Underwater Navigation.
Introduction
Remember your first open water dive? More than likely, you were thrilled with your first venture beyond a confined water or pool dive, but perhaps some what disoriented.Depending upon the dive site, you might have been surprised to find out that even though you were turned around, your instructor knew exactly where you were all along.
Your instructor demonstrated underwater navigation, an important diving fundamental that, as you discovered on your subsequent dives, you learn and apply easily through a few principles and practice.
The Navigation Dive in the Adventures in Diving program takes the rudimentary skills you’ve picked up, and expands them so you can use them with greater accuracy and under wider circumstances.
“Hey, I find my way around. What do I need a “nav” dive for”? Good question.
Navigation can be one of those things that you don’t recognize the benefits of until you really, really need it, or until you’ve followed a navigation ace who takes you straight from one place to the next with no wasted effort.
Almost any diver can wander around in a general direction and eventually end up in the right place, but you’ll find that greater precision brings with it at least five distinct benefits.
Reduces Anxiety and Confusion:
If you’ve ever been disoriented underwater, you know it can create anxiety, especially if you’re low on air and would prefer to avoid surfacing (due to boat traffic or chop for example).
You don’t know which way to go, which can be disquieting because you’re not sure where to head if you need to cut the dive short.
Or, you may have a general idea of where you are, but be confused about where you’re trying to go, which can be irritating as your air supply drops wile you search. It’s really annoying to find your “hot spot” just in time to leave due to low air.
Navigation eliminates stress and confusion because you will always know where you are, which way to go, and how far you are from the boat or shore.
Avoids Long Surface Swims:
If you’re not good at underwater navigation and your dive objective is some distance from the boat or shore, the only way to reach it without losing your way is to swim on the surface and then descend.
Likewise, if you get turned around during a dive, when you run low on air you have no alternative but to ascend where you are and swim back on the surface.
Not only are surface swims more tiring and less interesting than swimming underwater, but in some areas with high boat traffic, they may be more hazardous.
Increases the Effectiveness of a Dive Plan:
Navigation helps make a dive plan effective by eliminating guesswork about time and air needed to reach your objective and return.
For example, if you and your buddy plan to take pictures on a familiar part of the reef, you’ll swim straight there rather than waste time searching for it.
Navigation means you use more of your time doing what you came to do and less trying to find your way about.
Avoids Buddy Separation:
When you and your buddy plan a dive, navigation takes you together along the same path to an agreed upon destination, minimizing the likelihood that you’ll be separated from one another.
If you stray apart momentarily, you both know where to look and are more likely to find each other within a minute. This avoids spending time and air reuniting on the surface.
Conserves Air:
Anything that saves you time saves you air. Anything that helps you be confident and relax saves you air.
More air means more time doing what you like (taking pictures, observing fish, whatever), and makes for relaxing underwater swim back to the boat instead of a not-so relaxing surface swim.
Although underwater navigation benefits all diving, it’s especially valuable for some specialized activities.
For example, underwater navigation helps avoid disorientation during night dives and it’s easier to search for and recover a lost object when you know how to find your way.
Distance Estimation:
Although navigation requires some practice and applies several techniques to know where you are and where you are going: which way you’re headed and how far you travel. All navigation techniques accomplish one or the other of these.
Let’s look at distance estimation – knowing how far you travel. There are five methods commonly used: kick cycles, elapsed time, tank pressure, arm spans and measured line or tape.
Kick Cycles:
One of the most convenient ways to gauge distance is to count kick cycles. A kick cycle is the distance you cover when both of your legs complete one fin stroke.
To track kick cycles, choose either leg and count each time that leg returns to the same position.
The distance you travel in one kick cycle is usually consistent. During your navigation dive, you’ll count your kick cycles as you swim 30 meters / 100 feet.
If it takes you 40 kick cycles, you know you travel about .75 / 2.5 feet with each kick cycle. Then if you were to swim 100 kick cycles, you’d have traveled approximately 75 meters / 250 feet.
Gauge your kick cycles by swimming in the same, relaxed pace you use when diving normally. Measure kick cycles while swimming underwater because surface swimming is slower, and so your kick cycles will differ from your underwater swimming measurements.
You’ll find that kick cycles are most accurate in calm, still water, though in surge they’re also moderately accurate if you maintain a steady pace because the back-and-forth water motion tends to cancel itself out.
