Annex I- Regulations for the Prevention of Pollution by Oil

Appendices to Unified Interpretations of Annex I

Appendix 1 - Guidance to Administrations concerning draughts recommended for segregated ballast tankers below 150 m in length


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.


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

  .1 minimum draught at bow (m) = 0.700 + 0.0170L
  .2 minimum draught at stern (m) = 2.300 + 0.030L
  .3 minimum mean draught (m) = 1.550 + 0.023L
  .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

  .1 minimum draught aft (m) = 2.0000 + 0.0275L
  .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.