Divers can use their senses and observation skills to navigate their paths underwater. Natural navigation includes checking for moving water, temperature, color and light, sound, distance, underwater formations and the location of plants and animals.
Can’t figure out how to operate a compass? Don’t worry, you can use a plethora of other methods to find your way around underwater! Using all the senses of sight, sound, touch, smell and taste you can let nature be your compass.
Table of Contents
Natural navigation depends upon your powers of observation, common sense and basic outdoor skills. Just like scouts who learn that most grows on the north sides of trees or that animals rest with their noses into the wind to detect approaching trouble/opportunity, here are some categories of clues for natural underwater navigation.
* Moving water
* Permanent formations
* Changing formations
* Position of plants and animals
* Color and light
Currents are good ways to check your direction of travel. While currents may shift during a dive, they are good indicators. It is customary to execute a dive by swimming against the current and concluding by swimming with it.
If you are swimming into a current and suddenly feel it pushing on your side, you know you’ve turned to the right or left. If your dive plan was to swim offshore, crossing a longshore current to get to a wash rock, you should feel the current on one side of your body on the trip out. If anything changes you have shifted course.
In areas with tidal currents, diving is usually done at slack tide. If the tidal current picks up near the end of a dive, it is important to know which way the water is headed, so you can swim toward a pre-planned exit point. Hopefully, you remembered to plan a downstream exit.
Currents come in all sizes and speeds. Some are predictable, like tidal currents. Others exist at a certain depth range. One of my favorite dive spots almost always has a slight current at 60 to 70 feet. I can make a whole dive at less than 60 feet while staying above the current.
Using natural navigation to assess currents is to consider things relatively. For example, is the current stronger or weaker than it was earlier? Is my snorkel vibrating more or less than it was at the end of my last dive here? It usually doesn’t matter that a current is moving at precisely 1.2 knots, since you do not plan to calculate anything. It is more important to recognize that today’s current is much weaker than usual so diving should be OK. Or, if the current suddenly accelerates, you need to recognize that a change in the dive plan is required, perhaps getting ready to exit immediately.
Sport divers don’t have a way to measure current speed easily, so they use natural clues. Is the kelp bent over a little or sucked way underwater? The farther the stalks are bent over, the stronger the current. If the boat pulls into a cove known to have a great kelp pad and it has disappeared, look in the water. It may be completely sucked beneath the surface. This means the current is screaming and you need to select a different spot.
Are the seafans straight up and down or bent over? The more bend, the greater the water flow. Is the seagrass puffy and loose or whipping back and forth? Are the fans gently bending to and fro in a light surge or are they nearly folded over? Perhaps the fans are bent over to one side with the flow of a constant current. How far are they bent over?
If you aren’t sure of the direction of a current, look at the filter feeders. They are practical organisms that position their catch mechanisms perpendicular to the current. They must sit and wait until food drifts by, so they want to be lined up to catch the best meal.
Surge and swell are other water movements that can orient divers. Surge moves toward and away from the shore. You’ll know the shore is one of two directions by riding the surge. Swell is the up and down movement of the water column as a wave passes overhead. If you stay in a fixed position and a large wave passes overhead while you simultaneously read a depth gauge, the depth reading will be greater. If you are really feeling the swell on a dive and then it stops, the chances are you’ve gone deeper, not that the swell has stopped. The deeper you go, the less you’ll feel the effects of a swell.
The simplest navigation is following a reef finger from a shallow depth to a deeper depth, reaching the end of the formation, turning around and working your way back to the shallow end. It’s very common and a practical way to navigate. As you get bolder, try swimming out one reef finger, turning left and crossing three other fingers. Turn left again, then follow the last finger back toward shore. As you get shallower turn left again and swim back to the reef formation you started on. You’ve taken a square route underwater and used the reef fingers as two sides and a way to measure across.
While this works great on Grand Cayman’s West End, it is not ironclad. Sometimes the reef fingers jut off at angles or end. Some Bahamian waters are better known for coral reef mounds interspersed among fingers. The Great Barrier Reef is famous for its bommies – huge coral structures sitting in the middle of a sand flat. That’s when you adapt and do “bommie hopping” – or swim past two bommies, circle around the third and work your way back to the start.
