Rock beauties are a common sighting on many reefs. Other names for the fish include corn sugar, coshubba, rock beasty, and yellow nanny. I haven’t heard these, so stick with rock beauty and most people will know what you are talking about.

Physical description

Rock beauties are in the angelfish family, so they have the usual large-shaped, flat bodies of that species. They don’t get as big as most angelfish, topping out at around 12 inches (35 cm).

Rock beauties are most easily distinguished by their color rather than their body shape. They have a bright yellow head and caudal fin. Sometimes these two patches of yellow connect above and below the large black region on the rear of their body. They have big lips that are iridescent blue.

Juvenile rock beauties are almost entirely bright yellow, with a single black spot on the upper rear of their bodies. As they grow older, this spot grows until it covers most of the back of the fish.

Geography and Habitat

Rock beauties are reef fish in the western Atlantic down to the Gulf of Mexico, and can be found at all diving depths.

They hang around reefs, rock jetties, or any sort of crevices that offer some protection. They are very territorial, so you will rarely see them venture far from their shelter.

Fun facts

It is thought that rock beauties are monogamous, due to the observed long-lasting pairs they form.

Further reading

Wikipedia
Florida Museum of Natural History

Water conducts heat away from your body 20 times faster than air, so the only thing keeping you from freezing after 15 minutes of diving is your wetsuit. Excellent care is a must to keep it insulating well for a long time.

• After a dive

  Most people know this one. After a dive, rinse the wetsuit thoroughly in fresh water. Take a moment and run your hands over it, rubbing away any salt that may try to dry inside. This basic step will do more for your wetsuit than anything else. Don’t forget to do the same after pool dives! Chlorine kills everything—that’s why they use it in pools.

  Also, let the wetsuit dry inside out.

• After a trip

  Every once in a while it’s a good idea to wash your wetsuit down with a shampoo. There are a variety of specialty wetsuit shampoos, but as you know, I like to save money when possible. I find baby shampoo works just fine, and is substantially cheaper. Throw in a little baking soda as well to really neutralize any odors (read: pee smell).

• Storage

  You have two options for storage. Ideally, get a wetsuit hanger or a thick plastic hanger for storing your wetsuit in a closet. Make sure the wetsuit hangs in a form-fitting fashion, to prevent awkward creases. Don’t use a metal hanger.

  If hanging the wetsuit is not an option, you can fold it for storage. Be careful that you don’t put any creases in the wetsuit, and minimize the amount of folding needed. For instance, try to fold it once longways (putting the arms and legs on top of each other), and then one more fold across the waist area.

  Try not to squish it under anything. Permanent creases deteriorate the insulation quality of wetsuits.

• Repairs

  It’s a good idea to check for little holes or tears, while they are easier to fix. Most small tears can be repaired with neoprene cement. Loose patches and seams may have to be repaired with bonding cement.

  If the hole is too large to bond back together, a neoprene patch is probably required.

Follow these basic guidelines so your wetsuit keeps you warm for years to come. And remember, an old wetsuit doesn’t have to go in the garbage. Use them for activities where a wetsuit is needed but either the water is really warm (you don’t need perfect insulation) or you don’t want to use your new wetsuit. Pool dives are a great example.

This picture has been making the rounds on the internet. In Norway, a couple of guys dressed up in scuba gear and chased the Google Street car down the road.

Buoyancy is determined by a lot of competing factors on a scuba diver. The net effect, however, is that you are either positively, negatively, or neutrally buoyant. For recreational divers, you are usually positively buoyant (at the surface). Weights are used to offset this positive buoyancy and make you slightly negatively buoyant, in order to sink to depth. Choosing weights may feel largely like guesswork, but there are physical principle at work as you dial in to your ideal weighting.

Archimedes’ principle

The most basic principle at work is Archimedes’ principle, which states that an object in a liquid is buoyed up by a force equal to the weight of the liquid displaced by the object. Imagine we put a ball in a pool, and the ball is 5 liters in size. The ball will displace 5 liters of water, since the water has to move when the ball is placed in it. 5 liters of water weights 5 kg, so the ball feels like it weights 5 kg less when in the water. If the ball is less than 5 kg, then it becomes positively buoyant. If it is more than 5 kg, it is negatively buoyant, because an upward force of 5 kg is not enough to counteract the weight of the ball. If the ball is exactly 5 kg, it is neutrally buoyant. Archimedes’ principle relates the amount of a liquid displaced to the buoyancy provided.

