One choppy, gloomy Florida afternoon, I dug my fingers into the railing of the dive boat, focused on the shore, and attempted to breathe through my mouth. Not only was I new to scuba diving but I was new to boat rides, and I felt every pitch and roll of the boat in my stomach. Since I was concentrating on keeping a cheeseburger and french fries off the deck, I was only half-listening to the pre-dive briefing. While I understood the gist of the dive plan, I was not evaluating it. I just wanted to get off the boat.
My unthinking adherence to the guide's directions was a mistake because the dive plan was unsafe. The afternoon boat visited two dive sites - one at sixty feet and one at forty feet. The divers paired off into buddy teams to explore the reef, and would be supervised from the surface by the divemaster. Around thirty minutes into the dive, each buddy team was to check in by surfacing and waving at the boat. If we became lost, we should surface, find the boat, then descend and swim back to the anchor line. The instructions to repeatedly ascend and descend should have set off alarm bells in my head, but either because I was new or because I was desperate to get in the water, I blindly followed the guide's dive plan.
A dive profile in which a diver ascends and descends repeatedly is called a sawtooth dive profile. Sawtooth dive profiles are unsafe, and are thought to increase a diver's risk of decompression sickness. Most computer algorithms and and recreational dive tables cannot accurately track a diver's nitrogen absorption for such a dive profile, so a diver who ascends and descends multiple times during a single dive quickly loses track of his maximum bottom time and decompression status.
While a sawtooth dive profile may be unavoidable in certain types of advanced diving, such as wreck diving or cave diving, most recreational divers who follow this type of dive profile do so from ignorance or lack of skill. During my afternoon dives, my buddy and I ascended several times to check on the location of the boat without doing a safety stop. After sawtoothing up and down throughout the dive to keep track of out location, we dutifully completed a safety stop at the end of our dive. This wasn't very logical, but we were new divers and merely following instructions.
Now I know better and I would never instruct my divers to follow a sawtooth dive profile. Still, I observe divers inadvertently following sawtooth profiles during many of the recreational dives that I lead. These divers have either horrible buoyancy control or poor awareness; they either don't realize that they are yo-yoing up and down or they can't control it. To make matters worse, these divers tend float up faster than the maximum safe ascent rate and sink more quickly than they can equalize their ears. Such poor skills increase the risk of decompression illness and ear barotrauma.
What frustrates and frightens me is that ninety-nine times out of one-hundred, the divers I see sawtoothing refuse to admit they have a problem or fail to take the risk seriously. On countless occasions, I have surfaced after such a dive only to find the sawtoothing diver laughing about the fact that he found himself unexpectedly on the surface. This isn't funny or anything to be glib about! Even see-sawing up and down ten feet throughout a dive can be dangerous.
The ability to properly adjust a buoyancy compensator (BCD) to maintain a steady depth and to ascend slowly is one of the most important skills a diver can master. The knowledge that a sawtooth profile is unsafe should be emphasized in open water courses. If you, your buddy, or your students engage in such dive profiles, it may be time for a serious discussion about safe recreational diving practices and a review of buoyancy skills with a scuba instructor.
Speak Up! Do you think that sawtooth dive profiles are acceptable in recreational diving? Why or why not?
Image copyright istockphoto.com, Jman78