78 seamanship secrets
If your eyes are 6 feet above sea level, would you believe only 2.9 miles? Th e
distance to the horizon is limited by the earth’s curvature, which causes objects
beyond the horizon to appear to drop off the earth. In order to see more distant
objects, we must raise our height of eye (HE) farther above sea level—for example,
by climbing to the cabin coachroof or the fl ying bridge. Th is of course is why
lookouts in the whaling ships and sailing navies were posted in masthead crow’s
nests. (For more on distance to the horizon, see Chapter 7.)
CHOOSE A PROMINENT LANDFALL OBJECT
Before you make a landfall from off shore, pick a prominent charted object—such
as a mountaintop, lighthouse, or offshore light tower—on which to home
your approach. If you know the height of the object and your own height
of eye, you’ll know when to expect it to come into view on your horizon in
clear weather. The steps below describe the procedure for making landfall
on lighted and unlighted objects.
Making Landfall on a Lighted Object
- Find your height of eye and the height of the object. Estimate your
height of eye (HE). Assume, for example, that your HE will be 9 feet when
you’re standing on your coachroof. Th at fi gure includes the height of the
coachroof from sea level (3 feet), plus your own height (6 feet). Now read
the height of the Dry Tortugas Light from the chart: 151 feet. - Find the geographic range. Geographic range combines the distance to
your horizon and the horizon distance of the other object. Th e formula is:
Th e Dry Tortugas Light stands 151 feet above sea level. Th e 20M in the abbreviation next
to the light indicates the object’s nominal range in nautical miles. (Th is range takes into
account the light’s candlepower, but not its height; see text.)