Specific gravity

We have all we need to know to do computations in fresh water, but not for sea water (or for the general case of any fluid). The missing factor is how much the liquid weights per unit volume. This is the density of the liquid. Rather than dealing with the density of the liquid directly, we can just use the ratio of the fluid’s density to the density of fresh water, which weights 1 kg / 1 liter. This number is called the specific gravity¹ of the liquid.

The specific gravity of fresh water is exactly 1, because it’s the ratio of a number (the density of fresh water) to itself. The specific gravity of salt water is 1.03. This means a liter of salt water weights about 1.03 kg. This is enough for scuba diving. If you ever find yourself diving in anything else, you may need to look up the specific gravity of that liquid.

Example 1

Quick recap: Archimedes’ principle tells us that an object (including you!) in water is buoyed by the weight of the displaced water. Specific gravity tells us for a given volume of displaced water (either sea or fresh), how much it weights. We can use these to compute the exact amounts needed to make something neutrally buoyant, or positively / negatively buoyant by any amount.

Let’s say a diver weights 80 kg with all their gear on, and the volume taken by them (and all the gear) is 90 liters. We can ask the question

Is the diver positively, neutrally, or negatively buoyant in the ocean?

To answer this question we need to know how much the displaced water weights. The specific gravity tells us that 1 liter of sea water weights 1.03 kg. The problem says that 90 liters of sea water is displaced, so 90 liters of sea water weights 90 l * 1.03 kg / l = 92.7 kg. This means the water is “pushing up” on the diver with a force equivalent to 92.7 kg. However, the diver weighs 80 kg, so this is more than enough to stop them from sinking. Thus, the diver is positively buoyant.

How much weight is required to make the diver neutrally buoyant?

We know the diver is positively buoyant, but by how much? 92.7 kg – 80kg = 12.7 kg. If we put 12.7 kg of weights inside their pockets, they would be neutrally buoyant. Anything more than that would make them negatively buoyant, and they would sink.

Example 2

Example 1 showed how we can compute exact weighting requirements, but we don’t do this in real life. In real life finding the weight and volume of the diver would be too cumbersome. Instead, the first time with a gear setup in certain water we find the correct weighting through trial and error. We then make modifications in future dives based on that amount of weight.

Here’s a common question seen with these types of problems. Imagine we lose something heavy off the boat into the ocean, such as an untied anchor. The anchor weighs 100 kg and is 50 liters in volume. A person can’t lift the anchor from the bottom, so we want to attach a lift bag filled with air to buoy it to the surface.

How big of a lift bag do we need?

To answer the question, we first need to know how negatively buoyant the anchor is (if it sank it’s clearly negatively buoyant). It displaces 50 l * 1.03 kg / l = 51.5 kg of sea water, but the anchor weighs 100 kg. This means we need at least 100 kg – 51.5 kg = 48.5 kg worth of additional buoyancy from the lift bag to make the anchor float.

The problem asks for the size of the lift bag, which is in liters, but we only know the weight needed. This means we need to displace more sea water using the lift bag. How much sea water? 48.5 kg. How much volume will displace 48.5 kg? 1.03 kg of sea water is 1 liter, so we can convert. 48.5 kg / 1.03 kg / l = 47.09 liters. This is all air, which weights so little we can practically ignore it.

The answer then is that we need a lift bag that can hold at least 47.09 liters. By the way, this is how your BCD works. When you inflate it, your volume becomes bigger without changing your weight, so you displace more water and become more positively buoyant.

Another side question we can ask is

If the anchor is in 10 m (33 ft) of sea water, how big does the lift bag really need to be?

The lift bag needs to be 47.09 liters to make the anchor positively buoyant, but there is another principle at work here: as the lift bag moves towards the surface, the volume will expand. For a depth of 10 m, the volume will double as it reaches the surface. We not only need a lift bag that holds at least 47.09 liters to begin ascending the anchor, but it also must be able to hold at least 2 * 47.09 = 94.17 liters so that it doesn’t explode before reaching the surface.

These problems may seem confusing at first, but are easy after working through a couple. Even if you never find a use for them in real life, they are required for most divemaster-level examinations.

1. Modern science prefers the more descriptive term relative density over specific gravity, but many textbooks (including diving references) still use specific gravity, so we use it here.