Freshwater lakes are more of a challenge. Rocks are usually scattered across the bottom in no apparent pattern. If it is a quarry you can follow the ledges from mining or the ore car railroad tracks. Other permanent formations often found in Midwest lakes are airplanes, school buses, ice fishing houses and derelict boats. Stuff seems to litter most lake bottoms, either accidentally sunk or placed as a fish habitat. But, when visibility is six feet and you suddenly see a school bus, you know you’ve arrived at the dive’s destination.
The sandy bottom holds changing clues. Ripples or ridges in the sand are created by wave action. Most run parallel to the shore. The lip of the ripple faces toward the shoreline. The closer together the rows of ripples, the nearer they are to shore. Bottom ridges change daily in shape and density but the basic shape always points out the shore direction. Diamond or V-shaped wedges of sand are found in wave areas near shorelines. Waves stack the sand as they approach the shore, then pull it backward. The point of the V is usually headed toward the beach.
Temperature generally decreases with depth. The deeper you go the colder the water. Freshwater lakes have layers called thermoclines, where temperature markedly changes. You can feel thermoclines and often see them, too. The water shimmers differently where the temperature changes.
Freshwater divers know a summer dive above 30 feet in a favorite lake may not require a hood. But, drop below the thermocline at 30 feet and your head feels as if it is in a vice if you aren’t wearing a hood.
Position Of Plants And Animals
Earlier we noted that filter feeders position themselves so the current flows over their body parts that catch the food. Different fish will school into a current or down current. It just takes noticing what the animals are doing in a particular location. For example, schools of baitfish are generally found mid-water to the surface. If you see a big school of anchovies, you aren’t likely to be at 100 feet.
Various species of vegetation tend to live in definable zones since that habitat is conducive to their growth and propagation. For example, grasses are only found in shallow water, where they get maximum sunlight. Certain algae may only have a 10 to 30 foot depth range before the environment is outside their favored parameters. Hard corals need light and warmth and are thus depth restricted. Some vegetation thrives on sand washing over it and other types get ground to shreds. The key is to notice what types of plants and animals inhabit the zones you pass through on a dive. If you start a dive in eelgrass and move to a rocky reef, you know you have gone deeper without ever looking at a depth gauge.
Color And Light
Light is another handy indicator. Like land plants, underwater vegetation grows toward a light source. If there’s a doubt about up versus down, check your bubbles and the new growth edge of plants for bearing.
The color of what you see underwater also indicates depth. A general rule of thumb is that in clear water, red fades out by 10 feet. Orange fades by 15 feet, yellow fades around 30 and green diminishes from 40 to 60. After 60 feet, blue, indigo and violet are all that remain.
Ambient light decreases with depth. Mid-summer in an algae laden Minnesota lake it may be pitch black at 30 feet. Take the submarine off the wall in Grand Cayman and you’ll find an amazing amount of natural light at 800 feet.
Light rays stream through the water like hands on a clock. In the morning the rays angle from the east, at noon they are straight overhead and in the afternoon they slant from the west. Most dives don’t last long enough to use light rays for time clues but the light’s angle can orient you to east and west.
Commercial boats almost always have their generators running. You can hear them underwater and the louder the sound, the closer you are. The sounds of a boat combined with a visible anchorline will lead you back.
Sport divers generally use pretty loose measurements. Ask four people after a dive their estimate of the visibility and expect to get four quite varied answers. Other than depth and elapsed time to compute no decompression limits, recreational divers can’t be bothered with measurements and notes in logbooks – until they can’t locate a favorite dive spot!
If you would like to “measure” distances and have them be repeatable, you’ll need a simple formula. The formula for calculating distance is: D = SxT (D = distance, S = speed, T = time).
If you know your speed and time, you can find the distance. Here are some ways to ascertain some of the numbers to compute the unknown quantity. The common ways to measure distance include time elapsed, number of kick cycles, air used and line measurements. Time elapsed means to swim a certain number of minutes. Clearly the distance traveled varies tremendously from diver to diver, depending upon conditioning, type of fins, level of kicking or environmental conditions. Notes in your logbook about elapsed time have to be used very generally.
