2. The forecastle of a steel ship hull is to be extended in aluminium alloy, over the midships area by the structure shown below. Details of the existing steel structural midship section are as follows: Depth, keel to upper deck 7 m Neutral axis below upper deck 4 m Total area of section 4800 cm Second moment of area about NA 5 m Upper deck bending stress 12 kN/cm For the same bending moment, (a) calculate the stress in the deck of the alloy extension; (b) calculate the new stress in the steel deck and the new keel stress. The value of E for alloy should be taken as 1/3 that for steel. 1 11 3m 10 cm x 1cm