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HKIE Professional Assessment - Marine & Naval Architecture Discipline study materials
HKIE Professional Assessment - Marine & Naval Architecture Discipline study resources

HKIE Professional Assessment - Marine & Naval Architecture Discipline: Ship Resistance, Propulsion and Seakeeping

HKIE Professional Assessment - Marine & Naval Architecture Discipline · Work through your exam, one topic at a time.

All guide sections

Ship Resistance, Propulsion and Seakeeping

What this domain tests

Model-ship scaling, resistance components, propeller-hull interaction, powering margins, and the dynamic behaviour of the ship in a seaway, including the second-generation intact stability failure modes.

Resistance and powering

  • Froude number Fn = V / sqrt(gL); Reynolds number Re = V L / viscosity. Froude scaling governs wave resistance; Reynolds scaling governs friction.
  • ITTC-57 friction line: Cf = 0.075 / (log10 Re - 2)^2.
  • Total resistance coefficient Ct = (1+k) Cf + Cw + Ca, where (1+k) is the form factor. Effective power PE = Rt x V.
  • Added resistance in waves, wind and shallow water raise the required thrust; service conditions include a sea margin (commonly about 15%) and an engine margin.

Propulsion

  • Advance ratio J = VA / (nD), where VA is the speed of advance, not the ship speed; thrust and torque coefficients KT and KQ.
  • Open water efficiency eta_o = (J / 2 pi) x (KT / KQ); quasi-propulsive efficiency eta_D = eta_o x eta_R x eta_H, with hull efficiency eta_H = (1 - t)/(1 - w) using thrust deduction t and wake fraction w.
  • Propeller law: thrust varies with n squared, power with n cubed. Cavitation is judged by the cavitation number and blade area ratio.

Seakeeping

Roll natural period T = 2 pi k / sqrt(g GM); heave and pitch follow from RAOs; slamming, parametric roll, pure loss of stability, surf-riding and broaching, dead ship condition and excessive acceleration are the five second-generation failure modes to be assessed under the SGISC framework.

Worked example

A ship runs at 90% of its design rpm on the propeller curve. Power scales with the cube, so available power = 0.9^3 = 0.729, i.e. 72.9% of design power. Thrust scales with the square, so speed falls to approximately 90% of design speed. The lesson: small rpm reductions cut fuel sharply while costing little speed, which is why slow steaming is used for CII compliance.

Traps

Confusing ship speed with speed of advance; using LOA in the Froude number; omitting the form factor; applying the propeller law when the engine is torque-limited or constant-rpm; ignoring added resistance when quoting trial speed.