One result of 175 million years of evolution is a hard-wired response mechanism that's designed to preserve and protect us when we're faced with an emergency. Every living creature has - in one form or another - some form of flight or fight response. The more sophisticated the organism, the more complex the response. But no matter how complex, the flight or fight response's primary objective is to switch the focus from long-term to short-term survival, and it'll make the creature its working to defend do some pretty bizarre things to attain that objective. As a diver we need to understand a little of this process, because we need to manage one of its side-effects: PANIC.
Panic and diving are mutually exclusive states of being. That's to say, there is no place or time during a dive where panic is the appropriate response. In fact, panic during a dive will greatly increase the risk of serious injury or death. And that's why panic is something all divers need to avoid absolutely during all phases of their dive.
When we are faced with danger, the neurons in the hypothalamus region of our brain trigger the release of a series of hormones and within seconds, we can run faster, hit harder, see better, hear more acutely, think faster, and jump higher than we could only seconds earlier.
Under the influence of this process our heart pumps faster than its normal speed and adjustments in our circulatory system shunt blood away from internal organs and surface capillary beds increasing our blood-pressure and sending nutrient rich blood to the major muscles in our arms and legs so they can work harder - coincidently this also means we can sustain a surface wound and not bleed to death.
Panic is something all divers need to avoid during all phases of their dive
All functions of our body not needed for immediate action and short-term survival are shut down. Digestion stops, sexual function stops, even our immune system is temporarily turned off. And if necessary, excess waste is eliminated to make us lighter on our feet - and perhaps make us a less appetizing prospect for our pursuer!
All these actions are automatic - functions of our autonomic nervous system - and as such are close to impossible to control - unless you are a Zen master or practicing yogi. But we do need to understand how they work and although we can accept that an emergency in the water may raise our blood-pressure and quicken our heart-rate, we cannot allow our conscious minds to shut down and give way to uncontrolled PANIC. We do this through a three easily learned techniques.
The first is we decondition panic. This may sound difficult to learn since panic is a function of this hard-wired, autonomic system, but the lucky coincidence is that most divers have already mastered this technique to some extent during their initial open water scuba training.
Just about everyone has a story to tell about one skill or another they felt challenged by in their open water program. It may have been taking off their mask, doing a regulator recovery, even putting their head underwater and breathing for the first time. Whatever it was, they overcame it otherwise they would not be carrying a diver certification card.
How did we do that? Essentially the process of 'desensitisa-tion' or 'deconditioning' is achieved systematically by introducing the stressful situations - the events our brain classifies as emergencies - gradually and returning to them repeatedly. This technique helps to take the emotion out of the situation and settles our mind to its original working state.
An additional aid in deconditioning panic is to practice deep controlled breathing (not to be confused with breathe holding, which we certainly do not advocate). This method of breathing can take many forms - yoga, martial arts, meditative - but it is essentially the same. Something that works for many divers is to get into a structured breathing rhythm where inhalation takes twice as many beats as exhalation. By concentrating on this rhythmic breathing cycle one calms one's mind: a great aid in dealing effectively with in-water emergencies.
An associated step in deconditioning panic is understanding the limits of one's comfort zone and how to operate within it.
When we say that a diver is diving within their comfort zone we are describing a diver who is in a frame of mind where he is able to deal with any challenges that crop up during the dive without losing concentration, focus, purpose or falling victim to panic. In essence, the diver is prepared for and able to manage the extra task-loading that comes from dealing with an in-water emergency.
In the broadest sense, the easiest way to keep things within one's comfort zone is to work within the scope of one's training, to build experience slowly resisting the temptation to fast-track to more and more complex dives, and to restrict one's "pinnacle diving" to familiar and stable conditions wearing familiar and tested gear.
Near Panic Stress
Injury or Death Very Likely
Complete Sensory Shutdown,
Injury or Death Certain
Near Panic Stress
Injury or Death Very Likely
Complete Sensory Shutdown,
Injury or Death Certain
All those seem to be generally agreed upon guidelines... even cardinal rules... but let's look a little more closely at each of them.
