chart and publication secrets 5
the depth might be less that what is indicated on the chart (see Chapter 5 for
more on tides).
U.S. charts show soundings in feet, fathoms, or meters, with the latter
becoming more prevalent as charts are revised. Some charts in other countries
combine two or more of these units. Look in the chart’s title block or along
one of the white borders to find which units apply.
Charts that combine soundings, such as fathoms and feet, show a normal-
sized base number followed by a subscripted number, such as 24. Th e base number
indicates the major depth and the subscripted number the minor depth. For
example, in this case we have 2 fathoms and 4 feet, or 16 feet, of water over this
particular spot. A sounding of 1 5 on the same chart would indicate 1 fathom
and 5 feet, or 11 feet, over that spot. For more examples, see below.
Q soundings in fathoms
How many feet of water do these soundings represent?
(One fathom equals 6 feet.)
2 Answer: 2 × 6 = 12 feet
8 Answer: 8 × 6 = 48 feet
Q soundings in meters and feet
How many feet of water do these soundings represent?
(One meter is about 3.3 feet.) Round the fi nal answer
down to the closest lower whole number; this gives you a
margin of safety.
34 Answer: 3 × 3.3 = 9.9 + 4 = 13.9, or about 13 feet
11 Answer: 1 × 3.3 = 3.3 + 1 = 4.3, or about 4 feet
Q soundings in fathoms and feet
How many feet of water do these soundings represent?
14 Answer: 1 × 6 = 6 + 4 = 10 feet
35 Answer: 3 × 6 = 18 + 5 = 23 feetTHE IMPORTANCE OF BECOMING SEA BOTTOM SAVVY
Seabed characteristics continue to play a vital role for the modern-day navigator.
With this information you’ll know exactly which anchor you need to put down
to hold your boat overnight or in a blow. If you run aground, knowing whether
the bottom consists of mud, sand, rocks, or coral helps you choose the best way
to free your boat without damage.
Th ree descriptions paint a picture of the sea bottom: type, texture, and color
or contrast. Sometimes your chart will show only the basic bottom material
or type, but in other areas it might further describe the material color and
textures. Th e most common abbreviations used for sea bottoms are found in
the accompanying table.