OF SHIP CONSTRUCTION. 71 



Calculations similar to those made for the decks of the transversely framed vessel 

 show that the deck longitudinals are capable of supporting loads of 2,290 pounds and 

 3,310 pounds per foot length, for the upper and second decks respectively. Because 

 of the variations in the spacing of the longitudinals, this means that the maximum 

 safe load for the upper deck is 665 pounds per square foot between the hatches and 

 723 pounds per square foot between the hatch-end transverses outboard of the fore- 

 and-aft hatch coamings, while the second deck could carry a load of 945 pounds per 

 square foot between hatches and 830 pounds per square foot in the wings. 



This, however, does not take care of the strength of the decks at the wings 

 along the sides of the hatches. Here the loads on the longitudinals are transmitted 

 to the half -transverses that furnish the intermediate reactions. These half-trans- 

 verses have section moduli of 36.55 inches^ and 34.3 inches^ for the upper and second 

 decks, respectively. Assuming that the decks are uniformly loaded up to the smaller 

 maximum capacity found above for the space between the hatch-end transverses, and 

 that the load is concentrated at the points of support of the longitudinals, we can 

 proceed to determine the fiber stresses. In either deck the extreme outboard longi- 

 tudinal is directly supported by the transverse deck bracket, so that the loads borne 

 by that longitudinal and directly by the shell connection do not add to the bending 

 moment. For the rest of the transverse beam the bending moments are approxi- 

 mately 500,000 and 520,000 inch-pounds, giving fiber stresses of 13,600 and 15,200 

 pounds per square inch in the upper and second deck half -transverses respectively. 



The inboard ends of these half-transverses are supported by the fore-and-aft 

 hatch coamings, which in the Isherwood ship are somewhat stronger than in the trans- 

 verse vessel. The reactions of the fore-and-aft hatch coamings are in turn borne 

 by the hatch end transverses, which also receive the reactions from the ends of the 

 longitudinals between hatches and outboard of the fore-and-aft coamings, the last 

 loads being similar to those borne by the half transverses. These hatch-end trans- 

 verses are heavily built, and are reinforced by a lo-inch by 12-inch face plate for 

 the second deck, and a lo-inch by 0.70-inch face plate for the upper deck, although 

 these are not shown on the midship section (Plate 33). The loads are heavy, how- 

 ever, and the fiber stress at either deck is somewhat in excess of 40,000 pounds per 

 square inch. Since the bending moment, and hence the fiber stress, are directly pro- 

 portional to the loads, we may conclude that the safe loads found above are about two 

 and one-half times too great. The deck loads for the Isherwood vessel should, then, 

 be about 280 pounds per square foot for the upper deck and 330 pounds per square 

 foot for the second deck, as compared to the corresponding values for the trans- 

 versely framed vessel of 423 pounds and 510 pounds per square foot. 



Apparently, then, there is a loss in the strength of the decks amounting to 

 nearly 34 per cent for the upper deck and 35 per cent for the second deck. 



It was pointed out, in connection with the strength of the decks of the trans- 

 versely framed vessel, that a large margin of strength existed. Some reduction 

 could consequently be approved of, but it seems that it would be more advisable to 

 increase the strength of the hatch-end transverses and reduce the surplus strength 