Kick cycles are particularly useful for measuring medium to long distances, and have the advantage of allowing you to stop, if necessary, and then resume your distance estimation. However, changes in your gear will affect kick cycles from one dive to the next.
The size and stiffness of your fins, drag from a larger tank or accessories like cameras, or diving overweighted will affect the distance you cover with each cycle. If you change fins or anything that alters how streamlined you are, you’ll need to remeasure your kick cycles, though they’ll still be consistent within the same dive. Current and water motion can affect accuracy, too.
Elapsed time:
You can also gauge distance under water by measuring the time it takes to swim a known distance. If you know it takes you 30 seconds to swim about 30 meters / 100 feet, you can estimate your travel distance by timing your swim.
In addition to kick cycles, you’ll measure how long it takes you to swim 30 meters / 100 feet during your underwater navigation dive.
As with kick cycles, swim at your normal, relaxed pace. The primary disadvantage of measuring distance with elapsed time is that if you stop or pause, you can throw off the measurements. Current can also reduce your accuracy.
Tank Pressure:
You can use tank pressure to measure distance for navigating patterns like tracking elapsed time. When remaining at approximately the same depth and activity level, your breathing rate is uniform, so you can base your distance covered during a normal swim on the amount of air you use.
For example, if you’re navigating a square pattern, you could swim in a straight line until you’ve used 15 bar / 200 psi and so on until you’ve completed a square.
The advantages of using tank pressure that it is often simpler than using a watch and that you’re constantly monitoring your air supply.
It’s not very accurate for measuring specific distances, however, if your depth changes significantly or if your breathing rate changes due to increased or reduced activity.
But, you commonly use tank pressure as a general distance measure across different depths when you follow a course you’ll return on.
For instance, if you use 70 bar / 1000 psi swimming away from your entry point, assuming little or no current, you can plan to use about the same coming back.
Thus, you limit how far you go based on how much you need to return, plus a reserve.
Arm Spans:
An accurate way to measure short distances is with arm spans. You measure by reaching forward with one hand, pivoting on it and reaching forward with the other hand, pivoting alternately until you cover the distance.
It helps you to know your arm span length ahead of time, but a good rule of thumb is that your arm span is about the same as your height.
Measured Line or Tape:
The most accurate way to measure distance underwater is with marked line or tape.
Although this becomes unwieldy when you have to measure an extremely long distance or over terrain with obstacles, it is excellent for short to medium distances over relatively flat terrain. Measured lines are used for accurate measurement in wreck diving, underwater archaeology and search and recovery.
Natural Navigation Underwater:
From your previous dive experience, you’ve probably already begun to learn natural navigation, even if you don’t know it.
Finding direction from patterns in the sand, following the slope of a reef or swimming against the current are all forms of natural navigation.
Any given dive site has features that you can use as navigational references. It’s just a matter of paying attention to the small details and environmental features that tell you where you are.
Pre-dive Observations:
Natural navigation begins before you dive by looking at the environment for navigation references. From the surface, you can usually tell a great deal about what you’ll encounter underwater, and you can use that information to determine where you are when you’re diving.
Waves, current and tidal movement:
The direction of waves, currents and tides, while changeable, usually remain consistent over the length of a dive (though they will change on you once in a while – especially tides).
You can determine wave and current direction by watching floating debris, and in the case of tides, by consulting tide tables. Once you know which way the water flows, you can orient yourself by swimming relative to the flow.
Knowing the tides avoids having to fight them on the way out and on the way back.
Sun Angle:
Before getting in the water, check how shadows fall and where the sun is in relation to your planned travel direction. Even in turbid water you can usually tell where the sun is and use it to orient yourself.
Offshore objects and formations:
It is useful to note the position of reefs, piers, kelp beds, buoys and other objects so that you know where you are when you encounter them underwater.
Waves breaking offshore may indicate a shallow reef or sandbar, giving you reference even if the reef or sandbar does not reach the surface.
Depth finder:
If you’re diving from a boat with a depth finder, you’ll be able to see a “picture” of the bottom. Depth finders can show bottom contours, wrecks and reefs, and even schools of fish, all of which can tell you where you are during the dive. Well, not schools of fish. They move.
Descents and Natural Navigation:
Natural navigation begins with your descent because how you descend can influence your ability to navigate. Ideally, descend in a head-up orientation (feet below head level) to prevent vertigo and disorientation.
Either you or your buddy should face the direction you intend to go and reach the bottom that way. Note the speed and direction of any current as you descend. These steps ensure that you begin your dive properly oriented.
