Last week we talked about DEMA, the Diving Equipment and Marketing Association. We used the data they collected to answer the question “how many divers are there?” This week they’ve launched a new site to report on diving conditions in the gulf. It’s called www.GulfStateDiving.com. It may be a good site to bookmark for future reference.

DivePhotoGuide gives an awesome little rundown of the blue ring octopus. This creature is less than 7cm long, tip to tip, yet packs enough venom to kill 28 adult humans!

Natalie over at about.com’s scuba diving blog warns of the perils of being a Christmas tree diver. A Christmas tree diver is someone who has so many accessories and buckles that they look like a Christmas tree.

Noreen at Aquaviews has a two-part article on the 10 coolest places in the world to take a dip (Part 2).

A treasure hunter scuba diver found a lost engagement ring in a lake under 3 inches of sand—after a three year day search. I hate to ask what his hourly pay worked out to with a $750 reward spread over three years. Update: thanks to Lee for pointing out the mistake!

In recent news, Guam has passed proposed a bill banning scuba spearfishing on the island. Needless to say, many locals are upset.

The argument is that scuba spearfishing is not sustainable and that this ban will allow the fish populations to replenish. Spearfishing with scuba gear allows fishermen to remain underwater longer and thus catch more fish than breath-hold spearfishing.

I’m not the biggest fan of spearfishing, and prefer not to dive with anybody who is spearfishing. Nevertheless, I find a bill like this a little surprising given the nature of island nations like Guam.

If you’re planning a trip to Guam in the future, keep an eye out in the future for whether or not you should leave your speargun at home.

Traditional dive planning, the kind you learn as a beginning diver, has you following tables rather than using a dive computer. Even if you use a computer now, it’s a good idea to pre-plan your dives using tables to give yourself plenty of buffer and avoid decompression sickness.

That’s understandable, but the discrepancy between a square profile from a table and a dive computer can be quite large, costing you precious bottom time. One solution to give yourself more bottom time in the pre-planning stage is to use multilevel dive planning.

The problem

When dive planning with a table, you give it your depth, and it tells you how long you can spend at that depth. The problem with this is that it conservatively assumes you spent the entire dive at that depth, when in fact that’s never how it goes. You end up with a theoretical profile that looks like this:

Your dive times are limited based on this square profile.

A dive computer, on the other hand, constantly samples your depth to give you a very accurate profile:

This increased accuracy pays off in the form of more bottom time, while still staying within conservative limits. The table profile assumes you are at one depth for the entire dive, which is rarely the case. Multilevel dives strike a balance, although they err more towards the square profile side.

Multilevel dives

Multilevel dives assume more than one depth for the duration of a dive. However, it doesn’t give as accurate a profile as a dive computer. Instead, we get something in between:

For example, imagine we are diving to 70 feet (22 meters). Using my standard table, this gives me a maximum of 40 minutes of bottom time.

The problem is, I know I won’t spend all 40 minutes at 70 feet, and because my air will last longer, I’ll have to cut my dive short because of my limiting dive table. What I will actually do is begin my dive at the bottom of the reef, then gradually come shallower. In fact, I’ll plan on spending the first 20 minutes at 70 feet, then the rest of my dive at 35 feet (7 meters).

With this in mind, my total bottom time goes from a meager 40 minutes to practically unlimited. Once I move up to 35 feet, I can spend over 200 minutes at that depth! That’s more than enough for my air supply.

As another example, let’s say I want to dive to 90 feet (30 m). My maximum bottom time at that depth is 25 minutes. Let’s say I spend 21 minutes there and want to move up to 60 feet. Instead of ending my dive, I can spend 22 minutes at 60 feet, doubling my total bottom time.

The multi in multilevel

It gets even better. Nothing says you have to limit yourself to a two-level dive. You could even do a three level dive. While theoretically there’s nothing stopping you from a 4, 5, or 6 level dive, it can get a bit tedious at that point. Not in the planning stage, but when actually executing your dive.

The catch

The one catch is you need to actually follow your planned profile. This means keeping an eye on your dive timer and depth gauge, moving to the next level at the appropriate time. This becomes especially important when diving multiple times in a single day.

Should you miss one of your levels, take note of how long you were at each depth and modify your profile back on the surface. This way, you have an accurate measure for planning more dives.