First let's define what exactly is meant by diving within the scope of one's training. Clearly conducting a staged decompression dive with no formal training in decompression theory - except the operator's manual for a dive computer - and having no real understanding of how to optimize the off-gassing process would be a foolish practice and serves as a clear example of how one might operate outside one's scope of training. However, would this mean the person conducting the dive would be operating outside their comfort zone? Perhaps not - for as long as their computer continued to function and they were happy to follow its "advice" - but what if that computer malfunctions? Most likely at this point, their comfort zone will have shrunk and one more issue - albeit a minor one such as a partially flooded mask - will send them outside their comfort zone and into panic mode... and flight!
While this example is one the vast majority of divers would not paint themselves into, there are more subtle, but nevertheless as dangerous, situations that are far more common. For instance, how many divers conduct dives below 40 m / 132 ft without special training or the special equipment and planning these dives require? How many wreck divers regularly penetrate a sunken ship without any formal overhead training, specialized planning or the special kit these dives require? How many solo dive without special training, equipment, and planning?!
An average diver might get away with breaching these "beyond the scope of training" rules, until something goes wrong at which time, it's particularly bad news. That's the point where they suddenly find themselves outside their comfort zone, in a mess of trouble, and unable to think or act their way out from under: panic is the usual outcome.
Fast-tracking the process of building experience is a little harder to define, but a good example might be a diver who looks at the prerequisites for a course - let's say 100 dives to enrol in an instructor program - and decides to spend a week at a warm-water resort racking up a dozen 20-minute shore dives every day to get their numbers up! What real value is there in that experience? At the end of their week diving, our phantom diver "owns" the required number of dives but only has one extra week's worth of experience. Can we say that this person has built sufficient diving experience to behave correctly in an emergency situation with a student at depth?
By far the most effective and safest way to build experience and grow one's understanding of diving is to dive in a variety of conditions and environments and to allow the experience to build slowly. There is simply no substitute for sober second thought... the process of analyzing one's dives and learning from their lessons over time.
Dives should be a planned experience, and it's perfectly acceptable - encouraged - to plan dives that include time to practice drills and skills. By practicing things such as regulator failures, lost ascent line drills, mask removals, computer failure and all the other minor challenges that may crop up during a dive, we build a resistance to them and are better able to deal with them in a real-world situation. In essence, practicing this way helps to expand our comfort zone.
Practicing your diver skills helps expand your comfort zone
More Challen in Tough C<
Pinnacle / Complex Dives 30 metres to 40 metres 100 feet to 130 feet
The final rule surrounding the comfort zone is to restrict one's "pinnacle diving" to the familiar and the stable. A pinnacle dive is exactly what it sounds: A dive as complex and tough as one can manage within one's comfort zone, and one that requires the diver to be on peak form. Typically a pinnacle dive furthers a diver's experience and grows their comfort zone and is often deeper, longer or more complex than they have previously experienced.
For a newly certified diver a pinnacle dive might be a shallow reef dive from shore with small waves, great visibility, a gentle slope leading to the entry/exit point and a target depth of 15 m / 50 ft. For a seasoned diver it may be a wreck dive in the open ocean with poor visibility and heavy current. However, regardless of what the pinnacle dive is, one needs to understand that adding extra task loading and operational stress must be done in small increments so that the learning process is not overly taxing.