Natural References:
Once underwater, you orient yourself through a variety of natural references that cue you through sight, touch and sound. The six most common of these are light and shadows, water movement, bottom composition and formations, bottom contours, plants and animals, and noise.
Light and shadows:
Noting the sun’s angle predive as mentioned, underwater you have a visual reference almost any time of day, but especially in early morning or late afternoon when the sun’s lower on the horizon and casts distinct directional shadows.
To use the sun and shadows for navigation, note their direction relative to your planned course.
For example, at the start of a dive you note that the sun is on your right and/or underwater shadows are to the left. If you get disorientated during the dive, turn so that the sun’s on your right and shadows are to your left.
This faces you in your original direction. If you turn so the sun’s on your left, you face the direction you came from. Changes in light intensity can cue you to unnoticed depth changes.
Water movement:
Currents provide one of the surest means of underwater navigation. If you’re drift diving (see the Drift Diving section), or diving with the flow of a river, the current naturally navigates for you, carrying you where it will.
In most cases, however, you swim against the current with the flow giving you a constant bearing. Be aware that currents can shift direction during a dive, especially when tides change.
Plan your dive with this in mind, so that the current helps you return to your exit at the end of the dive. Pay attention to current direction and speed as you descend.
Surge is another reliable reference because the back-and-forth motion swings to and from shore or shallow areas.
Because waves passing overhead and then flowing back to sea cause surge, you feel it most strongly in shallow water.
However, large swells can make surge quite noticeable in even relatively deep water.
When diving in surge, note the water movement to determine the direction toward shore. If you’re disoriented to the point that you don’t know which “swing” is shoreward, follow the surge in one direction and watch your depth gauge.
In the majority of cases, shoreward will be shallower and seaward will be deeper, but it helps to know the dive site before hand.
Bottom composition and formations:
Changes in bottom composition are something else to note during a dive. You may find that various areas have distinctly different bottoms, ranging from rock, to sand, to mud or reef, depending upon the environment. Plant life (discussed shortly) can vary with bottom type.
Even when the bottom composition is the same, water movement may create patterns you can use for navigation.
Sand ripples are a good example; they form perpendicular to the water flow. In lakes and the ocean near shore, sand ripples always parallel shore; by swimming perpendicular to the ripples you head toward or away from shore (easily judged by whether you’re getting deeper or shallower).
Bottom contour:
The bottom almost always has notable contours suitable for navigation. You can follow a natural slope toward deeper water; rock ridges, coral reefs, kelp beds and in man-made lakes, even lines of felled trees form natural paths you can swim along.
To follow contour, simply keep the slope or other reference on your right or left. To reverse your course, turn around and keep the contour on the opposite side.
Plants and animals:
Aquatic plants and animals often have specific niches or characteristics that provide clues you can use for navigation.
Some organisms live only at specific depths, cuing you to deeper or shallower water nearby.
Other examples include sea fans, which always grow perpendicular to prevailing currents, and sand dollars (when alive), which typically themselves perpendicular to shore.
Finding fish is open sand may suggest a reef or habitat near by.
Through careful observation and training, such as offered in the PADI Underwater Naturalist Specialty course and during the Underwater Naturalist Adventure Dive (see Underwater Naturalist section); you recognize the different organisms that provide information about your location underwater.
Note how these organisms lie relative to your position and travel direction at the start of your dive, and you can use them as a reference to maintain your direction or reorient yourself. But schools of fish move, so forget those.
Noise:
As you learned in your Open Water Diver course, it’s difficult to determine sound direction. But, you can still use sound as a navigation aid by paying attention to its strength and your relative distance from it.
Organisms on reefs sometimes click or crackle, telling you you’re approaching or leaving it.
The sound of a boat compressor or generator, the clanking of an anchor chain or rocks tumbling in the surf can all provide reliable information about your distance from the boat or shore.
Using Underwater Patterns:
It’s much easier to know where you are and where you’re going if you follow a predetermined pattern instead of swimming around randomly. This might sound restrictive, but you can actually explore more of the dive site than you would by wondering around aimlessly.
You use your limited air and bottom time more effectively when you use a pattern suited to the dive site. Out-and-back-lines, squares/rectangles, triangles and circles are commonly used navigation patterns, each with its own characteristics.
Out-and-Back Lines:
The simplest pattern is a straight line out, then reverse course and return to your exit. This works well along narrow formations that form the line you follow.
