1 Regulation 18.15
of Annex I of MARPOL 73/78 relating to the measurement of the 2
m minimum width of wing tanks and the measurement of the minimum
vertical depth of double bottom tanks of 2 m or B/15 in
respect of tanks at the ends of the ship where no identifiable bilge
area exists should be interpreted as given hereunder. No difficulty
exists in the measurement of the tanks in the parallel middle body
of the ship where the bilge area is clearly identified. The regulation
does not explain how the measurements should be taken.
2 The minimum width of wing
tanks should be measured at a height of D/5 above the base
line providing a reasonable level above which the 2 m width of collision
protection should apply, under the assumption that in all cases
D/5 is above the upper turn of bilge amidships (see figure
1). The minimum height of double bottom tanks should be measured
at a vertical plane measured D/5 inboard from the intersection
of the shell with a horizontal line D/5 above the base
line (see figure 2).
3 The PA_{c}
value for a wing tank which does not have a minimum width of 2 m
throughout its length would be zero; no credit should be given for
that part of the tank in which the minimum width is in excess of
2 m. No credit should be given in the assessment of PAs to any double
bottom tank, part of which does not meet the minimum depth requirements
anywhere within its length. If, however, the projected dimensions
of the bottom of the cargo tank above the double bottom fall entirely
within the area of the double bottom tank or space which meets the
minimum height requirement and provided the side bulkheads bounding
the cargo tank above are vertical or have a slope of not more than
45° from the vertical, credit may be given to the part of the
double bottom tank defined by the projection of the cargo tank bottom.
For similar cases where the wing tanks above the double bottom are
segregated ballast tanks or void spaces, such credit may also be
given. This would not, however, preclude in the above cases credit
being given to a PA_{s} value in the first case
and to a PA_{c} value in the second case where
the respective vertical or horizontal protection complies with the
minimum distances prescribed in regulation 18.15.
4 Projected dimensions should
be used as shown in examples of figures 3 to 8. Figures 7 and 8
represent measurement of the height for the calculation of PA_{c}
for double bottom tanks with sloping tank top. Figures 9 and 10
represent the cases where credit is given in calculation of PA_{s}
to part or the whole of a double bottom tank.
w must be at least 2 metres along the entire length of
the tank for the tank to be used in the calculation of PA_{c}
h must be at least 2 metres or ,
whichever is less, along the entire length of the tank for the tank
to be used in the calculation of PA_{s}
If h_{db} is at least 2 metres or
, whichever is less, along entire tank length,
PA_{c} = h_{db}
× double bottom tank length x 2
PA_{s} = B × double
bottom tank length
If h_{db} is less than 2 metres or
, whichever is less,
PA_{c} = h_{db}
× double bottom tank length × 2
PA_{s} = 0
If h_{db} is at least 2 metres or
, whichever is less, along entire tank length,
PA_{c} = h × double
bottom tank length x 2
PA_{s} = B × double
bottom tank length
If h_{db} is less than 2 metres or
, whichever is less,
PA_{c} = h × double
bottom tank length × 2
PA_{s} = 0
If W is 2 metres or more,
PA_{c} = D × tank
length × 2*
PA_{s} = W × tank
length × 2*
If W is less than 2 metres,
PA_{c} = 0
PA_{s} = W × tank
length × 2*
If W is 2 metres or more,
PA_{c} = D × tank
length × 2*
PA_{s} = b × tank
length × 2*
If W is less than 2 metres,
PA_{c} = 0
PA_{s} = b × tank
length × 2*
PA_{c} = h × double bottom tank
length × 2*
PA_{c} = h x double bottom tank length
x 2*
If h is less than 2 metres or
, whichever is less, anywhere along the tank length, but h_{db}
is at least 2 metres or
, whichever is less, along the entire tank length within the width
of 2b, then:
PA_{s} = 2b × cargo
tank length
If h is less than 2 metres or
, whichever is less, anywhere along the tank length, but h_{db}
is at least 2 metres or
, whichever is less, along the entire tank length within the width
of 2b, then:
PA_{s} = B × cargo tank length
*
