Question
What is the effect of centre
of gravity of slack tanks?
As the vessel rolls the
fluid in any slack tanks can shift to the low side moving the center of gravity
towards that side. This is called the free surface effect. When the CG shifts
it reduces the righting moment making the vessel more unstable.
Question
What is the effect on
stability of ice formation on superstructure.
In
Ice build-up can be formed
from snowfall, sleet, blizzards, freezing fog and sea-spray in sub-zero
temperatures.
In the
Icing allowances must be
made for:
Rise in G.
Loss of
transverse stability.
Increase in weight.
Increased draft due to
increased weight.
Loss of
freeboard due to increased weight.
Decrease in under keel
clearance.
Contraction
of steel due to temperature.
Increased
brittleness in steel structures.
Non-symmetrical
formation of ice.
Angle of
list.
Angle of
loll.
Change of trim.
Impairment
of manoeuvrability.
Reduction
in forward speed.
Increase in windage area on side of ship.
Ice formation adversely
affects the seaworthiness of the vessel as ice formation leads to:
— An increase in the weight
of the vessel due to accumulation of ice on the vessel's surfaces which causes
the reduction of freeboard and buoyancy;
— A rise of the vessel's
centre of gravity due to the high location of ice on the vessel's structures
with corresponding reduction in the level of stability;
— An increase of windage area due to ice formation on the upper parts of the
vessel and hence an increase in the heeling moment due to the action of the
wind;
— A change of trim due to
uneven distribution of ice along the vessel's length;
— The development of a
constant list due to uneven distribution of ice across the breadth of the
vessel;
— Impairment of the manoeuvrability and reduction of the speed of the vessel