SHIP-BUILDING. 



By the refult of the above calculation it appears, that the 

 after-part of the bottom has a minus of 983.3224 feet, its 

 contents being 983.3224 lefs than the fore-part ; and was 

 the (hip to be conltrufted to fail on an even keel, it would 

 be necelTary to fill the after-part half the difference, or 

 491.6612 feet, and reduce tlie fore-part until it had lolt the 

 fame quantity ; but to alter the after-part of the fliip from 

 its prefent conflruftion, or to make it fuller, would retard 

 her velocity, and prevent the water coUapfing at the rudder ; 

 for the run of a (hip fhould be neither too fine nor too full, 

 but fo conftrufted that the column of water (hould exaftly 

 meet upon the ftern-poll, then the rudder will have its full 

 power. The quarter above the load-water-line rtiould be 

 very full, to fupport the (hip when rifing forward to a fea, 

 and alfo to enable her to feud. 



In regard to the failing trim of a vefTel, it is the decided 

 opinion of moll fcientific men, that (hips or veffels of the 

 larger clalTes (hould always be fo conftrufted as to fail on, 

 or nearly on an even keel, that is, fo that the (hip, when 

 trimmed for failing, (hould have her keel parallel to the fur- 

 face of the water ; therefore, by as much as the effort of the 

 wind on the fails and mads in forcing the (hip through the 

 water has a conftant tendency to deprefs the bow, fo much 

 fhould the (hip be trimmed by the ftern, as that will be found 

 moft advantageous both to their failing and fleering. 



Many think it inconfiftent to conltruft a fhip to fail on 

 an even keel, and yet to place the mid(hip-bend or greatell 

 breadth very forward. A fhip fo intended to fail, ought, as 

 they conceive, when launched, to have an equal bearing fore 

 and aft, in order that, before the ballad is (towed, (he may 

 be on an even keel ; and they think that the ballaft, if not 

 placed equally fore and aft, muft inevitably drain the (beer of 

 the (hip. Neverthelefs, experience convinces us it is not ma- 

 terially detrimental ; for many (hips, when launched, will fwim 

 four feet by the dern, more or lefs, and yet when trimmed 

 for failing, they are faund to go fader on an even keel, and 

 receive little or no damage if carefully dowed. 



Some (hips are too clean abaft, and require to fail by the 

 dern ; becaufe they have no bearing for fifteen or twenty 

 feet from aft, till the buttock is brought well into the 

 water ; and even then, for want of being fuller lower down, 

 when the fea leaves the buttock, the over-hanging of the 

 ftern will drain the (hip, and occafion her to tremble, till 

 tTie next fea, with redoubled force, ftrike the buttock as 

 the (tern is falhng, and fo fhake the (hip ; in which cafe it 

 will be well, if fome part of the mads be not carried away 

 by the (hock : however, this kind of motion muft retard the 

 velocity. This accident, though rare, is dangerous, and 

 '/hould be prevented in the conftruftion of the fhip. 



With rcfpedt to (hips that ought to fail fome feet by the 

 ftern, on account of their infuihciency abaft, it is the opi- 

 nion of many, that if a line were drawn to be well with the 

 lower fide of the keel, in the middle of the fliip's length, 

 and half the difference fet up at the aft-part of the ftern- 

 poft from the lower fide of the keel, and that part of the 

 keel and dead-wood were taken oft, and placed under the 

 fore-part of the keel, with the after-end that was before 

 to be forward, fo as to make the lower part of the keel 

 ftraight, as before, the (hip would then fail fomewhat fader, 

 and be the better : for wiien a fliip is brought fo much 

 down by the dern, the keel, not being parallel to the fur- 

 face of the water, (to wliicli the fhip generally fails pa- 

 rallel,) mud occafion a preffure at tlie under fide of the 

 keel, equal to the weight of water difplaced by the breadth 

 of the keel, and to the angle which the keel makes with 

 the furface of the water in its own length. This may 

 (hew why fo many lliips, differently condrudled, are found 

 to fail bed on an even keel, alUiough many of them were 



defigned by the conftruftor to fail by the ftern. Fnding the 

 refult rather in favour of an even keel, the 74, Plate I., 

 was fo conftrufted, as moft likely to anfwer every purpofe. 

