1849."] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



37 



firm point of attachment for a buoy-chain, in every direction 

 (fig. 5), and will oppose a powerful resistance even to a vertical 

 strain, which generally proves fatal to sinker moorings, depending 

 (as they do) chiefly on their specific gravity. 



Fig. 5. 



The first trials were upon a comparatively small scale; but their 

 success was so decisive, that the merits of the moorings were ac- 

 knowledged, and their use soon became extended. The depth to 

 which these moorings have been screwed varies from 8 feet to 

 18 feet ; the former is deep enough where the soil is of a firm and 

 unyielding desci-iption, and the latter depth is found to give suflS- 

 cient firmness in a very weak bottom. It is evident from its form, 

 that every part of the screw-mooring is so far beneath the surface, 

 as to prevent a vessel from receiving injury from grounding imme- 

 diately above it ; the mooring chain alone protruding from the 

 ground, and it is also obvious, that anchors, dropped in the neigh- 

 bourhood, cannot be hooked into, or get foul of the chain, one end 

 alone being attached to the ground. Although economy should 

 be the last consideration where a large amount of property and 

 many lives are at stake, still if the end can be safely attained by 

 less costly means, it is the duty of those having charge of public 

 works to consider the question. It is right, therefore, to state, 

 that screw-moorings, of the most powerful description, can be put 

 down at a tenth part of the cost of the span-chain mooring (fig. 1), 

 and at even less than the common stone mooring (fig. 2), provided 

 it be of equal power with the former ; setting aside the defects 

 which have been noticed. Indeed, with respect to the screw- 

 moorings, it may be stated, that where they have been longest in 

 use and are best known, they are most appreciated, as is well 

 shown in the recent agreement with the Corporation of Newcastle- 

 on-Tyne, who paid for the permission to use the patent in the 

 Tyne, as applied to moorings alone, the sum of 2,500/., within a 

 few months of the expiration of the inventor's privilege, and 

 when the renewal of it appeared doubtful.* 



In fixing these moorings in the ports and harbours where they 

 have been used, the persons hitherto engaged in the operation have 

 been generally compelled to avail themselves of any means within 

 their reach, for the construction of a floating stage or platform, on 

 which the men could execute the work. Barges, lighters, and pon- 

 toons have been therefore indiiferently employed ; those that were 

 without decks being planked over for the purpose. Two such ves- 

 sels being lashed broadside to each other, with a certain space be- 

 tween them, are securely moored over the spot, and the screw- 

 mooring lowered, with the chain attached to the shackle, from the 

 centre of the stage to the level of the water; and as it descends to 

 the bottom, the lengths of the apparatus for screwing it into the 

 ground are successively attached. This apparatris (fig. 6) consists 

 of a strong wrought-iron shaft, in lengths of 10 or 12 feet each, 

 connected with each other by key joints or couplings, the lower 

 extremity having a square socket to fit the head of the centre pin 

 or axis of the mooring. When the centre pin rests on the bottom, 



* The patent has been renewed for a term of fourteen years, firom the year 1847. 



a capstan is firmly keyed upon the shaft at a convenient height; 

 the men then ship the capstan-bars, and apply their power whilst 



travelling round 

 upon the stage, 

 the capstan being 

 lifted and again 

 fixed as the moor- 

 ing is screwed 

 down into the 

 ground. The ope- 

 ration is continu- 

 ed until the men 

 can no longer 

 move the shaft 

 round, or until 

 it is considered to have been 

 forced to a suflicient depth. 

 In the river Tyne, where 

 many of these moorings have 

 been laid down, a barge of 

 peculiar construction has been 

 prepared for the purpose, con- 

 taining within itself all that 

 is necessary to facilitate the 

 work. 



The most important purpose 

 to which the screw-pile has 

 hitherto been applied, to any 

 considerable extent, is for 

 forming the foundations of 

 lighthouses, beacons, jet- 

 ties, &c., in situations 

 where the soil or sand is so 

 loose and unstable as to be 

 incapable of supporting any 

 massive striicture, or where 

 the waves have so much power 

 of undermining by their con- 

 tinuous action, or beat so hea- 

 vily that the stability of any 

 mass of masonry would be 

 seriously endangered. Many 

 banks oft' our coasts are like 

 the Goodwin Sands, which, 

 although when dry scarcely 

 retain the print of a horse s 

 hoof, will, when covered by 

 the sea, swallow up the lar- 

 gest ship, and are moreover in 

 such exposed situations that 

 no solid structure erected 

 upon them could resist the 

 action of the sea for any 

 length of time. From the 

 number and dangerous nature 

 of the sand-banks and shoals 

 surrounding the United King- 

 dom, the means of placing 



Fig. 6. 



conspicuous and permanent marks upon them becomes an object of 

 the highest importance to navigation. But nothing of the nature 

 of a lighthouse upon a submarine sandbank was ever proposed 

 prior to the year 1 834, the project till then being considered ex- 

 tremely hazardous, if not impossible. 



The author having at that time satisfied himself as to the hold- 

 ing power of the screw-mooring, and made some successful experi- 

 ments with the screw-pile, was applied to by the Society of ftler- 

 chant Venturers at Bristol, to devise the means of placing a fixed 

 light on the Dumball, an accumulation of mud and other alluvial 

 deposit at the entrance of the Avon, and about the end of the year 

 1834. he laid before that society the plan, specification, and estimate 

 of a screw-pile lighthouse, similar in principle to those since erec- 

 ted by him and his son ; but the Corporation of the Trinity House 

 having subsequently undertaken to buoy and light the Bristol 

 Channel, the author's plan was abandoned, and a stone lighthouse 

 was placed on the firm ground in the neighbourhood. 



Between the years 1834 and 1838, some unsuccessful attempts 

 were made to introduce the plan in various localities. In the lat- 

 ter year, at the suggestion of Captain (now Admiral) Beaufort, of 

 the Admiralty, he laid a plan before the Corporation of the Tri- 

 nity House, by whom, at the recommendation of Mr. Walker, their 

 engineer, it was favourably considered, and in the month of August 



