Jökull - 01.12.1969, Blaðsíða 119

22 cm
M
Fig. 9. Icing meter, used to measure the rate
of icing.
and the trawler St. Romanus, most likely in
tlie North sea are still remembered by every-
body. At the same time as Ross Cleveland was
lost 4th February 1968, near ísafjördur on the
west coast of Iceland, the Icelandic fishing
vessel Heidrun II was lost with all on board.
No doubt icing has been the main reason for
these losses although the weather was very bad
at that time.
MEASUREMENT OF ICING ON SHIPS
WITH ICING-AIETER
It was mentioned before, that in Japan an
icing-meter was used in icing experiments in
1962 and 1963 (Tabata et al. 1963 and Ono
1964).
The purpose of the icing-meter is to mea-
sure the weight relation between sea water
spray at the place of the icing-meter and the
icing accumulated on the meter. As sea water
spray contains salt, all of it does not freeze.
Ice is crystallized from pure water from the
sea spray, the unfrozen brine being concentrat-
ed which decreases the critical temperature of
crystallization. A part of the brine flows down
on the surface of the accumulated ice, and a
part of it is confined in cracks of the crystalliz-
ed ice. The accumulated ice is therefore con-
sidered to consist of such confined brine and
pure frozen water. Due to downward percola-
tion of the brine on the surface of the ice, the
amount of accumulated ice is normally less
than that of sea water spray which is thrown
on the ship. The ratio of the weight of ice
accumulation to that of the sea water spray
is termed “rate of icing”, wliich can be used
as an index to assess the rate of growth of
icing. An icing-meter is shown on Fig. 9. Part
A of the figure shows a cylinder on which the
ice is deposited, and part B a jar which coilects
the downward percolating brine.
THE ICING OF CYLINDERS
IN CONDITIONS OF SIMULATED
FREEZING SEA SPRAY
Many parts on board of ships on which ice
is accumulating are cylinders, such as masts,
derrics, rigging wires, shrouds, hand rails etc.
The British tests on a model of a trawler in
an icing wind tunnel referred to earlier, were
Fig. 10.
Streamline airflow around a cylinder.
JÖKULL 19. ÁR 115