Hull Construction Regulations — 11
11 In this Division, (a) except where otherwise stated, (i) all linear measurements shall be in metres, (ii) all area measurements shall be in square metres, and (iii) all volumes shall be in cubic metres and calculated to moulded lines; (b) the load waterplane is that used in determining the subdivision of the ship, and is drawn parallel to the keel; (c) the margin line for a ship of standard form consists of two ordinary parabolas, each with apex at amidships and axis vertical, passing, at amidships and at the ends, through points 76 mm below the surface of the bulkhead deck at side; (d) the corrected margin line , if the actual margin line either forward or aft is not of ordinary parabolic form * or if its lowest point is not at amidships, a margin line of ordinary parabolic form shall be drawn with its apex amidships level with the lowest point of the actual margin line, and intersecting the latter either at a point one quarter of the ship’s length from amidships or at the perpendicular according as the actual sheer at the perpendicular is respectively greater or less than four times the actual sheer at the one-quarter length position, (see Fig. A in this Schedule); (e) the perpendiculars are taken at the extreme ends of the subdivision load water line; (f) amidships is the middle of the length between the perpendiculars; (g) the mean waterplane is midway between the load water plane and that drawn parallel thereto touching the lowest point of the margin line; (h) the length of the ship (L) is the length of a ship measured between the perpendiculars taken at the extremities of the deepest subdivision load water line, (section 2); no adjustment to this length will, as a general rule, be necessary unless the sectional area at the after perpendicular exceeds one tenth of the midship sectional area, in which case full particulars shall be submitted in order that an equitable length may be determined; (i) the breadth of the ship (B) is the greatest moulded breadth at or below the ship’s deepest subdivision load water line, (section 2); (j) the draught (d) is the vertical distance from the moulded base line amidships to a subdivision load water line, (section 2); (k) the freeboard (f) is the vertical distance amidships from the subdivision load water line to the margin line (corrected as necessary); (l) the block coefficient of fineness of displacement to the subdivision load water line shall be determined as follows: volume of displacement to moulded lines divided by (L.B.d.); (m) the freeboard ratio ( f d ) is the ratio between the freeboard (f) and the draught (d); (n) the sheer ratio forward or aft is the ratio of the sheer of the margin line (corrected as necessary) at the forward or after perpendicular respectively, measured from the horizontal line through the lowest point of the margin line (corrected as necessary), to the draught; (o) the mean waterplane area coefficient (a) is the actual area of mean waterplane divided by L × B; (p) the mean waterplane moment of inertia coefficient (n) is the actual moment of inertia of mean waterplane about a transverse axis through its centre of flotation divided by L 3 × B; (q) the sectional area coefficient (ß) for any transverse section is the actual area of that section up to the margin line divided by B × d; (r) the Standard Diagrams of Floodable Lengths, etc. ( or Plates ) are as set out in section 12 of this Schedule and the Plates referred to are the numbered Diagrams in that section. * A margin or ordinary parabolic form is one in which the sheer forward and aft measured at points 1/8, 1/4 and 3/8 of the length of the ship from the perpendicular is 9/16, 1/4 and 1/16 respectively of the sheer at the perpendicular.