In the case of ships having open superstructures on the
freeboard or superstructure decks, which open to wells formed by bulwarks
on the peripheries of the open decks, the Convention leaves to the
satisfaction of the Administration how the freeing port areas for
the open spaces within the superstructures should be calculated.
Since water can enter only through the end bulkhead openings,
the freeing port areas for the open spaces within the superstructures
should be a function of the breadth of the end openings and the extent
to which wells formed by the open decks and common spaces within the
open superstructures are covered by the open superstructures.
To determine the minimum freeing port area on each side
of the ship for the open superstructure (A
_{s})
and for the open well (A
_{w}), the following
procedure is recommended:

.1 Determine the total well length (l
_{t}) equal to the sum of the length of the open deck enclosed
by bulwarks (l
_{w}) and the length of the common
space within the open superstructure (l
_{s}).

.2 To determine A
_{s}:

.1 calculate the freeing port area (A)
required for an open well of length l
_{t} in
accordance with regulation 24(1) with
standard height bulwark assumed;

.2 multiply by the factor of 1.5 to correct for
the absence of sheer, if applicable, in accordance with regulation 24(2);

.3 multiply by the factor (b
_{o}/l
_{t}) to adjust the freeing port area for the breadth
(b
_{o}) of the openings in the end bulkhead of
the enclosed superstructure. (Note: This cancels the l
_{t} terms from the calculation);

.4 to adjust the freeing port area for that part
of the entire length of the well which is enclosed by the open superstructure,
multiply by the factor:
(l—l
_{w}/l
_{t}
^{2})
where l
_{w} and l
_{t} are
defined in 4.3.1 above;

.5 to adjust the freeing port area for the distance
of the well deck above the freeboard deck, multiply by the factor:
0.5(h
_{s}/h
_{w})
where h
_{w} is the distance of the well
deck above the freeboard deck and h
_{s} is one
standard superstructure height.

.3 To determine A
_{w}:

.1 the freeing port area for the open well (A
_{w}) should be calculated in accordance with .2.1 above, using l
_{w} to calculate (A') and then adjusted
for the actual height of the bulwark (h
_{b})
by the application of one of the following area corrections, whichever
is applicable:

.1.1 for bulwarks greater than 1.2 m in height:
A
_{c} = l
_{w} (h
_{b}1.2)/(0.1) (0.004) m^{2});

.1.2 for bulwarks less than 0.9 m in height:
A
_{c} = l
_{w} (h
_{b}0.9)/(0.1) (0.004) m^{2});

.1.3 for bulwarks between 1.2 m and 0.9 m in height:
A
_{c} = 0.00 m^{2};

.2 the corrected freeing port area (A
_{w} = A' + A
_{c}) is then adjusted
for absence of sheer, if applicable, and height above freeboard deck
as in .2.2 and .2.5 above, using h
_{s} and h
_{w}.

.4 The resulting freeing port areas for the open
superstructure (A
_{s}) and for the open well
(A
_{w}) should be provided along each side of
the open space covered by the open superstructure and each side of
the open well respectively.

.5 The above relationships should be summarized
by the following equations, assuming l
_{t}, the
sum of l
_{w} and l
_{s},
is greater than 20 m:

.1 freeing port area A
_{w} for
the open well:
A
_{w} = (0.07l
_{w} + A
_{c}) (sheer correction) (0.5h
_{s}/h
_{w}); and

.2 freeing port area A
_{s} for
the open superstructure:
A
_{s} =
(0.07l
_{t}) (sheer correction) (b
_{o}/l
_{t})^{2})(0.5h
_{s}/h
_{w}),
Where l
_{t} is 20 m or less, the basic
freeing port area is A = 0.7 + 0.035l
_{t} in
accordance with regulation 24(1). Units
should be consistent with those in the Convention.