Underwater Navigation

Navigation Defined• The process or activity of accurately

ascertaining one’s position and planning and following a route

• Can be accomplished a variety of ways:– GPS– Compass– Landmarks– Wind/water movement

• You need two primary pieces of information!– Direction– Distance

Nav. Terms

• Course– Your planned route, usually marked on a map or

chart.– Can be more than one “Leg”.

• Bearing– The direction from your current location to any

distant point, given in degrees from North.• Heading– The direction you are currently pointing.

N

45°

40°

84°

2 knot current!!!

You are here, what is your course? What’s missing?

Notice that this Rose has a blue arrow and a red arrow… Why?

Magnetic North vs. True North

• Charts are presented relative True North

• A compass will mark Magnetic North

• True North IS NOT Magnetic North…

• The difference between True and Magnetic is called Magnetic Declination– 20.4° W in this example

What are your true headings in this scenario?

45°

40°

84°

On the first leg, your compass reads 45°.

Take the declination given on the Rose, and subtract the value from your compass bearing.

If the declination is East of North, you will need to ADD to your compass bearing!

Declination changes with time…

2014 Declinations

A note on Declination and Diving• Declination is only relevant over long

distances, or when you are using a map to navigate.

• B/c we work in low visibility most of the time, no adjustments are necessary as long as we are consistent… And commonly, we can’t even SEE the compass.

Using a Compass

Direction of GO (DOG)

Magnetic needle, red points to Magnetic North

Orienting arrow, also called the “Shed”

Rotating bezel

Diving Compass

• Everyone use your compass to find 60°• Dive compass have some slight differences…

Using a Compass Cont.• Identify your course (What

direction do you want to go?)– Let’s say East, or 90°

• Hold your compass level in front of you and turn the bezel so that your desired course is lined up with your DOG.– NOTE: metal WILL CAUSE YOUR

COMPASS TO DIVERT!!!• Turing your body, not just the

compass, put the red (red side of the magnetic needle, OR North arrow) in the orienting arrow (Shed).

• You are now heading on course…

We have Direction, now we need Distance

• What are some ways to measure distance underwater?– What if you can’t see the transect tape?!?

• Kick Cycles, Pace Count, Wing Span– Calibrate yours to a number that is easy to work with (i.e.

10 meters)– Pros/Cons for each?

• CRITTERS CAN HELP YOU FIND THINGS!– Follow the fish, they usually go to structure

• You will calibrate your kick cycles/wing span at Vortex.

Final Notes…• Currents

– Can bias your distance and direction, adjust your calculations

– Use a line, orient w/ the current…– Touch the bottom– Make marks on the bottom

• Use landmarks/topography– Coral fingers– SE banks limestone piles.

• Surge• Particulates

• Easterly Current and Easterly Wind…