As we briefly discussed at the beginning of this chapter, there are many tools a diver can use for underwater navigation. One of the most popular is the use of natural markings and unique underwater signs, also known as Natural Navigation.
Natural navigation techniques can help the diver follow a route from the beginning to the route’s end and back to the exit point, all without having to use a compass. Using natural navigation techniques also help prevent long surface swims back to the boat, due to an ascent made too far away from the exit point.
There are a number of different elements divers should be able to recognize and use as natural navigation tools. These may include, among many others, the properties of light underwater, the seafloor’s texture, and the motion of water.
Lighting
The orientation of the sun’s rays can help a diver determine his position while under water. Prior to submerging, make note of the sun’s position as it may help you to determine general direction later in the dive. In conjunction with the time of day, the location of the sun’s rays can tell you which way you are traveling and the general direction to go to return to where you came from. However, when the sun is at its apex, usually around 12:00pm, its rays will be nearly perpendicular to the surface, which negates any helpful orientation information.
To make use of the sun as a navigation tool, imagine a clock dial. The 12 o’clock position is the direction you are pointed and the location of the sun is the hour hand. A the start of the dive take note of the “time” by facing in the direction you plan to travel and note the sun’s location. If it is directly to the right of you, that would be considered the 3 o’clock position.
When you are ready to return to the starting point, align the sun on your imaginary clock so that is opposite of your starting time, 9 o’clock. Work your way back, keeping the sun in the 9 o’clock position.
During night dives, a visible moon can have these same benefits if it is bright enough to be able to see under water.
Fixed Points
Fixed points are clear, immobile, and easily distinguishable objects on the seafloor that are either man-made or natural marine formations.
Man-made objects that act as fixed points could be wrecks, anchors, abandoned fishing traps, statues, or signs that have been intentionally placed. These objects are ideal navigational points, as they are often unique in nature and unmistakable under water.
Some of these objects — a wreck, for example, may be the purpose of the dive plan, though usually represent the start of the dive, or the point of return.
Marine formations that are used for fixed-point navigation should be immobile yet easily distinguishable from the surrounding environment. A unique coral formation, a massive sponge, or outcropping reef structures that can be potentially be used for reference points.
Fixed points in combination with compass navigation will be discussed later in this section.
Seabed Composition
The composition of the seabed is another, yet often overlooked, feature that may be used by the diver to determine his position.
Sand covered bottoms often display ripples in the sand. The ripples are caused by water movement and run parallel to the shore. Should you find yourself swimming over a sandy bottom, the shoreline will likely be on the uphill side of the ripples.
The slope of the bottom is also a very good indicator of position. Swimming along a downward slope of the bottom is almost always a good indication that you are moving away from shore, while swimming in an upward direction is usually indicative of moving towards the shore, or at least to a shallower location.
Seabed composition can also assist you with your general navigation.
Making a mental note of the seabed orientation and composition at the start of the dive will help you recognize the return route.
Motion of Water
The motion of the water in a particular area is a useful tool for navigation. The water in many areas will move specifically based on the formations around it, which can be used to help identify the area.
Another good potential indicator of direction is water current. As you learned in your Open Water Diver course, you should always begin your dive swimming against the current because that is when you have the most energy. At the end of the dive, the current will help carry you back to your starting location.
Depth
The depth of a fixed navigation point must always be considered and used in relation to the diver’s depth.
For example, if a diver identifies a unique reef outcropping as a reference point, but fails to note its depth of 60 feet (18 meters), he may become disoriented when looking for it again from a different depth.
For this reason, you should always take note of the depth of your reference points, particularly the depth of the boat anchor or ascent line.
Other Elements
The pre-dive briefing is perhaps the greatest tool in regard to underwater navigation. The dive leader will most likely provide a description of the dive site, the route and fixed points to look for during the dive. It is important to pay attention to the dive leader’s briefing and take notes if necessary. If you dive in a location that has specific boundaries, or is new to you, it may be useful to draw a map of the site on your slate to reference during the dive.
When you conduct a dive using natural navigation references, it is important to carefully observe the surrounding environment. Objects don’t always look the same when viewed from a different angle. When you start the dive and identify potential fixed reference points, be sure to look at them from the other side, after you have passed them, so you will know what they look like when you are heading back.
Understanding the key features of natural navigation and knowing how to manage your dive without having to rely on someone else, or follow a dive guide increases your comfort and confidence under water. It is also an indications of a more advanced diver.
While it is not navigation or an orientation specific parameter, gas planning should always be included in dive planning discussions when a particular route is involved.
It is recommended that the dive team follow the rule of thirds. The dive begins and continues until a team member has used a third of his gas supply. At which time, the team turns around and returns to the ascent point. The remaining third is used for the ascent and any other issues that may arise. For planning purposes, the dive plan should be based on the gas consumption of the member of the team that uses his gas the fastest.