Ship Design and Construction - Design Spiral, Scantlings and Build Quality
Ship Design and Construction
This domain covers the design spiral, general arrangement, structural scantlings, welding and block erection. In the PRC, newbuildings are designed to the CCS 钢质海船入级规范 and the IACS Common Structural Rules (CSR) for bulk carriers and oil tankers where applicable, plus the MSA statutory technical rules for the flag.
Core rules and concepts
- Design spiral: displacement, speed, power, capacity and stability are iterated; each turn freezes one variable. A beam increase buys stability but costs resistance and steel weight.
- Midship section: net scantlings from CSR plus corrosion addition t_c; as-built thickness is t_net + t_c, then rounded up to the standard plate series (never down).
- Materials: normal-strength A/E and higher-strength AH32–EH40 grades; higher-strength steel does not remove minimum-thickness or buckling requirements.
- Construction: block subdivision, accuracy control (精度管理), welding procedure qualification (WPS/PQR), and NDT (RT/UT/MT/PT) percentages per the approved inspection plan.
- Coating: PSPC (SOLAS II-1 Reg. 3-2) applies to dedicated seawater ballast tanks; the Coating Technical File must be delivered with the ship.
Worked example
A deck plate in a 60 m coastal cargo ship requires t_net = 12.5 mm in a location with corrosion addition t_c = 1.5 mm. Required as-built t = 12.5 + 1.5 = 14.0 mm. Since 14.0 mm is a standard mill plate, no rounding arises; had the total been 14.2 mm, the correct choice would be 15.0 mm, not 14.0 - rounding is always upward. A common error is to show only 12.5 mm on the drawing and let the yard apply the addition; the approved drawing must carry the as-built value.
Traps
Confusing CSR net scantling with as-built thickness; assuming high-tensile steel removes t_min; accepting a WPS without a qualified PQR; applying PSPC to cargo tanks; treating the general arrangement as a fixed input rather than a spiral output.