SHIP.BUILDING. 



eflimating the weight or difplacement, it was found, that 56 

 liundredths of an inch balanced 42 tons at three feet ; and 

 it will be found by the following operation, that 53.445 

 hundredths of an inch in Plate I. will balance 42 tons at 

 three feet, Plate I., difplacement 2829 tons I75lb3. = 

 3829.078 X 53.445 = 151200.0-r 1200= 126. 



We now find that the dillance of the centre of gravity is 

 removed from the line of fupport 53.445 hundredths of an 

 inch. After this, it will be eafy to diicover how far the 

 centre of gravity is below the meta-centre, fince there will 

 be the fame proportion betwixt the diftance of the plumb- 

 line from the heel of the maft, and the height of the maft, 

 that there is betwixt the diftance of the centre of gravity 

 from the line of fupport. Thus, the length of the maft is 

 i 12 feet, which multiplied by. 53.445 = 5985.8 -;- 1200 = 

 4 ft. n|in., the diitance of the centre of gravity below the 

 meta-centre nearly agrees with the calculation above given. 



Tonnage or Burthen. 



By the tonnage of a (hip, is meant to convey the idea of 

 tlie weight of the cargo flie is intended to carry from her light 

 to her load water-line, or feat in the water, when bcft 

 equipped for fea. It may alfo be called the fliip's real bur- 

 then. Therefore, to afcertain the true burthen or tonnage 

 by calculation, is a queftion of equal importance and diffi- 

 culty, as preceding difplacement, &c. 



It is of importance, becaufe it is by this that the mer- 

 chant or freighter judges of the fitnefs of the fliip for his 

 purpofe ; and although cuftomary rules are given for com- 

 puting the tonnages of fhips, the bare infpeftion of them 

 will prove how futile they are. It would be very difficult 

 to fix upon any general rule which fhall be very exaft, be- 

 caufe it depends not only on the cubical dimenfions of the 

 fliip's bottom, but alfo on the fcantling of her whole frame ; 

 and, in fliort, on the weight of every article to complete the 

 faid (liip ready to receive on board her cargo. The weight 

 of timber is variable ; the fcantling of the frame being no 

 lefs fo. 



The following rules for computing the tonnage of a fhip are 

 commonly adopted and made ufe of between the eontraftor 

 and tiie builder, at a certain rate per ton for the building, 

 and will be found to be quite unconne&ed with the above 

 definition of a (hip's tonnage ; for as the depth is out of 

 the queftion, the contraftor finds a faving in Icfs breadth 

 and great depth, which make againft ftability, and confe- 

 quently injure the velocity : on the contmry, great breadth 

 and lefs depth will be found more advantageous to the 

 builder : thus are the intcrcfts of the two parties oppofitely 

 concerned in the refult, and both, when carried to the ex- 

 treme, are exceedingly injurious to the conftruftion of 

 vefi'els. 



The general Rules ohfer-ueJ for meafuring the Tonnage of Ships 

 in the Royal Navy and the AJerchants' Service. 



Let fall a perpendicular from the fore-fide of the ftem, 

 at the height of the upper deck, or middle deck, in three- 

 deck (hips, and another perpendicular from the aft-fide of 

 the main-poft, at the height of the wing-tranfom. In mer- 

 chant-(hipB, the forcmolipcrpendicular is let fall from the 

 fore-fide of the item, at the height of the wing-tranfom. 

 From the length between thefe perpendiculars, deduft three, 

 fifths of the extreme breadth, (that is the thicknefs of the 

 bottom plank on each fide added to the moulded-breadth,) 

 and hkewife as nianv 2^ inches as the wing-tranfom is above 

 the upper edge of the keel, and the reniainder is reckoned 

 the lengtli of the keel for tonnage. 



Then multiply the length of the keel for tonnage by 

 the extreme breadth, and that product by half the extreme 

 breadth ; then dividing by 94, the quotient will be the 

 burthen, in what may be denominated builder's tonnage. 



Calculation of the burthen in tons of the 74-gtin (hip, 

 Plate I., according to the common rule. 



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

 the height of the upper deck, to the I 

 aft-fide of the main-poft, at the height f 

 of the upper fide of the wing-tranfom J 



F(. In. 

 182 9i 



Three-fifths of the extreme 1 

 breadth is - - - J 



The height of the wring- ^ 

 tranfom is 26 ft. 10 in., { 

 which produces for every C 



Ft. In. 



29 



5 6J 



2^ inches 



34 9i 



Length of the keel for tonnage 

 Multiplied by the extreme breadth 



Multiplied by half the extreme breadth 

 Divided by 94 



:om-1 



Burthen in tons, according to the com- 

 mon rule - . - - 



Eftimate, fhewing the real burthen of the 

 Plate I. 



The weight of the (hip at the launching 1 

 draught of water - - - - J 



The weight of the furniture, including 7 

 the flieathing - - - - - 3 



The weight of the fhip at her light 1 

 water-mark - - - - -j 



The weight of the fhip at the load water- 1 

 mark - - - - - -J 



From which deduft the weight at the J 

 light water-mark - - - - J 



Real burthen ..... 



Burthen in tons, according to the com. 

 mon rule - - . . 



Difference .... 



:om.7 



74-gun fhip, 



Tons. lbs. 



1377 2198 



204 1040 



1582 998 



2829 175 



1582 998 



1246 I417 



1864 763 



617 1585 



By the above it may be readily fcen, that the 74-gun 

 fhip (Plate I.) will not carry the number of tons Ihe is 

 rated for, by 617 tons 1585 lbs. j and lience the impro- 

 priety of fuch a rule being made general, as it will always 

 be found greatly to increale the tonnage of fharp-built 

 veffels ; while thofe that are full-built, as (hips in the Fall 

 India Company's fervice, will carry a great deal more. 

 We fhall, therefore, calculate the tonnage of the Eaft India 

 (liip {Plate XII.) both ways as above, in order to prove the 

 great inaccuracy of the rules with rcfpctt to tliofe »eflcl»j 

 as well as to fhips of war. 



3 Y 2 Calculation 



