SHIP-BUILDING. 



will be increafed in proportion to the cube of the breadth ; 

 for example, without altering the other dimenfions, let the 

 breadths be doubled, we thereby double the weight, which, 

 by aaing upon the arm of a lever, double the length will be 

 quadruple, lo the (hip will acquire eight times the liability. 



Thus we fee an increafe of breadth will produce an iu- 

 creafe of ftability ; for a fhip that is broad and fhallow has 

 much more itiffnefs than one that is narrow and deep ; but 

 the failing of the (hip may be much retarded, as (he certainly 

 would be leewardly under little fail, which ought to be par- 

 ticularly guarded againll, efpecially in conftrufting large fhips 

 of war. The expence in the building would alfo be ma- 

 terially increafed, according to the ufnal mode of computing 

 the tonnage, as may be readily feen in the next fettion. 



If the depth only is increafed, without enlarging either the 

 length or breadth, all the ftability that can be gained will be 

 in the ftowage. To increafe the depth or draught of water 

 would lower the centre of gravity, and increafe the weight ; 

 this would operate againlt velocity, becaufe the refiftiJice is 

 as the quantity of water to be removed ; or nearly as the 

 area of the thwartfhip feftion of the immerfed part of the 

 body at the midfhip-bend. It would at the fame time render 

 the immerfed body of a figure lefs proper to feparate the 

 line of fupport from the centre of gravity, fo that the effect 

 on one fide would be in fomemeafure deftroyed on the other; 

 and, by lowering the centre of gravity too much, the fhip 

 would labour exceflively, and endanger the mails, too large 

 a draught of water being both dangerous and inexpedient. 



Ships having a fufBciert degree of ftability arifing from 

 their conftruftion, will certainly fail fatter than others, which, 

 in order to carry the fame quantity of fail, require to be 

 ballafted with a much greater weight ; for the latter, fo bal- 

 lafled, will be much more liable to roll than the former. 



The following circumftance will prove, that inftability in 

 the conftruftion cannot be reftified to any confiderable de- 

 gree by the ftowage, although, on the contrary, that the 

 ftability of many fhips, however perfeft in conftruftion, may 

 be materially injured by improper trim, or an injudicious 

 mode of ftowage. 



And, firft, as there is nothing of more importance to the 

 well-being of a fhip than its ftability, it will not be improper 

 to mention an opinion which prevails with feamen in general, 

 that the ftability depends chiefly on the ftowage of the hold ; 

 and at the fame time, in order to (hew that a very great change 

 in that refpeft will produce a very trifling difference in the 

 ftability, we fhall quote a profefTional author of great merit, 

 M. de Romme, in his book L'Art de la Marine, page 105. 

 " As to the pofition of the centre of gravity, no doubt it 

 may vary, but the hmits to which it is confined are very 

 ftraight, efpecially in (hips of war. An example in the Scipio, 

 of 74 guns, armed for the firft time in 1779, was hardly in 

 the road before (he was fufpefted of inftability. It was im- 

 portant in time of war to clear up thofe doubts, and to make 

 the neceffary experiments to prove this dangerous defeft, if 

 it exifted. Firft, the lower-deck guns were run out on one 

 fide, while houfed on the other, which heeled the fhip thir- 

 teen indies ; the fliip's company were then ordered to their 

 quarters at the fide the guns were out, which increafed the 

 inchnation to twenty-four inches. After thefe cfiays the 

 fails were fet, and in fine weather the (hip was found fo crank, 

 as to render the ufe of the lower-deck guns difficult and 

 dangerous : thus, her inftability being proved, fhe was or- 

 dered to port to be remedied. 



