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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.