(a) The tonnage depth. The depth generally referred to as "the tonnage depth" is located at the middle point of division of the tonnage length and is found in a manner similar to the other depths of transverse sections.

(b) Tonnage depth in a vessel measured in parts. Should a vessel be required to be measured in parts, and each part measured as a separate unit; then a tonnage depth shall be found for each part or unit at one-half its tonnage length. (See Figure 14 (§ 2.65).)

(c) Tonnage depth is the first depth measured. The tonnage depth governs the number of parts into which it and all the remaining depths of the part in which said depth is located, is divided.

(d) Divisions of tonnage depth. If the tonnage depth at the middle of the tonnage length of the vessel or part of same does not exceed 16 feet, divide each depth into 4 equal parts; but if the depth at the middle of said length exceeds 16 feet, divide each depth into 6 equal parts.

(e) Intervals. The common intervals between the points of division of depths, also one-third common intervals are to be carried to the nearest hundredth of a foot.

(f) Purpose for dividing tonnage depths. Depths are divided to indicate points at which tonnage breadths are to be measured.

§ 2.30 Tonnage breadths.

(a) Breadths. An inside horizontal breadth is to be measured at each point of division of the depth marked on the sliding rods placed in position as directed in § 2.13(b) and also at the upper and lower points of the depth. Extend each measurement to the inboard face of the ordinary frames, or line of same, or inboard face of ceiling, or battens, or insulation of average thickness if fitted. (See Figure 15 (§ 2.65).) Care must be taken that the sections shall be parallel to each other and at right angles to the axis of the vessel.

(b) Upper breadth. In finding the upper breadth of each transverse section make no allowance for the excess of the deck-beam shelves, etc., over the per

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missible thickness of ceiling, if any, thereunder.

Referring to Figure 16 (§ 2.65), observe that after the deck is laid the upper breadth (represented by the line U B) passes through the deck on each side. Hence, it is impossible to take it at its true position. In such cases take it on the deck, allowing within the extended line of frames the thickness of the ceiling if any on the frames under deck, as shown by line T B in the figure.

Owing to deck-beam shelves or other obstructions, it can be more conveniently and accurately taken here than under the deck, and, besides it will be only a few inches from its true position. In vessels which have upright sides the said breadth so taken will be correct, but in the case of vessels with inclining sides the necessary allowance must be made for the deviation of the sides from the upright in the few inches above the true position of the said breadth.

(c) Bottom breadths. Bottom breadths are taken only so far as the flat of the floor extends. (See B B, Figures 4 and 5; Figure 15; and B B, Figures 17 and 18 (§ 2.65).)

When bottom frames rise immediately from the keelson, or combined keel and keelson, and bona fide floor timbers or floor plates are not fitted, bottom breadths are equal to the breadth of keelson, or combined keel and keelson as the case may be. (See B B, Figure 19 (§ 2.65).)

The bottom breadths of transverse sections of vessels of longitudinal construction falling in the hold where there is no double bottom and where there is a dead rise of the bottom out to the sides of the vessel may be considered to be equal to that part of the bottom plating not affected by dead rise.

(d) Bottom breadths in case of rise or fall of double bottom. Bottom breadths falling in way of a double bottom the top of which rises or falls from the midship longitudinal plane to the wings are measured from and to the inboard end of the frame brackets (or ceiling thereon if fitted), connecting the double bottom with the frames. (See B B, Figures 12 and 13 (§ 2.65).) §2.31 Measuring the tonnage length.

(a) The cubic capacity of the space below the tonnage deck is determined by use of the tonnage length together with the areas of a prescribed

number of transverse sections as hereinafter described.

(b) To determine the extreme points of the tonnage length as indicated by § 2.27 and T L in Figures 10 and 11 (§ 2.65), observe the following:

(1) Vertical bow and stern. In vessels having a vertical bow, also a vertical stern, both above and below the tonnage deck, measure horizontally the depth of frames, also the thickness of ceiling thereon if any, at the extreme forward and after ends immediately under the tonnage deck. Mark these measurements on the upper side of the tonnage deck, from the outer shell and in the direction in which the frames were measured. Then draw through the points thus obtained, lines parallel to the shell. The forward and after points of intersection of these lines indicate the points from and to which the tonnage length is to be measured.

