Navigation TIPS & TRICKS
SOME RARE INDIVIDUALS are blessed with the gift of always knowing exactly where they are in relation to anywhere else.
Like migrating birds, they have an uncanny ability to find their way from point A to point B. My friend David is not one of them.
A few years ago, he was on a day trip, diving the Ribbon Reefs on the outer edge of Australia’s Great Barrier Reef. He had been there a few times before.
His buddy Hugh had not. “Don’t worry,” said David, “I’ll lead.”
In warm, tropical waters with visibility at 30m-plus, they swooped through gullies and swam between coral heads among clouds of purple and gold reef fish.
Drifting over the top of shallow corals towards the end of the dive, David saw a boat-ladder above him.
He attracted Hugh’s attention, pointed up and indicated that they should ascend. Hugh wagged his finger, “No!”
David guessed that he wanted to extend his safety stop for a few more minutes, and ascended anyway. He grabbed the bottom of the ladder, removed his fins and climbed up.
It didn’t take him long to realise that this was not the boat from which he had started the dive. Embarrassed, he climbed back down the ladder, put his fins on and went back down to join Hugh, who was still waiting patiently on the reef.
During his brief sojourn on the surface, David had spotted their boat a couple of hundred metres away, and they made their way over to it without any further difficulty.
Back on board, Hugh diplomatically did not refer to David’s faux pas but David thought he should mention it.
He had thought up a number of excuses, and trotted these out in order to try to save what was left of his face, ending by saying that “most boats look similar from below.”
“That’s probably true,” agreed Hugh with a straight face, “but our boat is a single-prop mono-hull and the one you climbed up on was a twin-prop catamaran.”
FINDING YOUR WAY
Instructors and guides have to know how to find their way under water all the time when leading customers or students, even when we are diving in new or unfamiliar locations. What is the secret? How is it done?
The good news is that becoming a capable underwater navigator is well within your grasp. It starts with four steps:
STEP 1: CONCENTRATE
There is a lot going on down there. The ocean is entertaining and distracting, and it’s easy to let your mind drift away.
However, if you watch your instructors and dive-guides closely, you will notice that, no matter how much fun they’re having, they are always working. They’re looking for cool things, keeping the group together, making mental notes of their surroundings and monitoring their computer and gauges.
If you are to take charge of your own dive, you need to concentrate similarly.
STEP 2: LEARN
Add a compass to your dive gear and learn how to use it. The navigation dive on your Advanced Diver Course will teach you the basics, and then it’s just a matter of practice.
Trust your compass. If it ever seems to disagree with your memory, instincts or common sense, believe your compass. It is far more likely to be correct than you are!
STEP 3: PREPARE
Before the dive, when you are looking out at the patch of water where you will be diving, try to visualise the underwater scenery.
Look for rocks or sandbars breaking the surface. Notice how and where the colour of the water changes with depth.
If you are diving close to shore, remember that the underwater landscape often mirrors the contours and features of the coastline. For example, a cliff-line or a rockfall is likely to continue below the water.
Again, still while on the boat or the beach, use your compass to plan your outbound and return compass headings and note these on a slate.
Memorise the position of the sun. This is the best natural reference there is, as long as the water is clear.
When diving wrecks (which are often made of steel, in which case you’ll find that your compass is not a reliable tool), do a little research in advance on the shape and features of the wreck, then make a drawing on your slate and remember to take the slate with you.
STEP 4: OBSERVE
You didn’t learn to dive just so that you could spend the whole time staring at a compass under water. Your powers of observation can help you to navigate naturally.
On a boat dive, as you descend, look up and see what the boat looks like from underneath. Remember the shape of the shadow it makes and the depth you need to be at to see this.
On a shore-dive, find a prominent feature close to your entry-point and memorise its depth.
After you descend and before you set off, check your depth, look around you and notice any unusual features.
Throughout the dive, be alert for significant landmarks and waypoints and, after you have passed a good waypoint, turn round and see what it will look like on the way back.
When returning in sandy areas, where there may be fewer good waypoints, look for silt trails created by your fins on the way out.
Sand ripples are a great navigation aid, as they normally run parallel to the shore and the more pronounced the ripple, the closer you are to the beach.
Combining compass use with natural navigation can be very effective. Knowing the direction in which you want to go, you can look across the compass and identify waypoints ahead of you, then use them to guide your way before referring back to your compass and repeating the process.
RETURNING TO BASE
To know how far away you are from your starting point and when you need to start looking up for the boat or returning to the shallows on a shore-dive, you need to know how far you have come. The best way of measuring distance under water for navigation purposes is by keeping track of time.
If there is no current and the pace of the dive remains the same, then the time it takes you to get to the point when you turn to come back should be the same time it takes you to return to the boat. However, a dive is rarely that straightforward.
The strength and the direction of any prevailing current will have an impact on how long it will take you to get back.
Before you head out, assess what current is present and which way it is heading. When the professionals plan a dive where they need to return to a fixed point such as a pier or an anchored boat, they will normally start the dive against the current so that the return journey, when legs are tired, is easier and takes less time.
If a strong current is present, then the only practical way to do the dive is with a mobile chase-boat to follow you.
To be sure you will make it back safely to your starting point with plenty of air left in your cylinder, a good procedure is to copy what cave-divers do. They call it the “rule of thirds”.
You look at how much air you have at the beginning of the dive, say 200 bar, then calculate what your cylinder pressure will be when you have used a third of this (133 bar.) This is your “turn pressure”.
The first diver in your team to reach his or her turn pressure turns the dive. As long as you do not swim deeper on the way back (and assuming there is no current) you will use more or less the same amount of air on the return leg, and get back to “base” with 67 bar or so remaining.
Following this procedure also means that you have a little extra air in case you need to deal with a current that picks up suddenly, or in the event that you need to share air with a buddy.
There are more accurate ways of measuring distance than using time and air supply but they are not really practical.
Counting fin-kicks and arm-spans are useful techniques if you are involved in a search and recovery mission, but they require a lot of concentration and it is unlikely that you will ever persevere with them on a fun dive.
When diving in very low visibility, there is no substitute for a reel and line. Tie off at your point of descent and run line out as you go, so that you can always find your way back.
This is an excellent technique to deploy if you have dropped a descent line at a wreck-site and missed it.
You can run the reel out and back in various directions until you find the wreck, then tie it off to give you a continuous path back to the surface.
Cavern-diver, cave-diver and wreck-diver courses offer good opportunities to learn how to run a reel and line correctly.
When laying line, it is important to wrap it or secure it regularly as you go. You want the line to be taut so that it doesn’t float around in the water, where there might be a danger of it getting you or others all tangled up.
Running the reel and laying the line are best done as a two-man task, with your buddy checking the wraps and placements on the way out and unwrapping them on the way back as you reel the line in.
Practise first on land, in the woods or around the house.