An extremely common question I see is whether or not certain gear (mainly regulators) can operate with enriched air / Nitrox. Many manufacturers even claim in their manual that Nitrox is not supported.

It is commonly accepted amongst scuba diving professionals that mixes with less than 40% oxygen are treated as air (with respect to equipment). Enriched air specialties only qualify you to use up to 40%. This means your “air-only” regulator is perfectly fine with any recreational Nitrox mix. No special assemblies or upgrades required, and your tank will not explode on your back underwater.

Interestingly, the flip side of the above “rule” is that any mixes with more than 40% oxygen are treated as pure oxygen.

Last week we looked at how to choose a wetsuit. Today we’ll cover guidelines for choosing weights. These numbers aren’t set in stone, but should act as a general guide to start your proper buoyancy check. This is the first step towards perfect buoyancy control.

Naturally, if you are leaner or, um, less leaner you should adjust accordingly.

Women should add 4-5 lbs (about 2 kg) if diving in salt water, or subtract 4-5 lbs (about 2 kg) if diving in fresh water. Men should add 6-7 lbs (about 3 kg) if diving in salt water, or subtract 6-7 lbs (about 3 kg) if diving in fresh water.

I’ve also heard an additional 5 lbs / 2 kg recommended if diving with an aluminum cylinder, due to how buoyant they become when near empty.

Sand divers are an interesting fish. While they can be thought of as a reef fish, you are more likely to see them beside the reef than actually on it.

Physical description

Sand divers are in the lizardfish family and share most of the same characteristics. They have longer, cylindrical shaped bodies. They range in size from 4 – 14 in (10 – 35 cm), although you may occasionally see a larger one.

Their heads resemble that of a lizard, with a wide mouth and prominent eyes. They have a fanned dorsal fin on the middle of their back, and two pectoral fins that usually are on the sea bottom so that they almost look like little legs.

Sand diver bodies have a white / tan base that resembles sand, with dark splotches all over their body that look like ink-blotted rings. This is, no doubt, to hide them in the sand from predators.

Geography and habitat

Sand divers live in tropical and sub-tropical waters across the world.

Sand divers are bottom-dwelling fish. You will usually find them in sand patches that neighbor reefs, often underneath or near a rock or coral for pretection from their rear.

It’s hard to decide what exposure suit to wear. Here’s a guide to help in the process, which I’ll walk you through using.

To begin, find out the temperature range for the water you’ll be diving in. Let’s pretend I’ll be diving in water that is 72-75 degrees fahrenheit. Next, we’ll modify this range based on several factors:

• Depth – Deeper water tends to be colder, so if this is a deep dive (around 30m / 100 ft), consider subtracting about 5 degrees from your temperature range. In my example, I’ll be diving normal depths around 20m / 60ft, so the range remains 72-75F.
• Duration – What’s your air consumption like? If you tend to dive for over 45 minutes, subtract 5 degrees from the range. My dives will be around 45 minutes, so again, no change.
• Number of dives – Repetitive, multi-day diving needs to be taken into account. If you will be doing this kind of diving, subtract another 5 degrees. Let’s say I’m diving for a week, so my range now becomes 67-70F.
• Female – Women generally get colder than men, so if you’re female, subtract 5 degrees. I’m a man, so no change needed.
• Personal experience – What kind of diving are you used to? Does cold water not bother you much? Depending on your answer, choose a number from near the bottom or top of the range you currently have. I tolerate cold decently, but by no means am I in the Polar Bear Club. Based on personal preference, I’ll use the middle temperature, 70F.

You now have a temperature (in the example, 70F). Plug this into the following table to get a recommended exposure suit. If you find yourself where two ranges meet and aren’t sure what to do, err on the side of too much exposure suit.

Click to enlarge

For our example temperature of 70F, I have the option of a 5mm fullsuit, a 7mm fullsuit, or a 7mm fullsuit with hood. I’ll be diving quite a bit, so I’ll be cautious and dive with a nice, thick 7mm wetsuit. Just for safe measure, I’ll pack a hood in case I get cold later in the week.

A Sydney newspaper reports that certain marine areas are overcrowded with scuba divers. These complaints come mainly from swimmers and anglers. The fishermen, in particular, are upset that divers scare off the catch of the day.