(2) Raked bow or stern. In the case of vessels having a raked bow or stern at the level of the tonnage deck, the extreme points of the tonnage length are, when practicable, to be determined at the under side of the tonnage deck. The distance from these points to a hatch coaming, bulkhead, etc., should be measured and transferred to the upper side of the tonnage deck as indicated in Figure 20 (§ 2.65).

(c) Should it be impracticable to determine the extreme points of the tonnage length at the under side of the tonnage deck, and should the thickness of this deck be considerable, as in the case of a wooden deck, the rake of the bow or stern within the thickness of the deck is to be taken into account. This is done after having first proceeded as indicated in paragraph (b) (1) of this section by measuring the thickness of the tonnage deck and determining by means of a hinged rule, or any other instrument for finding angles under similar circumstances, the angle of the rake which the bow or the stern forms with the tonnage deck. Transfer thereafter this angle on the deck by drawing the lines A B C shown in Figure 21 (§ 2.65), A B represents the upper side of tonnage deck and B C the after side of the stem or the inside of the shell at the stern, as the case may be. The perpendicular B D represents the thickness of the tonnage deck. The points T, L, in Figures 10 and 11 (§ 2.65) marked on the upper side of the tonnage deck are then to be moved for

ward at the stern or aft at the stem, as the case may be, for a distance equal to D E, representing the rake within the thickness of the deck.

(d) It should be borne in mind that the condition for applying the method of setting out the angles on the upper side of the tonnage deck is that the stem or stern have the same angle of rake above and immediately below the tonnage deck. If the angle of rake at or immediately below the tonnage deck is a different one, then this last angle must be used.

(e) Should a vessel as referred to in paragraph (b) (2) of this section have a square bow or stern, it will be necessary to make a correction for camber where such exists. This is done by increasing the thickness of the deck B D in Figure 21 (§ 2.65) by one-third of the round or one-half of the pitch of beam at the extreme point of the tonnage length. Divisions of tonnage length.

§ 2.32

(b) The points of division of the tonnage length, also each end of the length indicate the common intervals at which a depth is measured.

Intervals and one-third intervals are to be carried to the nearest thousandth of a foot.

§ 2.33 Transfer of location of sections to keelson.

(a) The tonnage length having been ascertained and the number of sections to be measured and the interval between them determined, a line is then to be extended down the main hatchway, at the middle line of the vessel, in a perpendicular direction.

(b) The distance of the midship tonnage section is then to be set off from this line in the same direction on the keelson, which gives the position of the midship section on the keelson, and the positions of the other sections are ob

tained on the keelson by setting off forward and abaft the midship section the common interval between sections as already determined.

The position of the midship tonnage section may be determined by any other practical means.

§2.34 Transverse areas, rule for finding.

(a) Assuming the tonnage length exceeds 250 feet requiring that it be divided into 16 equal parts, and the tonnage depth at the middle of the tonnage length exceeds 16 feet, requiring it to be divided into 6 equal parts:

(1) Measure the depth at each of the 15 points of division of the length as required, also at the extreme forward point (Section 1) and at the extreme after point (Section 17) of the length. (See Figure 22 (§ 2.65).)

(2) The extreme points of the length at the bow and stern, though described as being the positions of the first and last areas, do not in vessels of usual form yield any area for practical purposes. Therefore, in the computation for tonnage, where the first and last sections yield no areas, a cipher must be employed in their places. In vessels of unusual form, as, for instance, in barges or other craft in which the bow and stern are upright, with breadth also at those places, sections at the extreme points of the length will yield areas; in which cases such areas must be measured and used in the computation.

(3) Then measure the inside horizontal breadth at each of the five points of division of the depth, also at the upper and lower points of the depth.

(4) Number the breadths from above, numbering the upper breadth 1 and so on down to the lowest or seventh.