Last weekend we were in a local dive shop killing some time. We saw some fabric paint for sale that was meant for writing your name on gear, or drawing pretty pictures, who knows. How much? 8 bucks.

Looking closer, we saw that the label, which said something like, “Scuba Dive Gear Paint”, was actually affixed on top of another manufacturer’s label. My girlfriend, Maritza, pointed out the manufacturer, telling me they sold that brand in Michael’s, the arts and crafts store.

Later that day we happened to pass by a Michael’s, so we stopped in. Sure enough, we saw the exact same bottles of paint. Cost? One dollar.

If you’re looking to mark up your gear, don’t buy “specialized” paint from a dive shop. Go to an arts & crafts store for the same stuff. Here is the kind of fabric paint we bought.

This week we have yet another standard resident of the reef, the soldierfish. Soldierfish are in the squirrelfish family, so you may hear them referred to as such, but they actually are a little more specific.

Physical description

As a member of the squirrelfish family, soldierfish also have red bodies. As you might expect, though, this tends to fade out with depth, yet the fish should still be recognizable. They are nocturnal, and thus have large eyes for seeing in low light. They usually grow to 6-14 in (15-35 cm) in length.

Soldierfish have a forked caudal fin. They also have an easily visible, long anal fin, with a nearly-identical adipose fin (between the dorsal and tail fin). You usually see soldierfish with a rayed dorsal fin. The dorsal fin lays almost flat until the fish becomes defensive.

There are many species of soldierfish, some named after physical characteristics, such as the blackbar soldierfish, whitetip soldierfish, and the bigscale soldierfish. They can sometimes be distinguished from ordinary squirrelfish by their “spikey” dorsal fin (although I believe a few species of squirrelfish have this). Squirrelfish also usually have a more distinctively tapered snout.

Geography and Habitat

Soldierfish are found in all tropical regions of the Atlantic, Pacific, and Indian oceans, at depths ranging from shallows to well past recreational limits.

Being nocturnal, they are most often found under ledges and in small “caves” during the daytime. Sometimes you will see them alone, and sometimes with a group of other squirrelfish. They can be highly territorial, raising their dorsal fin if you approach their crevice in a reef.

Further reading

Saltwater fish
Aquarium of the Pacific

Disclaimer: Do not attempt to dive with enriched air unless you have completed the appropriate speciality course. Doing so without complete training can be very dangerous.

Enriched air can mean any gas blend other than the standard 21% oxygen / 79% nitrogen that comprises what we call “air.” For our purposes in this article, enriched air will refer to a blend of oxygen and nitrogen in which the oxygen content has been raised, more commonly called “Nitrox” (or EANx, Enriched Air Nitrox). We won’t be concerned with Tri-mixes and the like—usually the domain of tech diving.

Nitrox blends increase the oxygen content of a cylinder, which simultaneously lowers the nitrogen content. This is usually accomplished by partially filling a cylinder with air (21% oxygen / 79% nitrogen), then “topping it off” with pure, 100% oxygen. Some basic math tells us the final oxygen content.

For example, imagine we fill a cylinder to 2500 PSI with air, then fill to 3000 PSI with pure oxygen. What is the final oxygen content? 500 PSI (3000 PSI – 2500 PSI) is 100% oxygen, while 21% of 2500 PSI is also pure oxygen. 2500 PSI * 0.21 = 525 PSI. Add the two together to get 500 PSI + 525 PSI = 1025 PSI oxygen. Divide by the total contents of the cylinder to get the percentage of pure oxygen, 1025 / 3000 = 0.3416 = 34.16% oxygen. That means the remaining 65.84% must be nitrogen (ignoring trace amounts of other gases in the air). We call our blend is EANx35, Enriched Air Nitrox 35 (you round up with enriched air blends).

Why enriched air?

What advantages does Nitrox provide divers? Nitrox reduces exposure to nitrogen compared to diving with air. Nitrogen is known to instigate Decompression Sickness (DCS), so less exposure is always good.

Divers take advantage of this benefit in two ways. Bottom times provided by dive tables and computers are controlled by estimates of nitrogen exposure. Less exposure means more bottom time. So the maximum bottom time on a Nitrox dive to a given depth is always higher than the maximum bottom time of an air dive to the same depth. My dive table says that an air dive to 60 ft (18 m) has a maximum bottom time of 47 minutes. The same dive on EANx32 has a maximum bottom time of 77 minutes, half an hour longer!

