1:1 ON YOUR DATE
Position lines and Position fixing
Three point fix:
Position lines are obtained from usable navigational aids on land or sea. Lines can be defined by:
The intersection of two (preferably 3) or
more position lines gives a fix, but you must allow for errors in measuring angles, identification
and plotting. Apply Variation to the compass bearing to get True bearing (subtract
A hand bearing compass is assumed to have no Deviation.
Note that navigation buoys can be off station, or even completely missing.
Dipping distance M = 2.08 × (√eye height m + √height of light m)
A light ‘dips’ when you can first see the ‘blink’ above the horizon.
Before that you can see the ‘loom’ when it is still below the horizon (like the sun before dawn).
Height of eye in a yacht is about 2 - 2.5 metres
The table in the back of the Training Almanac tabulates dipping distances for various heights of eye and light.
If the tide is below MHWS it increases the height of the light above sea level while the height of eye stays the same, so you can see the light from a greater distance.
posted 5th November 2009