SDI Solo Diving Mtiiui.il
For example, let's imagine a well-experienced diver who has more than 100 logged dives in fresh water lakes and quarries. He is familiar with his gear and has worked hard with his regular dive buddy to hone the basic skills of buoyancy, trim, awareness and communications. His maximum logged depth is 35 m /115 ft and he has about a dozen multi-level dives in that range for long enough to get his computer into mild decompression (one seven-minute stop). On occasion both he and his buddy have experienced equipment problems during their dives together but they have weathered those storms well. It would be fair to say that a pinnacle dive for this diver would be a multi-level quarry dive to 40 m / 132 ft with 10 to 12 minutes of bottom time at maximum depth wearing his regular kit. This dive would load our diver with some additional stress - more depth -- but it would do so in familiar conditions, and this should serve to expand his comfort zone and add to his experience within the bounds of operational safety. It would be a mistake for this diver to add a stage bottle to his kit and execute the dive 20 nautical miles out in the open ocean. There are simply too many additional stressors for this to be a wise dive - greater depth, unfamiliar kit, conditions outside the purview of his experience.
In addition to respecting these simple guidelines, everyone with dive experience knows that their degree of comfort on a dive can vary from one day to another. One day they may feel perfectly comfortable exploring a massive wreck at 35 m /115 ft in marginal visibility and the next day the exact same dive may spook them badly. What changed? Were they over tired, stressed from getting suited up in a rush, worried about something happening at home or work, did they add a new piece of gear to their kit?
Take notice of your feelings before and during a dive and always work within our comfort zone
Are they under or over weighted? All these factors also contribute to the size and shape of our comfort zone, and most of them we can control.
When many of us think about fitness for diving we leave out mental fitness. Before every dive we need to ask ourselves: "Am I in a good frame of mind to do this dive: am I relaxed and confident about doing it and how does my mind feel about donning layers of gear and jumping off a perfectly good boat/dock/beach/et al into a totally alien environment?" By answering these questions we are basically giving ourselves one final "mental" check if we are prepared to conduct the dive we are about to do.
If we understand the boundaries of our comfort zone when planning and executing a dive, we can use it as a kind of 'mental stress meter' and use it to direct our behavior. If we take notice of our feelings before and during a dive and always work within our comfort zone, the probability that a sudden emergency will result in panic is greatly lessened.
The best way to develop proficiency in self-rescue skills is to practice them as often as you can... certainly try to practice some skills on every dive. Here is a checklist to remind you.
Buoyancy Skills - practice hanging in the water motionless and as horizontal as possible at 9 metres / 30 feet, 6 metres / 20 feet and 3 metres / 10 feet
Gas Emergency - practice switching from main regulator to bail-out regulator while swimming at depth
Deploy lafftbag / SMB - practice deploying SMB and ascent from moderate depth. Try breathing principle gas and when breathing bailout gas
Navigation - practice navigating to landmarks at varying distances and bearings from entry point and then back to starting point. (Do this in conditions that are benign in case you have to surface to get bearings!)
Swimming kick/breathe cycles - practice and re-measure kick/ breathe cycles every few months and in a variety of conditions
1. _must be absolutely avoided during all phases of the dive.
2. What are the 3 techniques to avoiding panic?
3. _technique helps to take the emotion out of the situation and settles our mind to its original working state.
4. The most effective and safest way to build experience and grow one's understanding of diving is to dive in a variety of
_and_and to allow the experience to build_.
5. Make a note here to describe what type of dive is within your comfort zone and what currently, you would consider your "pinnacle" dive?
Staying Too Long Going Too Deep Getting Lost
In this chapter, you'll learn about:
Entrapment and entanglement
Emergency up lines and SMB ascent
Staying on route
Waypoints in dive plan
Defining "personal distance limit"
The risks associated with inattention to time, depth, and location have equally unpleasant end-results whether one dives with or without a buddy; however, being unable to find an ascent line with only a couple of minutes before one's computer goes into decompression mode is much more stressful when one is diving alone. In addition, extricating oneself from a mess of fishing line is a challenge for even the most level-headed solo diver. It follows then that as solo divers we leave nothing to chance and must include some simple but effective strategies in our dive plans to help manage these risks.
