Navigation

Learning Objectives

• Explain the differences between pilotage and dead reckoning.

• List at least 7 items of equipment for diving navigation.• List at least 6 aids to natural navigation.• List at least 5 ways to measure distance underwater

and state which is most accurate.• Compare the following: heading, bearing, course, and

fix.• Describe variation and deviation and state the cause

and effect of each.• Explain how to circumnavigate an underwater

obstacle.• Contrast true north and magnetic north.

Main Points

• Methods of Navigation

• Measuring Distance Underwater

• Natural Navigation

• Fixing a position

• Compass Navigation

Methods of Navigation

• Pilotage – Confirming location using visual checkpoints

• Dead Reckoning– Estimating position based on distance and

direction. – This system requires keeping track of

speed, time, and direction of travel.

• Combination– Using one system to confirm the other

Measuring Distance Underwater

• Measured line/tape measure – most accurate

• Arm spans

• Kick cycles

• Air consumption• Time

Natural Navigation

• Underwater landmarks– pick something permanent.

• Ripple Marks– parallel to the wave front– deeper/steeper ripples = waves feel bottom more– ripples closer together = waves closer together

• Surge– typically onto and off of shore– strongest toward shore

• Currents• Bottom contours• Sunlight or changes in light

Fixing Position

• Ranges– Establishes 1 line of position (LOP)

• Fixes– Use multiple lines of position to establish

position

Compass Navigation

• Terminology– True North

• Geographic North pole– Magnetic North

• Point near the North Pole towards which a compass needle points.

– Variation• Local differences between True and Magnetic North.

– Deviation • Difference between Magnetic and Compass North.• Caused by

– Metal– Magnetic source

Compass Navigation cont.

– Bearing • Angular direction from an object expressed in

degrees. Bearings may be expressed in terms of True, Magnetic, Compass or relative degrees.

– Heading • A course followed or to be followed

– Leeway • Sideways slipping due to wind or current.

Compass Navigation Cont.

• Uses of a compass– Follow a specified heading/direction/course– Establish bearing/direction to an object– Fix position

Compass Navigation Cont

• Parts of a compass – North seeking needle

• needle always points– Compass card

• card with course numbers always points north– Lubber line

• used to determine direction of travel– Sights– Index marks– Rotating Bezel– Navigators window

• allows you to read the course from the side of the compass• Provides actual compass course

Compass Navigation Cont

• Siting a course– best way is to site across the compass– alternatively align lubber line with center of

diver and desired course.

Compass Navigation Continued

• Patterns – Straight line/reciprocal– Squares/Rectangles– Triangles– Circumnavigating

• 90° turns• Constant distance

Compass Navigation Cont

• Common Errors– Not paying attention– Compass not level– Not believing the compass and following

your nose– Compass pointed in the wrong direction– Not keeping track of distance

Compass Navigation Cont.

• Miscellaneous Equipment– Slates– Markers– Floats– Compass board– Charts

Main Points

• Methods of Navigation

• Measuring Distance Underwater

• Natural Navigation

• Fixing a position

• Compass Navigation

Learning Objectives

• Explain the differences between pilotage and dead reckoning.

• List at least 7 items of equipment for diving navigation.• List at least 6 aids to natural navigation.• List at least 5 ways to measure distance underwater

and state which is most accurate.• Compare the following: heading, bearing, course, and

fix.• Describe variation and deviation and state the cause

and effect of each.• Explain how to circumnavigate an underwater

obstacle.• Contrast true north and magnetic north.