A diver who has good trim has a nearly horizontal position in the water, with his feet and fins at or above his horizontal body line. Proper trim in scuba diving a combination of body positioning and equipment configuration. When training for proper trim, a diver should work first on his body positioning and second on his equipment configuration. Doing so allows a diver to determine what, if any, changes need to be made to his gear. In most cases, divers can get very close to proper trim without making any changes to their equipment.
So how does a diver get himself into a streamlined, horizontal position? He must adjust the position of several areas of the his body, beginning with his core.
2. Hips and Butt:
In all cases, a diver's legs and fins should not extend below his horizontal body line while he is still. Some kicks, such as the flutter kick, cause a diver's fins to drop below his body while in motion. Although this is acceptable in recreational scuba diving, it is usually better for a diver who is concerned about his trim to learn a more advanced kick such as the frog kick or the modified flutter kick.
Essential Concepts for Scuba Diving:
While hovering, the easiest and most stable way for a diver to position his legs is to bend his knees at a 45° to 90° angle and gently flex his ankles so that his fins are parallel to the floor. While many technical training organizations insist on a 90° bend, keep in mind that it may be more comfortable or more stable to have the knees bent at a slightly gentler angle. The key is to keep the fins up above the horizontal body line and to keep them parallel to the floor.
After making all of these adjustments, a diver should attempt a trim test. To conduct a trim test, the diver hovers without moving his fins or his hands at all. This is more difficult than it sounds, as most divers are accustomed to making small hand and foot motions to keep themselves stable.
Enter the water with a buddy, adjust your body position as suggested above, and hang completely motionless in the water. See what happens. Have your buddy give you feedback on your body position, and once you are sure that your body position is correct, notice if you tend to roll head down, feet down or to one side or the other. If you notice a tendency to list in one direction, it is time to begin adjusting your equipment.
Also keep in mind that proper trim should be comfortable. Many divers seem to obsess about an absolute horizontal position in the water. In my opinion, this is not proper trim because the diver cannot look forward and see where he is going (unless he has an exceptionally long neck). A slightly head up position is acceptable, but only if a diver can maintain the position while hovering motionless in the water.
The Take-Home Message About Body Position Adjustments for Proper Trim:
Proper trim will make scuba divers more comfortable and stable when they hover, and will increase their swimming efficiency this reduces drag. Remember that proper trim is achieved through a combination of body position and equipment configuration. If a diver finds holding himself still difficult after adjusting his body position, he should consider adjusting his equipment configuration to optimize his trim.