Every dive IS a decompression dive, but some dives require more decompression than others. For the majority of sport divers, the extent of their required decompression is a 10 metre per minute (or 30 feet per minute) steady ascent to a three-to-five minute safety stop about half an atmosphere from the surface. Sport divers are taught to stay within the so called No Decompression Limits (NDL) of their computers (or tables in the case of non-SDI divers). A true staged decompression dive is outside that NDL and requires timed stops at one or more levels below a safety stop depth (at nine, six, or three metres for example (30, 20 and 10 feet)).
Since this is not a course on staged decompression (TDI, our sister agency, teaches that program), and since SDI does not recommend conducting staged decompression dives without a buddy, we can assume that any required decompression a diver finds herself needing is unplanned and the result of some kind of accident or oversight. Either she stayed at her planned depth for longer than she intended - perhaps because she was concentrating on her camera rather than her computer - or she strayed deeper than intended and racked up required stops that
Chapter 5 | Staying Too Long, Going Too Deep, Getting Lost
way. In either case, she has wandered into a potentially dangerous situation and will need to have a set plan to find the best way out.
First, let's make it perfectly clear that IF our hypothetical inattentive diver started her dive well rested, well hydrated, was in reasonable physical shape and follows some simple steps on her ascent; the chances are good that she will be fine. It's important that she understands this and is comfortable with it because she needs to stay level-headed and in control to get out of her predicament with the best possible outcome.
Here are some options: Once she realizes that she has overstayed the NDL, she must ask herself two vitally important questions: "Do I have a sufficient volume of gas to complete the full ascent (and if she followed good gas management techniques and operated within the rule of thirds, the answer will be an empathic "Yes"). The second question is: "Is my computer functioning as a decompression aid or has it locked me out?" The answer to this will depend somewhat on the model and type of computer she is wearing but let's assume it is showing ascent time, stop ceilings and is not locked up.
A personal dive computer working to calculate a "safe ascent" is a huge bonus in this situation. Since a personal dive computer is a required piece of equipment for all SDI divers regardless of their certification level and experience, she can use it to feed her the required information she needs to ascend within safe parameters.
Where in the water column she will stop, how long she will be required to stay at each level, and her ascent speed between stops will depend somewhat on the gas she is breathing (nitrox or air) and the algorithm her computer is programmed to follow, but without special training in decompression, the best advice to our diver is not to second guess her computer, but to follow the ascent and stop times it displays, and once it's clear, for her to do an additional safety stop for three minutes at three metres / ten feet (gas volume allowing) before her final SLOW ascent to the surface. Once there, she should not overexert herself and she should hang up her fins for the next 24 hours. She should also drink plenty of clear fluids - water preferred - while self monitoring for any signs of DCI.
In case of a computer failure-it is advised to carry a set of backup dive tables
So the most straight forward response to over staying the NDL is to ascend following the computer's guidance, but occasionally, this is not possible. Some computer models lock out when they go into more than a few minutes of required decompression. As a precaution, you might want to read your owner's manual and check to see if your personal dive computer is one of this type. If it is, read the following paragraphs carefully!
It is impossible to give a magic bullet answer to the question "How much decompression do I need to do now that my computer is not functioning?" However, there are some rough guidelines we can use, but remember these are for contingency purposes only!
Every contentious diver is well advised to carry a set of backup dive tables to use in an emergency. Even if your computer does display decompression information, it's smart to back it up in case of battery or some other form of failure. If you have a personal dive computer that does not work as a decompression aid, then backup tables are essential.
There are several different types of decompression tables available. You may recall from your Open Water training that US Navy tables and the related Buhlmann dive tables have been used extensively by divers for many years. Get yourself a set — ask your SDI instructor for his or her recommendation - learn how to read them and carry them with you on every dive especially every solo dive.
As a general rule, it is best to "pad" the ascent times given by tables such as the US Navy and Buhlmann because these decompression tables were designed for "planned" staged decompression and not strictly speaking for contingency
use. If you are beyond the NDL, choose the next longest time or next deepest depth on the table to find out your required decompression time. In addition, ascend halfway from your maximum depth to the surface and wait there for two to three minutes. Then proceed to the required stop at three metres or 10 feet per minute.
