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Introduction
1 Three formulations are set forth as guidance to Administrations concerning
minimum draught requirements for segregated ballast tankers below 150 m in length.
2 The 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 Recognizing the nature of the underlying work, the widely varying arrangement
of smaller tankers and each vessel’s unique sensitivity to wind and sea conditions, no
basis for recommending a single formulation is found.
Caution
4 It 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. In any case the stability should be examined
independently.
5 Formulation A
.1 mean draught (m) = 0.200 + 0.032L
.2 maximum trim = (0.024 – 6 ×
10–5L)L
6 These expressions were derived from a study of 26 tankers ranging in length
from 50 to 150 m. The draughts, in some cases, were abstracted from ship’s trim and
stability books and represent departure ballast conditions. The ballast conditions
represent sailing conditions in weather up to and including Beaufort 5.
7 Formulation B
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.1 minimum draught at bow (m) |
= |
0.700 + 0.0170L |
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.2 minimum draught at stern (m) |
= |
2.300 + 0.030L |
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or |
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.3 minimum mean draught (m) |
= |
1.550 + 0.023L |
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.4 maximum trim |
= |
1.600 + 0.013L |
8 These 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
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.1 minimum draught aft (m) |
= |
2.0000 + 0.0275L |
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.2 minimum draught forward (m) |
= |
0.5000 + 0.0225L |
10 These expressions provide for certain increased draughts to aid in the
prevention of propeller emergence and slamming in higher length ships.
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