Page 352 - Practical Ship Design

Freeboard and Subdivision 309

The standard freeboard is then corrected for the following features:

(i) Hutch cover correction
If the hatches on a type B ship are not of the pontoon or similar type (i.e., are old
fashioned covers on portable beams)
Approx addition = 50 + 3 [L - 1001 mm
(max error 25 mm)
The fitting of the type of hatch covers which necessitate this addition is now very
rare.

(ii) Ships of L < 100 m where the enclosed superstructures are less than 35% L
Addition = 7.5 (100 - L) (0.35 - E/L) mm

(iii) Block coefficient correction

If C, > 0.68
SF(C, -0.68)
Addition =
1.36
where SF is summer tabular freeboard

(iv) Depth correction

If depth exceeds W15
Addition = R(D - L/15) mm

where
R = W0.48 for L < 120, and
R = L/250 for L > 120
If D < W15, the freeboard can be correspondingly reduced, but only if there is an
enclosed superstructure amidships of at least 0.6 L

(v) Correction for efficient erections
A deduction is made for erections based on their location, their breadth and the
proportion of the ship’s length which these occupy.
Standard heights are specified for erections on a basis of length, and if the actual
height is less than the standard or if the erections do not extend to the ship’s side,
the actual length (S) of these is reduced pro rata to give an effective length (E).