The edge of a reef or a wall may mark your line, or you may use a compass heading, watch for cross currents, which can push you off your intended path.
Square/Rectangle:
Squares and rectangles cover more area than a line. You can make 90 degree turns easily whether or not you use your compass, so they’re suitable patterns for either natural or compass navigation.
A typical rectangle pattern might be to swim out from shore, turn 90 degrees and swim parallel to shore (perhaps following a reef), then turn 90 degrees and swim toward shore. In shallow water you might turn 9 degrees again to swim (perhaps at safety stop depth) parallel to shore to your exit.
Triangles:
You don’t commonly use triangles in natural navigation, but more so when using a compass.
A triangle covers a wider area than a straight line and may be useful in areas where a rectangle or square is impractical, but again, it’s difficult to navigate a triangle using only natural navigation.
Triangle patterns without a compass usually happen when underwater features create a triangle that you can follow conveniently.
Circles:
It’s nearly impossible to swim in an accurate circle with either natural or compass navigation.
For this reason, you use circles primarily for underwater searches with a line. One diver holds the line while the other pivots around in a circular search pattern.
You can learn more about using circular patterns in the Search and Recovery Adventure Dive and in the PADI Search and Recovery Specialty course.
Effective Pattern Use:
There are six ways you can use underwater patterns more effectively. First, discuss and agree on a pattern with your buddy as part of your dive plan.
This helps prevent confusion and buddy separation.
Second, try to visualize the pattern both before and during the dive, so that you’ll have a ‘map’ in your minds eye.
Third, use a small pattern and swim slowly along it. Large patterns are more difficult to follow accurately.
Fourth, if you leave the pattern to look at something, remember where you were and the general heading so you can resume the pattern.
Fifth, have one buddy navigate and follow the pattern. Sixth, if you become disorientated, surface slowly and carefully and check your position.
If you’ve deviated from your pattern, you can swim to intercept and resume your original pattern, or you can develop a new navigation plan based on where you are.
Compass Navigation:
You can compare navigating underwater to navigating in the air. In clear weather, a pilot can navigate by following landmarks and roads, but in poor weather, at night,or in the clouds, the pilot relies on instruments.
Similarly, while you use natural references for much underwater navigation, when you navigate in poor visibility, at night, or in midwater where you can’t see the bottom, you’ll rely on your compass.
Let’s review and build upon what you learned about compasses and compass use in your Open Water Diver course.
Compass Features:
The first step in underwater compass navigation is to invest in one suitable for the job. The ideal underwater compass has all of the following features:
Liquid filled.
A liquid filled compass withstands pressure and dampens needle movement so it’s easier to read.
Free-swinging needle.
Choose a compass with a needle (or compass card – a disk with the needle printed on it) that rotates even if the compass isn’t perfectly level (which is frequently the case underwater).
Numerical degree markings.
You need degree numbers, rather than just north, east, south and west markings, to navigate patterns and when noting bearings in your dive log.
Luminous features.
Glow in the dark markings and needle will help at night and in low visibility because you won’t have to point your light at the compass and try to use it at the same time.
Lubber line/direct sight and bezel.
As you learned in your Open Water Diver course, you normally use your compass by swimming along an imaginary line straight through the center of the compass face (or along the compass side) that you use to align yourself with your travel direction.
A direct sight compass has no lubber line, but uses a sight over the compass face to accomplish the same purpose. You use the moveable bezel to set your desired heading.
A few new electronic compasses accomplish the same tasks with digital readouts. Some models display the heading you’re facing, while others display a compass face similar to a standard compass.
Features for setting headings while navigating vary greatly from one electronic compass to the next – see manufacturer literature for specifics.
Holding the compass.
A compass is no more accurate than the person using it, and accuracy starts with how you hold it. Holding it incorrectly probably accounts for the vast majority of compass navigation errors divers experience.
To hold a compass correctly, whether you wear it on your arm or carry it in your instrument console, align the lubber line with the center line of your body.
If you wear the compass on your arm (lets assume your left), hold your right arm straight ahead and grasp it with your right arm straight ahead and grasp it with your left hand so that your middle finger rests in the depression behind your right elbow.
This should put your compass squarely in front of you. If not, adjust your grip and/or the compass position until it does.
If you carry your compass in a console with both hands centered in front of you, with your elbows tucked it your sides, again so the lubber line aligns with your body center-line.
Swimming with the compass.
Holding the compass properly, you swim with the compass lubber line centered with your body’s center-line, looking over (not down on) the compass face.
