ship as possible, since the passage of the ship through
the water tends to mix surface water with water from the
keel level of the ship. The "bucket" should also be cast
ahead of where the observer is standing so that the
bucket fills as it drifts by the observer. As the
movement of the ship carries the bucket astern of the
observer, the bucket should be retrieved. A standard
thermometer is then inserted into the water sample, and
the water is slowly stirred with the thermometer until
the temperature reading stabilizes. The temperature is
read to the nearest 1/10 degree Fahrenheit.
The next best method is to obtain a sea surface
temperature from an expendable bathythermograph
Procedures for conducting a
bathythermograph sounding are covered in a later
module. Bucket temperatures should be conducted
occasionally to verify that the recorded
bathythermograph surface temperature is accurate.
Sound velocimeterreadings may also be used in lieu of a
Seawater Injection Temperature
The least accurate method is the seawater injection
temperature reading. Seawater injection temperatures
are read in the engineering spaces and are usually
readily available by shipboard phone from the "main
engine room control" watch/operator.
constantly taken onboard for cooling the engines and
for conversion to freshwater. The seawater injection
ports are located well below the water line, sometimes
as deep as 60 feet on aircraft carriers. Therefore,
temperature readings at that point do not accurately
reflect a sea surface temperature, but rather a near
surface temperature reading.
In tropical waters, the difference between the
surface temperature and the near-surface temperature is
usually slight. But in certain regions of the mid- and
high-latitudes, a strong surface thermocline may exist,
which will cause a rapid decrease is temperature from
the surface to the injection level. This may cause the
difference between the actual surface temperature and
the injection temperature to be very large. If injection
temperatures are used, they should be routinely checked
against bucket temperatures and bathythermograph
temperatures, and adjusted if necessary.
Q56. Define wet-bulb temperature.
What is the normal result of air being cooled to
below the dew-point temperature?
Given an air temperature of 82.5°F and a dew-
point temperature of 70.0°F, calculate the dew-
What is meant by the term "frost-point
List three methods for manually obtaining the
sea surface temperature.
LEARNING OBJECTIVES: Describe wind
speed and wind direction. Define and identify
how to determine true-wind direction, relative-
wind direction, and magnetic-wind direction.
Explain wind character and wind event. Define
The atmosphere is essentially an ocean of air
surrounding earth. Temperature is unevenly distributed
over the earths surface, varying with latitude and with
the seasons. Therefore, all of earths atmosphere is
continuously in a state of fluid motion. Wind is the
observed effect of horizontal transport of air masses
over earths surface. Surface winds are the movements
of air within 50 feet of the ground. The term winds
usually refers to both wind speed and direction.
Different reporting codes require that observations be
made over certain periods of time. Some conventions
require a 2-minute observation period, while others
require a lo-minute. These time periods are specified in
NAVMETOCCOMINST 3141.2 and NAVMET-
Winds are observed by using the equipment
discussed in chapter 2. Automatic observation
equipment will immediately report and record winds;
other wind-measuring equipment can show a detailed
graph of speed and direction over time. Winds are
described by wind direction, wind speed, and wind
Wind direction is the average direction from which
the wind is blowing during a specified period. Airflow
from the north toward the south is referred to as a "North
Wind direction always shows minor
fluctuations. These minor fluctuations are normally
"averaged out" when determining a wind direction.