184.9 ] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



129 



DOCK ENTRANCES. 



CWitIi an Engraving, Plate \U.) 



Remarks on the Formation of Entrances to Wet and Dn/ Dorhs, 

 situated upon a Tidewag; illnstrated bg the principal examples in the 

 Port of London. By John Baldrv Redman, JM. Inst. C.E. — (Read 

 at the Institution of Civil Engineers.) 



The importance of this subject is so E;reat, that lengthened pre- 

 fatory remarks would be superfluous; the instances which may be 

 observed on tlie Thames, show that there lias been consideralile 

 variation in the 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 of London, and the value of ground upon its banks: 

 the question therefoi-e is — What should be the projier direction and 

 shape of a duck entrance in reference to the run of tide? 



The practice in the Port of London is to dock a sliip 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 new vessels from the building slips. Tlie 

 angle these docks and entrances make with the line, or direction 

 of the run of tide, is a very important element for consideration; 

 much greater working facilities being atforded at some tlian at 

 others, where, from their particular direction, expensive additional 

 timber outworks have been rendered necessary, to afl^ord those 

 facilities 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. 



Fig. 1. — The entrance at Blackwall of the East India Docks is 

 considered by sbipwi-ights and pilots of the port to be well situated; 

 it points upwards, at an 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 efl^ect is, that on a vessel entering, her stern 

 being driven upwards by the action of the tide upon her starboard 

 quarter, she is drawn by warps without much difficulty into the 

 lock; this, however, is to an extent only, as, with the wind on 

 shore, a vessel is sometimes driven athwart the entrance, and 

 nipped between the lower pier and the projection of the Bruns- 

 wick Wharf, against which her larboard quarter is driven by the 

 flood and wind. This position is shown by the form of a vessel 

 within the 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 means so labo- 

 rious as if it had been placed at right angles to the stream. To 

 the natural position of this entrance, however, much of its supe- 

 riority is attributed, tliere 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 formerly hang until the slack of 

 tide, whereas now, with the assistance of steam-tugs, vessels may 

 be docked as soon as there is sufficient depth of water. 



This entrance was formed for the purpose of docking a limited 

 number of large vessels on any one tide. It has been stated, that 

 it was with this view tliat the outer lock-gate was projected so far 

 outwards towards the river; the circumstances and conditions of 

 the look 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. Tliis would preclude docking more than one or 

 two vessels upon the same tide, which, however, would have sufficed 

 for the original requirements of the India trade. 



The majority of the docks and slips at the respective establish- 

 ments of the Messrs. ^Vigram, and Messrs. Green, at Blackwall, 

 point more acutely to the flood tide. These docks are considered 

 by ship-builders to be well placed, — they aie, 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 

 ship-builder, having only one, or at most two, vessels to take into 

 one dock, can afford to wait for the slack tide. 



Fig. 2, shows tlie entrance at the Blackwall end of the AVest India 

 Docks and of the City Canal, now the AVest India South Dock. 

 This was influenced no doubt by the position, and the object of 

 the latter, which was to effect a thorough communication for the 

 navigation, and to cut off the reaches round the Isle of Dogs; hut 

 whicli 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 wlien tlie West India Docks were first com- 



pleted, the danger to loaded ships was so great, that it became 

 necessary to lengthen the upper pier, by additional timber external 

 works. The entrance, in its present state, bears a very good 

 character. 



This entrance was formed with a view to docking 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 not found practicable, it being necessary (as is now done), 

 to bring the vessels up with head to tide, and allow them to dro]) 

 up from the buoys off the entrance, across ivhich the flood tide 

 runs up with strength; it was also found necessary to carry out a 

 timber jettv to low-water mark, off the South, or Upper Pier, to 

 prevent vessels from tailing round with the flood on to the shore. 

 The great width thus eventually obtained between the wings is 

 advantageous, as it allows a vessel to kant across, and to enter 

 without the assistance of a quarter-rope, or a steamboat; 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 same time within the entrance. 



Mr. Pitcher's graving docks, to the westward of the canal en- 

 trance, are in nearly the same direction. 



Fig. 3. — The Blackwall entrance 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 in a 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 wliicli 

 vessels have, when docked upon the flood, to tail upon Mr. 

 Pitcher's ways. 



Fiyx. i and o. — The AVestern, or upper entrances of the AVest 

 India Docks and City Canal, or South Dock, at Limehouse, are 

 favourably situated, as they point acutely up the stream, and con- 

 siderable facilities are att'orded to vessels entering by the West India 

 Dock entrance, on account of its direction; the admission and 

 exit of 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 tliere is great variety in the direction of 

 tlie building slips and of the graving docks: some are nearly S(iuare 

 to the stream, in other instances they point slightly up, and in 

 others downwards — forming an acute angle with the liue of flood 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 

 Dockyard," points up acutely to the flood; 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 properties appear to have had as much influence upon the 

 direction of these slips and docks as any other considerations. 



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 Commercial Docks entrance point in a similar 

 manner, showing that the disposition of one property has influ- 

 enced the otlier, as regards directitm. 



From the particular local set of tide, the angle of direction 

 upwards is very mucli reduced. 



At each of these two entrance locks, two dolphins are placed in 

 a line with their upper sides; they are pro tanto elongations of tlie 

 upper wings. 



On the opposite side of the river at Mill-Wall, Blackett's 

 Graving Dock is nearly square with the stream, pointing slightly 

 downwards. 



The Graving Dock above this (jMitchell's), below Messrs. Sea- 

 ward's factory, points up very acutely with the line of flood. 



The docks of Messrs. Fletcher, situate between the Limehouse 

 entrances of the West India Docks, are nearly at right angles 

 H ith the river in their immediate neighbourhood; but as regards 

 the general contour of the Reach, point slightly up the stream. 

 Very nearly the same remark will apply to tlie docks of Messrs. 

 Young, at Limehouse; the character these docks bear on tlie river 

 is very similar, except that as Fletcher's docks lie in a bight, they 

 are less exposed. 



Limekiln or Limehouse Dock points up the stream; the small 



Na. UO.-YoL. XII.— May, 1349. 



IS 



