Regulation 39 - Minimum bow height and reserve buoyancy
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - International Conventions - Load Lines, 1966/1988 - International Convention on Load Lines, 1966, as Amended by the Protocol of 1988 - Annex I - Regulations for Determining Load Lines - Chapter III - Freeboards - Regulation 39 - Minimum bow height and reserve buoyancy

Regulation 39 - Minimum bow height and reserve buoyancy

  (1) The bow height (F b), defined as the vertical distance at the forward perpendicular between the waterline corresponding to the assigned summer freeboard and the designed trim and the top of the exposed deck at side, shall be not less than:

F b = is the calculated minimum bow height, in mm;
L = is the length, as defined in regulation 3, in m;
B = is the moulded breadth, as defined in regulation 3, in m;
d 1 = is the draught at 85% of the least moulded depth, in metres;
C b = is the block coefficient, as defined in regulation 3;
C wf = is the waterplane area coefficient forward of L/2: C wf = A wf/ {(L/2) x B};
A wf = is the waterplane area forward of L/2 at draught d1, in m2.

 For ships to which timber freeboards are assigned, the summer freeboard (and not the timber summer freeboard) is to be assumed when applying paragraph (1).

  (2) Where the bow height required in paragraph (1) is obtained by sheer, the sheer shall extend for at least 15% of the length of the ship measured from the forward perpendicular. Where it is obtained by fitting a superstructure, such superstructure shall extend from the stem to a point at least 0.07L abaft the forward perpendicular, and shall be enclosed as defined in regulation 3(10).

  (3) Ships which, to suit exceptional operational requirements, cannot meet the requirements of paragraphs (1) and (2) of this regulation may be given special consideration by the Administration.


  • (a) The sheer of the forecastle deck may be taken into account, even if the length of the forecastle is less than 0.15L, but greater than 0.07L, provided that the forecastle height is not less than one half of standard height of superstructure as defined in regulation 33 between 0.07L and the forward perpendicular.

  • (b) Where the forecastle height is less than one half of the standard height of superstructure, as defined in regulation 33, the credited bow height may be determined as follows:

    • (i) Where the freeboard deck has sheer extending from abaft 0.15L, by a parabolic curve having its origin at 0.15L abaft the forward perpendicular at a height equal to the midship depth of the ship, extended through the point of intersection of forecastle bulkhead and deck, and up to a point at the forward perpendicular not higher than the level of the forecastle deck (as illustrated in figure 39.1). However, if the value of the height denoted ht in figure 39.1 is smaller than the value of the height denoted hb then ht may be replaced by hb in the available bow height.

    • (ii) Where the freeboard deck has sheer extending for less than 0.15L or has no sheer, by a line from the forecastle deck at side at 0.07L extended parallel to the base line to the forward perpendicular (as illustrated in figure 39.2).

Figure 39.1

 Figure 39.2

hf = Half standard height of superstructure as defined in regulation 33.

  (5) All ships assigned a type 'B' freeboard, other than oil tankersfootnote, chemical tankersfootnote and gas carriersfootnote, shall have additional reserve buoyancy in the fore end. Within the range of 0.15L abaft of the forward perpendicular, the sum of the projected area between the summer load waterline and the deck at side (A1 and A2 in figure 39.3) and the projected area of an enclosed superstructure, if fitted, (A3) shall not be less than:

Fmin = is calculated by: Fmin = (F0 f1) + f2;
F0 = is the tabular freeboard, in mm, taken from table 28.2, corrected for regulation 27(9) or 27(10), as applicable;
f1 = is the correction for block coefficient given in regulation 30; and
f2 = is the correction for depth, in mm, given in regulation 31.

Figure 39.3

Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.