SHIP-BUILDING. 



Calculation of the burthen in tons of the Eaft India (hip, 

 {Plate XII.) according to the common rule. 



Length from the fore-fide of the ftem, at") 

 the height of the upper fide of the | 

 wing-tranfom, to the aft-fide of the }> 

 main-poft, at the faid height of wing- | 

 tranfom, is - - 



Feet. 



159 



Three-fifths of the extreme | 

 breadth is - - - j 



The height of the wing- 

 tranfom is 24 feet, which | 

 produces for every ai | 

 inches . - - 



- -J 



Feet. 

 22.6998 



27.6998 



Length of the keel for tonnage 

 Multiplied by the extreme breadth 



Multiplied by half the extreme breadth - 



Divided by 94 - 



Burthen in tons, according to the com- 1 

 mon rule j 



27.6998 



>3i-3 

 37-«333 



4967.5122 

 18.9166 



93968. 



999tt 



Eftimate, (hewing the real burthen of the Eaft India 

 fhip, Plate XII. 



The weight of the (hip at the launching 1 

 draught of water - - - - J 



The weight of the furniture, including J 

 the (heathing - - - - - j 



The weight of the (hip at her light 



water-mark ... 



■•} 



The weight of the (hip at her load water- 1 

 mark - - - - - - J 



From which deduft her weight at the 1 

 light water-mark - • - - j 



Real burthen ...... 



Burthen in tons, according to the com-") 

 mon rule, as above - - - - j 



Difference -.--.. 



Tons. lbs. 

 748 1 07 1 



62 1782 



811 613 



2029 597 

 811 613 



I217 2224 



999 1477 

 21B 747 



We now find that the Eaft India fhip will carry 218 tons 

 747 lbs. more than ftie is rated for by the common rule ; 

 which, it plainly appears, is in confequence of her body 

 being formed fo full ; and the greater the contrail between 

 full and (harp bodies, the greater will be the error in the 

 tonnage eaft by this rule ; which (hews the impropriety 

 of the erroneous method praftifed for cafting a (hip's 

 tonnage. 



Hence it is obvious, that no dependence can be placed 

 en the common rules for afcertaining the true ton- 

 nage of veffels. Indeed we neither have, nor expeft to 

 have, any rule that (haU be quite exaft ; becaufe the ton- 

 nage depends not only upon the cubical dimenfions of the 

 fliij's bottom, but alfo on the weight and Icantling of her 



whole frame. For inftance, a (hip built at Archangel of 

 fir, will carry confiderably more than another of the fame 

 plan in every refpeft, built at the Havannah of live oak ; 

 nor is there a greater difference in fome (hips, when the 

 weight of every thing which properly makes a part of the 

 (hip, as to the faftening, &c. &c. is confidered. We muft, 

 therefore, be contented with a rule that approximates nearer 

 to the truth ; and fuch is the following, propofed by the 

 late Mr. Parkyns, of Chatham-yard. 



Rule I . For jbarp Jh'tps, particularly thofe of the royal 

 navy. 



ift. Take the length on the gun-deck, from the rabbet 

 of the ftem to the rabbet of the ftern-poft, or between the 

 perpendiculars. Then take ,5 ^ths of this length, and call 

 it the keel for tonnage. 



2dly. To the extreme breadth add the length of the gun- 

 deck, or length between the perpendiculars. Then take 

 ^ijd of this fum, and call it the depth for tonnage. 



3dly. Set up this depth from the limber-ftrake ; and, at that 

 height, take a breadth alfo from out to outfide of the plank 

 at dead-flat, and another breadth between that and the 

 limber-ftrake : add together the extreme breadth and thefe 

 two breadths. Take one-third of the fum, and call it the 

 breadth for tennage. 



Laftly. Multiply the length for tonnage by the depth for 

 tonnage, and the producl by the breadth for tonnage, and 

 divide by 49. The quotient will be the burthen in tons 

 nearly. 



The following trials have been made, to prove the aecu. 

 racy of this rule. 



Rule 2. For Jhipi of burthen, or commercial fh'tps in 

 general. 



I ft. Take the length of the lower deck, from the rabbet 

 of the ftem to the rabbet of the ftern-poft. Then take =, jds 

 of this length, and call it the keel for tonnage. 



2dly. To the extreme breadth add the length of the 

 lower deck. Then take .^s-ths of the turn, and call it the 

 depth for tinnage. 



3dly. Set up this depth from the limber-ftrake ; and, at 

 that height, take a breadth alfo from out to outfide of the 

 plank at dead-flat ; take another at two-thirds of this height, 

 and another at one-third of the height : add the extreme 

 breadth and thefe three breadths together, and take one- 

 fourth of the fum for the breadth for tonnage. 



Laftly. Multiply the length for tonnage by the depth 

 for tonnage, and the produft by the breadth for tonnage, 

 and divide by 36.6666 or 36I ; and the quotient will be the 

 burthen in tons. 



The following trials, among njany others, (hew that this 

 rule does not deviate much from the truth. 



Granby> 



