Introduction
Three formulations ar e set forth a s guidanc e to Administrations concernin g minimu m draugh t requirement s for segregated ballast tankers below 150 m in length.
2 Th e formulations are based both on the theoretical research and surveys of actual practice on tankers of differing configuration reflecting varying degrees of concern with propeller emergence, vibration, slamming, speed loss, rolling, docking and other matters. In addition, certain information concerning assumed sea conditions is included.
3 Recognizin g th e natur e o f th e underlyin g work , th e widel y varyin g arrangemen t o f smalle r tanker s an d eac h vessel's unique sensitivity to wind and sea conditions, no basis for recommending a single formulation is found.
Caution
4 I t must be cautioned that the information presented should be used as general guidance for Administrations. With regard to the unique operating requirements of a particular vessel, the Administration should be satisfied that the tanker has sufficient ballast capacity for safe operation. I n any case the stability should be examined independently.
5 Formulation A
.1 mea n draught (m) = 0.20 0 + 0.032 L .2 maximu m trim = (0.02 4 - 6 x 10-5L)L
6 Thes e expressions were derived fro m a study of 26 tankers rangin g i n lengt h from 5 0 to 15 0 m . The draughts, in some cases, wer e abstracted from ship' s trim and stability books and represen t departure ballast conditions. The ballast conditions represent sailing conditions in weather up to and including Beaufort 5.
7 Formulation B
.1 minimu m draught at bow (m) = 0.70 0 + 0.0170 L .2 minimu m draught at stern (m) = 2.30 0 + 0.030 L
or
.3 minimu m mean draught (m) = 1.55 0 + 0.023 L
.4 maximu m trim =1.60 0 + 0.013 L
8 Thes e expressions resulted from investigations based on theoretical research, model and full scale tests. These formulae are based on a Sea 6 (International Sea Scale).
9 Formulation C
.1 minimu m draught aft (m) = 2.000 0 + 0.0275 L .2 minimu m draught forward (m) = 0.500 0 + 0.0225L
10 Thes e expression s provid e for certain increase d draught s to ai d i n th e preventio n o f propelle r emergence an d slamming in higher length ships.
of regulations 18.12 to 18.15
"Protective location of segregated ballas t spaces"
1 Regulatio n 18.15 of Annex I of MARPOL relating to the measurement of the 2 m minimum width of wing tanks and the measuremen t of the minimu m vertica l dept h o f double botto m tanks of 2 m o r i n respec t o f tanks a t the ends of the ship where no identifiable bilge area exists should b e interpreted as given hereunder . N o 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 Th e minimum width of wing tanks should be measured at a height of abov e 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 i s 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 Th e PAC 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 th e assessmen t of PAS to an y double botto m tank , par t o f which doe s no t mee t the minimu m dept h requirement s anywhere within it s length . If , however , th e projecte d dimension s o f the botto m o f the carg o tank abov e the doubl e 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 b y the projection of the cargo tank bottom.
For simila r cases where the wing tank s abov e the doubl e botto m ar e segregate d ballas t tanks o r void spaces , suc h credit may also be given. This would not, however, preclude in the above cases credit being given to a PAS value in the first case and to a PAC value in the second case where the respective vertical or horizontal protection complies with the minimum distances prescribed in regulation 18.15.
4 Projecte d dimensions should be used as shown in examples of figures 3 to 8. Figures 7 and 8 represent measure- ment of the height for the calculation of PAC for double bottom tanks with sloping tank top. Figure s 9 and 1 0 represent the cases where credit is given in calculation of PAS to part or the whole of a double bottom tank.
Figure 1 - Measurement of minimum width of wing ballast tank at ends of ship Section view
w must be at least 2 m along the entire length of the tank for the tank to be used in the calculation of PAC
Figure 2 - Measurement of minimum height of double bottom tank at ends of ship Section view
h must be at least 2 m or - whicheve r is less, along the entire length of the tank for the tank to be used in the calcula- tion of PA„
Figure 3 - Calculation of PAC and PAS for double bottom tank amidships Section view
If hdb is at least 2 m or whicheve r is less, along entire tank length, PAC = hdb x doubl e bottom tank length x 2
PAS = B x doubl e bottom tank length If hdb is less than 2 m or whicheve r is less,
PAC = hdb x doubl e bottom tank length x 2 PAS = 0
Section view
If hdb is at least 2 m or whicheve r is less, along entire tank length, PAC = h x doubl e bottom tank length x 2
PAS = B x doubl e bottom tank length If hdb is less than 2 m or whicheve r is less,
PAC = h x doubl e bottom tank length x 2 PAS = 0
Figure 5 - Calculation of PAC and PAS for wing tank amidships Plan view
If W is 2 m or more,
PAC = D x tank length x 2 * PAS = W x tan k length x 2 * If W is less than 2 m,
PAc = 0
PAS = W x tan k lengt h x 2 *
* To include port and starboard.
Figure 6 - Calculation of PAC and PAS for wing tank at end of ship Plan view at D
Section A-A
If W is 2 m or more,
PAC = D x tank length x 2 * PAS = b x tank length x 2 * If W is less than 2 m,
PAC = 0
PAS = b x tan k length x 2 *
Figure 7 - Measurement of h for calculation of PAC
for double bottom tanks with sloping tank tops (1) Section view
PAC = h x double bottom tank length x 2*
* To include port and starboard.
Section view
PAC = h x doubl e bottom tank length x 2 *
Figure 9 - Calculation of PAS for double bottom tank without clearly defined turn of bilge area - when wing tank is cargo tank
If h is less than 2 m or , whichever is less, anywhere along the tank length, bu t hdb is at least 2 m or whicheve r is less, along the entire tank length within the width of 2b, then:
PAS = 2fa x carg o tank length
To include port and starboard.
Figure 10 - Calculation of PAS for double bottom tank without clearly defined turn of bilge area - when wing tank is segregated ballast tank or void space
tf h is less than 2 m or whicheve r is less, anywhere along the tank length,
but hdb is at least 2 m or whicheve r is less, along the entire tank length within the width of 2b, then:
PAS = B x carg o tank length