Compass Navigation:

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 centerline.

 

 

 

Swimming with the compass

Holding the compass properly, you swim with the compass lubber line centered with your body’s centerline,

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.  (Guess which is most likely. 

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 indexmarks;

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.)