2 Downflooding opening protected by coaming
3 Example of engine air inlet
Figure C.1 — Approximate method for downflooding angle
ISO/FDIS 12217-1:2001(E)
26 © ISO 2001 – All rights reserved
Annex D
(normative)
Determining the curve of righting moments
D.1 Method
The curve of righting moments can be determined using any of the methods described in D.3, D.4 or D.5. In all
cases the mass and centre of gravity used shall conform to D.2.
D.2 Mass and centre of gravity
Where preliminary estimates are used at the design stage, these shall be subsequently superseded by the use of
data for the boat as finally built.
D.2.1 Mass
The mass used can be found using any of the following methods:
a) direct weighing using crane weigher, weighbridge, load cells or similar, corrected to the appropriate
displacement mass;
b) calculation from the lines plan using a waterline observed on a boat afloat in a known load condition, by means
of freeboards or draughts, and using a measured specific gravity for the water, and corrected to the
appropriate loading condition;
c) calculation based on the mass of a closely similar boat derived by either a) or b) above, with the mass of
known changes determined solely by calculation.
Method c) shall only be used where the change in mass in the light craft condition is less than 10 %.
D.2.2 Vertical centre of gravity
The vertical position of the centre of gravity (VCG) can be found using any of the following methods:
a) an inclining experiment in water (see 3.5.6), the results being corrected to the appropriate displacement
condition;
b) an inclining experiment in air using a known length of suspension and moving weights transversely (as in
water), the results being corrected to the appropriate displacement condition;
c) calculation based on the calculated mass and centres of gravity of individual components, raised by an
addition of 5 % of (FM + TC).
Method a) shall not be used for boats with a metacentric height greater than 5,0 m, since inclining experiments in
water for such boats are liable to significant inaccuracies.
Method c) shall not be used for boats with a metacentric height of less than 1,5 m, since significant inaccuracies
may result. It may, however, be used for preliminary assessment.
ISO/FDIS 12217-1:2001(E)
© ISO 2001 – All rights reserved 27
For the purposes of determining the curve of righting moments, the vertical disposition of the mass of the crew shall
be
a) at the highest main control position for calculations for the minimum operating condition, or
b) that used in the offset-load test as described in normative annex B for calculations in the loaded displacement
condition.
D.2.3 Longitudinal centre of gravity
The longitudinal position of the centre of gravity (LCG) can be found using any of the following methods:
a) methods b) or c) in D.2.1;
b) calculation based on the calculated mass and centres of gravity of individual components;
c) suspension of the boat in air, identifying the LCG using a plumb line from the suspension point.
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