Having thus ascertained the transverse area at each point of division of the length of the vessel, as required above, proceed to ascertain the register-tonnage of the vessel, in the following manner:— Number the areas successively one, two, three, ete., number one being at the extreme limit of the length at the bow, and the last number at the extreme limit of the length at the stern ; then, whether the length be di vided according to table into six or sixteen parts, as in classes one and six, or into any intermediate number, as in classes two, three, four, and five, maltiply the second and every even-numbered area by four, and the third and every odd-numbered area (except the first and last) by two ; add these products together, and to the sum add the first and last, if they yield any thing ; multiply the quantities thus obtained by one-third of the common interval between the areas, and the product will be the cubical contents of the space under the tonnage-deck ; divide this product by one hundred, and the quotient, being the tonnage under the tonnage-deck, shall be deemed the register-tonnage of the vessel, subject to the additions hereinafter mentioned.
5. If there be a break, a poop, or any other permanent closed-in space on the upper decks or the spar-deck available for cargo or stores or for the berthing or accommodation of pass engers or crew, the tonnage of such space shall he ascertained as follows :— Measure the internal mean length of such space in feet, and divide into en even number of equal parts of which the distance asunder shalf be most nearly equal to those into which the length of the tonnage-deck has been di vided ; meaeure at the middle of its height the inside breadths,—namely, one at each end and at each of the points of division,— numbering them successively one, two. three, etc.; then to the sum of the end breadths add four times the sum of the even-numbered breadths and twice the sum of the odd numbered breadths, except the first and last, and multiply the whole sum by one-third of the common interval between the breadths; the product vvill give the mean horizontal area of such space ; then measure tho mean height between the planks of the decks, and multiply it by the mean horizontal area ; divide the product hy one hundred, and the quotient shall be deemed to be the tonnage of such space, and shall be added to the tonnage under the tonnage-deck ascertained as aforesaid.
6. If the vessel has a third deck, or spar deck, the tonnage of the space between it and the tonnage-deck shall be ascertained as follows :— Measure in feet the inside length of the' space, at the middle of its height, from the plank at the side of the stem to the plank on the timbers at the stern, and divide the length into the same number of equal parts into which the length of the tonnage-deck is di vided ; measure (also at the middle of its height) the inside breadth of the space at each of the points of division, also the breadth of the stem and the breadth at the stern ; number them successively one, two, three, and so forth, commencing at the stem ; multi ply the second and all other even-numbered breadths by four, and the third and all other odd-numbered breadths (except the first and last) by two; to the sum of these products add the first and last breadths; multiply the whole sum by one-third of the common inter val between the breadths, and the result will give, in superficial feet, the mean horizontal area of such space ; measure the mean height between the pfank of the two decks, and multiply 'it by the mean horizontal area„ and the product will be the cubical contents of the apace ; divide this product by one hun dred, and the quotient shall be deemed to be the tonnage of such space, and shall be added to the other tonnage of the vessel ascertained as aforesaid. And if the vessel has more than three decks, the tonnage of each space between decks above the tonnage-deck shall be severally ascertained in the manner above described, and shall be added to the tonnage of the vessel ascertained as aforesaid.
In ascertaining the tonnage of open vessels, the upper edge of the upper strake is t,o form the boundary-line of measurement, and the depth shall be taken from an athwartship line extending from the upper edge of said strake at each division of the length.