Just about any dive professional will agree that mastering buoyancy control is a challenge for new divers. Those professionals will also tell you that a basic cause of buoyancy problems is overweighting. Proper weighting produces all sorts of benefits, some immediately evident, others more difficult to recognize.
Advantages of Proper Weighting
If your underwater profile resembles the diver in photo 1, you need to read this article thoroughly and then make a point to put the recommendations into practice. With his upper torso elevated, the diver appears to be heading for the surface, but he is not. He is just swimming along taking in the sights. But why is he diagonal in the water column?
Look closely; all of his weights are being carried on a web belt fastened around his waist. That in itself is not necessarily a problem if the amount of lead he is wearing is the correct amount. But in this case it isn’t.
Look again; notice that his buoyancy compensator (BC) is inflated more than normal. When a diver is overweighted he or she must add excess air to the BC to offset the negative buoyancy caused by the extra weight. This elevates the upper torso, causing the diver to plow diagonally through the water rather than cut a streamlined, horizontal swath.
The goal of every diver should be to expend as little energy as possible and use only as much air as is necessary. When a diver plows through the water he pushes a wall of water in front of him. This requires extra energy and results in increased air consumption.
A streamlined diver cuts through the water like a dolphin — sleek and smooth. This requires less exertion, reducing the amount of air his body needs to sustain normal functions. Using less air means that his air supply will last longer. (For more information, see “Why You Use So Much Air: and What to Do About It,” Dive Training, July 2005.) This allows the diver to stay down longer than he would if he were overweighted and plowing through the water.
Proper weighting has other advantages as well. To compensate for the excess weight, overweighted divers must add more air to establish neutral buoyancy. But as they change depth and excess air in the BC expands, they are forced to dump air to maintain neutral buoyancy. Adding and venting air to compensate for being overweighted becomes an endless cycle.
Overweighted divers struggle more than those wearing the correct amount of lead. On the surface an overweighted diver must add significant amounts of air to the BC just to remain afloat. This becomes a problem if the diver is in a situation in which he must orally inflate the BC. Being overweighted can be stressful. As a properly weighted diver nears diving depth he adds a couple of quick shots of air to the BC to establish neutral buoyancy. If an overweighted diver waits till he nears diving depth to become neutral, he most likely will exceed the planned maximum depth limit before halting his descent. All this uncertainty adds stress.
The solution to this problem is diving properly weighted. But how do you know the correct amount?
The Weighting Test
Aside from during certification training, few divers ever perform a weighting test, at least not correctly. Most view it as an inconvenience, especially at the dive site where they are itching to go diving. However, they fail to realize that being properly weighted can mean the difference between a truly enjoyable dive and one they remember as a series of frustrations.
A weighting test should be performed during open-water training to establish the diver’s baseline weight needs. After that, a diver’s weight requirements should be retested whenever he or she:
1. Goes from fresh water to salt water or vice versa for the first time. This gives the diver a baseline weight requirement for both environments.
2. Wears a different type, style or thickness of exposure protection.
3. Uses a different type or style of BC, fins or regulator.
4. Uses a different type or size of scuba cylinder.
5. Wears a hood or gloves for the first time.
6. Carries different accessory gear.
7. Gains or loses several pounds of body weight.
Each time a weighting test is performed the proper amount of weight should be recorded in the diver’s logbook, along with the gear used, body weight, equipment and exposure protection worn and the diving environment — salt or fresh water.
For the most accurate results, the weighting test should be performed using an air cylinder containing less than 1,000 psi. This is because tanks become positively buoyant, or at least less negatively buoyant, as the air inside is used up. Performing the test with a nearly empty tank ensures that the diver will be properly weighted while performing the safety stop at the end of the dive. Performing the test with a full tank is better than no test at all, but unless a pound or two of lead is added, it could result in the diver being underweighted at the end of the dive.
The weighting test is performed in water that is too deep for the diver’s fins to touch the bottom. He wears standard scuba equipment and preferably a nearly empty tank.
The diver enters the water and positions himself clear of any objects. With all gear in place and the regulator in his mouth, he inhales and holds a full breath as he vents all the air from his BC.
With arms relaxed and at his sides, he hangs motionless. After bobbing a few times the diver will stabilize and float at a constant depth. It is important that he continue holding his breath until he has stopped bobbing.
A properly weighted diver will float at eye level, half the mask window be below the water, half above.
