As a diver, it’s all about staying underwater as long as possible, so as to enjoy everything there is to see. It’s also why we return time and time again; after all, you can only stay so long! Extending our time underwater to see and enjoy as much as possible has been the goal of divers since the beginning of underwater exploration, and it's still true today.
There are several factors that determine how long you can stay underwater at any given depth without going into a decompression. After all, as recreational divers avoiding going into decompression on a dive is paramount. Aside from factors such as nitrogen and oxygen loading, depth and time limitations, whether your breathing air or enriched air (nitrox), factors that determine a divers bottom time can include cylinder capacity, lung capacity, rate of breathing, energy being exerted, proper weighting, being streamline, currents and water temperature to name a few. This means there are some things you can teach your students that can help them improve their bottom time.
In this article, we'll look at Proper weighting, cylinder size and capacity, streamlining yourself, breath control, energy conservation, efficient fin kicks (good swimming techniques) and thermal protection as ways a diver can improve their air consumption to increase bottom time.
I’ve seen many instructors talk about proper weighting but very few actually teach and assist student divers with proper weighting. All too often, for many instructors, proper weighting means weighing students down with too much weight to ensure they get down and stay down during training! Believe me, spending a little extra time properly weighting their students by distributing the weight over the student divers entire body goes a long way in ensuring they are both safe and efficient. Remember, you want them to have fun in your class. You need to go beyond the general rule of thumb when teaching students about weighting. During your confined/confined open water training, use ankle weights and various clip on weights to distribute weight over their entire body to demonstrate how proper placement of the weights, in addition to using the appropriate amount of weight, will not only help them get down and stay down, but will help them be more streamlined in the water without being over weight. With integrated BCD’s, don't just jam all of the weight into the pockets/pouches. Just because the BCD is weight integrated doesn't mean you cannot incorporate other types of weight systems to ensure proper weighting.
Here in Southern California the water is considered "temperate." Most people dive in 7mm wetsuits with hoods or they dive dry to stay warm. To dive comfortably, many use ankle weights, especially the dry suit divers. However, ankle weights are not limited to use by divers using around their ankles. Be creative. You can use ankle weights to help distribute the weight more evenly by placing them around the tank neck, through the chest strap, etc.
Breathing efficiently underwater is one of the main keys to maximizing bottom time. The key is to get your students relaxed enough to slow their breathing rate down as much as possible, avoiding holding their breaths. I liken it to being so relaxed you almost begin to fall asleep. I remind my students and instructor candidates that diving is an activity that's more of an adventure, something to be enjoyed and savored for as long as possible. Slow deep breaths with an emphasis on exhaling completely will help slow their breathing rates down. To help students with their breathing, I will ask them to time themselves using their watch. How long does it take to inhale a full breath vs. exhaling it. I tell them it should take almost twice as long to exhale while diving. This really helps students to slow their breathing rates down.
Another very important consideration is their fin kicks. The emphasis is not on what fin kick they use, i.e. traditional kick, dolphin kick or frog kick but rather on efficiency and proper technique. We’ve all seen the “bicycle kick.” Slow deliberate kicks using the proper technique or kick stroke, is the key to efficient fin kicks. Keep in mind that energy conservation is also very important. I instruct my students to glide through the water using as few kicks as possible. To further emphasize the benefits of moving less and gliding more, I remind students that an added benefit of more gliding and less kicking is being able to see more sea life by moving more gracefully like "fish."
Streamlining yourself in the water helps to slow air consumption and maximize bottom time. The more streamline you can be in the water, the easier you can move through the water and the less energy you have to expend getting from one place to the next.
Another consideration is cylinder size and capacity. When considering a cylinder you'll want to balance all of these factors in order to help them make the best choice. We know that steel tanks are heavier than aluminum and tend to be smaller/shorter while holding the same amount of air as an aluminum cylinder of equal capacity. With that, depending on which type of cylinder they select they'll need to factor their weight system into the equation as well as their own height.
Lastly, thermal protection can affect bottom time too. A diver that is too cold can have the tendency to use more air than a warmer diver as the body works harder to keep the vital organs warm. As the body starts to shiver it can also cause the diver to breath very shallow and rapidly which leads to faster air consumption. Ensure the proper amount of thermal protection to maximize their bottom time and to minimize potential safety issues.
As you discuss all these factors with your students ensure they see and understand the important relationship each one has on the other. The equipment they use should make diving more comfortable and safe, not just possible. Doing so makes for a richer course for your students and greater satisfaction for you as an educator.
