Remarks on the Formation Of

DOCK ENTRANCES. 159 February 29, 1S48. JOSHUA FIELD, President, in the Chair. No. 777.--" Remarks on the Formation of Entrances to Wet and Dry Docks, situated upon a Tideway ; illustrated by the prin- cipalexamples in the Port ofLondon." * ByJohn Baldry Redman, M. Inst. C. E. THEimportance of this subject isso great, that lengthened prefatory remarks would besuperfluous; the instances which may be ob- served on theThames, show that therehas been considerable variation inthe opinions and practice of engineers, or that the subject has not been considered important, though, at the same time some allowance must be made for the peculiar circumstances of the Port ofLondon, and the value of groundupon its banks; the questiontherefore is, whatshould be the proper direction and shape of a dock entrance in reference to the run of tide. The practice in the Port of London is to dock a ship upon the flood, just before high water, and to undock her at about the same period of tide ; high water is also selected, for obvious reasons, as the time for launching newvessels fromthe building slips. The angle these docks and entrances make with the line, or direction of the run of tide, is a very important element for consideration, much greaterworking facilities being afforded at some than at others, where, from their particular direction, expensive additional timber outworkshave been rendered necessary, to afford thosefacilities which the entrances, when finished, did not afford. It is only necessary to refer to the particular position of some of the principal entrances, to exemplify this. Plate 7, Fig.].-The entrance at Blackwallof the East IndiaDocks isconsidered by shipwrights and pilots of the porttobe well situated ; it pointsupwards, atan acute angle with the line of' flood, and is at the same time covered, to some 'extent, by a projecting pier on the lower side ; the effect is,that on a vesselentering, her stern being driven upwards by the action of the tide upon her starboard quarter, she is drawn bywarps without much difliculty into the lock; this, however, is toan extent only, as, withthe wind on shore, a vessel is sometimesdriven athwart the entrance, and nipped between the * The discussion on this Paper extended over portions of three evenings ; but an abstract of the whole is given consecutively. Downloaded by [ University of Liverpool] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 160 DOCK ENTRANCES. lowerpier and the projection of theBrunswick Wharf, against which her larboard quarter is driven by the flood and wind. This position is shown bythe form of a vessel withinthe entrance. In'this state of affairs it becomes necessary to wait for slack tide at high water, which sometimes, with a large and heavily laden ship, is a dangerous experiment; or else, to heave her stern down against the tide from the starboard quarter. This operation, with an entrance so placed, is by no meansso laborious as if it had been placed at right angles to the stream. To the natural position of this entrance, however, much of its superiority is attributed, there being plenty of room in the river in front of it, nor does the tide set strongly across it ; but with easterly gales, large ships would for- merly hang until the slack of tide, whereas now, with the assistance of steam-tugs, vessels maybe docked as soon as thereis sufficient depth of water. This entrance was formed for the purpose of docking a limited number of largevessels on any one tide. Ithas been stated, that itwas with this view that the outer lock gate was projectedso far outwards, towards the river ; the circumstances and conditionsof the lock are consequently similar to those of a graving dock, and it is supposed that it was so formed with the view of waiting for the slack of tide, this would preclude docking more thanone, or two vessels upon the tide, which, however, would have sufficed for the original re- quirements of the India trade. The majority of the docks and slips at the respective establish- ments of the Messrs. Wigrams and Messrs. Greens, at Blackwall, point more acutely to the flood tide. These docks are considered by ship-builders to be well, placed ; they are, however, much ex- posed, as the flood tide sets right into them ; this, however, is not of such importance as for the entrance of a wet dock, because a shipbuilder, having only one, or at most two vessels to take into one dock, can afford to wait for the slack tide. Plate 7, Fig. 2, shows the entrance at the Blackwall-end of the WestIndia Docks and of the City Canal, now the West India SouthDock. This was influenced nodoubt by the position, and the object of the latter, which was to effect a through com- munication for the navigation, and to cut off the reaches round the Isle of Dogs ; but which failing as a canal, has long been used as a lie-by for ships and timber. The entrance is nearly in an opposite direction to that of the example first quoted, and forms rather an obtuse angle, or at least a right angle with the flood. It is stated by gentlemen who have been many years connected with the port, that when the West India Dockswere first completed, Downloaded by [ University of Liverpool] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. DOCK ENTRANCES. 161 the danger to loaded shipswas so great, that it became necessary to lengthen the upper pier, by additional timber external works. The entrance, in its present state, bearsa very good character. Thisentrance was formedwith a view todocking the largest possible number of vessels upon one tide (having reference to the arrival at that period of the West India ships in fleets). The basin was formed as a tide receptacle for these vessels as they came up the river, the water being drawn down to about half tide level in the basin, for that purpose; the great width of entrance was no doubt allowed for vessels to sheer in as they came up; this, however, was not found practicable, it being necessary (as is now done), to bring the vessels up with head to tide, and allow them to drop up from the buoys off the entrance, across which the flood tide runs up with strength ; it was also found necessary to carry out a timber jetty to low-water mark, off the South, or Upper Pier, to prevent vessels fromtailing round with the flood onto the shore. Thegreat width thus eventually obtained between the wings is advantageous, as itallows a vessel tokant across, andto enter without the assistance of a quarter-rope, or a steam-boat ; another advantage is, that in undocking, sufficient space is allowed for the outward-bound vessel to pass out, the inward-bound vessel being at the samectime within the entrance. Mr. Pitcher’s gravingdocks, to thewestward of the canal entrance, are in nearly the same direction. Plate 7, Fig. 3.--The Blackwallentrance of the South Dock answers well as regards direction, although, like the last, it is nearly at right angles to the stream,as, from its being more ina bight, there is a slack of tide across it; it, however, requires a dolphin upon the upper side at low water,to counteract the tendency whichvessels have, when docked upon the flood, to tail upon Mr. Pitcher’s ways. Plate 7, Figs. 4 and &-The Western, or Upper entrances of the West India Docks and City Canal, or South Dock, at Limehouse, are favourably situated, as they point acutely up the stream, and considerable facilities are afforded to vessels entering, by the West India Dock entrance, on account of its direction; the admission and the exitof light vessels can thus be well and expeditiously con- ducted. The West India Dock entrance is considered well adapted to the purposes of trade, as there is deep water on the north side, and there is an easy run of tide across it towards high water. At Woolwich Dockyard there is great variety in the direction of the building slips and of the graving docks, some are nearly square to ‘the stream,in other instances they point slightly up, andin [ 1848.1 M Downloaded by [ University of Liverpool] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 162 DOCK ENTRANCES. others downwards, forming an acute angle with the line offlood in some instances, and an obtuse angle in others. At Deptford Dockyard there is equal variety ; at the lower part of the yard they are nearly at right angles to the stream; the entrance to the lower basin points slightly up the stream ; that to the Transport Dock is nearly square ; a dock above it is in the same direction ; but the dock above, in what is called ‘‘ Dudman’s Dock- yard,’’ points up acutely to theflood ; a building slip above this is in the same direction, and a dock entrance still higher up, points upwards at a less acute angle. The conditions of the several pro- perties appear to have had as much influence upon the direction of these slips and docks as any other considerations. Plate 7, Figs. 6 and 7.-The entrance lock to the East Country Dock points slightly upwards, as also that to the Commercial Docks: both are considered good working entrances; the Graving Docks on either side of the Comnlercial Docks entrance point ina similar manner, showing that the disposition of one property hasinfluenced the other, as regards direction. Fromthe particular local set of tide, theangle of direction upwards is very much reduced.

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