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By the end of this topic, you should be able to answer these questions: 1 What are the techniques for controlling your buoyancy using a dry suit and wing/BCD? 2 What is the technique for switching to a redundant (double bladder) wing/BCD? 3 How does good breath control benefit you as a technical diver? 4 What is the ideal body position for technical diving and why? Take Control As a recreational diver you know that when wearing a wet suit you add and release air from your BCD to make larger changes in your buoyancy. This also applies to technical diving. To maintain a horizontal trim position, you may use a dump valve intended for use in horizontal position. This is usually near your hip, or for sidemount wings, may be on your lower back. With a dry suit, most technical divers use both their wing/BCD and their dry suit. The dry suit is not usually used for primary buoyancy control, but has enough gas to provide insulation and good trim. This differs from the recreational diving practice of primarily using a dry suit underwater to control buoyancy (except with neoprene dry suits). In tec diving, the wing/BCD is used for large buoyancy changes. During descents, especially if your gear makes you very negative, go slowly to allow time to add gas to your wing/BCD and dry suit. Maintaining a good trim position and releasing gas from a dry suit takes practice. As you gain experience, you’ll be able to achieve the same release without sacrificing trim. Using both your wing/BCD and dry suit requires more practice, especially during ascents when you need to vent gas from both to control ascent rate image placeholder for 730x365 During ascents, set the dry suit dump valve to release expanding gas automatically. It's okay to raise the shoulder with the valve to vent gas from your dry suit. Also manually deflating the wing/BCD using the dump/deflator allows you to maintain trim position. As with a dry suit, if you need to change position to vent gas, do so. Redundant Wing/BCD With redundant wing/BCDs, you do not use the backup unless your primary bladder fails. Inflating both simultaneously can damage or cause the entire BCD system to fail. If your primary fails, switch to the backup, and use it just as you would the primary as you end the dive. Some divers have their redundant bladder connected and working throughout the dive so that there is no delay if they need to use it. It’s important to stow your backup where it can be easily reached, doesn’t get depressed accidentally and can be monitored for leaks. Other divers check that their redundant bladder is functioning, then disconnect it to avoid accidental inflation or leaks into the bladder. This comes at the expense of having to connect the LPI hose before you can use the inflator in an emergency. Weigh up the best option for yourself. Position backup inflators that use oral inflation where they can easily reach your mouth. Breath Control While technical diving you use breath control to fine-tune your position in the water, the same as you do in recreational diving. Mastering the use of breath control can help you: Achieve the precision buoyancy control necessary for effective decompression. Improve propulsion techniques by coordinating breathing and finning. Offset external changes in buoyancy, such as by exhaling when inflating a DSMB. Control anxiety by purposefully breathing slowly and making sure you exhale fully with each breath. Body Position As you recall from your previous training, your "trim" is the angle and orientation of your body in the water. For moving around underwater, the ideal trim or body position is horizontal. This position has several benefits: It presents a smaller surface area making propulsion more effective. Finning, or other propulsion techniques, move you forward without wasted effort. When decompressing, this position theoretically maximizes the available lung surface area for gas exchange. When your torso is horizontal, your fins remain at or above body-level making it easier to avoid damaging the environment or disturbing visibility. image placeholder for 730x365 Photo credit Jon Milnes Streamline Your Equipment Your equipment has a big influence on the position(s) you can comfortably hold underwater. Take the time to adjust your equipment and make sure it conforms to your trim position, otherwise it counteracts the benefits of good body position. Sidemount cylinders should be inline with the body. This is primarily achieved by adjusting the rigging and attachment set-up. You may need to re-adjust aluminum cylinders during the dive for optimal position. Some sidemount harnesses have more than one hip attachment point to facilitate this. Deco/bailout/stage cylinders should be as streamlined as possible when in a horizontal position. Adjust the rigging and attachment points to achieve the optimal position. Get Horizontal Neutral buoyancy is vital to being able to maintain a horizontal position. If you're not neutrally buoyant, you'll waste effort kicking to maintain depth and/or constantly adjusting your wing/BCD. Although you may need to practice your buoyancy in a new equipment configuration, you should have good buoyancy control before undertaking tec diver training. Correct weighting is an important factor in establishing good trim. Distribute your weights and cylinder positions until you can easily remain horizontal as well as move into other positions as needed. Practice Body Control Once you have good buoyancy control and your equipment is well-balanced, you need to be able to hold your body under a little tension. You’ll practice this and propulsion techniques in Practical Application One. Look forwards, relax your shoulders, tighten your stomach muscles and hold your glutes. Take care not to over arch your back or strain your neck. It may take time to achieve the ideal position. If you’re not used to it, this position may feel very strange at first, but will get easier with practice. Everybody is different and, like perfect neutral buoyancy, a perfect body position is something you will continually work towards. The goal is to have a position that is effective. Your instructor will work with you to make sure your body position allows you to move through the water easily and effectively. Keep in mind that you don’t have to be completely horizontal throughout the entire dive. Small variations are normal and, in some circumstances, you may need to use other positions.