Keep the compass as level as possible so the needle doesn’t lock, and keep the needle inside the index marks on the bezel (more about setting the bezel in a moment). With practice, you’ll be able to swim in a very straight line.
Setting the compass.
Setting the compass is based on two points: First, the compass needle always points to the magnetic north pole. If you find the needle no longer within the compass index marks when you’re navigating, either you’ve turned off course or the north pole moved thousands of kilometers.
Actually, the magnetic north pole does move, but so slowly it requires decades to affect your readings.
This movement causes magnetic declination, which is a difference between true north and magnetic north. This difference has no practical effect on basic underwater compass use). Second you always travel along the lubber line.
The bezel and index marks help you maintain he relative angle of the lubber line (direction of travel) to the needle (north) so that you swim in a straight line.
Setting a heading.
To set a heading, point the lubber line in your desired travel direction. Next, rotate the bezel to set the index marks over the compass needle.
Now swim along the lubber line as you just learned, keeping the needle between the index marks.
If the needle leaves the marks, you’re off course. Turn until you return the needle within the marks, and resume swimming.
Setting a reciprocal (return) heading. After swimming along a specific heading, you may want to return along a reverse heading.
Turn the bezel to put the index marks 180 degrees from the original heading. Turn until you centre the compass needle between the index marks; you should be facing back to where you came from. Return by swimming along the reciprocal heading.
Navigating a square/rectangle.
To compass navigate a square or a rectangle, begin by setting a heading for the first side and swimming the desired distance (use your distance estimation techniques to measure).
Rotate the bezel 90 degrees and turn to realign the needle with the index marks. Add 90 degrees for a right turn, or subtract 90 degrees for a left. (When adding, due North is 0 degrees; when subtracting it is 360 degrees.)
Swim along the new heading the desired length and then rotate the bezel another 90 degrees in the same direction (right or left) for the next turn. Repeat the process until you complete the pattern.
Navigating a triangle.
Using your compass in a triangular pattern is the same as with a square or rectangle, except that you turn the bezel 120 degrees for each turn.
(Note: A compass measures the outside of each turn,which is why triangle pattern turns are 120 degrees rather than 60. Make five 60 degree turns if you want to navigate a hexagon.)
Useful hints for compass use.
Here are a few pointers that will make using a compass easier and more accurate.
Trust your compass.
Sometimes it feels like your compass is ‘wrong’, but the compass works based on laws of physics, whereas your sense of direction is based on the same intuition you use to predict the weather. Go with the compass.
Use natural references.
The combination of natural navigation with compass navigation is the most effective navigation.
The compass closes gaps where you cant effectively navigate with landmarks, and natural navigation helps offset any mistakes you make using your compass.
Practice on land.
Become familiar with your compass by using it on land. Set headings and walk through the patterns you intend to use while relying entirely on your compass (but watch were you’re going so you don’t step into an open manhole or something).
You’ll have a chance to practice with your instructor before making your Underwater Navigation dive.
Allow for the effects of currents.
A compass helps you swim in a straight line, but water movement such as currents or surge can carry you off course. If currents are common in your local area, your instructor may teach you how to navigate accordingly.
Be prepared to navigate around obstacles.
This is usually accomplished with four 90 degree turns detouring the obstacle. The first and last legs of the detour should be the same length.
Share responsibilities mid-water.
If you’re navigating in mid-water, have one buddy read the compass and the other monitor depth. The depth buddy can hold the compass buddy’s arm to keep the team together while watching instruments.
Use intentional error on long distances.
If you’re looking for a small, specific destinations a long distance away, chances are you’re going to miss.
Sorry, but even the best underwater navigation just isn’t that precise when you start swimming hundreds of meters/feet. So, aim for slightly to the right or left of your target. If you miss your mark (probably) you know which way to search.
Use compass aids for accuracy.
A compass board extends the compass lubber line, thus increasing your accuracy. Heading calculators like the Nav-finder let you map irregular courses, and show you compass headings for patterns without having to calculate in your head.
Understand the limits.
Underwater navigation, with or without a compass, is useful in relatively small areas. If you need to cover a long distance, you may be better off swimming on the surface or surfacing periodically to check your location.
Plan your dive within the reasonable limits of underwater navigation.
Take your time.
Effective navigation relies on taking your time, relaxing and paying attention to your compass and other navigational clues. The more you hurry toward a destination, the more likely you are to end up somewhere else.
