1855.] 



LIGHTHOUSE ON THE NEW SOUTH SHOAL, NANTUCKET, U. S. 



123 



posed, but also the character of the cage, the arrangement and 

 finish of the dwelling, and passage thence to the watch-room 

 and lantern of the latter ; and also the arrangements for secur- 

 ing the boat for taking in stores ; the position of the fug-bell ; 

 the keeping of the oil, water, and fuel, &c. &c.; and all other 

 particulars, even to the size of the material employed, &c. 

 Talbotypos of the elevation and vertical section of each reduced 

 in scale to about 1-282, are also appended to the report. 



It is now necessary to explain in what manner it is proposed 

 to establish either work on the shoal. It was stated, when 

 describ'ng the applicability of screw-piles and pneumatic-piles 

 for founding the proposed structures, that as the latter required 

 no mechanical force to insert them into the bottom, for em- 

 ployment of a fixed staging, from which to apply such force 

 as was required in the use of the former, would be unneces- 

 sary; and th:it although a floating body might, by well digested 

 measures, in favourable weather, be successfully employed in 

 sinking them singly, it would not be practicable to give the 

 number of piles required to found the work their proper rela- 

 tive positions from so unsteady a footing. The utter hopeless- 

 neis of constructing a fixed platform, under the cireum-stances, 

 at so exposed a point as New South Shoal, at least by such time 

 in the working-season as to render it available for the intended 

 purpose, was also shown. What other course, then, .shall be 

 adopted in the emergency ? It is, in my opinion — not lightly 

 formed — to carry out and deposit on the shoal, by one bold 

 measure, the entire lower or foundation portion of the structure 

 described as the octagonal prism, and by Dr. Pott's process, 

 so simple in its character and wonderful in its results, to sink 

 it in the sand to the required depth. It will not escape atten- 

 tion, that in taking this course, the necessary bracings, down 

 to the very level of the shoal, will be secured to the work ; 

 whereas, in putting down the piles separately, the attaching of 

 them is barely possible under the most favourable circum- 

 stances, at so exposed a point. 



The foundation or lower portion of the structure, already in 

 part described, is formed of nine piles, occupying the angles 

 and centre of the prismatic figure, bound together by two sets 

 of horizontal braces — one 20 feet from the bottom, the other 

 at the top — and by three sets of diagonal braces between these 

 planes. It is necessary to state here, that the lower part of 

 each pile is received by a cylinder having a conical base or 

 foot, through which, bj' a separate pipe, provided for the pur- 

 pose, extending to the top of the framing, it is designed to 

 excavate the sand by the pneumatic process. By this arrange- 

 ment, the advantages of the two systems — of the screw-pile and 

 pneumatic pile — have been combined ; the means, on the one 

 hand by which the soil may be penetrated to the required 

 depth, and the use, on the other, of a shaft, presenting, with a 

 proper bearing, the least exposure, strength considered, to the 

 action of the sea. For the character of this arrangement, and 

 for all other details, reference is respectfully made to the model 

 of the foundation section, on the scale of 1-24, which will be 

 deposited in the bureau. The work, as designed, including 

 the cylinilors with the conical bases to receive the solid piles, 

 and all neces.sary appendages, such as air pump and receivers, 

 and air and sand piles, &c. &c., fur sinking ii into the bottom, 

 weighs 238 tons. To receive and float this great weisrht, dis- 

 tributed as it is throughout such large bounds, will require twin- 

 camels, each at least 100 feet in length, 15^ feet beam, and 10 

 feet depth of hold, or say about IGO tons. These camels, when 

 light, will draw little over oi feet of water ; and when loaded 

 about 7 feet. Carrying the foundation as proposed, with the 



lower set of horizontal braces resting on the rail, the cones or 

 shoes of the cylinder will extend nearly 4 J feet below the 

 keels. In this same position, Gl tons of the weight will be 

 suspended below, while the balance, or 177 tons, will stand 

 above the rail. It will be time enough, should the present 

 design be approved and ordered to be carried out, to digest all 

 necelsary details, to insure a full efficiency to the camels ; to 

 determine whether they shall consist, as now proposed, of two 

 similar vessels of ordinary model, or of two having, when com- 

 bined the general outline of a single vessel ; the most perfect 

 way of securing them to each other, and to their burden ; 

 the best arrangement for towing, mooring, and flooding; 

 and, finally, the" proper mode of removing them from under 

 the framing when it rests in position on the .shoal. It is even 

 now evident that it is desirable so to modify the lower framing 

 that a larger proportion of the weight may be carried below the 

 body of the camels than the present arrangement provides for. 

 A"-ain, it further appears, as far as experiments with the model 

 may be relied upon, that to insure the uniform descent of the 

 foundation, it is neces.sary to have either an air-pump for each 

 pile, or, if one air-pump only is used, to communicate ^yith the 

 soil-receivers by air-pipes of equal lengths. The weight on 

 each pile, when resting on the bottom, is 26-2 tons, which dir- 

 tributed over 19-6 feet, the area of the base of the cones,_ 5 

 feet in diameter, gives 1-33 ton for each foot. The entire 

 weight of the lighthouse structure is 640 tons; of the beacon, 

 46G"tons; giving 71-1 tons on each pile, or 3-6 tons on each 

 superficial foot in the case of the first, and 51-6 tons, on each 

 pile or 2-6 tons on each superficial foot, in the case of the 

 second work. To sink the cylinders 19 feet in the sand, the 

 depth proposed, will require the raising in each case of a column 

 of sand of that height, 5 feet in diameter, or 373 cubic feet, 

 or about seven times the contents of the receivers, calculated 

 at 54 cubic feet. As there is, however, a large admixture of 

 ■water with the sand, raised by pumping, the descent of the 

 cylinders will necessarily call for the filling of the soil-receivers 

 much more frequently. 



In recommending the carrying out of the foundation in one 

 body to the shoal, the hazards which belong to the entire pro- 

 ceedino-, from the dep.arture of the camels with their burden 

 from the selected harbour, to their arrival, and the complete 

 establishment of the work at the site, are, it is believed, in no 

 wise underrated. So far from this being the case, it is not 

 improbable that, by dwelling on the subject, I may have rather 

 maa;nified them. The towing the camels in a sea-way with their 

 load, a larce proportion of which is, on the one hand, high 

 above their decks, and on the other, far below their water-line; 

 the placing, and then securely mooring them at the selected 

 .site ; the "flooding the camels, and then relieving the founda- 

 tion! on resting on the bottom, from them, without injury frocu 

 the iieave of the sea to either, particularly thefin-mer; and, 

 lastly, the sinking of the piles by the pneumatic process, are 



all operations, under the circumstances, of much delicacy, 

 liable to great risks, and, as a consequence, involving the issues 

 in much uncertainty. The velocity and ever-changing direc- 

 tion of the currentsat the site, and through the group generally; 

 the exposure, and the distance of the .shoal from the land ; and, 

 above all, if it be possible to draw a distinction where each 

 controlling conditi..n holds so important a place, the distance 

 of the point of destination from a harbour, all go to show that 

 the dilfuulties ami dangers of the operiitiim are of no ordinary 

 character. As its success depends on the vici.ssitudcs of the 

 weather, that is the Uue turuiug-point in carrying out the finaj 