" Opinions were divided as to the caufe of the defeft ; 

 fome imagining it to proceed from the form of the hull ; 

 otiiers from the ill arrangement of the charge. The firft 

 engineer was ordered to attend at Rochfort, and direft the 

 choice of meafures to give the Scipio, as well as two other 

 6 



fhips, the Pluto and Hercules, built from the fame plan, th* 

 ftability they wanted. He judged that new ftowage would 

 remedy the defeft, and his opinion was adopted by the ma- 

 rine council. The Scipio was unloaded, and charged anew, 

 under the direftion of the chief engineer. In the firft charge 

 (he had 84 tons of iron, and 100 tons of ftone ballaft, and 

 was re-loaded with 198 tons of iron, and 122 tons of ftone 

 ballaft ; and as her draught of water, or difplacement, could 

 not be altered, it was neceflaryto dimini(h 130 tons of water 

 to prelerve the fame line of floatation ; by this means 135 

 tons were placed, in the fecond loading, eight feet lower 

 than in the firft ; yet when the (hip was completed with the 

 new ditlribution of her charge, fhe was found pi-ecifely as 

 deficient as before, inclining twenty-four inches, with the 

 men at quarters, and the guns out. She was afterwards 

 doubled with hght wood, a foot thick at the extreme 

 breadth, and ten feet under water, decreafing to four inchet 

 length and depthways." 



M. de Romme very judicioufly obferves, that the defeft 

 of inftability was not fo much owing to a want of extreme 

 breadth, as feveral other 74-gun fhips had had the fame, or 

 even lefs, but in diminifhing the breadth at the plane of float- 

 ation too quickly forward and aft, which at once leflened 

 the capacity and pofition of the line of fupport. 



A French 36-pounder weighs, with carriage, &c. 4^ 

 French tons, and their increafed length caufes their centres 

 of gravity, when run out, to be removed 45 feet ; fo that 

 the moment produced by running out the lower-deck gun* 

 of a French 74, the oppofite fide houfed, is more than 

 double the moment for an Englifh 74, in the fame cir- 

 cumftance. 



It is certain this change of place in the centre of gravity, 

 which lowered it nearly five inches, muft have contributed 

 to increafe the ftability, and have occafioned nearly a dif- 

 ference of three inches in the greateft inchnation ; but as the 

 experiment where the men are ftationed at quarters is liable to 

 fuch irregularity, an error of this magnitude is to be ac- 

 counted for from the men running to the fide, to mark more 

 ftrongly the defeft of a bad (hip. 



Secondly, the ftability of many (hips, however perfeft in 

 the conftruftion, may be materially injured by an improper 

 trim, or an injudicious mode of ftowage ; for was the 

 centre of gravity raifed toe high by the weightieft part of 

 the cargo being placed uppermoft, the fhip would not only 

 be rendered incapable of carrying a fufficient quantity of 

 fail, but in danger of being overfet ; and was the cargo lead, 

 or any other fuch weighty body, and placed too low in the 

 hold, the centre of gravity would confequently be fo lowered 

 as to endanger the (hip's rolling away her mafts. When a 

 fhip is fo loaded, as that her centre of gravity is carried too far 

 forward, the fhip will pitch and labour heavily ; and when 

 too far off, fhe will occafionally be expofed to the dangerous 

 circumftances of a pooping fea, &c. 



As it is of the utmoll importance to the well-being of a 

 fliip to afcertain its ftability, the greateft attention muft be 

 given, in the conftruftion, to the finding of the exaft dif- 

 tance, between the meta-centre and centre of gravity, that 

 every fhip requires, according to her form ; the maximum 

 of which is, that the fliip fliall not, by the length of lever, 

 either become too ftiff, or be fubjeft to fudden motion or 

 rolling ; nor, on the contrary, from the lever's being too 

 fhort, the ved'el is unable to carry fail. Therefore, in the 

 conftruftion, to afcertain the height of the meta-centre 

 above the centre of gravity of the immerfed part of the bot- 

 tom, the half feftion of the load-water-line muil be taken 

 as was divided to find the difplacement. Then the fum of 

 the cubes of the half feftions, or ordinate is to be multi» 

 plied by the diftance between them, and ' rds of the 



produft 



