SHIP-BUILDING. 



may he cnCily accounted for, by the weight of anchors, 

 cables, men, ballalt, &c. as additional weight in the fhip 

 at that time. Take 1377 tons 2198 lbs., the weight of the 

 hull cxclufively, from the fcale of tons, and fet it off from 

 the perpendicular line A H, along the line A B, or bafe ; 

 whence fquaro up the perpendicular K i, to interfeft the 

 curve of difplacement. That depth we find by the fcale of 

 feet to be 13 feet 4 inches, a difference of 1 1 inches, ac- 

 counted for as above. 



Now to prove the real burthen of the fhip by this fcale of 

 difplacement, we have found, by the ellimate, that the 

 (hip, with her furniture, &c. difplaces 1582 tons 998 lbs. 

 at her light water-mark. Take 1582 tons 998 lbs. from 

 the fcale of tons, fet it off as before, and raife the perpendi- 

 cular L / to intcrfecl the curve of difplacement ; and ano- 

 ther perpendicular at 2829 tons 175 lbs., taken from the 

 fcale of tons, which is the weight of the (hip at her load 

 water-hne, as L /. Then take the dittauce between the 

 two perpendiculars laft drawn, and apply it on the tonnage 

 fcale, and we have 1247 tons nearly, the real burthen, as 

 before (hewn by calculation. 



Again, take the height where the perpendicular L / 

 interfefts the curve of difplacement, and apply it on the 

 fcale of feet, and we have 20 feet 6 inches, the medium 

 height of the load draught of water, which was 20 feet for- 

 ward, and 21 feet abaft. 



Now the perpendicular L being the utmoft limit of the 

 quantity of water, expreffed in tons, difplaced by the bot- 

 tom of the (hip, when (lie is brought down to her load 

 water-line, it is evident, from what has been already faid, 

 that if the number of cubic feet of water which the (hip dif- 

 places, when light, or, which is the fame, the number of 

 cubic feet below the light water-line, be fubtrafted from the 

 number of cubic feet contained in the bottom, below the 

 load water-line, the quotient will be the real burthen or 

 tonnage. 



Any other cafe to which this fcale may be apphed is 

 obvious, particularly to merchant-ihips. Let it be re- 

 quired to find the number of cubic feet difplaced, when the 

 draught of water is 17 feet 7 inches, and the additional 

 number of tons required to bring the (hip down to her load 

 water-line. 



Take 17 feet 7 inches from the fcale of feet, and fet it 

 up upon the perpendiculars A N and L /, above the bafe 

 line A B, and draw an horizontal line through thofe fpots, 

 interfefting the curve of difplacement at ; from thence 

 drop the perpendicular O 0. Take the diftance 0, in the 

 horizontal line, to the perpendicular A N, and apply it on 

 the tonnage fcale, it will meafure 2205 tons 1706 lbs., the 

 difplacement anfwerable to that draught of water ; and the 

 meafurement from o, taken to the perpendicular L /, applied 

 on the tonnage fcale, will give 623 tons 708 lbs., the addi- 

 tional weight neceffary to bring the fhip down to tlie load 

 ■water-line. Again, 623 tons 708 lbs. added to 1582 tons 

 998 lbs., give Z2o; tons 1706 lbs., as above, and thus it is 

 proved that the perpendicular O is equally diftant from 

 the perpendiculars M m and L /. 



The meafurement of the tonnage might be facilitated, by 

 drawing the tonnage fcale reverfed on the bafe line A B, 

 and at the load water-line, as in the plate. 



Now if the draught of water be required, correfponding 

 to any weight intended to be put on board, it may be 

 readily known as follows. 



Find the given number of tons, fuppofe 928, in the fcale 

 on the line ml, through which drop a perpendicular to 

 interfect the curve of difplacement, as at Pp ; and at * 

 draw an horizontal line. Now the perpendicular diftance 



between the bafe line A B, and interfeftion of ^, being ap. 

 plied on the fcale of feet, will give 19 feet, the draught of 

 water required. 



Many ufeful difcoveries may be made by blocks or 

 models of (hips, and with as great certainty as by the niceft '; 

 calculations ; for it muft be allowed, as before obferved, ; 

 that in calculating from a draught drawn from a quarter I! 

 of an inch fcale, it will be liable to fome inaccuracies, which ^ 

 cannot be obviated in praftice, by reafon of various little f 

 alterations which may be made in laying off the fhip in the |i 

 mould-loft ; confequently the draught and the (hip will, in » 

 thofe points, difagree. And likewife, upon Itridl exa- 

 mination, we fhall be enabled to find, that there are not 

 many fhips that have both their fides exadly equal in every 

 refpeft. 



Let the block, or model, be conftrufted to a fcale of 

 one-quarter of an inch to a foot of the correfponding parts 

 on the (hip ; and care (hould be taken to provide the wood 

 as light and dry as podible. 



The model being accurately conftrufted, it may be alfo 

 proved by fufpending it by a line, faftened to a hook in any 

 part of a ftraight line, drawn from the middle line of the 

 ftem to that of the (tern-poft. This hook may be moved 

 forward and aft to different places in the middle line, and a 

 weight may be fufpended from the upper part of the middle . 

 line, on the poft. If the two fides be exaftly of equal di- | 

 menfions, and homogene, they will then be of equal weight. 

 A plane palling through thefe three lines, whatever part of 

 the middle line the hook be in, will likewife pafs through 

 the middle line of the keel, ftem, and poft: therefore, if 

 the model (lands this proof, it will be as true to work fronj 

 as the niceft calculations. 



The model, having ftood this teft, may be fufpended by 

 the fame line, or filk, in different pofitions, until it points 

 out the centre of gravity ; which will be found, when the 

 block hangs in a ilate of equilibrium. Thjs praftice is, 

 doubtlefs, very fimple ; but it will be found very convenient. 

 Further, the model being fufpended by tVie hook, the line? 

 hanging at the ftem and poft correfponding to their middle 

 lines, and to that which fufpends the block, we may hold a 

 batten out of winding with the liue that fufpends it, ani, 

 with a pencil, draw a line upon it. A plane paffing 

 through this pencil line, at right angles to the keel, and 

 pafTing likewife through the line that fufpends the block, 

 will likewife pafs through the centre of gravity, which, 

 therefore, muft be fomewhcre in this plane. Again, move 

 the hook to fome other part of the middle line, and let the 

 block be fufpended from that point ; draw alfo another 

 pencil line, out of winding with this laft line of fufpenfiouj 

 and the interfeftion of the two lines will crive thehefifht of the 

 centre of gravity above the keel, and likewife its diftance 

 from the poft and ftem ; and if the hoek be mfjved to any 

 other part of the middle line, and a pencil line be drawn as 

 before, it will likewife interfeft in the fame p oint ; or, let 

 there be ever fo many points affumed in the mi ddle line, and 

 the block fufpended by each, and pencil liwis drawn, they 

 will all interfeft in the fame point ; and a-s the centre of 

 gravity will always be in that plane whia'a palTes through 

 the middle line of the keel, ftem, and poft, it may with 

 certainty be marked on the draught. 



This will certainly require the greatel't nicety ; but, if 

 well executed, it will agree with that fou.nd by calculation, 

 provided the dimenfions be taken very ejj aftly, and likewife 

 from a true fcale of equal parts. 



By the fame model may be found the true tonnage of a 

 (hip, thus : Let tiie light and load wat er-lines be marked on 

 it ; then put the model in water, anv'i load it until the fur- 



