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ON THE MEASUREMENT OF SHIPS FOR TONNAGE. 87 
Rule I.—1. Measure the length of the ship in a straight line along the 
upper side of the tonnage deck from the inside of the inner plank (average 
thickness), at the side of the stem to the inside of the midship stern timber 
or plank there, as the case may be (average thickness), deducting from this 
length what is due to the rake of the bow in the thickness of the deck and 
what is due to the rake of the stern timber in the thickness of the deck, and 
also what is due to the rake of the stern timber in one-third of the round of 
the beam ; to be termed the length for tonnage. ‘“ The height for tonnage to 
be taken from a base line at the underside of the false keel to the medium 
height of the tonnage deck. The breadth for tonnage to be the extreme 
breadth, exclusive of doubling. Divide the length so taken into the follow- 
ing number of vertical sections required for the measurement of transverse 
areas at nearly equal distant divisional points.” 
Table. 
Class 1. Ships of which the tonnage deck is 50 feet long or under, into 
four parts, for the measurement of “three transverse areas at the main 
breadth section, and other divisional points of the length.” 
‘Class 2. Ships of which the tonnage deck is above 50 feet, and not exceed- 
ing 120 feet, ‘‘into sections for measuring five transverse areas.” 
Class 3. Ships of which the tonnage deck is above 120 feet, not exceeding 
180 feet, “into sections for measuring seven transverse areas.” 
Class 4. Ships of which the tonnage deck is above 180 feet, not exceeding 
225 feet, “into sections for nine transverse areas.” 
Class 5. Ships of which the tonnage deck is, according to the above mea- 
“surement, above 225 feet, into 12 sections, for measuring eleven transverse 
areas at the point of division. “The length of the tonnage deck from stem 
to stern, on a scale of quarter-inch to a foot as a base line, from which the 
transverse areas being set off on a scale of ten square feet to quarter-inch at 
each point of division and marked on the scale. A curve, run fair from the 
stem through these marks to the stern, will form the curve of areas of exter- 
nal bulk.” 
(Rule 1.) “ For external measurement to be ascertained when the vessel is 
on the stocks during the progress of building, or in dry dock, or otherwise 
on the ground, and according to the following rule, No. 1, (that is to say) 
determine the length between the perpendiculars by setting up from the 
under side of the false keel two-thirds (2) the medium height of tonnage 
deck, to cut the outside of the rabbets (or these produced) of the stem and 
_stern post, these intersections squared down to the keel to give the positions 
of the perpendiculars, and having taken off the number of transverse sections 
of the hull, stated in the table.” 
* Compute the correct external bulk (exclusive of any wooden sheathing 
which may have been brought on to the proper planks of bottom) to the 
medium height of the tonnage deck, by means of a curve of areas constructed 
from the areas of the aforesaid sections; in the case of a break on the deck, 
the medium height to be ranged fair through in continuation of the deck, 
as if there had been no break. Record the correct mensuration in cubic 
ad thus obtained as the external bulk, to medium height of tonnage 
eck.” 
“To form scale of displacement.— Divide this bulk by 35, the quotient will 
_Tepresent the tonnage displacement of the hull immersed to that height 
above keel. By similar areas and curves, compute the tonnage displace- 
“ment loaded to 2-3rds the height of deck, or between the perpendiculars, as 
well as the light line, immersed 1-3rd from the keel. These three quantis 