 By that means the water-Hnes were drawn parallel to the keel, 

 and were thereby more ufefiil as well as more properly placed 

 to form the body ; for when the fquare timbers, and the 

 water-hnes, being fquare to the timber, properly agree with 

 each other, and are fair curves, the ribband-lines, or any other 

 feftion, will likewife be fair, or as fair as they ftiould be, 

 allowing the preference to the water-lines and fquare timbers. 

 When water-hnes are not defigned to be parallel to the 

 keel, the draught is generally formed by ribband-lines, be- 

 caufe the water-lines differing in height at every timber, 

 require the fquare timbers to be formed before their height 

 can be fet off; and when the water-lines are run, if not ap- 

 proved of, much of the work mud be done over again, the 

 water-hnes being more regarded than the ribband-lines ; for 

 many (hips are condrufted by ribband-lines only, which feem 

 to produce fair curves, yet forward, and aft efpecially, they 

 make a very unfair body, which is detrimental to velocity. 



Small veffels, as cutters, &c. draw much more water aft 

 than forward, and their bows are more full in proportion to 

 the after-part ; nor would it anfwer fo well were their line 

 of floatation nearly parallel with the keel, but fpreading as it 

 does aloft, efpecially towards their bow, the bow meets the 

 fluid in a more flmting direftion, and experiences far lefs 

 refidance ; and the deprelfion of the ftern, with the impulfe of 

 the aftermoft fails, caufes a proper counter-balance, and pro- 

 pels the veflel through the water with greater velocity than 

 if otherwife condrufted ; for the after-part of thofe veffels 

 is generally very clean or tapering, which neceffarily con- 

 tributes to make the veffel weatherly, and caufes it, under 

 judicious management, to turn as it were on a pivot. 



A fhipmay bebuilt to a precife draught of water, by which 

 the conftruftion will be founded upon true principles ; but 

 when a fhip is not built to one precife draught more than 

 another, it will be a very difficult, and one of the moft com- 

 plex quedions in (hip-building to determine this point. It 

 may be imagined that no more is ncceffary than to make the 

 (hip fwim in the water, fo as to be capable of carrying the 

 greated fail ; but when a fhip is very deep in the water, it will 

 greatly incrcafe the refidance, and confequently retard her 

 failing ; hence a long flup will draw lefs water than a fhort 

 one, which is a good property, and the refidance at the ftern 

 being lefs, (lie will therefore fail fader. The refiflance, how- 

 ever, mud be calculated, not abfolutely, but relatively, and in 

 proportion to the fail (he fpreads. 



In fhips of war, the load-water-line muft be governed by 

 the height of the lower ports above the water in midfliips ; 

 and this we find in line-of-battle fhips fhould invariably be 

 from five to fix feet, in frigates from fix to feven feet, and in 

 (loops, cutters, &c. from four to five feet. 



Sliips for commerce are generally condrufted to carry a 

 certain cargo, and their principal dimenfions are determined 

 according to the trade for which they arc particularJy de- 

 figned ; therefore the line of floatation, or load-water-line, it 

 not confined in them (o exaftly to a certain height. 



Ships of the line, from long praftice, have been found to 

 fail bed when inclined one foot, cr rather more, by the 

 dern. Thus, the 74-gun (hip in Piute I. load- water-line, 

 when fitted for fea, was 20 feet forward and 2 1 feet abaft ; 

 therefore it only remains to be afcertaincd, whether the 

 whole difplacement of the bottom under the lo.id-water-line 

 agrees with tlie edimated weight of the fhip, &c. when fit for 

 fea, by multiplying the mean area of the load and upper 

 horizontal water-lines by fix inches, the mean depth, and add- 

 ing it to the difplacement already found : as in the follow- 

 ing operation. 



Area 



