Ship Construction
What the exam tests
Ship Construction tests hull structural members, framing systems, watertight subdivision, double-bottom construction, hatch and deck arrangements, materials and welding. Questions ask you to identify load paths and to calculate simple bending or section-modulus values.
Core rules
- The keel is the baseline member; keelsons, floors, frames, longitudinals, girders, stringers and pillars distribute loads into the shell and bulkheads.
- Transverse framing uses closely spaced frames and is common in smaller ships; longitudinal framing uses longitudinal stiffeners with widely spaced web frames and suits long ships subject to longitudinal bending.
- The double bottom provides grounding protection, ballast or fuel tank space and longitudinal strength. Watertight bulkheads limit flooding and support the collision bulkhead requirement.
- Hatch openings interrupt deck strength; coamings, hatch covers and girder compensation restore continuity.
- Bending stress σ = M/Z, where M is bending moment and Z is section modulus. For a simplified section, I = ΣAd² about the neutral axis and Z = I/y.
Worked example
A simplified hull box has two equal flange areas of 0.20 m², each 5 m from the neutral axis. I = 2 × (0.20 × 5²) = 10 m⁴. The extreme fibre distance is y = 5 m, so Z = 10/5 = 2 m³. If the design bending moment is 20 MN·m, the nominal bending stress is σ = 20/2 = 10 MPa. Real hulls have many members and effective breadth effects, so this is only a teaching estimate.
Traps
Do not assume the neutral axis is always at mid-depth; unequal flanges shift it. Use consistent units: MN and m³ give MPa. Do not confuse gross with net scantlings after corrosion. A watertight bulkhead is not automatically a tank boundary.