Page 254 - Rules of Navigation2020

strake, after deducting the average thickness of the ceiling which is between the bilge
planks and the limber strake. Then, if the depth at the mid ship division of the length

(1)
does not exceed 16 feet, divide each depth into four equal parts ; then measure the
inside horizontal breadth at each of the three points of division, and also at the upper

and lower points of the depth, extending each measurement to the average thickness
of that part of the ceiling which is between the points of measurement. Number these
breadths from above (i.e. numbering the upper breadth 1, and so on down to the

lowest breadth).
Multiply the second and fourth by four, and third by two; add these products together,

and to the sum add the first breadth and the fifth. Multiply the quantity thus obtained
by one-third of the common interval between the breadths, and the product shall be

deemed the transverse area; but if the mid ship depth exceed 16 feet, divide each
depth into six equal parts instead of four, and measure, as before directed, the

horizontal breadths at the five points of division, and also at the upper and lower
points of the depth, number them from above, as before, multiply the second, fourth,
and sixth by four, and the third and fifth by two; add these products together, and to

the sum add the first breadth and seventh.
Multiply the quantity thus obtained by one-third of the common interval between the

breadths, and the product shall be deemed the transverse area
(Art.4) The area of the transverse sections can also be measured with the same precision by
the following method of polar co-ordinates:

Divide each transverse half-section into five angular sectors, having the same angle
at the apex (This angle is equal to 90/5 of a degree = 18 degrees), and take for the

area of each of these sectors the area of the sector of the circle comprised between its
extreme radii, and described by the mean radius. In making the measurement,

measure the mean radius of each sector, of which the two extreme radii would make,
the one with the horizontal line and the other with the vertical line, an angle of 9

degrees, while the others are uniformly 18 degrees apart.
In order to obtain their directions, place on the plane of the section a semi-circle
properly divided, and turned so that its horizontal diameter may pass through the third

of the round of the beam, and that its center may be found in the central longitudinal
vertical plane of the ship; the radii are to be measured by means of a tape fixed in the

center of the semi-circle. In order to calculate the area of the section, square the mean

1 ) A greater number of division is not prohibited so long as they are an even number.
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