11.8.1 The centre of gravity (KG) of a vessel
should be established by an inclining experiment and curves of statical
stability (GZ curve) for the loaded departure 100% consumables and
loaded arrival 10% consumables should be produced.
Notes:
1. The above conditions may include a margin for growth up
to 5% of the lightweight, at the discretion of the Certifying Authority, with the VCG
positioned at the upper deck amidships.
2. Buoyant structures intended to increase the range of
positive stability should not be provided by fixtures to either a mast, rigging, or
superstructure.
3. For standard production series built vessels, the
statical stability (GZ) may be derived from an inclining experiment conducted on another
vessel of the series, subject to corrections for differences in outfit, to the
satisfaction of the Certifying Authority.
4. Maximum free surface moments should be included within
the loaded departure condition, and as a minimum, factored according to tank percentage
fill for the loaded arrival condition.
11.8.2 The GZ curves required by Section 11.8.1
should have a positive range of not less than the angle determined
by the formula in the table in Section 11.9.5, or 90°, whichever
is the greater.
11.8.3 In addition to the requirements of Section
11.8.2, the angle of steady heel obtained from the intersection of
a "derived wind heeling lever" curve with the GZ curves referred to
in Section 11.8.1 above should be greater than 15 degrees (see Figure 11.1).
In Figure 11.1
|
'DWHL' |
= |
the "derived
wind heeling lever" at any angle θ degrees |
| = |
0.5 × WL0 × Cos1.3θ
|
where
|
WL0 |
= |
|
Figure 11.1
Noting that, when using this method:-
-
WL0 is the magnitude of the actual wind heeling lever at
0 degrees which would cause the vessel to heel to the 'down flooding
angle' (θf) or 60 degrees whichever is least.
-
GZf is the lever of the vessel's GZ at the 'down flooding
angle' (θf) or 60 degrees whichever is least.
-
θd is the angle at which the 'derived wind heeling'
curve intersects the GZ curve. (If θd is less than 15 degrees
the vessel will be considered as having insufficient stability for
the purpose of the Code).
-
θf is the 'critical down flooding angle' and is deemed
to occur when openings having an aggregate area, in square metres,
greater than:-
Moreover, it is the angle at which the lower edge
of the actual opening which results in critical flooding becomes immersed.
All openings regularly used for crew access and for ventilation should
be considered when determining the downflooding angle. No opening
regardless of size which may lead to progressive flooding should be
immersed at an angle of heel of less than 40 degrees. Air pipes to
tanks can, however, be disregarded.
If as a result of immersion of openings in a deckhouse a vessel
cannot meet the required standard, those deckhouse openings may be
ignored and the openings in the weather deck used instead to determine θf.
In such cases the GZ curve should be derived without the benefit of
the buoyancy of the deckhouse.
It might be noted that provided that the vessel complies with
the requirements of Section 11.8.1, 11.8.2 and 11.8.3 and it is sailed
with an angle of heel which is no greater than the 'derived angle
of heel', it should be capable of withstanding a wind gust equal to
1.4 times the actual wind velocity (i.e. twice the actual wind pressure)
without immersing the 'down flooding openings', or heeling to an angle
greater than 60 degrees.
11.8.4 Vessels complying with ISO 12217 Part 2
'Small craft - Stability and buoyancy assessment and categorisation
- Sailing boats of hull length greater than or equal to 6 metres',
assessed using Options 1 and 2 of Section 6.1 -
'Requirements to be applied', may as an alternative and in lieu of
11.8.2, be assigned a permitted area of operation in accordance with
section 11.9.5, provided that the righting lever curve produced for
this standard, is verified and corrected in accordance with Annex 12 before performing the calculations.
In this case the calculated steady heel angle required by 11.8.3 is
to be reduced by 10%.
11.8.5 A Stability Information Booklet, based
on the Administration's model booklet, should be submitted to and
approved by the Certifying Authority and placed on-board the vessel.
The booklet should include details of the maximum steady angle of
heel for the worst sailing condition. The steady angle of heel is
to be calculated in accordance with Section 11.8.3 or 11.8.4. The
booklet should also include curves of maximum recommended steady angle
of heel for the prevention of down flooding in the event of squall
conditions. Details of the development of such curves are given in
the Model Stability Information Booklet.