Here's an example using the US Navy tables. Let's say your dive was to 30 metres or 100 feet and your total bottom time is 40 minutes. You are into some serious decompression! The US Navy tables indicate you must take three minutes to ascend to three metres / ten feet and stay there for 15 minutes.
Using the method described above you would look up the ascent time for 33 metres / 110 feet for 40 minutes: two minutes at six metres / 20 feet and 21 minutes at three metres / ten feet. In addition, you would ascend at 10 metres / 30 feet per minute from depth to about 15 metres / 50 feet and wait for two to three minutes and then ascend to the first stop at six metres / 20 feet at an ascent rate of three metres / ten feet per minute.
As you can see, this is a complex skill and it's vital to note that we do not recommend planning to exceed the NDL without special training and supervision of a qualified TDI decompression procedures instructor. The method described above is within the guidelines for emergency decompression but is no guarantee you will not suffer a DCI episode.
One final thought for you, as you progress through the step-by-step process of contingency planning, you may want to consider wearing or carrying a back-up computer or depth
Planning and excuting decompression dives as a solo diver is not recommended and should be avoided gauge and bottom-timer in the event one computer goes into lockout mode or zones out for some other reason. If your choice of back up is a depth gauge and bottom-timer rather than a second computer, you should also carry a set of dive tables and understand how they work.
Which brings us to one very important point: If you think you may be bent, get medical assessment and any necessary treatment as quickly as reasonably possible. DO NOT DELAY!
As a responsible diver each of us needs to be aware of the things our body tells us after a dive, and particularly following any dive that has pushed a limit - one with an emergency ascent, contingency decompression, or a dive that was colder or harder work than anticipated.
If you feel strange and present signs and have symptoms such as extreme fatigue, nausea, dizziness, trouble keeping your balance, weakness, tingling or lack of sensation in one area of your body, trouble urinating, joint pain or tightness and swelling around joints, blotchy skin, get yourself checked by a health-care professional who has some knowledge of diving maladies.
Entrapment usually describes a situation where a diver's exit - say from a wreck or cave - is blocked. It is also used to describe a situation when falling debris or material pins a diver down.
Entanglement on the other hand is used when a diver becomes tangled in fishing line, fish nets, hanging cables or vegetation such as kelp. We can create contingency plans for all sorts of equipment failures and associated challenges, but the best contingency for entanglement and entrapment by far is avoidance.
Since SDI does not sanction solo diving in an overhead environment, avoiding entrapment should simply be a question of following the rules. However, do consider that overhead environments to be avoided as a solo diver include a "simple" swim-through on a coral reef or a sunken conduit at the local quarry. And please remember that entrapment when the diver is swimming alone is likely to be fatal.
Good environmental awareness and solid buoyancy are often enough to avoid entanglement. By paying attention to her surroundings, and looking out for loose line and hanging cable a savvy diver can swim away from entanglement hazards long before they get an opportunity to reach out and grab her.
That said, sometimes the monofilament fairies play tricks and when that happens, even the most experienced divers can find themselves caught. A diver can certainly lessen the risk of serious entanglement by streamlining gear, paying particular attention to the cylinders, first stages and harness or BCD: everything in fact that rests out of eyesight behind one's back. Look for potential line snags and places where line can "disappear" and eliminate them whenever possible. These include valves, fin straps, and stage bottles or cameras hanging one's side. Those that cannot be eliminated remain an obvious risk but this can be better managed if you familiarize yourself with their location.
If you happen to get entangled, stop travelling as soon as you recognize there's a problem. Movement will make the problem worse and will complicate getting yourself free. As well as stopping backward and forward motion, keep neutral, going neither up nor down in the water column.
