Jökull - 01.12.1969, Blaðsíða 121

Þvermál sívalninga í tommum
Fig. 14. Effect of cylinder diameter on the
icing efficiency (vertical scale).
the differences in the shape of the ice accre-
tions on a horizontal and a vertical cylindrical
objects, no significant difference in icing effici-
ency was apparent. ft was therefore possible
to combine the results from all the tests as
shown in Figs. 13 and 14. They show the
effect of temperature and cylinder diameter
on the icing efficiency. The manner in
which the icing efficiency increases with de-
creasing cylinder diameter (size) confirms with-
out slightest doubt the vital necessity to keep
the number of rails, stays etc. at minimum, and
when possible one larger diameter strut should
replace several smaller ones.
THE INFLUENCE OF ICING
ON THE STABILITY OF SHIPS
Icing of a ship reduces both the weight sta-
bility and the forrn stability. The top weight
of the ice accumulation raises the centre oí
gravity (G) (Fig. 15). The centre of buoyancy
is Bi in the inclined position. The total weight
of the ship being W, the moment GZxW is
a righting moment in the Fig. 15 a and the ship
is stable, but in the Fig. 15 b, the moment
GZxW is an upsetting moment, thus the ship
is unstable. When G moves upwards due to
icing the moment arm GZ will decrease until
the uprighting moment will not be sufficient
to withstand the force of wind and sea, and
the ship will capsize. Fig. 16 shows the effect
of the raising of the centre of gravity G. The
GZ curve will decrease and finally only small
external forces will be needecl to capsize the
vessel.
But the icing has also other effects on the
Fig. 16. Etfect of raising of the centre of
gravity, G, on stability.
Fig. 15.
Stable ship
and unstable.
JÖKULL 19, ÁR 117