the average swell wave height, use the height of all of
the swell waves, not just the highest 1/3, as used for sea
waves. Similarly, when determining average period,
count and time all of the rounded swell wave crests
passing the fixed reference pointed. Make swell wave
observations from the side of the ship the waves are
approaching from to see the wave pattern better. The
swell wave direction should be determined from a
relatively high position on the ship so that a larger area
of the sea may be observed.
Frequently more than one group of swell waves
may be observed, each coming from a different
direction. When this happens, you should attempt to
determine average height, average period, and direction
for each swell wave group. Swell wave groups should
differ in direction from each other or from the sea waves
by 30° or more to be considered and reported in an
Further information on sea and swell wave
observations is contained in NAVMETOCCOMINST
3144.1, as well as H.O. Pub 603, Practical Methods for
Observing and Forecasting Ocean Waves.
Shipboard Aerographers Mates are occasionally
tasked to recommend Romeo Corpin for underway
replenishment (UNREP) operations, including
connected replenishment (CONREP) and vertical
replenishment (VERTREP). Romeo Corpin is the best
course and speed a ship should "come to" to minimize
the effects of the seas and swell on the ship. Wind is also
an important consideration. The most desirable course
gives the ship the most stable passage to minimize roll,
pitch, and yaw of the ship, while limiting the apparent
winds across the deck to a safe working level for
personnel. During VERTREP operations, Romeo
Corpin may be limited by the relative wind
requirements for the helicopters involved.
guidance for determination of Romeo Corpin is found
in Underway Replenishment, NWP 4-01.4. Much of the
necessary guidance for the best replenishment course
depends on how each individual ship type handles in
different sea conditions. This information may be
obtained from a qualified Underway Officer of the
Deck. All requests for Romeo Corpin should be
referred to the Forecaster.
Q68. Define wave height.
Q69. What factors will determine the maximum height
of sea waves for any location?
What would be the average wave height with a
sea state of 5?
Define wave period.
How is wave direction determined?
What is meant by the term "significant wave
How do swell waves differ from sea waves?
How is swell wave height determined?
LEARNING OBJECTIVES: Define ice
accretion. Describe the characteristics of ice
accretion. List elements to be included in the
observation of ice accretion.
Ice observations are conducted as part of general
shipboard weather observations. Ice accretion is the
accumulation of clear ice (glaze) or rime ice on the
outside structures of a ship. Ice may form on a ship
when the air temperature is below freezing and
hydrometeors are present. Glaze commonly forms
when the air temperature is between 32°F and 25°F
(0°C and -4°C) with dense fog, freezing rain or drizzle,
or blowing spray.
Below 25°F the probability of
freezing precipitation drops sharply. As the
temperature approaches 14°F, (-10°C), fog and blowing
spray form rime ice rather than clear ice, because the
freezing occurs too fast for the trapped air bubbles to
escape. Ice tends to accumulate first on wires, railings,
masts and exposed fittings, and then on flat surfaces
receiving little heating from the interior of the ship. Ice
accumulates last on decks and bulkheads heated from
within the ship. Ice accretion is dangerous not only to
personnel who must walk across or work on the weather
decks, but to the ship as well. Ice accumulations may
break wires and antennas. If the accumulation is heavy
enough, the added weight on the superstructure may
cause the ship to roll excessively or capsize.
Observations of ice accretion include a
determination of the source of the moisture, such as fog,
blowing spray, or freezing precipitation, as well as an
average measurement of the thickness of the
accumulated ice, in centimeters. The observation also
requires a determination of the rate of accumulation or