When Donald learned to dive, his instructor gave him a weight belt to fasten around his waist. But heavy weights around a diver’s middle can drag a diver’s feet down and out of the more efficient horizontal swimming position. Divers often correct this by swimming harder to straighten up. Only perpetual motion keeps the problem at bay — stop and you drop. In this fourth part of our series, we’ll address poor air consumption when scuba diving and its relation to weight placement and trim.
Poor Air Consumption When Scuba Diving: Weights
BCD manufacturers are becoming more aware of this problem and producing models that allow the placement of lead weights higher up on the diver’s body in rear shoulder-mounted pockets. It’s also possible to thread a pound or two of lead into the BCD’s tank strap up near the top of the tank. The key is to not have too many weights in these secondary locations; you still need to dump enough lead quickly in an emergency to become positively buoyant.
Splitting the location of a diver’s weights will help them straighten out and be able to stop dead in the water without tilting their head or feet downwards. We call this “maintaining a horizontal trim,” which is your appearance or position in the water column. Water is dense and the more streamlined we are, the less resistance there will be and the more efficient we will become. More significantly, we will breathe much more efficiently and increase our bottom times.
Maintaining good trim underwater requires all three ingredients of good buoyancy control: proper weighting and positioning of those weights; proper use of the inflate/deflate controls of your BCD to remain neutrally buoyant; and a horizontal position in mid-water. By understanding the formula, you’ll always be able to make this work no matter what you’re wearing, what your tank size or material, or where you’re diving.
Let’s revisit our example diver, Donald. He relocates four of his 18 pounds (two of his eight kilos) to the tank strap of his BCD, where they are now around three feet (1 m) away from his waist. The second dive is a long drift over a coral garden in the Ras Mohammed National Park of the South Sinai in the Red Sea.
Donald and his fellow divers again drop to 82 feet (25 m) again, but this time he stops dead, checking his position against the reef and swimming slowly with the mild tail current. His feet are not moving as much on this dive — kick, kick, glide; kick, kick glide — followed by a pause as he gracefully drifts through the water.
Every few minutes, Donald stops and admires the fish swimming among the coral formations. He doesn’t flap or kick his legs, but remains still, in control and perfectly neutral in his new horizontal world.
On land Donald is six feet tall, but his height when finning in proper trim is just 18 inches. If he wishes to stand up and look around he can, but he’s still neutral. He makes regular corrections with his inflate/deflate buttons and checks his position against the reef. He is calmer and more relaxed. Back on the boat, a guide stands by with a clipboard, recording the dive profiles of the returning guests.
“Name?”
“Donald”
“Time?”
“Sixty-five minutes”
“Ending pressure?”
“1,000 psi”
By guest author John Kean
John Kean is the author of four books. He holds the PADI Master Instructor rating along with TDI’s Advanced Trimix Instructor qualification. Since 1997 he has amassed over 7,000 dives, trained over 2,000 students and project-managed several world record deep dive events. His book is available here.
