. This means a full aluminum cylinder will sink while an empty will float. This makes it harder to pin down a perfect weighting for the entire length of a dive.

If you’re curious, a standard steel cylinder weights about 30 lbs, while an aluminum tank weighs about 35 lbs. If aluminum tanks are heavier, then how can they be more buoyant? For the same reason they’re not as strong as steel: aluminum is less dense than steel, and thus has a lower specific weight.

I hope you learned something about cylinders today. Next time you go diving, take a quick second to identify what type of cylinder you’re using. Use this information to adjust your weighting, instead of defaulting to being overweighted. Keeping note of the tank type (when different than what you usually use) in your log book could also be useful.

Scuba dive for any length of time and you’ll start wanting your own equipment. A natural follow-up question then is, “What equipment do I buy?” Let’s look through all the equipment a diver needs, which you should buy, and in what order.

Your own mask is usually high up on the list of equipment to own. This could be for a few reasons. Having a properly-fitted mask increases the comfort of your dives. Masks are one of the more “personal” items you own, so having your own that you are comfortable with is an advantage. They also are small and easy to travel with. Factor in the price on top of that, and a mask is one of the first things you should own.

Snorkels are almost always bought in conjunction with a mask, so all the previous applies.

Fins complete the trio of a beginner’s set: mask, snorkel, and fins. Some shops even require that you own each of these before beginning your open water certification. These three items also double as snorkeling gear, so their uses extend beyond scuba diving.

I was debating where to put wetsuits. In my opinion, I would rather have my own wetsuit than my own pair of fins. So why did I put it after? Buying a wetsuit is not so easy, since you feel like you are committing to a single diving locale by having to choose one thickness of wetsuit. Having to make this decision early in your diving career can be confusing. Thus, I say buy your mask / snorkel / fins set and use it for a while, then when you have a good idea where you’ll do most your diving, purchase a wetsuit (follow our wetsuit guide for help).

Having said that, owning your own wetsuit is wonderful. I personally love knowing that I’m the only person that’s peed in mine. Add a hooded vest for additional comfort and versatility.

Now we’re getting into serious diving. A BCD is not a purchase for the casual diver. They are often bought by those beginning divemaster training, or people who have been scuba diving for years and are finally tired of paying BCD rental costs.

When buying a BCD, you don’t need anything expensive or flashy (unless that’s your thing). Make sure it has enough lift and fits you well, and you can get out with your wallet intact.

Regulators often go hand-in-hand with BCDs. This time, things can get pricey. Go with a solid regulator, even if it costs a little more. Remember, you’re gonna be breathing off this thing under 90 feet of water.

I’m lumping pressure gauges, depth gauges, and octopuses into this category, since you will usually buy them with the regulator.

Weights are boring, but required gear. Don’t bother buying them unless you often go diving locally without a shop. Traveling with them is unnecessary, since you can find weights anywhere.

Ditto for a cylinder. If you’re in the market for one, you already know it. Otherwise, be glad you can get away with renting one.

This is all the required gear for scuba diving. Naturally there is other equipment, like computers, that comes up, but does not fit into this guide.

One last thing, buying gear is a big decision, but it’s not life-changing. There are a lot of choices, so don’t get too bogged down out there. Some people prefer to buy inexpensive gear as a beginner, and then upgrade later. The life on most of this equipment is in the 4-5 year range, so keep some perspective when making your purchase.

What are your thoughts? Would you recommend buying gear in a different order? Make your opinion heard in the comments.

I really want a pair of spring fin straps. Slipping my foot into my fin and pulling the spring around it seems much nicer than awkwardly tightening straps. You only fit spring straps once, to buy the right size for your fit and fin. After attaching them, you get a perfect fit every time.

They’re also really nice for anyone who does a lot of shore diving, where you don’t always have the luxury of sitting down to put your fins on. Even when sitting down, putting on fins can be difficult.

For anyone buying a pair, look for the recommended straps for your fins, but don’t hesitate to check if any generic spring straps will work just as well.

