Jökull - 01.12.1969, Page 123

ministration should give consideration to more
severe requirements.
If comparing the IMCO recommendations
30 kg|m2 on open weather decks with the dia-
grams in Fig. 3, taking the specific gravity of
icing to be 0.85, the thickness of ice on decks
will be 3.5 cm, which is “moderate” on the
diagrams. To this should be added however tEie
weight of the lateral area icing according to
IMCO.
It is of interest to collect more data of icing
of Icelandic ships to see how they compare
with these figures. It is not possible to ensure
stability of a ship regardless of the amount of
icing. Tlierefore further measurements are
needed of the actual icing of ships at sea, to
enable a decision to be taken on the reason-
able amount of icing to be considered when
calculating intact stability.
The specific gravity of icing on a trawler
was measured in Reykjavík harbour on Janu-
ary 14th and 15th 1969. The ship received
rather heavy icing when passing Reykjanes
(Figs. 1 and 2). The rnean value of the specific
gravity was found to be 0.847 (g/cm3).
The measurements were carried out by cutt-
ing out ice blocks of icing on different places
on deck, on wire, ropes etc. These ice blocks
were measured, and their volume calculated.
Each block was then put in a separate glass
container and the content weighted at a
laboratory. The salinity was also measured,
and found to vary from 9.11 to 17.39%0.
METHODS TO REDUCE DANGER
OF ICING OF SHIPS AND
EQUIPMENT TO REMOVE ICE
In order to reduce clanger of icing of ships,
the following is of importance: At the design
stage of a ship ice collecting items on deck
should be kept at minimum. Wire rope rigging,
open handrails etc. accumulate considerably
more ice than tripod masts and plate bulwarks.
The hull form and freeboard should be such,
that sea spray is kept at a minimum, and form
stability as good as possible. All super-structure
should be fitted with watertight closing appli-
ances on main deck. When icing starts to form
on a ship, the speed and course of the ship
should be sucli as to keep sea spray at minim-
um, even though fishing has to be stopped.
Nets, derrics, wires and other lose equipment
ehould be lowered, both to reduce topweight,
and to reduce icing. Freeing ports should be
kept clear and open at all times. All equip-
ment for removing ice should be kept ready
for immediate use. It is important to keep an
eye on the icing, and start removing it before
is has reached any considerable weight. It is
not considered adviceable to seek shelter at
the edge of the sea-ice area. The icefield is
not a shelter against wind, but here the air
and sea temperature are very low. Shoukl the
direction of the wincl change, being parallel
to the ice-edge, the sea spray will increase
rapidly, and the ship will then be subject to
dangerous ice accumulation.
Besides the ice axes and other direct mech-
anical means to remove the ice by hand, several
other equipment and outfit have been tested
ancl will be tested which are safer and more
easy to apply for removal of ice.
Steam- and hotwater pipes and hoses on deck
are useful to assist the mechanical removal.
Electrical heating of decks, masts and super-
structure makes mechanical removal of the ice
also easier. By covering areas such as the front
of the weelhouse with rubber or plastic
material, pulsating air-pressure hoses between
the flexible covering and the structure can
break off the ice, if it has been permitted to
form thick enough deposit to be broken but
not to yield. Special paints have also been
tested in order to find out if it is possible to
reduce the adhesion between the structure and
the ice which would make mechanical removal
more easy.
Doubtless further development of equipment
for removal of ice will reduce the danger from
icing of ships. More experience in forecasting
icing with the weather forecasts, for dangerous
icing-areas, will also no doubt be of great
value to increase the safety of ships in north-
ern waters, but today we still have to keep in
mind the views expressed in the report on
icing of trawlers from the British Shipbuilding
Research Association: When icing conditions
are encountered, the only safe protection for
the ship is to withdraw from these conditions
as quickly as possible.
JÖKUL.L 19. ÁR 119