Equipment

Obviously, you’ll need a watch (timer) of some sort and a depth gauge, so you know when to change depth. You’ll also need a planning table appropriate for multilevel dives.

Ordinary tables are not designed for multilevel dives. Using them as such can push you over known limits for preventing decompression sickness.

PADI used to use The Wheel, but have discontinued it. They now use the eRDPML (electronic Recreational Dive Planner, Multi Level). Other organizations have similar devices. Contact your local dive shop for more info on what you need.

Unfortunately, I can’t describe the process without knowing what you are planning with. Nonetheless, planning is simple with just about all devices, especially with instructions right in front of you.

Dive computers

A lot of this information may seem largely irrelevant with a dive computer, and that’s partially true. With a dive computer, there is no need to painstakenly track your dive profile—the computer does it for you.

However, dive computers usually have a very limited dive planning. This is often restricted to allowing you set one depth and it tells you what your no decompression limit is. You may want more planning power.

While you can’t start using multilevel dive planning in between dives, you can use it at the beginning of the day to give you an idea of what your day will look like, including about how long your surface intervals should be. This can be useful for many things, including coordinating non-diving activities, meals, and more.

Specialty courses

Most agencies would be more than glad to offer you a multilevel dive planning specialty course. Let me say, though, it’s really not necessary. Purchase the required dive planning equipment and read the instructions. You should get a decent feel for how it works. If you are really not sure, or are scared of messing up, talk to a professional, and take a class if that’s what they recommend. Diving safe is the number one priority.

The humphead wrasse is also called the Maori wrasse, Napoleon wrasse, and even Napoleon fish. You can call yourself lucky if you run into one of these relatively rare fish underwater.

Physical description

Humphead wrasse are the largest members of the wrasse family, with males reaching over 6 feet (2 meters) and females over 3 feet (1 meter) in length.

It has two distinguishing characteristics. The first, of course, is the large hump on its head, above the eyes. This protrusion becomes more noticeable as the fish ages. The other characteristics is the fish’s thick, Charles Laughton lips. Angelina Jolie wishes she had lips like these!

Female humpheads and juveniles are a red-orange color on top, and red-orange to white on their bellies. Juveniles may also be a light green color. Males, however, range in color from bright blue and green to purple.

Despite the abnormalities, humpheads have a normal, albeit larger, shaped wrasse body. This includes the fanned caudal fin.

Geography and habitat

Humphead wrasse are found in coral reefs in the Indo-Pacific oceans.

Adults maintain an open habitat at pretty much all depths, while juveniles like to maintain their privacy in seagrass or inside of dense coral.

Conservation

Humphead wrasse are declared rare by the World Wildlife Foundation, and in many countries they are protected.

Further reading

Wikipedia
World Wildlife Foundation
Dive the World

Photos by Electric Images

On Tuesday we talked about underwater white balance, what it is and how you can do it. If you recall Step 2 of the process,

Point your camera at something you know is white and “take” a picture or press the appropriate button. The camera will record your settings.

This is potentially a problem. How many pure white objects are there in the ocean? Much less one that is a nice flat surface for setting white balance.

If you’re even semi-serious about getting good underwater pictures with your point-and-shoot, I recommend picking up a dive slate. Usually used for communicating via writing underwater, a dive slate makes for a nice flat, white surface perfect for manually setting white balance.

As a side bonus, slates are inexpensive. They often have a buckle or strap of some sort to attach to your BCD.

A dive slate is a useful gadget to have anyways, but becomes indispensable when you need to set white balance.

The other day I mentioned problems Internet Explorer 6 and 7 users were having viewing The Diving Blog. Namely, the sidebar was showing up at the bottom of the page.

I believe these issues have been remedied, but let me know if you’re still having problems.

Also, I still recommend upgrading your browser if you are using Internet Explorer 7 or older.

I hope everyone is surviving the summer (winter for you southern hemisphere folks). My weather widget reads triple digits right now, but I’m surviving.

Aquaviews highlights the Radisson Blue Hotel in Berlin, and their enormous indoor aquarium. Unfortunately, it doesn’t look like guests are allowed to dive it.

There’s a relatively new scuba forum at www.TheCyberDiver.com. If you’re looking for a place a little more inviting than the larger scuba forums out there, then click on over and get involved from the start. If you see me (username: dharmon), say “hello!”

Over at DivePhotoGuide, underwater photographer David Barrio walks us through the setup and technicals of his award-winning backlit shark embryo photo.