Kick cycles (a cycle is one complete up, down, up movement) are an easy way to determine distance or speed. Conduct a speed experiment by swimming with normal equipment a distance of 100 feet on the surface at your regular, comfortable pace. Rest on the surface after the swim, then descend to a shallow depth and swim the same distance back at a normal pace. This tells you the amount of time it takes to cover 100 feet on the surface and at depth. If you can, take a 100 foot length of rope and place it on the bottom as a guide, you’ll swim in a straighter line and know your 100 foot test length is accurate. If laying a line on the bottom isn’t practical, use a marker (pile of rocks or natural formation) to mark the start, reel out 100 feet of line to measure the distance, then reel the line back in.
Next, discover your speed/time by comparing distance measurement against kick cycles. Using the 100 foot non-floating line on the bottom, swim the length of the line using your normal kick and pace. Count the number of kick cycles required for you to cover the distance.
For example: 100 feet = 2 feet of travel per cycle 50 kick cycles
Entries in your logbook might contain reference to 400 kicks out to a reef. You can calculate that 400 kicks at an average of two feet of travel per kick cycle equals 800 feet or a 266 yard swim.
If you want to test the consistency of your kick cycle, find a flat, sandy bottom. Swim a 10 kick by 10 kick square pattern while dragging a knife or snorkel tip to lightly mark your path. When you finish, look at the pattern scribed on the bottom to check the squareness of your route. Did you end up at the starting point? If your 10 kick pattern was accurate, try it again with 20 kicks. The farther you travel the tougher it is to be consistent but that is the key to repeatable navigation.
The amount of air used in a given period of time is another way to measure distance traveled. If you have a favorite dive spot you may be able to exit the beach at a big tree, swim perpendicular to the shore for 200 pounds of air and arrive close to the dive site. It is a personal estimate that depends upon your air consumption, water conditions and equipment. There’s a big difference if you increase your drag by carrying a camera and strobe arm or if a current is running.
If an exact distance is important, you’ll need a more fixed measuring tool. For short distances, arm spans (one arm stretched down at your side and the other stretched above your head) will typically be five to six feet. For fun, have your buddy measure your height, then measure your arm span. Are they nearly the same? Measuring on the bottom by arm spans is a tedious process, with a high potential for slippage or going off course. To use this method count your arm spans moved and then multiply by your arm span to find the distance in inches. Convert to feet.
A line and take-up reel is an easier application. Tie the end of the line to a rock or other fixed object. Don’t tie it to the end of a kelp stalk or a bunch of eel-grass, which will move or be pulled out of the bottom. Unreel the line until you reach the designated place. Distance may be pre-marked on the line with knots, colored threads interwoven in the line or rings of tape at set distances. If you use a flat reel board or handle, you can count the number of turns as you unreel or rewind a line. This isn’t extremely accurate, since it takes more line to complete a wrap the more line there is on the reel. If you plan to use this system buy a 12 inch reel for easy calculations. An 8 inch reel makes for messy math!
Colored threads work nicely for marking line if you put one heavy duty thread or small ribbon at the first mark point, two at the second mark point, etc. Depending upon the line length, you may choose to use 10 or 25 foot mark points. If you plan to use 300 feet of line, mark the first 100 feet in one color, use a different color for the second 100 feet and a third color for the final 100. Select colors that are very different, such as yellow, red and black. Don’t get fancy and use three shades of blue or you will be very confused underwater. If you plan to use the lines at depth remember, the color we see changes with depth. If you choose red, orange and yellow, they will look very similar at 90 feet.
Navigation by nature’s signposts is effective, adds to the enjoyment of a site and your overall appreciation of the environment. As you assimilate more clues, your navigation skills sharpen and diving becomes less stressful. You no longer worry about how to get back to the right place on shore or to the boat. With a general overview of the dive’s terrain in mind, you can make mid-dive detours and still execute the original overall plan. You can learn to use currents to ride back to an intended exit point. You can quickly find dive sites, rather than wandering around underwater and hoping to swim over the school bus or reef before you have to head back to shore.
Use your fabulous computer brain to record the details of a dive and the memories will become directional billboards on future dives. It also helps if you make an effort to remember unusual formations. With experience you will recognize the seascape and know if you have been there already. Diving is a lot more fun if you never spend a minute looking for your buddy or wondering if you are lost or if you can find the boat without a long surface swim.