Then think and look. Try to see what it is that you have swum into and try to feel or get a sense of where the hold-up is. Chances are good that whatever it is holding onto you or your equipment is behind your head. If it's something solid and fixed - like fallen wood or a thick cable - the easiest way out may be to simply back up either using a reverse kick or pushing yourself gently backwards with a hand. If this does not work, reach behind and try to feel for the problem.
If the issue is line or thin cable, the quickest way out may be to cut your way free. Using the appropriate tool, reach back and cut through the line, while making sure hoses and other equipment are not in the way of sharp steel cutting edge of your knife or the jaws of your shears!
A well prepared solo diver not only carries at least two cutting devices (accessible with either left or right hand) but also knows how to use them and practices regularly.
Emergency Up lines and Surface Marker Buoy (3MB) ascent
Losing the ascent line or not being able to find your way back to an ascent line usually translates into a stressed situation and at best a long surface swim. Because of this, solo divers are advised to carry a surface marker buoy (SMB) and reel or spool on their dives and with these two pieces of equipment are able to deploy an emergency ascent line when needed. Ascent lines are often tied to a wreck and so we'll discuss emergency ascent or up lines in that context; however, the technique is transferable to non-wreck sites.
There are several ways to deploy and emergency ascent line or emergency up line, but the most common - and most straightforward
- while wreck diving is to deploy the SMB within reach of the wreck making sure there is sufficient gas in the buoy for it to float readily on the surface and sufficient line on the spool or reel to reach the surface taking into account any scope needed to compensate for current (one and a half times depth as a general rule). Once the buoy is on the surface, tighten the line and tie it off to a suitable spot close to the wreck. Respect for the preservation of wrecks
- especially freshwater wrecks - should always be considered but personal safety is always the uppermost concern and if there are no suitable alternate tie-off, use a portion of the wreck that is robust and secure. Once the line is securely fastened (you may opt to leave the reel in place and return on a later dive to retrieve it and the line) ascend using the line as a guide and surface close to the SMB. An alternative in low to no current situations is to deploy the SMB and rewinding line as you ascend.
Both methods are good alternatives to a true blue-water ascent and in both cases the appearance of your SMB alerts surface support that you have a "problem."
Staying on Route
The first principle of staying on route is that there must be a route to stay on. And so it follows that every good dive plan includes some form of rudimentary route map. Essentially this means that someone has thought about where the dive starts, where it finishes and has pin-pointed at least a handful of points in-between. In addition, this person has let every person on the dive know where they are expected to go and roughly when they are expected to be there.
Even though a solo diver has chosen to dive independently, there's no excuse for not taking the time to plan his route for the upcoming dive. Simply put, planning a route helps the solo diver with gas planning and time scheduling. And while there may not be a buddy to share the information with, a solo diver's route map should be shared with other divers who may be in the water at the same time, with a crew member or divemaster if they are diving from a boat or with a reliable person back on shore if they are shore diving.
An example of a simple route or dive pathway for a wreck dive might go something like this: "The dive boat is tied into the starboard mid-ships castle. I am going to descend to the rail, at a depth of approximately 24 metres / 80 feet, collect myself and get my camera adjusted just aft of the bridge and then swim forward to the forepeak, circle it, duck over the port side of the hull to the anchor and nameplate, take my photographs and then swim back along the port side rail to mid-ships. I should maintain a depth of no more than 24 metres / 80 feet for all this part of my swim and as I cross back to the starboard side (swimming over the engine room skylight) on my way back to the ascent line I will gradually work my way up to about 18 metres / 60 feet (the tie in point) and from there up it to my safety stop at 6 metres / 20 feet. The total duration of my dive will be 45 minutes - including ascent time - and I will start with 2900 litres /104 cubic feet of gas in my primary cylinder and with 850 litres / 30 cubic feet in my pony. My planned dive will require 1400 litres / 50 cubic feet of gas, which means my consumption gas volume is within the rule of thirds."
This type of outlined route is extremely straight-forward and extremely easy to follow. But perhaps most importantly, it is a simple route to track during the dive, because the dive itself has been divided into waypoints and these waypoints are easily recognized at depth and mentally ticked off as reached or achieved. By doing this, the diver knows precisely where he is relative to the diver's start and finish... especially the finish.
