It can take a while to get used to hearing sound underwater. You are constantly receiving visual input through an entire dive, so your brain learns to compensate for refraction and other visual properties of water. However, audible input is not constant, so each time a boat drives by it catches you by surprise. What makes sound different underwater?

The largest difference is speed. At the surface, sound travels at about 340 m/s. In sea water that increases to about 1500 m/s, over four times faster! You constantly use the speed of sound to distinguish the audible world around you; your brain is unable to cope with this drastic increase, and thus noises sound like they are coming from all over.

With the relatively slow speed of sound in air, your brain uses the distance between your ears to pinpoint the sound’s origin (through a process called triangulation). For example, let’s say you hear a sound immediately to your left. The sound will reach your left ear before your right. If your ears are a distance of 8 inches = 0.2032 meters apart, we can determine the time difference as t = 0.2032 m / (340 m/s) = 0.000597 s. Small, yes, but large enough for your brain to detect. If the sound reaches your ears at the same time, then the sound is coming from directly in front, above, or behind you (ignoring sound waves bouncing off walls). Visual input fills in the missing blanks to pinpoint the sound’s origin.

Now let’s repeat the same calculation underwater. The time differential from a sound immediately to your left is t = 0.2032 m / (1500 m / s) = 0.000135 s; below the threshold your brain can distinguish. Combine this with no visual input directly in front of you, and your brain just assumes that all sound is coming from directly on top of you. Humans don’t like loud noises (such as those from boat engines) from directly above, so this tends to trigger fear reflexes.

Sound bounces off walls and objects, further aiding your brain in the triangulation process. The ocean is a much wider expanse in which sound travels freely, further altering your underwater perception.

This time we discussed how the location of sound underwater is perceived. Next time we’ll look at how the actual sound is altered.

Previous posts have discussed the importance of proper buoyancy. Here I describe how to do a simple weight check in the water.

1. Initial weight

   If you don’t know where to begin, take about 10% of your body weight. If diving in tropical waters with a thin wetsuit, subtract 4-6 pounds; if diving in cold water with lots of exposure protection, add 4-6. This will give you a starting weight to tweak.

2. Enter the water

   Begin at the water surface with full diving equipment and an inflated BCD.

3. Hold a normal breath and deflate your BCD

   At this point you should find out if you are properly weighted. If you sink, you are overweighted, if you bob out of the water, you are underweighted. An ideal weight will keep you approximately eye-level.

4. Repeat

   Based on feedback from the previous step, adjust your weight accordingly and repeat until you float at eye-level.

5. Compensate for your cylinder

   If you are doing this check with a full cylinder, you should add about 4 pounds to compensate for the end-of-dive when the cylinder will be more buoyant. Trust me, it won’t be fun kicking to stay underwater during the safety stop.

That’s it! Once you have a proper weight, note it in your dive log to save time in similar diving environments with the same exposure protection.

PADI training dictates it is acceptable to share your primary second stage or your octopus with a buddy in need of air.

It is a good idea to work this out with your buddy ahead of time. Should the need arise, it could lead to an awkward underwater shuffle if a buddy needs air and doesn’t know which to take. This frustration may lead to panic–a bad situation for everyone.

So take a quick second and decide which second stage is for sharing.

Some regulators come with adjustable second stages. This is usually in the form of a knob to rotate or a lever to slide. First of all, this serves two purposes:

1. It allows you to adjust the sensitivity of the air flow, making it harder to free flow. If you are in a strong current at the surface, for example, your second stage might normally be inclined to free flow.
2. As the service date approaches, the performance of regulators decreases slightly. This may mean it requires more energy to pull air from the second stage. An adjustable second stage allows you to “open it up” during this time, maintaining a steady performance.

You may be tempted to use the adjustment knob to limit air flow in an attempt to save air. This is a bad idea.

First of all, it won’t even work. If it requires more energy to breath, you are going to end up needing more air than you would otherwise. Secondly, limiting your supply of oxygen is always a bad idea.

To use an adjustment to extend your air supply, do just the opposite. Open it up so that air is supplied to you with minimal effort.

Note: This post applies only to males.

I always see male divers wearing bathing suits or board shorts under their wetsuits. This requires awkwardly stuffing all the excess fabric into the wetsuit legs, and not to mention, the suit tends to ride up. I did it once for my Open Water certification and hated it.

There are options, however. Even if you would never wear it otherwise, I highly recommend wearing some kind of form-fitting lycra swim material. This doesn’t have to be the legendary Speedo briefs; I wear something similar to these Speedo jammers and think they’re great. You can also get the square shorts for something smaller than the knee-length jammers, but with more coverage than briefs.

I went to a local dive store this morning and picked up one of these neoprene mask strap covers. As soon as I got home I put it on my mask. Sitting in my kitchen with bone dry hair the mask slipped on and off painlessly.

This should prove incredibly useful, especially as I begin my divemaster training, where I will constantly be removing and replacing my mask. I wish I had bought one when I originally purchased my mask. I couldn’t find a plain one with no words or pictures, so instead put it on my mask backwards where all you see is plain black.

Anyways, I highly recommend picking one up. It’s an incredibly inexpensive way to increase your comfort level.

