The most important factor in avoiding unnecessary contact with your underwater surroundings is awareness of and control over your body’s positioning and movement. To accomplish this, it’s important to have excellent buoyancy control. But before you can develop good buoyancy skills you need to understand the variables that affect your ability to achieve and maintain neutral buoyancy and how they apply to diving situations. We know that the correct amount of weight is the least that you can wear and still descend without struggling, maintain neutral buoyancy at depth with minimal air in your buoyancy compensator (BC) and comfortably complete a safety stop without floating upward. The appropriate amount of weight for a dive depends on a number of factors. Before each dive carefully review your equipment. Have you changed anything since your last dive? A new BC retains air in the padding and therefore may require an extra pound or two. Are you using the same type of air cylinder? Steel tanks weigh more than aluminum and therefore require less additional weight.
The water you dive in also affects weighting. Salt water is about 2.5 percent heavier than fresh water (64 vs. 62.4 pounds per cubic foot). Therefore you are more buoyant in salt water and require more weight — theoretically 2.5 percent more.
Water temperature is also significant because it affects the amount of exposure protection worn. Every additional bit of air space that divers add to or subtract from their body — such as a thick wet suit, a hood or a dry suit — changes the amount of lead weight required. Planned depth may affect weighting as well. Experienced divers often choose to carry less weight on deep dives to avoid having to put a lot of air in their BCs to achieve neutral buoyancy at depth. Conversely, on shallow dives, slightly more weight might be appropriate, especially where surge is present. While fine-tuning your weighting system may amount to changes of only a pound or two (1 kg) in total weight, it also involves adjusting your trim. In recreational scuba, we usually prefer a horizontal orientation when moving through the water, creating a streamlined profile. This lessens drag, decreasing exertion and conserving air.
With all their lead at or near the waist, some divers tend to swim at a diagonal orientation, either head lower, legs higher or vice versa. Trim can be improved by moving a small amount of weight down (e.g., ankle weights) or up (e.g., tank strap weights). The same holds true for divers with a tendency to roll to one side. Adjust trim by distributing lead as needed to offset the roll (i.e., more on the opposite side). Some newer BC models have nonditchable weight pockets that allow you to stow a small amount of weight along the upper back portion of the BC. However, it’s important that the majority of your weight be configured no it’s easy to ditch in an emergency.