If a diver wanted to make a route like this more detailed, he could add timing at target depths, gas consumption estimates at certain waypoints, arrival times at each of the waypoints and so on.
He might also write the way-points on an underwater slate and physically tick them off as each is passed. There is no hard and fast rule about what constitutes a good waypoint. You will learn what works for you with practice and experience, but try to have at least five waypoints for a simple dive. Typical waypoints could include the first "go, no go" check during descent; arrival at target depth; reaching the dive's pre-arranged turning point; arrival back at ascent point and departure from bottom; arrival at safety stop.
Setting and tracking dive waypoints is an excellent habit to cultivate, and an invaluable tool for complex dive planning for both independent divers and dive team leaders.
Planning a route and following it requires an understanding of basic navigation. Basic navigation for the average diver boils down to using a compass to set a heading (getting from point A to point B); working a reciprocal heading (getting from point B back to point A); and knowing how far a kick/breath cycle moves them and their gear through the water so that they can measure off distance and time when travelling.
These are things a diver with your experience should know but let's recap them quickly before we move on to the advanced techniques for solo diving. We'll start with a technique we can use to measure distance and time.
At some point most divers measure off a short distance between two points underwater and swim back and forward a couple of times while recording how many fin kick cycles it takes to covcr the distance. They then divide the distance by the number of fin kick cycles and arrive at an average distance per kick cycle that is then used a rough measure to estimate distance on future dives.
Kick/breathe cycles are slightly more involved and take a little more effort initially but give a more accurate measure of distance and time for day-to-day "operations."
To start, one needs a measured distance of at least 30 metres or 100 feet with no current. One of the best measuring sticks is a shipwreck of a known length but some divers use knotted line strung between rocks or stakes. Now each diver swims his normal stroke and gets into a set rhythm synchronizing the power portion of his kicks with inhalations or exhalations. It's usual for a diver to get two to four kicks per breath cycle. The measured distance should be swum at least four times and the total number of kick/ breath cycles added together and then divided by the total number of metres, yards or feet swum. This gives an average distance per kick/breath cycle.
The exercise is completed by doing the whole swim again at the same speed but timing how many breaths the diver takes per minute. This is a secondary figure and can be used to work out roughly how many metres - or feet - the diver covers in a minute, and this can be used to compute an approximate speed. See the definition of a knot below for help with this final step.
You may also find it's worth the effort to work out at least two k/ b cycle speeds: one normal for cruising and one slow for searching.
As a minimum, every diver at this level should carry and know how to use an underwater compass. An UAV compass should have a turning bezel and a clearly visible lubber line and a free swinging needle with north indicated - usually with a blob of red paint - or better yet a compass rose with north, east south and west indicated, or a digital readout - in the case of a digital compass.
All U/W compasses are worked in similar ways. The fixed lubber line is oriented in the direction of travel and should be aligned to be parallel to the diver's center line. The rotating bezel, which contains needle centering bars and marks for degrees of heading, is rotated until the required heading (in degrees) is set in the center of the lubber line. Once this is done, the diver orients herself so that the needle or compass card sits with its north / south marks between the centering bars. The compass lubber line is now pointing to the desired heading.
Console mounted compasses are an alternative to wearing one on the wrist, but also consider one mounted on a navigating board or slate if you intend to do any complex navigation, since the slate is a great way to carry notes, a diagram of the intended route and waypoints for the dive. When a diver uses a compass, it is helpful to consider that an U/W compass will be affected by variation and deviation.