One of the first purchases I made after becoming Open Water certified was a point and shoot camera (Canon PowerShot SD1100IS) and an underwater housing. I enjoy taking pictures in “real life” and wanted that to carry over into diving. A lot of my pictures really sucked, though, and I wanted to get better. Unfortunately I found a lot of the information on the web is for expensive SLR cameras, with tips pertaining to things like aperture settings and strobe placement–not things relevant to my little cheapo. As a result it’s taken me a while to figure out some of the basic do’s and don’t. Here’s some of the things I’ve picked up that I hope save you some time.

1. Under water is the same as above water, mostly

   Things pertaining to framing, composition, lighting, and so on apply equally well underwater. Particularly that you should be taking LOTS of pictures. Memory is cheap, so load up.

2. Learn your camera

   Even my simple camera has tons of features that I could easily never find. Go to your camera’s manufacturer’s website and download the manual. Browse the table of contents for anything of interest. Keep an eye out for things like “scenes” or “modes”. For instance, my camera has an underwater setting that compensates for the strong blue tint everything has. Bingo!

3. Don’t use digital zoom

   It looks like crap above water, and it looks like crap under water. I know that stingray is swimming away too fast to catch, but digital zoom isn’t going to do much to capture the moment.

4. Learn to use the macro mode

   The manual should tell you how to activate macro mode, and also when it should be used. For my camera, that’s when the object of interest is between 1.2in and 12in away from the lens. For everything else, use the normal, or “infinity”, mode.

5. Use the flash when appropriate

   When you are taking a picture of something less than about 3ft / 1m away, use the flash to put some color in your photo. Your underwater housing probably came with a flash diffuser, make sure that’s connected.

6. Don’t use the flash when inappropriate

   If your fish is farther than about 3ft / 1m away, don’t bother with the flash. It will only cause backscatter, which is where light reflects off all the floating particles in the water. Even water with 100ft visibility will have it.

7. Get fast with your camera

   Part of learning your camera is getting fast with it. You will most likely not keep your camera in macro mode the whole dive, nor want the flash off the entire time. Learn to turn these features on and off quickly.

   At the beginning or before the dive, figure out what you want your “home” settings to be: those that the majority of your pictures will be taken under. This can be based on the environment of your dive or just past experience with the pictures you usually take. From my experience I can tell you this should probably be flash on with camera in macro mode, but it can vary with the type of dive.

8. Be liberal with video

   Video mode on point and shoot cameras is a godsend for diving, and it doesn’t take up nearly as much memory as you might imagine. It only uses about 1MB / 1 second, so keep rolling! Practice keeping a steady hand, cause trust me, your exciting footage will look terrible later on your computer where shakiness becomes painful to watch.

These are just a handful of tips for getting started. As I learn more, I will share what I learn here, including more technical details, possibly using pictures I take as case studies.

Is there anything you wish you had been told when you first started with underwater photography?

Communication underwater can be a problem, and is usually restricted to a small set of hand signals. It can be even more challenging to get the attention of your dive buddy, however. It happens to me all the time, I see something really cool, but my dive buddy is looking in the completely opposite direction. Unless I’m within reach, I have no way to get their attention. This articles addresses presents our options for making noise underwater.

Commercial options

Many stores would be glad to sell you a remedy. Here are a few common choices:

• Shaker / Rattle

  

  Probably the most well-known option, many dive instructors carry one of these clipped to their BCD. Most are pretty solid and make a clear sound that can be heard from a moderate distance. Expect to spend about $15 USD.

• Horn

  

  These devices usually connect between your low pressure hose and your BCD, using the air from your cylinder to make noise. I imagine you can hear these from pretty far, even on the surface. They are not cheap, however, and run around $60 USD.

• Tank banger

  

  A pretty rudimentary device, the tank banger is some sort of hard material on an elastic band. You wrap it around your cylinder, and snap the hard plastic / metal against your tank to make noise. I find these a good solution, especially since they are the cheapest of the commercial alternatives, running around $5-10 USD. I’ve heard complaints that they can break easily, and are sometimes hard to use when the band is still new and stiff.

Homemade options

The commercial options technically resolve the issue, but can be expensive when you consider the likelihood of leaving it on your rental BCD or cylinder. Here are some options you can whip together at home, and that are cheap enough where losing it doesn’t matter.

• Shaker / Rattle

  

  At its core, this is identical to the commercial shaker, comprised of some hard metal inside an airtight canister. Old camera film canisters are a popular choice, but are becoming harder to find. A medicine bottle is another option. For the metal, anything from BB’s to a simple nut will suffice. Not all canisters will have a way to easily connect it with a BCD, so you may have to improvise, or keep the shaker in your pocket.

• Ring

  

  This is a great solution, since it doesn’t require clipping anything to equipment. A metal band is a great noisemaker underwater when banged against your tank. You don’t have to get married to use this one, since any metallic band will do. The noise is softer than the other options, which I like because it only catches the attention of those within your vicinity.

• Tank banger

  

  Here’s something we put together the night before a dive in Mexico. It’s a hairband with a keychain clipped on it. Buy a pack of hairbands and a pack of keychains to keep with your dive gear and you have the makings for a number of noisemakers, without worrying about losing one. Like the ring, these make a softer noise that I prefer.

Whatever solution you go with, be courteous to other dives. Use it sparingly so you don’t annoy everything else diving, including your dive buddy. Check with the divemaster in case she also has one, and that she doesn’t have a problem with yours. And lastly, when in the water, do a quick test so that your buddy learns your “call”, especially if there are multiple noisemakers in the water.