Port economics

Bibliographic data

Monograph

Identifikator:: 173564191X

URN:: urn:nbn:de:zbw-retromon-111718

Document type:: Monograph

Author:: Cunningham, Brysson http://d-nb.info/gnd/1055472266

Title:: Port economics

Place of publication:: London [usw.]

Publisher:: Pitman

Year of publication:: 1926

Scope:: IX, 134 S

Digitisation:: 2020

Collection:: Economics Books

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Chapter II. Explanation of terms used in connection with ports and harbours

Collection:: Economics Books

EXPLANATION OF TERMS USED } A graving dock necessitates a sound, natural foundation at a reasonable depth and a disposition of site which frequently involves the appropriation of a considerable area of valuable land. A floating dock, on the other hand, requires a sheltered position with an adequate depth of water which, if not obtainable naturally, will have to be gained by dredging. The depth of water to be obtained for a floating dock must be sufficient to cover (a) the draught of the ship, (5) the depth of the pontoon floor, and (¢) the necessary clearances of a foot or two each between the floor of the pontoon (i.e. the top of its keel-blocks) and the ship, and between the underside of the pontoon and the river, or estuary, bed. In cases where there is a tidal variation, the amount of this must be added, if the dock is to be available at times of low water. In this country, as already stated, the tidal range may be anything up to 50 ft., and 15 to 20 ft. is quite general. For a modern ship of average size, drawing 28 to 30 ft. of water, the pontoons would be, at least, 20 ft. deep; this means that the available depth of the floating dock berth below high water level should be about #0 ft.—a very considerable depth for dredging. It must be admitted, however, that this depth is paralleled in graving dock construction and exceeded in at least one case (Havre), where, owing to the defective foundation, the floor of the graving dock has been made as much as 35 ft. in thickness, which, added to the draught of the vessel, has meant a total depth below coping level approaching go ft. The cost of a graving dock is generally considered to be greater than that of a floating dock, though the variation in particular circumstances renders it difficult to make any general dogmatic statement on the point. On the other hand, a floating dock can be constructed in about half the time required for a graving dock. In the case of a graving dock of any importance, a couple of years is generally necessary for the purpose of carrying out the 3—(6010) 2 -

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