when sea water temperatures averaged 1.02C, with
researchers found icing rates to be greatest on those
parts of the ship that face the seas and winds (Tabata et
67% of all cases occurring in temperatures between
1.0 and 3.0C (Ryerson 1991). Jorgensen (1982) indi-
al. 1963). These relative winds also produced the great-
est icing, in concert with low temperatures, when ve-
cates that when wind speeds are high, and air tempera-
tures are lower than 5.0C, seawater temperature has
locities were greater than 10.8 m s1 (Ono 1968). Iwata
(1975) observed icing on patrol boats at relative wind
a negligible effect on icing rate.
speeds of 10.3 to 20.6 m s1. Gashin observed the most
Seawater salinity was also infrequently sampled on
intense icing on the trawler Aysberg when wind speeds
the USCGC Midgett because of dangerous weatherdeck
were greater than 20.6 m s1 (Borisenkov and Panov
conditions (Ryerson and Longo 1992). However, dip-
1972). The relative winds encountered by the cutter, as
ping bucket samples indicate that average salinities dif-
measured on the Beaufort scale, averaged from Force
fered by only about 1‰ between the two icing events.
5 to 6 during the two events, with a maximum of Force
Though Shellard's (1974) review found the importance
9 during the February icing event, and Force 8 during
of sea water salinity to be small in influencing icing
the March event (Table 1). According to Jorgensen
rate, others have found it to be important in assessing
(1982), Beaufort Forces 56 are the most common lower
the mass and thermodynamics of icing (Brown and
limits for ship icing.
Roebber 1985). Jorgensen (1982) reports icing to
Seas were generally heavier during the February
begin at higher temperatures when salinities are lower.
icing event, with the mean and extremes being larger
Makkonen (1987) and Gates et al. (1986) make a strong
for wave height, swell height, and combined wave and
case about the effect of salinity on the "sponginess" of
swell height. For the two events together, however,
ice, its thermodynamics, and its mass. The salinities
waves averaged about 1.0 m, with maxima of 1.2 to 1.8
and their variation observed aboard the cutter fell well
m, and swells averaged about 1.5 m with maxima of
within values observed in other ship icing studies
2.1 to 2.4 m (Table 1). Combined seas reached 3.4 to
(Shellard 1974).
4.3 m. Fishing trawlers suffer from icing most often in
Accreted ice thickness
waves of about 1.5 m and swells of about 1.8 m off the
east coast of North America, comparable to those mea-
Superstructure ice never accreted to more than 4.4
sured during icing of the cutter (Ryerson 1991).
cm thickness aboard the cutter (Table 2). Samples of
Relative wave direction and relative swell direction
ice were taken at the end of the February icing event,
were computed similarly to relative wind, with 0 at
but no samples were taken during it (Fig. 7). Thick-
the stern. In general, waves and swells struck the cutter
nesses of samples ranged from 1.6 cm on the forward
on the port side because of vagaries in the ship's track,
bulkhead to 3.2 cm at location F1 on the deck forward
geographic position, and weather patterns. During the
of the 5-in. gun (Fig. 8, Table 2). During the March
February icing event, waves arrived about 10 off the
icing event, samples were taken at three different times
port bow, but swells arrived about 60 off the port bow.
during the event (Fig. 7). Up to 4.4 cm of ice formed
The March event actually received waves and swells
on the main deck during the March event, and 3.4 cm
from nearly bow-on to 20 to starboard (Table 1).
of ice formed on the port vertical surfaces of the 5-in.
Kultashev et al. (1972) observed maximum spraying
gun housing. As in the February event, ice thicknesses,
on trawlers when winds and seas approached the ship
overall, were small, and most ice formed on the port
3040 off the bow.
side because, in both events, seas approached princi-
Water temperature was measured at the engine cool-
pally from port.
ant intakes by the quartermasters. It was also recorded
The mean thickness of ice on horizontal surfaces at
by bathythermographs, and by the CRREL researchers
the end of the February icing event was 2.6 cm, and the
using dipping buckets (Ryerson and Longo 1992). From
average thickness on vertical surfaces was 2.2 cm.
these combined sources, best estimates of seawater tem-
During the March icing event, horizontal surfaces
perature were derived (Table 1). Water temperatures
averaged 2.0 cm of ice, and vertical surfaces averaged
averaged about 1.8C during the February event, and
1.5 cm, indicating that ice on vertical surfaces was about
2.2C during the March event. In a literature review,
75% of the thickness of ice on horizontal surfaces
Shellard (1974) found little agreement about the
(Ryerson 1995).
importance of seawater temperature to icing rates. How-
Automated time-series measurements of ice thick-
ever, he indicates that there generally is no icing when
ness on the ship, though not highly accurate in absolute
water temperatures are above 8C. Lower water tem-
terms, did provide trends in ice thickness through icing
peratures contribute to heavier icing, but the air tem-
events (Ryerson 1995). These trends suggest that there
perature is the overriding factor. On trawlers off of the
are accretion and ablation sub-events within the pri-
east coast of North America, icing was most common
mary ice-accretion event. These sub-event patterns,
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