Freeboard and sheer

The problems associated with freeboard include the 'distribution of freeboard' along the ship's length. The sheer produces a freeboard distribution with accentuation of the ship's ends. It is here (and particularly at the forward end) that the danger of flooding caused by trimming and pitching in rough seas is most acute. This is why the freeboard regulation allows reduction of the freeboard amidships if there is greater sheer. Conversely the sheer can be decreased or entirely omitted, increasing the freeboard amidships. For constant underdeck volume, a ship without any sheer will have greater draught than a ship with normal sheer. The increase in draught depends also on the superstructure length

The advantages and disadvantages of a construction 'without sheer' are:

C Better stowage of containers in holds and on deck. C Cheaper construction method, easier to manufacture. C Greater carrying capacity with constant underdeck volume.

Figure 1.10 Ship with and without sheer with same underdeck volume (the differences in freeboard are exaggerated in the diagram)

— If the forecastle is not sufficiently high, reduced seakeeping ability.

— Less aesthetic in appearance.

A lack of sheer can be compensated aesthetically:

1. The 'upper edge of bulwark' line can be extended to give the appearance of sheer (Fig. 1.11).

Figure 1.11 Visual sheer effect using the line of the bulwark

2. Replacement of sheer line with a suitable curved paint line or a painted fender guard (Fig. 1.12).

Figure 1.12 Paint line with sheer-like profile

Figure 1.12 Paint line with sheer-like profile

For ships with camber of beam, care must be taken that the decks without sheer do not become too humped at the ends as a result of the deck beam curvature, i.e. the deck 'centre-line' should have no sheer and the deck edge line should be raised accordingly (Fig. 1.13). Modern cargo ships, especially those designed for container transport usually do not have camber of beam, which avoids this problem.

Figure 1.13 Forward end of deck without sheer

Figure 1.13 Forward end of deck without sheer

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