Not everyone wishes to dive for an hour and a half, however. The other advantage, then, is that with two identical dive profiles, one with air and one with Nitrox, the Nitrox dive will have a higher buffer of nitrogen exposure, significantly decreasing any risk of DCS. This isn’t a big deal for any one dive, but for many consecutive multi-day dives, where DCS causes are less understood, this buffer becomes important. The benefit of Nitrox also decreases required surface intervals, allowing a diver to easily fit four dives in a day.

What’s the catch?

Diving with Nitrox introduces a few more variables to track. For one, you must always check your cylinder for what percentage Nitrox it contains. The blender uses the above calculations, but any errors can affect your diving in a bad way, so for safety it is not only recommended, but required that the diver personally check their enriched air before every dive. Shops will have the appropriate equipment for doing so. I would refuse to dive with an enriched air mix I have not personally checked.

Fortunately, most dive computers come equipped for enriched air, making it straight-forward to dive with Nitrox. However, Nitrox requires modified dive tables, due to different exposures. Shops sell tables for common mixes such as EANx32 and EANx36, and your Nitrox specialty course may even come with them. The most versatile method is using something called Equivalent Air Depth (EAD).

Equivalent Air Depth calculations tell you, given a specific Nitrox blend, at what depth you would have to dive with air to get the same nitrogen exposure. With this depth, you can use normal dive tables to plan dives. Since Nitrox contains less nitrogen, this depth is always less than the actual dive depth. We can compute EAD as

EAD = (1 – O%) * (D + 10) / 0.79 – 10,

where O% is the percentage of oxygen, and D is the depth of the dive, in meters. Suppose we are planning a dive to 60 ft (18 m) with EANx34 and don’t have an appropriate table. We compute our EAD as (1 – 0.34) * (18 + 10) / 0.79 – 10 = 13.39 m, or 45 ft. We then use our ordinary dive tables, entering 45 ft (or 13.39 m) as the dive depth. This gives me a 63 minute bottom time.

Oxygen exposure

Diving with air within recreational limits, oxygen exposure never reaches critical limits—our body is always able to metabolize the available oxygen. However, with Nitrox oxygen content is increased to amounts that could be dangerous.

For instance, it is known that exposure to oxygen partial pressure beyond 1.6 can be fatal. Oxygen partial pressure is the portion of pressure due to oxygen at a given depth. Air at 1 atm has an oxygen partial pressure of 0.21 * 1 = 0.21. At 2 atm it’s 0.21 * 2 = 0.42. With this knowledge, we can calculate a maximum allowable depth on any gas blend. For air, this maximum is 1.6 / 0.21 = 7.619 atm, which corresponds to a depth of about 66 m (215 ft). In practice, it is recommended (and wise) to use 1.4 as the maximum oxygen partial pressure, to build in a safety buffer. For air then, we wouldn’t want to exceed a depth of 1.4 / 0.21 = 6.6 atm, or 56 m (185 ft). I’m guessing that won’t be a problem for most of you.

We can repeat these calculations for our Nitrox blends. Given EANx36, the maximum depth is 1.4 / 0.36 = 3.8 atm, or 28 m (93 ft), which is above the recreational limits! Keep this in mind for high oxygen content blends. What is the maximum allowable depth for EANx40 (the highest oxygen content permitted with most certifications)?¹

This is a maximum partial pressure in a single dive, but over multiple dives, your body accumulates excess oxygen that it can’t burn. Given enough time this oxygen can become toxic. Therefore, you must also track accumulation of oxygen over a running 24 hour period. You will learn how to do this and be given the appropriate tables in your Enriched Air Diver specialty course.

If these advantages sound appealing to you, I highly recommend completing your Enriched Air specialty. Most regular divers will do it at some point. Don’t let the calculations and variables deter you; they become easier over time. Again, let me reiterate that you should not dive with Nitrox unless you have completed such a course. It can be done in an evening, with no dives required (at least with PADI).

1. 82.5 ft (25 m)

I wouldn’t normally write about something like this, but People magazine reports that Tiger Woods is building a 61-foot luxury diving boat. It’s well-known that Woods is a NAUI divemaster, and that he and his wife-for-now Elin are avid divers.

I’m guessing this is a me-so-sorry gift for being a sleezebag (taking a page out of Kobe Bryant’s playbook). The boat, appropriately named Solitude, is supposed to provide some much-needed family time. I’m sure that plan will work out great. Have fun on your new boat, Tiger.