Sounds like its time for a sit-down to establish proper etiquette between the competing groups.

Visibility is one of the most subjective aspects of diving. Ask 10 people after a dive what they think the visibility was, and you’ll get 9 different answers. The last person will spend a half hour trying to guess.

Defining

People generally suck at estimating visibility (“viz”). Why is that? I think it comes down to a lack of common definition. I will attempt to define visibility in concrete terms.

The best place to start for this sort of thing is the dictionary. Webster’s defines visibility as

The distance at which something can be seen.

We’re getting closer, but what exactly is the “something” to be seen? I’ve heard a few options: the distance at which hand signals are no longer recognizable, the distance you can’t see a diver’s bubbles, and the distance at which you can’t distinguish an object. The first might be too strict for general use, but the last two start to get the point. Let’s define visibility as the distance at which an object cannot be discerned. The point at which you can’t tell for sure if that is a diver in the distance is the extent of the visibility.

Measuring

That was the easy part, now comes the hard part. How do we measure viz? Believe it or not, there is an established manner. It requires something called a Secchi disk. The disc is attached to a line and gradually moved from the measurer. The distance where the disk cannot be seen is recorded, with the length of the line being the visibility. Even more advanced methods with higher precision exist using photometers.

That’s nice for Jacques Cousteau, but not for Joe Diver who doesn’t have a Secchi disk on hand.

First of all, don’t feel bad. Viz is hard to guesstimate, but gets easier with experience. Even then, in general a range is a better indicator for estimating viz rather than a hard, fixed number. Try to get the lower end where things get blurry and the upper end where things can no longer be seen. As you get better with distances, this range will get smaller and the “true” viz will probably lie somewhere in between.

One rule with measuring viz for scuba: it measures horizontal distance. Vertical distance can be deceiving, as light from the surface increases visibility. However, it can be useful both for an upper bound on your range (vertical viz will always be higher than horizontal) and for estimating distances, since you always know your depth. Some, as a rule of thumb, define the viz as the vertical visibility (the depth where you can no longer see the surface) minus 3 m / 10 ft. Probably a good guideline, but useless in most of the tropics, where the viz always exceeds the dive depth.

Try to use anything you have to your advantage. Length of a wreck, for instance. You can find this out easily and use it to gauge distances more accurately.

Utilizing

I’ll let you in on a secret: it doesn’t really matter. Viz is cool for bragging (“We could easily see over 100 meters!”), but there aren’t too many practical reasons where an accurate number is necessary. There are exceptions, however. For instance, a photographer probably cares more so than others, since the equipment they take can depend on these numbers.

In general, ranges are fine, and even broad descriptions sufficing as well. A scale that goes something like amazing -> great -> good -> ok -> where’s my buddy? -> I can’t see my hand, is descriptive and covers most situations. Make an educated guess, compare to the guesses of others to refine your estimation abilities, but don’t get too hung up on the ever-elusive viz.

I’m going back to Bonaire in a few weeks to complete my PADI divemaster training. Along with all my gear, one thing I’ll be taking is the book Bonaire Shore Diving Made Easy (BSDME).

BSDME is a small book describing 75 dive sites in Bonaire. Officially, there are 63 dive sites in Bonaire (not counting Klein), so the book more than adequately covers most diving spots. In particular, it shares the easiest entry and exit points. This can be a huge time saver for shore dives, where rocks and waves make entry and exit challenging.

BSDME also gives a brief description of the dive site, including slopes and formations that are helpful for planning dives. Sometimes it will indicate what type of marine life to expect on a particular site, and where to look for it. There are no pictures in BSDME, if that’s what you are expecting. This page on the book’s website gives a sample for the Andrea II dive site. Expect 75 of those, nothing more, nothing less.

73, actually. As of 2009, the Town Pier and Salt Pier sites were closed to the public after structural damage from Hurricane Omar. The 5th edition of BSDME still has these sites listed, so they may be removed from future editions.

Most dive shops in Bonaire have a copy of this book lying around for customer perusal. However, I recommend picking up your own copy to keep with you. It’s fairly inexpensive, and is a handy reference for dive planning the night before, and especially while at dive sites when on-the-fly adjustments are required.