Despite what you might think from the last few weekly links, I’m fairly indifferent to household pets. Nevertheless, here’s a profile of a scuba diving dachschund. I never could even get my pets to poop where I wanted them to.

If you’re new to underwater photography, one thing you’ll quickly realize is that all of your pictures come out blue. If you want to know why, read my article on colors underwater.

Now that you know why, you want to know what you can do about it. Before you bought your camera, you looked at magazines and online photo galleries. None of those pictures have that blue haze.

To remedy this problem, you basically have two options: a strobe (flash) and adjusting white balance.

Underwater strobe / flash

Water (more specifically, stuff in water) absorbs frequencies of light the farther the light travels. Very quickly then, red light is absorbed, leaving everything a blue tint. One option is to then reintroduce white light, which contains all frequencies, into the environment.

If you’re taking a picture of a piece of coral at 10 meters, the light seen by your camera reflected off the coral has traveled over 10 meters, and will thus be dominantly blue, even if the camera is less than 1 meter away from the coral. By using a strobe, the camera will see not only the light that has traveled 10 meters, but the white light from the flash, which reintroduced the missing reds.

There are two downsides, however. First, the most common flash is the camera’s built-in flash. While fine for taking pictures of friends on land, underwater it tends to produce backscatter, where the light reflects off of particles in the water. The only way to prevent this with a built-in flash is to only use it up close (less than a meter).

Even if you manage to avoid backscatter, on-camera flash tends to be a bit harsh, giving you a fish equivalent of that “deer in headlights” look. An alternative is an external strobe which is attached by an adjustable arm. This lets you control the lighting more finely, both by arranging the direction (via the arm) and the strength to get a perfect exposure.

External strobes are expensive, but the vast majority of professional underwater photos you see used them. In the future we will look at them in more detail (as I learn more about them).

White balance

The other option available is by adjusting your camera’s white balance. You can adjust white balance two ways: on your camera and on your computer. However, you can only really adjust it on your computer if the picture was taken in an appropriate format (like RAW). This doesn’t apply for most point-and-shoot cameras. If you want to learn how to “cheat” white balancing on a computer, read my article on color balancing underwater pictures.

Most point-and-shoot cameras do support manual white balance, though. Check your camera’s documentation, but the process usually goes like this:

1. Set to manual white balance. Enter your camera’s system menus. You will probably find some settings for taking pictures indoors, on a sunny day, at night, etc. You are looking for anything that says “white balance” or maybe even “AWB” (automatic white balance). When you find it, you will want to change to manual.
2. Change the white balance. While still in the menu, you need to set the white balance. Point your camera at something you know is white and “take” a picture or press the appropriate button. The camera will record your settings.
3. Take your pictures. You can now take pictures as usual. Because light is absorbed differently at different depths, a white balance setting is only appropriate for around the depth it was set at. If you go deeper or shallower, you will need to repeat step 2.

Below I have side-by-side photos of the same coral with and without manual white balance.

The difference should be clear. Notice also how the after picture still isn’t quite perfect. While it’s much better, you may want to still touch up your pictures on the computer later.

What is white balance?

Cameras just record what they see, which is a bunch of colors (light). These colors are the result of some light source and how that light is absorbed and reflected. Above water, light is not usually absorbed significantly, but light source colors can vary. For instance, indoor fluorescent lighting can be a harsh white, or some lights can be orangey.

To account for this, cameras allow you to change the white balance. This redefines what the camera thinks of as white by allowing you to intervene with your knowledge. If you know a wall is white, but it appears yellow because of the room’s lighting, you can point your camera at it and “tell” it that “this is white”. The camera will then shift internally to account for this. If the camera were a person, it would say, “Aah, this wall looks yellow, but is actually white (my owner told me so). This means everything in the room is going to look a little yellow. I will compensate for this by removing yellows.”

Underwater, we are doing the same thing, except instead of compensating for off-colored light, we are adjusting for red light frequencies being absorbed. When we tell the camera that something is white that looks blue, the camera adjusts by removing blues.

I hope this helps your understanding of white balance. The best way to understand it is to play around with it. Get out your camera manual and play, even above water. If you don’t have your manual, look for it online at your camera manufacturer’s website. Try silly things, like pointing to a blue wall and setting manual white balance. What does is do to your pictures? Think about what it will do first, then try it and see if you were right.