As divers who have perfected their buoyancy know, finally getting it right is a watershed moment that opens the door to true freedom underwater.
Good buoyancy is the key to getting the most out of your underwater experiences, from protecting the underwater environment and maximizing efficiency and air consumption, to taking good quality photos and video. Most importantly, good buoyancy control is essential to diver safety. Poor buoyancy control and improper weighting are major contributing factors to a significant percentage of diving accidents. According to the Diver’s Alert Network (DAN), 45 percent of the victims in 100 diving fatalities that occurred in Australia and New Zealand between 1980 and 1987 were over-weighted. Six primary factors affect buoyancy: the amount of lead a diver wears, the amount of inflation in their BCD, their trim, exposure suit, depth and breath control. With so many factors to consider, buoyancy can take new divers a long time to perfect. To help, here are a few basic tips that can make mastering this essential skill little easier.
1. Understand Boyle’s Law
Several laws of physics pertain to diving. One of the most important is Boyle’s Law, which states that when you multiply the pressure surrounding a gas by the volume of the gas, the resulting number will always be the same. Put simply, this means that when the surrounding pressure increases, the volume of the gas decreases and vice versa. When applied to buoyancy, this law means that the volume of air in our BCD, exposure suit, cylinder or lungs decreases as we descend and water pressure increases, and increases as we ascend and water pressure decreases. This is an important concept to understand, because it helps explain how our equipment and breath control affects our buoyancy. There’s one caveat: Boyle’s Law only works at a constant temperature. Once the temperature of a gas rises or falls, the equation no longer applies.
2. Weight Yourself Correctly
Improper weighting is the most common cause of buoyancy problems for new students. This stems from a tendency among instructors to overweight new divers in order to prevent uncontrolled ascents, and to make performing skills on the seafloor easier. Upon qualifying, divers are reluctant to experiment with the weights that they used in their initial course and spend years being over-weighted as a result. Divers compensate for excess weight by adding air to their BCDs, which increases drag and, as the air in the BCD expands and contracts with depth changes, requires excessive adjustment to find a balance. Generally, buoyancy control is most easily achieved when a diver uses the minimum amount of weight, therefore requiring very little BCD inflation.
3. Adjust weight according to equipment and conditions
Weighting is a delicate balance, and changes according to the thickness and style of exposure suit and type of cylinder. Steel cylinders are less buoyant than aluminum ones, and all cylinders become more buoyant as they empty of air. The general rule is to wear an additional 5 pounds of weight to counter the 5 pounds of air used when a full tank is breathed down to 500 psi. All exposure suits are buoyant due to air trapped in the neoprene; for example, a new men’s wetsuit has approximately 2 to 3 pounds of buoyancy for every millimeter of thickness. As you dive deeper, the air in your wetsuit compresses, buoyancy is lost and you will need to add air to your BCD in compensation. Unusually deep dives, dives taking place in strong current, and changes from saltwater to freshwater or vice versa will all require alterations to normal weighting. A diver who is neutrally buoyant in saltwater will be negatively buoyant in freshwater, and will need less weight accordingly.
4. Perform a buoyancy check
Although weighting requirements vary according to dive conditions, a simple buoyancy check can give you an idea of how much weight you’ll need for a specific equipment set up on a given day. Test your buoyancy towards the end of your first dive; performing a buoyancy check with an empty tank takes into account the buoyant properties of a full one. With a near-empty tank, empty your BCD of all air while on the surface. Then, take in and hold one normal breath — you should float at eye level. Use the results of your test to alter your weighting for the rest of the day’s dives. When correctly weighted, you should be only slightly negatively buoyant on your 3-minute safety stop. You can use your safety stop to experiment. Get your buddy to help you add or take away weights to see which configuration works best for you.
5. Perfect your body positioning
Body positioning, or trim, makes a big difference to buoyancy control. If your fins are not aligned horizontally with your body, your fin-kicks will send you either up or down rather than forwards. You will feel the need to compensate for the sudden ascent or descent by adding or dumping air from your BCD, which will swiftly disrupt the balance needed to achieve neutral buoyancy. To make sure that your trim is correct, achieve neutral buoyancy and then get into a horizontal position with your legs stretched behind you. If they sink or float, you can alter the positioning of your weights to correct the problem. Too much weight around your waist will drag your hips down, making it difficult to maintain a good swimming position, while unevenly spaced weight will pull you to one side or the other, affecting streamlining in the water. Women especially may find that their legs are particularly buoyant, which can be easily counteracted with ankle weights. Unless instructed otherwise, descending feet first is usually a good idea, because it allows the BCD to be completely emptied of air.
6. Familiarize yourself with your BCD
Your BCD is obviously your most important piece of equipment when it comes to buoyancy control. It follows therefore that being properly acquainted with yours is an important part of achieving good buoyancy. A study investigating 533 diving accidents recently reported that 57 of those accidents were associated with BCDs, usually because the diver did not properly understand how their equipment functioned. Be aware of where all your dump valves are and how they work, so that you can use the most appropriate one depending upon your position and situation. Most entry-level divers are only taught how to use their inflator hose to release air from the BCD, but in a head-down position, this is the least efficient way of doing so. A well-fitting BCD is equally important. One that is either too big or too small makes achieving good buoyancy unnecessarily difficult. You must have sufficient lift for the amount of weight you are wearing and the conditions that you are in, and your BCD should support your body without pinching or restricting it.
7. Master breath control
One of the hardest lessons when learning to dive is to never, ever use your inflate button to ascend. Instead, good buoyancy control depends upon learning to use your lungs to ascend and descend. Continuous adjustments to BCD inflation result in over-compensation and awkward buoyancy; the key is to breathe in to go up, and breathe out to go down. Similarly, because breathing does affect your position in the water column, make sure to breathe evenly and continuously in order to prevent unwanted alterations to your buoyancy. Many new divers have to over-weight because anxiety makes them breathe in too deeply, which in turn makes them more buoyant than they otherwise would be. Those who have problems descending after dropping weights should breathe out; often, this will be enough to help them sink below the surface. Relax while diving, and always try to adjust buoyancy using your lungs before resorting to using your BCD.
8. Don’t use your hands
Using your hands to counteract negative or positive buoyancy is inefficient and messy. All of your power underwater comes from your legs, so using your hands to control direction and position is a waste of energy and consequently air. Additionally, using your arms and hands to correct your buoyancy keeps you from learning how to do it correctly with your lungs, BCD or fins.
9. Enroll in a course
PADI offers a diver specialty course called Peak Performance Buoyancy, while the SSI equivalent is the Perfect Buoyancy course. Enrolling in a course like this is an excellent way to learn more about buoyancy techniques and to practice them in a controlled environment under instructor supervision. These courses should teach you how to streamline yourself, make precise weight and trim adjustments, configure your equipment and practice helpful relaxation techniques. Where students might have been too focused on completing skills in entry-level courses to address buoyancy control issues, these courses give divers the opportunity to focus solely on correcting and perfecting their buoyancy.
10. Log your dive
Don’t forget to log your dives. A number of variables affect buoyancy, and recording the amount of weight that you use with different exposure suits and in different conditions can help you get your weighting right the next time you dive. That way, instead of relying on the estimation of your dive guide when choosing your weights, you can make an informed decision and take responsibility for your own buoyancy control.