Understanding Balance & Trim by Quest
| BY TAMARA KENDEL
Good trim requires that a diver move through the water in a horizontal position with the feet up. Most divers swim in a foot-down position using a kick that gives downward thrust. This attitude increases the surface area of the diver that must be pushed through the water, which requires more energy and increases air consumption. Also, much of the downward thrust caused by the kick is effort wasted against poor buoyancy control-- part of the kick must compensate for the diver’s lack of neutral buoyancy. It is also crucial to realize that the feet-down position will lead to dead coral, bad visibility and damaged cave, all of which should be important issues for divers.
It is fairly easy to evaluate trim. If a finning technique that gives downward propulsion is used, a diver will receive a resulting lift to their body. Divers who fin in this manner will notice that when they stop kicking, they have to add gas to their BC to keep from sinking. When they begin kicking again, they will then need to dump air to keep from becoming positively buoyant. Good trim and propulsion techniques preclude having to adjust buoyancy whenever stopping or resuming swimming.
An effective method to develop good trim is to frequently stop swimming during a dive. The diver should not rise or sink. If buoyancy does change, the diver should adjust it and their trim, and then continue. Eventually, buoyancy and trim will improve and the diver will have make adjustments less often. An alternative is to use the frog kick, since its long glide phase allows divers to sense their buoyancy and trim as they continue forward progress.
Many divers are able to stay in an efficient trim position until they need to use a reel or solve a problem requiring a stationary position. Losing trim position during an emergency situation can worsen the problem and make it more difficult to handle. One reason divers tend to lose their trim during emergencies is that they were taught in open water class to flood and clear their masks by first become negatively buoyant and kneeling on the bottom of the pool. This detrimental practice carries over to the open water where divers can often be seen stopping, kneeling and clearing their masks before continuing their dives. It is obviously not necessary to kneel in order to clear a mask; experienced open water divers clear them while swimming. When cave students enter the cave they commonly enter with good trim, but the moment they start to tie off the reel, they kneel on the bottom. This, too, is unnecessary and it is also damaging to visibility and the preservation of the cave. Making a conscious effort to keep your legs up will eventually make the posture second nature.
The other aspect of having good trim involves equipment: there is specific gear that makes it easier or more difficult to stay in good trim. When divers use aluminum cylinders, they usually need weight belts which are worn on the lower half of the body. This puts divers in a feet down position. To complicate matters, the traditional jacket-style BC that is generally worn lifts the upper portion of the body, making it even more difficult to keep a trim position. This conflict of buoyancy caused by aluminum cylinders and jacket-style BCs makes it very difficult to keep a trim position. A steel cylinder can be used to rid the diver of a weight belt. This distributes the weight across the length of the diver’s torso, primarily above the lungs where it is specifically required. If a steel cylinder is not available, then a stainless steel back plate, and/or a BC Keel (a contoured, coated piece of lead that is cam-strapped high on the back of the cylinder) can be used to remove weight from a belt. A stainless steel back plate ranges from five to 12 pounds and a BC Keel from six to 11 pounds. Divers wearing double cylinders can wear a v-weight, a contoured piece of lead that fits between the cylinders and the back plate, which weighs between six to 11 pounds. Regardless of which method is used, the diver must be sure to match the weighting to the buoyancy requirements of the dive, just as when using a weight belt.
Wearing a set of buoyancy wings, rather than a jacket, back-mount or horse collar style BC, will disperse the lift on the diver evenly across the torso to effectively compensate for the weight of the cylinders. Also, a crotch strap helps to stabilize all of the equipment worn by the diver. This strap is attached to the bottom of the back plate, with a loop sewn in the front for the waist belt.
Overall, the equipment most conducive to achieving good trim is a set of steel cylinders with a back plate, harness with crotch strap, and wings. Additionally, consider taking a video camera on a dive. Watching yourself diving is often a surprising, but educational, experience. A buddy who is willing to give constructive criticism is also a valuable tool. Together, these diving practices and equipment choices will enable you to achieve good buoyancy and trim skills, making your dives much more enjoyable and efficient.
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