The duration of your dive is limited by your own rate of air consumption, which in turn depends on how much energy you expend. Good finning technique, buoyancy control, and a streamlined profile will all make your movement underwater more energy-efficient.
Your movement through the water should be driven and controlled by your legs. If you watch experienced divers, you will notice that they use their arms very little, and move effortlessly through the water, saving energy, minimizing air consumption, and avoiding damage to reel’s and the marine environment.
Swimming with fins should be an extremely efficient way of propelling yourself through the water, but many divers are let down by a poor finning technique. There are several different strokes you can use, but all should be carried out with strong, rhythmic movements, fully extending the leg (or legs) with each kick. Uncontrolled thrashing and incomplete kicks will simply waste energy. It is worth asking your buddy to give you feedback on your technique even to photograph or film you. You may be surprised at the results.
Scuba diving is not a race, and the faster you go, the less you see. Learning to pace yourself and move at a leisurely speed will help you to relax, and a relaxed diver is an aware, efficient, and safe one.
Profile and Buoyancy
To achieve the most streamlined (and therefore most energy-efficient) swimming position, you should be almost horizontal in the water. Your hips will be slightly lower than your upper body due to that area being weighted. During a dive, you should look forward and downward most of the time raising your head too much will lift your upper body and make your profile less streamlined.
Carrying the correct amount of weight is important. Being overweighted will drag your hips and lower body downward. Swimming will then require greater effort due to your unnatural angle in the water, which will produce increased drag. You can improve your profile by repositioning the weights in your BC, or refining your weight requirements.
Achieving neutral buoyancy is the key to maintaining a good dive profile with ease, and also increases your efficiency. If you are positively buoyant, you will be constantly swimming downward; if negatively buoyant, you will have to swim upward all the time or crawl along the bottom – all of which require more effort than horizontal, neutrally buoyant, swimming.