(5) Multiply the second, fourth and sixth by 4, and the odd numbered breadths by 2, except the first and last which are multiplied by 1.

(6) Add these products together. (7) Multiply the sum thus obtained by one-third of the common interval between the breadths, and the product shall be deemed the transverse area.

(8) This process will be repeated for every section.

register tonnage of the vessel in the following manner:

(1) Number the areas successively 1, 2, 3, etc., No. 1 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.

(2) Then multiply the second and every even numbered area by 4 and the third and every odd numbered area by 2, except the first and last which are multiplied by 1.

(3) Add these products together and multiply the sum thus obtained by onethird of the common interval between the areas, and the product will be the contents in cubic feet of the spaces under the tonnage deck.

(4) Divide this product by 100, 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.

(c) In every case when finding the capacity under tonnage deck, or a part thereof; whether the length be divided according to the table into 6 or 16 parts, as in classes 1 and 6, or in 2 or 4 parts as provided for in § 2.35 (a) and the depths into 4 or 6 parts, thus requiring 5 or 7 breadths respectively to be taken; the above formula shall be used; i. e., even numbered breadths shall be multiplied by 4, and odd numbered ones by 2 except the first and last which are multiplied by 1. Similarly when running areas through the multipliers, the even numbered ones shall be multiplied by 4 and odd numbered ones by 2, except the first and last, which are multiplied by 1.

§ 2.35 Breaks in double bottom.

(a) The tonnage length of a vessel having a break exceeding one-half of a foot in height, or a number of such breaks in the line of her double bottom, is to be divided into longitudinal parts establishing transverse vertical planes at such breaks. The length of each such part so found is then to be divided into a number of equal parts according to the class in the above table to which it belongs, just as if it were the length of a separate vessel: Provided, That such parts as are 20 feet or under in length may be divided into 2 equal parts, and those above 20 feet and not exceeding 40 feet in length may be divided into 4 equal parts instead of into 6, as indicated in the table in § 2.32 (a).

(b) When a vessel is required to be measured in parts, and each part measured as a separate vessel, the sum of the tonnages of the several parts is the capacity under the tonnage deck.

§ 2.36

Vessels having side tanks may be measured in parts.

Vessels having side tanks extending above the floor line or double bottom, and through which tanks tonnage breadths normally pass, may be measured in parts. The length of the first part will extend aft to the line of the forward bulkheads of the side tanks. (See Figures 23 and 24 (§ 2.65).) The length of the second part is equal to the length of side tanks, and the depths extend, at proper intervals under the tonnage deck, down to athwartship lines forming continuation of the side tank tops. (See Figure 25 (§ 2.65).) The third length immediately below the second part should equal that of the second. breadths are taken between the inboard faces of the side tank bulkheads, and depths from athwartship lines forming continuation of the side tank tops. The fourth part will extend from a line athwart the after bulkhead of side tanks to a point aft where tonnage lengths usually terminate. Measure separately a side tank, the tonnage of which is to be doubled, assuming both tanks are identical as they usually are; then the sum of the tonnage of the several parts thus found shall be deemed the capacity under tonnage deck.

The

(a) In the case of vessels with square ends having head blocks extending from the deck to the bottom longitudinals on the rake of the bottom, the termini of the tonnage length will be at the inboard face of said block, and the area of the first and last section will equal the area of the inboard face of said block. (See Figure 27 (§ 2.65).)

(b) Should the head blocks extend inboard of the inboard face of the end frames (see Figures 28 and 29 (§ 2.65)), or should the head plates be excessive (see Figure 30 (§ 2.65)), consider the termini of the tonnage length to be at points inboard from the ends of the vessel, equal in distance to the thickness of the shell plating, depth of side frame, plus ceiling if fitted. Rubbing strakes to be excluded. § 2.39

Between decks.

(a) If the vessel has a third deck, the tonnage of the space between it and the tonnage deck shall be ascertained as follows:

(1) Measure the inside length of the space at the middle of its height, from the ceiling at the side of the stem to the ceiling on the midship stern timber; or, if there is no ceiling take the length from a point forward where a continuation of the lines of inboard faces of the side frames intersect the center line of the vessel aft to the inboard face of the midship stern timber. Divide the length into the same number of equal parts into which the length of the tonnage deck is divided.