I love hooded vests. They are one of the most versatile pieces of equipment I own, for a few reasons:

1. They keep you extra warm. This one’s obvious. Hooded vests make any wetsuit useful for another 10 degree drop in temperature, so factor that in when choosing a wetsuit. It’s also useful to warm you up at the end of a week of diving.
2. They are easy to pack. Taking all my gear isn’t always an option for trips where diving is not the sole purpose, but I’d like to get a dive in if possible. This means using a rented wetsuit. Shove your perfect-fitting hooded vest into your suitcase and it’ll partially make up for that awkward-fitting rental.
3. Forget the wetsuit completely. Don’t even bother with a wetsuit at all. In warmer climates you can get away with wearing a bathing suit and a hooded vest. Most heat loss comes from the head, with the next largest amount coming from the torso. A hooded vest keeps these two areas well insulated. You can laugh at everyone wrestling to put on their fullsuits.

Add one to your collection and start reaping the benefits. I’ve used the same one by itself in balmy Bonaire¹ and underneath a fullsuit in cold California.

1. I have one additional recommendation: If wearing it alone, wear a rashguard underneath it. My shoulders got severely burned during long surface swims.

Few things ruin a dive as quickly as a poorly-sealed mask. I had this problem the other day, and it disrupted my dive by being distracting and making me run through my air supply by constantly clearing it.

I started playing around with something that I think helps a little. Next time your mask is leaking water, instead of clearing it as usual, exhale a little stream of bubbles out your nose. Sometimes this will keep a small leak cleared by forcing the water out of the mask.

This approach managed to keep my mask clear without costing my air supply. I have to exhale anyway, so I just exhaled at the same usual rate but out of my nose instead of my mouth.

This may not work with all bad seals, but I imagine if the problem is at the bottom of your mask you may find it helps. It’s certainly better than repeatedly stopping to clear your mask.

When you train to be a Rescue Diver, and especially when you reach a professional level, you will be expected to have a pocket mask.

I looked around at some before ordering, beginning at scuba dive shops. I noticed that they aren’t so cheap. Neither are the official Red Cross masks.

It didn’t take long until I found these pocket masks at Amazon. $8 each is the lowest price I found, and much lower than the price quoted at dive shops. As long as it has an O2 inlet and covers the mouth / nose, you’re good.

Overpressure relief valves are pretty much standard on today’s BCDs. You can identify them as the vent-like areas, either on the shoulder and / or bottom rear of the jacket. Often they have a ball-and-string assembly attached called a “dump valve.” Pulling on this will release air from the BCD through the valve. This allows the diver to vent air easily from almost any orientation underwater, without awkwardly holding their inflator hose toward the surface.

As their name implies, the primary purpose of overpressure relief valves is to prevent the accidental over-inflation of BCDs. BCDs contain what are called bladders, or basically, air bags. These air bags have a finite amount of air they can hold, and exceeding this amount, either by over-filling it or by ascending to a depth that increases the air’s volume enough, would ordinarily cause it to rupture.

The trick is to put a hole in the bladder, but a hole that only leaks air when there’s too much of it. This is accomplished by holding a plug in place over the hole with a spring. This plug effectively corks up the hole. The spring has to be perfectly strong enough to hold the plug in place while air enters the BCD, but weak enough so that the plug pushes out, releasing air, when the pressure inside the bladder gets too high.

BCDs have some maximum pressure they can withstand. This is easy enough for the manufacturer to find out. Just fill the BCD until it explodes. The pressure right before it pops is the maximum pressure, although they’ll lower this a bit for a built-in tolerance.

With this maximum pressure p_max, we can figure out the strength, or stiffness the spring should be. We do this using Hooke’s law, which states that the force of the spring is equal to the deformation of the spring times a spring constant (the stiffness of the spring), or,

F = -k x,

where k is the spring constant that we want to find. We know what force is keeping the plug in place, it is the maximum pressure times the area of the part of the plug that feels the BCD’s air pressure (pressure is force per unit area), or p_maxA. The spring is also be deformed slightly to hold the plug firmly in place. How much the spring is deformed gives us x, which tells us the force exerted by the spring on the plug. With that number we can rearrange and compute the spring constant as

k = -p_maxA / x.¹

If the pressure increases, the spring won’t be strong enough to hold the plug in, and the BCD will release air. You can also manually override the valve by pulling the plug yourself, which is what you are doing when you pull the cord.

Like most parts on a BCD, the overpressure valve is an incredibly simple device. The simplicity of this device helps make BCD inspections a fairly easy process, especially when compared to overhauling a regulator.

1. We are ignoring the mass of the spring and the plug.