Variation is the difference between true north (which points to the North Pole) and Magnetic North (which points to Prince of Wales Island in Canada's Arctic region, which although it's a long way north, is not the North Pole). Compass Variation for an area is the same underwater as it is on the surface, and the variation for each geographical region can be a considerable number of degrees off true north. Compass variation also changes from year to year. You will find the compass variation for an area marked on marine charts and topographical maps, and it's also available on the internet. However, that said, most basic navigation for diving can be achieved well within acceptable limits by using magnetic headings rather than "true" ones. Not true if you are searching for
Chapter 5 | Staying Too Long, Going Too Deep, Getting Lost
hidden treasure or wrecks perhaps, but certainly OK if you are simply using your compass as a guide to get you out and back to your starting point.
Compass deviation on the other hand, may be more troublesome and more completely devious. Deviation describes the effects of iron and steel on compass readings. Steel tanks may be a factor you need to take into account, and if you do find deviation errors in your readings, try repositioning the compass or try adjusting your equipment. One real advantage of a compass mounted on a navigation slate is that it can be held far away from the body or even left on the sea bed and viewed from a body length away. As with any handheld compass, things like a huge steel shipwreck will contribute greatly to deviation. You need to be aware of this effect, and accept that sometimes, there is nothing you can do to correct it.
Heading and Bearing are sometimes incorrectly used interchangeably, but actually describe two different, although closely related things.The head on a sailing vessel was the foremost point of the bow and heading is the direction it's pointing. At least that's one way to remember it. Headings are usually expressed in degrees with North 00 degrees, East 90, South 180 and West 270.
Bearing is the direction of actual travel. You may set a heading of 90 degrees on your compass, but the wind, current and tide may all influence your travel and make your bearing many degrees different. One way to remember that bearing is the actual direction of travel is to think of the expression "to get one's bearings..." which means to gain an awareness of one's position or situation relative to one's surroundings.
Dead Reckoning (DR) is the technique where an object's position is estimated based on the distance it has traveled in its current direction from its previously computed position, and is usually plotted on a chart or map. Done with care, DR can return extremely accurate results, but it's less and less a factor in surface navigation since cheap and incredibly accurate hand-held GPSr units make working a DR plot a dying art. However, for dive planning DR is the favored technique since GPS signals do not penetrate water to diving depths.
In its simple form, DR works like this. A diver plans out a route, with distances and headings, and draws it out on waterproof paper or a slate. During the dive he swims along this pre-planned course line, using the compass and diagram for guidance and measuring off kick/breathe cycles for distance. He is able to determine his relative distance covered as he goes and hence can plot his position relative to his route on the fly.
For instance, if a diver followed a magnetic course of 200° for a total of 100 kick/breathe cycles, turned around and followed the reciprocal course of 20°, he could expect to arrive back at his starting point by about the 100th kick/breathe cycle. By tracking this modified DR method on a navigation board, an U/W writing slate, or even in his head, an attentive diver knows his position at all times.
The most useful navigation slates are specifically made for the purpose and have gridlines and a compass attached to them or at least a compass rose printed on them; however, any medium-sized slate with a pencil or graphite marker will be helpful.
45 k/b cycles 90'
Less'than 30 k/b cycles 270'
Figure 5.2 shows an example of a Dead Reckoning (DR) plot of a mildly complex search pattern (the type best accomplished with the help of a navigation slate).
The diver heads east for 45 kick/breath cycles, turns south and kicks for 15 cycles. He then turns east for 5 cycles and then heads back north for 10 cycles. He repeats this pattern and once it is complete heads back to the shore line, which he knows will be less than 30 k/b cycles away. He sees the shore line after about 26 or 27 cycles and follows the shore in a north westerly direction to his exit point.
Importance of navigation and dead reckoning should be extremely clear. There are few sights more disheartening for the diver who surfaces expecting to see her companions peering over the transom of a waiting dive boat and finding instead a small spec far off in the distance. With a little effort and practice, you can become proficient at underwater navigation and course plotting. These skills coupled with observation of underwater "landmarks" such as unusual rock formation, wave patterns in sand, coral outcrops, clumps of unique looking flora and fauna, will help you to avoid getting yourself hopelessly lost during your solo underwater adventures.
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