A Treatise On The Principles And Practice Of Dock Engineering

225 CHAPTEK VI. ENTRANCES, PASSAGES, AND LOCKS. General Aspects of the Subject—Site—Effect of Wind, Wave, and Current_ Direction— Size—Draught of Water in Approach Channel—Arrangement and Types—Simple Entrances, Locks, and Half-tide Basins—Maintenance of Fairway—Sluicing—Velocity of Efflux—Friction of Culverts—Coefficients of Discharge — Sluicing Arrangements at Liverpool, Ostend, Honfleur, Ramsgate, Dover, and Dublin—Scraping and Scuttling—Dredging Lock Foundations — Boils and Springs — Instances at Hull and Liverpool ___ Suggestions for Treatment— Grouting—Stock-ramming—Sand Concrete— Lock Construction — Sills — Platforms — Recesses — Walls — Culverts _ Penstocks or Cloughs — Stoney Sluices — Fan Gates — Pivottbd Gates __ Duration of Levelling Opérations — Examples of Dock Entrances at Liverpool, Dunkirk, Buenos Ayres, Kidderpuh, Eastham, Barry, Ardrossan, Hull, and Bremerhaven. General Aspects of the Subject—The subject of dock entrances is one demanding the most careful attention, seeing that the utility and value of an entire dock system depend to a very large extent, if not mainly, upon the safety and accessibility of its entrances. If the docking and undocking of ships could be carried on invariably in calm weather, and with smooth water, many of the most acute difliculties of the problem would at once disappear. But ships have to be docked in foul weather as well as fair, and, apart altogether from the desirability of their obtaining sheiter at the earliest possible moment from rough winds and tempestuous seas, there is the more cogent reason that the exigencies of modern commerce will not allow of a ship missing her berth in dock by one hour more than is absolutely necessary for her actual voyage ; neither will they admit of her failing to leave her berth at the specified time. Every hour of extra detention in port represents to her owners a large sum in wages, maintenance and interest, unprofitably expended. Consequently, it becomes a qualification of the highest importance for a dock entrance to be available at all times and under all conditions. It must certainly be admitted that, as yet, many commercial seaports are unable to comply with this requirement, owing to obstacles arising from natural causes, such as an extreme range of tide, a shallow bar, strong currents, and sudden floods. But it is increasingly evident that the qualification will ultimately become the sine quâ non of a flourishing port. At the present time extensive operations are in progress at various places, notably at Liverpool, with the object of increasing the period of accessibility and eventually of transform- 15