1819.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



131 



as "parallel with the cun-ent," in i-eference to which he subse- 

 quently says: — 



Inasmuch as the vessels are not required to deviate from the direction of 

 the current (i.e. to lie across it), not only is their introduction not made dif- 

 ficult by the motion of the water, but actually accomplished by it without 

 risk. 



Of the docks in the port of London, Mr. Palmer says : — 



When we contemplate the immensity of the traffic on the Thames, and 

 the extent of accommodation afforded to the shipping, as compared with 

 other ports, it is surprising that the entrances to the numerous docks should 

 be less convenient than those on rivers whose navigation is more difficult. 

 The entrances are all narrower, so that when the head of a ship arrives 

 within its confined space, the stern is opposed to the action of the current. 



Mr. Palmer then describes the entrances to the principal public 

 docks, and the laljour entailed at the graving docks on account of 

 their position; in reference to this he says: — 



Now as the force of the water upon the ship is the same between the 

 same parallels, the strength required to resist it will be the same, whether 

 the head points up or down the stream. But it is argued, that if the 

 entrance coincide with the direction of the stream (i.e. points down), the 

 vessel may he forced against one of the side walls ; and if no exertion be 

 made to prevent such an effect, it undoubtedly would sometimes occur. 

 But the vessel must he controlled by ropes at the stern, connected with a 

 mooring, with less force in this position than when laid across the stream, 

 and proportionally so in all the intermediate angles. 



Now if the entrance point up the stream, the vessel must be allowed to 

 pass first above the entrance, and then be drawn towards it with a force 

 greater than that required to resist her motion, as in the former case, because 

 the motion of the stream is added to that of the vessel. Although the 

 difference in the quantities of force and labour may not be great, the direc- 

 tion of the entrance, if narrow, sliould be guided by localities, such as the 

 position in the river, the position of moorings, &c. 



After stating that the above reasoning applied to narrow en- 

 trances, with the gates close to the river, inapplicable for the 

 London Docks, and referring to the want of width at most of tlie 

 entrances, and the too close proximity of their gates to the stream, 

 Mr. Palmer describes his plan for the Shadwell entrance, in ac- 

 cordance with the principles above laid down, and which was sub- 

 sequently carried out under that engineer. 



That entrance, however, by additional outworks, resolves itself 

 into a very different form. 



Fiy. 12. — The entrance to the Grand Surrey Docks and Canal, 

 Rotherhithe, points slightly down the stream; but from tlie local 

 set of the tide from the opposite shore, its line of direction forms 

 a very obtuse angle with the set of the flood. The effect produced 

 by this is evinced in an external timber jetty and dolphin, oft' the 

 upper side, by which a vessel is brought up upon the flood, in the 

 right position in a line with the entrance, which is obviously insuf- 

 ficient as to width and length, when the set of the tide is consi- 

 dered, without these external works. The direction of this 

 entrance has probably been influenced by local circumstances con- 

 nected with neighbouring properties. 



Fig. 13. — The AVapping, or central entrance of the London 

 Docks is situated at right angles to the stream. Its direction in 

 such a position must no doubt have been influenced by local cir- 

 cumstances. Its direction for the two purposes of docking and 

 undocking is tolerably eligible; but there is a deficiency of length 

 towards the ri\'er, and splaj'iug out of the wing walls; dolphins 

 have consequently been rendered necessary, but they are placed at 

 such a distance out as to act similarly to the moorings at other 

 entrances. There is a local eddy of the tide off this entrance, 

 which makes its direction of less consequence. It is principally 

 used for small vessels and barges. 



The upper entrance of the London Docks, called the Hermitage 

 entrance, is nearly square to the stream, or inclining slightly 

 downwards. This entrance is not used; the principal trade is 

 thus carried on at the lower eastern entrance at Shadwell, where 

 large sums of money have been expended in the repairs and im- 

 proN'ement of the immediate outlet or entrance. 



St. Saviour's Dock entrance, on the opposite side of the river, 

 points very much down the stream; but it is supposed by persons 

 connected with the port, that its original formation was out of 

 some natural inlet in the shore, outside the marsh wall, and, being 

 only a tide dock, the direction of the entrance was not considered 

 so much an object as in the neighbouring works. It would, 

 however, be supposed, that the direction of the entrance to such a 

 dock was a consideration of importance; but a comparison of this 

 example with that of Limekiln Dock on the opposite side, and 

 which has before been quoted as pointing acutely up the stream, 

 shows how various have been the modes of treating these tidal 

 constructions. 



Fig. H. — The St. Katharine's Dock entrance points slightly 

 down the stream. There is at that spot a great depth of water, 

 and ships are frequently docked after the tide has fallen, according 

 to the judgment of the dock-master, whether it can be done safely. 

 Under these circumstances the direction up, or down, is not of the 

 same importance as in other examples. But an evil is entailed at 

 these docks, by the small amount of width between the wing walls 

 at the entrance; the particular locality must, however, have neces- 

 sarily involved this, and the wings were probabl)' projected and 

 splayed out as much as the nature of the site would allow. The 

 object here also was to dock ships quickly, and also upon a falling 

 tide. For this the lock has three pairs of gates, the outer pair 

 being placed as close to the river as possible. The fact of a public 

 street here running parallel to the river, and the entailment of a 

 swing bridge over the lock also prevented any great splaying out 

 of the wing walls. 



In reference to the general question it may be observed, that 

 the foregoing examples resolve themselves into three classes — 

 viz., dry or graving docks, wet or floating docks, and building slips. 



Ser 



of 



TUnd 



Fig. 15.— Proposed Graving Dock. 



Fig. 15. — 'With examples of the first class, viz., the dry or 

 graving docks, the great desideratum appears to be, to get them 

 placed at such an angle to the course of the tide, that ships may 

 be docked upon the flood with the greatest facility. There exists 

 but one opinion among persons acquainted with the practice of 

 docking ships upon the Thames as to what this direction should 

 he — viz., an acute angle to the flood, or in other words, pointing 

 upwards; some recommending (if the site will allow it) a direc- 

 tion nearly up and down the stream, others an angle of about +5°, 

 with a dolphin half the length of the ship, above the entrance, to 

 keep her from tailing on the ground if the wind should be on 

 sliore. It is obvious, that the greater the degree of obliquity, the 

 more the river frontage will be required for each entrance. Ships 

 are usually docked head fir.st, and turned out stern first, from dry 

 docks. If the line of direction of the dock points downwards, 

 and forms an obtuse angle with the direction of the flood coming 

 up, or is even square to it, considerable labour and difficulty are 

 involved in heaving down the stern of the vessel against the tide, 

 so that she may be in a line with the dock. This very force of the 

 tide is taken advantage of, and assists in placing the ship in a 

 proper position, when the dock points up the stream. This direc- 

 tion is equally advantageous in undocking vessels from dry docks, 

 as the almost invariable practice is to turn them out stern fore- 

 most; thus the vessel's quarter first meets the tide, is carried 

 upwards, and her bow is brought against the tide in the most con- 

 venient position for mooring her. 



Fig. 16. — "W'ith wet or floating docks the case is altered as 

 regards undocking, and this has been met by the greater width at 

 the entrance, formed by the spreading wings on either side. The 

 circumstances attendant upon a ship entering are precisely the 

 same as when approaching a graving dock; hut in undocking a 

 loaded vessel from a wet dock, she is brought out head first. If 

 the entrance pointed up the stream, the vessel's bow would require 

 to be kanted up immediately she met the tide; this would cause 

 considerable inconvenience to an outward-bound vessel, which 



IS* 



