The Grunge Line
by E.R. Cross
Recreational diving can be almost anything a diver wants it to be. It can range from the undiluted pleasure of breath-hold (free) diving to the hard work (and it is hard work) of mixed gas diving. Regardless of the diving mode a definite pattern should be followed.
For a safe dive certain actions are involved in assembling and donning necessary equipment. Then there is the entry and descent followed by the dive at depth and, finally, a safe ascent to the surface. Regardless of the level of diving experience, the condition of the water;what it is doing and how it may change;should be taken into consideration. This can be determined by reading the water. Simply defined, this means determining the present and future condition and how these will affect dive safety.
READING THE WATER UNDERWATER
It was suggested in previous Technifacts that reading the water should start before the dive. It should be continued during preparation and while underwater. One of the clues to look for, both topside and underwater, is a debris line, called the grunge line by many divers. Topside this will look like a line of discolored foamy water containing floating debris (the grunge); usually material discarded by on-shore humanity. This indicates a definite change in the current at or under the grunge line and may become important to maintaining a safe dive pattern. A drastic change in the water temperature may also occur with a change in the current. Awareness is the key to successful interpretation of water conditions.
There are several considerations when reading the water during a dive. Any change in the currents could be important to dive safety. Even in tropical, fairly clear water, a change in currents will be evidenced by a change in the water clarity. The grunge line will appear, usually at the limit of visibility, as a mass of discolored water. To determine the approximate direction and rate of flow of the current, hold a handful of sandy-silt a couple of feet off the bottom and allow it to trickle down. If it seems the grunge line is approaching the dive site, it may be wise to plan for a change in the dive profile. Drastic changes in visibility and temperature can sometimes occur with a change of water.
Many other readings can be made during the dive. Be alert for indications of surge caused by ocean swells. Any kelp or other marine growth, as well as free swimming critters, will be washed back and forth with the surge. Also, sand and coral rubble may appear in shallow windrows. These will arrange themselves parallel to the face of the topside swell or underwater surge. As long as the diver can control the dive, surge is not considered hazardous. In fact, surge may be used to accomplish some phases of the dive. Ride in a desired direction then get a hand-hold on the bottom and allow the surge to retreat. Repeat until youve gone as far as desired.
Be with Technifacts next month for more techniques that have been tested and proven helpful for entering and exiting the water from the shore.
DIVING BY THE BOOK
In almost all sports, the ultimate learning tool is personal experience. However, reading diving and related publications can enhance diving skills and safety. I feel strongly that skills learned in breath-hold diving will lead to a heightened degree of watermanship and greater dive safety. The Australian Freediving and Spearfishing News is for freedivers and underwater hunters. It is a quality magazine of international news, stories about freediving equipment, interviews with great divers and reminiscences of the past. For details, write to Barry Andrewartha, AFDSN, P. O. Box 167, Narre Warren, Victoria 3805, Australia.
Several readers have requested a source for back issues of SKIN DIVER Magazine. David Way wrote, I have available a varying number of back issues. Also in Ways latest 20 page catalog are hundreds of other listings of diving publications. Included are several titles on freediving, underwater swimming, snorkeling and other related books that will improve basic watermanship. To receive this valuable source of out of print diving information send $1 U.S. to David Way, The Divers and Watersportsmans Library, 10 Cedar Road, Preston, Paignton, Devon, TQ3 2DD, England.
THE HUMAN BODY
Several months ago a reader wrote asking for information on the physiological and physical effects of pressure on the human body during a dive. This reader also wanted to know if the helmet equipped diver was affected by same pressure changes as a scuba diver. First, an answer to the last part of the readers question. Yes, any diver subjected to the pressure of the water will experience the same physical and physiological effects of the pressure. The effects will depend to some extent on the breathing gas used and the total pressure (depth) of the dive. Also, in some cases, the duration of the dive may influence the effects of the breathing gas. Best Publishing Company, Flagstaff, Arizona 86003-0100 has several publications dealing with this subject. Write to P. O. Box 30100, for its latest catalog of related subjects.
This reader also asked, I am particularly interested inÉsurgical procedures for improving my ability to deal with pressure. I feel rather strongly that a diver in need of surgery to deal with pressure should not consider diving. One of the prime requirements for diving is that the prospective diver can readily equalize pressure and that he/she will not be adversely affected by the physiological effects of the dive.
The science and practice of all phases of diving are changing almost daily. Technifacts readers are urged to keep in touch with SKIN DIVER Magazine and publishers of books related to diving. Visit your library and check its publications on diving. Libraries can often order books for their readers. Regardless of the source, read and study. Think about diving techniques that can, with practice, improve your diving skills and lead to a greater ability in the water. You will be glad you did.