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MARINE REVIEW. 5 Steel Ship Construction.--Part V. STRENGTH AT CARGO HATCHES. It will be observed, by reference to the preceding article that by cutting a hole in the deck: for a cargo hatch the area of the deck plating in the ship under consideration is diminished, 67 inches. 'The unavoidable weakest section governs the con- struction of the vessel, for no part should be weaker than this section. Itis necessary that compensation be made for this weakness and the vessel made as strong at an opening as at the line of rivet holes across a beam. Fig. 1 illustrates how this strength may be retained without increasing the strength be- tween the openings, and keeping the vessel similar in area throughout. At AA, Fig. 1, the rivet holes are spaced ten di- ameters apart, center to center, thus reducing the number of rivet holes at this section to seven instead of eleven at the un- avoidable weakest section. The stringer plate, coaming and inch rivets necessary to fasten the doubling to stringer plate before and abaft the hatch openings, the doubling plate forming a butt strap at the line of the rivet holes through BB. 'The doubling plate C is continued for two beam spaces beyond the hatch hole and seventy-three rivets are put in, that number being the amount necessary to resist a strain tending to fracture the vessel through BB. . BB, Fig. 1, is a weak part noticeable in lake vessels. 'T'he hatch coaming. and -carling at AA have a strength of 225 tons. _ At BB the hatch coaming is continued around the opening, soas to get five rivets through the beam and five in the butt strap, equaling 84 tons. There are four rivets connecting the end of the carling to the beam, which are equal to 40 tons, or 124 tons in all. 'This section is, accordingly, 1o1 tons weaker than the section AA for each side of the vessel. When stringer plates are 60 inches wide they should be a Kiet | a3 SS | gas a a . - STR VE FR | OES | ol Lh | eae Tels 7 O28 i oll ° oak QO | --~DGUBLINGE = oor lel ENE sie I au ey -- ° 6 eibe Raeae 2 | Sep eo eye 2 ae Seely = Be oes ty Q| HATE HH CoAmiNnG carling minus the rivet holes has an area of 34.875 square inches, leaving a weakness of 24.375 square inches for each side of the vessel. Cin Fig. 1 is a doubling plate, 36 inches wide by %- inch thick, having an area, minus the rivet holes, of 24.75 square inches, which is equal to the lost area for one. side of the vessel. The number and size of rivets connecting the doubling plate to the stringer plate beyond BB is of consederable impor- tance, as it is possible for the stringer plate to give way at the line of rivet holes through BB when the ship is under tension. Let us suppose that a fracture occurs at BB by the stringer plate breaking and shearing in the end of the coaming, through the beam and butt-strap; also pulling rivets out of beam 53, Fig. 2, at the end of the carling. There would be a strength of 945.25 tons, or 831.25 tons weaker than at unavoidable weakest section. By dividing 831.25 by 11.5 we will arrive at the number of 7- | o | \s | ~ INNER SrRincer-| 2 on ibaa | (| o | Toi a rey | fitted in two plates, and then there would not be so much de- pending upon the rivets. If the plates were lapped the area of the section would be increased by the width of the lap. Fig. 3 is the plan of stringer in two plates. At AA the section is 30 tons stronger than in Fig. 1. At BB the doubling | plate and stringer plate are continued inside the line of the hatch, so as to give more area and be equal in strength to AA. Should the stringers be fitted edge and edge and 'strips fitted between the beams, there would be no additional strength, but if the strips were continuous the strength would be greater than the lap, there being metal equal to two-laps. pe oe : It has been claimed that "a vessel with considerable sheer has no assistance from the deck plating in resisting tension or compression." It appears likely enough that under compres- -- sion the deck would bend until it closed both ends, but unde ~--