Jökull - 01.12.1969, Blaðsíða 111

Icing of Ships
HJÁLMAR R. BÁRDARSON,
ICELANDIC STATE DIRECTOR OF SHIPPING, REYKJAVIK, ICELAND
REASONS FOR ICING OF SHIPS
Icing o£ ships, which is usually due to £reez-
ing o£ sea spray that is blown over the vessel,
is a well known problem in northern waters.
(Icing refers generally to the formation of ice
on ships, aircraft, power-lines, aerials and other
man made installations or equipment). The
sea spray is partly shipgenerated, and partly
derived blown from wave-tops. The formation
o£ ice on ships is often considerable on fore-
castle deck, on rails, masts and rigging and on
other super-structures. Icing is forméd by an-
other reason when undercooled fog or rain
freezes, thus creating fresh water icing. This
type of icing is more common in typical arctic
waters, and will not be considered here.
In icing conditions the danger for a ship is,
of course, primarily due to the fact, that the
ice-accreation increases the top-weight of the
vessel, thus moving the center of gravity up-
wards and reclucing its weight stability. At the
same time added weight will decrease the free-
board and therefore reduce the formstability
of the ship. Furthermore accumulation of ice
in masts, rigging and other super-structure will
increase the el’fective wind area and therefore,
increase the effect from a wind-moment, which
would further reduce the stability of tlie ship.
This effect will be evaluated later. Several loss-
es of ships are definitely known to be due to
icing, but several other ship losses, are also
considered to be due to icing. Many nations
have carried out research on icing of ships, the
main object often being to study the process
of icing, the accumulation rate and external
factors influencing icing. The aim of some of
these studies has focused on the possibility of
predicting icing, that would permit broadcast-
ing the danger of icing with the weather-fore-
cast. For sucli predictions consiclerable amount
JÖKULL 19. ÁR 107