by

Larry "Harris" Taylor, Ph.D.

Divegeek Content Page:   Home     About "Harris"     Articles      Slides     War Stories     Editorials        Fini

The term navigation is derived from two Latin words: navis meaning a ship or vessel and agere meaning to direct. So, we define navigation as  the process of safely moving from one place to another. The process of navigation requires that you accurately know:

the direction needed to travel to reach the desired destination,

estimates of distance to be traveled (and related factors like time needed, gas to be consumed, etc.),

any environmental factors, like wind, currents or obstructions that will influence the path actually taken between starting and ending points.

So, underwater navigation requires that the diver has information about both distance traveled and the direction needed to travel between two points.

Desired direction of travel and distance can be estimated while in the water by sighting (taking a bearing) on target object or from a chart prior to the dive.

Kick Cycles

Divers need a way of estimating distance traveled underwater. One of the most common methods for determining underwater distance traveled is the "kick cycle" One kick-cycle is counted every time the diver kicks with one particular leg (i.e. half the total number of kicks). This is determined by measuring the time and number of kicks-cycles it takes to swim a measured underwater course. We typically use a 100 foot line and average time, counted kicks, and air pressure readings for three determinations. This is usually done as a buddy team with one diver counting kicks and recording air pressure readings, while the other determines time.

For example, assume a diver averages 1.5 minutes to swim 100 feet. This corresponds to: (remember we want velocity which is distance divided by time):.

100 ft  / 1.5 min = 66.57 ft / min

This diver also counted 25 (taken for ease of calculation) kick cycles for the 100 ft. course. This corresponds to  a distance per kick of

100 ft / 25 kicks = 4 ft. per kick cycle

So, in this hypothetical situation, if the diver needed to swim 600 feet to an underwater object, the diver would reach the object (assuming swimming in a straight line and no current influences):

600 ft / 4 ft/kick cycle  = 150 kick cycles

The 150 kick cycles would take (assuming constant speed)

150 kick cycles x 4 ft/kick cycle x 1/66.6 ft/min  =  9 minutes

Kick cycles combined with  Estimating Air Consumption represent a reasonable method for approximating dive parameters and making decisions on the dive site feasibility, especially when working from a nautical chart.

The Compass

The compass uses a north seeking magnetic needle to indicate the direction of the North magnetic pole. As with land orienteering devices, the underwater compass is divided into 360 degrees. Typically, on land, the the north-seeking needle is aligned with the North marker on the compass and the base plate arrow is rotated so that the "direction of travel" arrow is aimed at the destination. Often, once the direction is established, the user moves toward a visible object along the path of travel without referencing the compass.

With the underwater compass, the  bezel is first rotated such that the lubber line marks are centered around the desired direction of travel. The diver then moves so that the north-seeking needle lies between the lubber line marks (or red lubber line trace). The diver then swims keeping the needle between the lubber line marks

 Land Orienteering Compass Underwater Compass UW Compass Parts

The compass is most often mounted on a console. The console acts like a mini compass board and facilitates holding a steady course. The preferred placement of the compass on the console is closer to the diver, as opposed to the far end of the console. Compass boards are often homemade, although the board, without instruments, and expensive tactical devices can  be purchased. We prefer a side reader compass since this arrangement facilitates taking a bearing (getting intended direction of travel) while still in the water.

Compass boards typically have a compass, timing device, depth gauge, and a level. In general, compass boards are considered more reliable than a compass mounted on a console. Our navigation compass boards use a capillary depth gauge since navigation training occurs in shallow water.

Based on watching students learn compass skills, we prefer a compass on a console (or a board) as opposed to mounted on a wrist since it is extremely difficult to be consistent with a wrist mounted device.

 Console "T" Arrangement "Linear" Arrangement Compass Slate RJE Tactical Board

The Towel Exercise

It is critical that the diver and compass move as one unit (avoiding the natural tendency to simply move the console with the hands to align the off course needle.) The best way to keep the compass and body moving as a single unit is to hold the console in both hands (equally spaced on either side) and to lock the elbows tightly into the body. This forces the body and the console to move as a single unit. (Imagine a straight line thru the long axis of the body extending through the lubber line of the compass.) To facilitate practicing this procedure, we use the "towel exercise:"  While on shore, students take a bearing towards a landmark and set their compass bezel.  They then place a towel over their heads, lock their elbows tight along the body and walk forward keeping the compass needle aligned with the lubber line marks. This develops the oneness of compass and self.

 Taking A Bearing Covering Head Hitting Landmark

Once successful on land, they are ready to practice underwater.

The Practice Course

In the words of legendary football coach, Vince Lombardy, "Practice does not make perfect; only perfect practice makes perfect performance." So, an important aspect in learning underwater navigation is practice that provides successful results. To this end, I have the students set up a diamond shaped practice course. Using distance-marked line, the students place an anchored dive flag or swim noodle ( See Noodles for assembly directions) at 100 feet from shore to form 2 points of the diamond. While they are doing this, I add a center point ~ 50 feet from shore as well as the farthest tip of the diamond. A more detailed description of our two practice courses is given Here.

The students first swim the short distance (~ 50 feet) from shore to the center marker. They are almost always successful on their first attempt. It not, then they practice this short distance until they hit the center marker. Then, as a buddy team (one spotter and one navigator), the students sequentially target each point of the diamond, alternating roles at each leg. The spotter looks forward to hopefully detect the target. The navigator locks the console close to the body such that the console is directly below the eyes. This minimizes tendency to move the hands/console when the needle strays outside the lubber line. The navigator counts kick cycles and, if the object is not spotted after 10% beyond estimated number of kicks, the team surfaces, moves toward the missed target and then sights on the next target. Typically, after a few laps, the team runs the entire diamond course without the need to surface.

 Success!

Conclusion: Using the towel exercise and a defined practice course facilitates learning underwater navigation skills.

Top

Divegeek Content Page:   Home     About "Harris"     Articles      Slides     War Stories     Editorials        Fini