Jökull - 01.12.1969, Page 122

Fig. 17. Effect of increased freeboard on the
stability.
stability of a ship. Due to the weight of the
ice, the freeboard of the vessel will be reduced,
and therefore also the form stability.
This effect on the GZ curve is shown in
Fig. 17. The GZ-curve I is the basic curve.
The GZ-curve II a shows the efíect of in-
creased freeboard as compared with curve I.
Curve II b shows again the effect of raising
the centre of gravity. In all cases the angle 0°
is the angle of inclination of the ship. The
third effect of the icing on the stability of the
ship is the increased wincl area of rigging and
super-structure, so that a smaller wind gust is
sufficient to capsize the ship.
(the area A on Fig. 18), and not less than
0.09 metre-radians up to 0 = 40° or the
angle of flooding 0f, if this angle is less
than 40°. Additionally, the area under the
righting lever curve (GZ curve) between
the angles of heel 30° and 40° or between
30° ancl 0(, if this angle is less than 40°,
should not be less than 0.03 metre-radians.
(Area B on Fig. 18).
(b) The righting lever GZ should be at least
0.20 m at an angle of heel equal to or
greater than 30°.
(c) The maximum righting arm should occur
at an angle of heel preferably exceeding
30° but not less than 25°.
(d) The initial metacentric height GM0 should
not be less than 0.35 m.
When calculating the intact stability of fish-
ing vessels it is recommended by IMCO that
a certain amount of icing should be included,
when considering vessels operating in certain
northerly and southerly waters. Weight of ice
per square metre of all exposed weather decks
and gangways is to be assumecl not less than
30 kg/m2, with the addition of a weight of ice
per square rnetre of projected lateral area of
the portion of the vessel above water plane
not less than 15 kg/m2. For vessels operating
off the east coast of Canada during the winter
nronths IMCO is recommending that each Ad-
THE IMCO INTACT STABILITY
CRITERIA FOR FISHING VESSELS,
WITH ICING
A special subcommittee has been working
within IMCO, The Inter-Governmental Mari-
time Consultative Organization in London, on
the safety of íishing vessels, especially the in-
tact stability, with the aim to work out re-
commended stability criteria. The results have
now been published, and are schematically
shown on Fig. 18.
The following criteria are recommended for
fishing vessels:
(a) The area under the righting lever curve
(GZ curve) should not be less than 0.055
metre-radians up to 0 = 30° angle of heel
1 1 8 JÖKULL 19. ÁR
Fig. 18. IMCO stability criteria for fishing
vessels.