(2) Measure also at the middle of its height the inside breadth of the space at each of the points of division of the length, the breadth at the stem, and the breadth at the stern (if round, as in the case of poops of similar form). Number the breadths successively 1, 2, 3, etc., commencing at the stem.

(3) Multiply the second and all other even numbered breadths by 4 and the odd-numbered breadths by 2, except the first and last which are multiplied by 1. Multiply the sum of these products by one-third of the common interval between the points at which the breadths were taken; the result will give, in superficial feet, the horizontal area at the mean height of such space.

(4) Multiply the mean horizontal area by the average height taken between the planks of the two decks and the product will be the cubical contents of the space; which, divided by 100 shall be deemed the tonnage to be included among the items comprising the vessel's gross tonnage.

(b) If the vessel has more than three decks, the tonnage of each of the between decks above the tonnage deck shall be severally ascertained in the manner above described and shall be added as items comprising the vessel's gross tonnage.

(a) Permanent erections. Permanent erections; i.e., forecastle, bridge, poop, break, etc., on or above the upper deck, shall be measured tier by tier, and, exclusive of closed-in exemptible spaces, and open spaces, shall be included in the gross tonnage.

(b) Length. Measure at half height the mean length of such a space along its center longitudinal line, from and to the line of the inboard faces of the frames, or stiffeners, or ceiling if fitted. Divide the length into an even number of equal parts the common intervals of which shall be most nearly equal to that of the parts into which the tonnage length was divided. (See Figure 31 (§ 2.65).)

(c) Breadths. Measure at the middle of its height the inside breadths; namely, one at each end and one at each point of division of the length, numbering them successively 1, 2, 3, etc., the number one breadth being at the extreme forward end of the length.

(d) Round-end erections. If the after end of an ordinary poop or a house is in the form of a continuous arc of a curve, its breadth at the extreme after end of its length shall be one-half of the preceding breadth. If the after end of such a poop or house is in the form of an arc of a curve which is broken at its extreme after end by a decided

flat, its breadth at the extreme after end of its length shall be two-thirds of the preceding breadth. (See Figures 32 and 33 (§ 2.65).)

(e) Round-end erections. If the forward end of a house is in the form of a continuous arc of a curve, its breadth at the extreme forward end of its length shall be one-half of the succeeding breadth. If the forward end of such a house is in the form of an arc of a curve which is broken at its extreine forward end by a decided flat, its breadth at the extreme forward end of its length shall be two-thirds of the succeeding breadth.

(f) Multipliers. Multiply the even numbered breadths by 4, and the odd numbered ones by 2, except the first and last which are multiplied by 1.

(g) Horizontal area. Multiply the sum of the products by one-third of the common interval between the points at which the breadths were taken; the result will give the horizontal area at the mean height of such space.

(h) Height. Multiply the mean horizontal area by the average height measured between the decks, or the extended line of same. (See B and C in Figure 9 (§ 2.65).) Divide the product by 100 and the quotient shall be deemed the tonnage of such space.

(i) Superstructures having breaks. Superstructures having breaks in their covering deck or side lines shall be measured in parts. (See Figure 34 (§ 2.65).)

(j) Superstructures on small craft. Superstructures on small craft, shall be measured similar to the method for finding the gross tonnage of larger structures. When a superstructure is erected over a cut-away portion of the tonnage deck, the height of such superstructure is to be taken from the under side of its covering deck to a line of continuation of the tonnage deck. Should there be no camber to the tonnage deck, allow for same, in the covering deck of the erection if it exceeds 0.15 foot. After subtracting the tonnage of exemptible spaces in the superstructure, the remainder shall be listed under a name describing the erection, among the items comprising the gross tonnage.

(k) Height of a turtleback. The mean height of a superstructure referred to as a "turtleback" may be found by taking a height at each point of division of its length, at the after terminal of its length, and at one-third common interval abaft the forward end of the length. The sum of the heights so