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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 Hydrostatics, Stability and Subdivision

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

All guide sections

Ship Hydrostatics, Stability and Subdivision

What this domain tests

The hydrostatics table, the righting lever curve, free surface effects, and the subdivision framework (deterministic and probabilistic) under SOLAS Chapter II-1. Questions are usually numerical or ask you to judge whether a loading condition is acceptable.

Core relationships

  • BM = I / volume, where I is the waterplane second moment about the centreline; KB from the hydrostatic curve; KM = KB + BM; GM = KM - KG.
  • Free surface correction FSC = i x density / volume (summed over slack tanks); the corrected KG is KG + FSC, so free surface always reduces GM.
  • TPC = A_W x density / 100 (t/cm); MCT1cm = displacement x GML / (100 x L).
  • GZ = KN - KG sin(theta), with KN from cross curves.
  • IS Code 2008 intact criteria: initial GM at least 0.15 m; area under the GZ curve to 30 degrees at least 0.055 m.rad; to 40 degrees (or the flooding angle) at least 0.09 m.rad; between 30 and 40 degrees at least 0.03 m.rad; GZ at least 0.20 m at 30 degrees; maximum GZ at an angle not less than 25 degrees.

Subdivision

Deterministic rules (Part B-1) use the margin line, floodable length and permeability; the probabilistic rules (Part B-1, applied to cargo ships of 80 m and over and to passenger ships built on or after 1 January 2009) require the attained subdivision index A to be at least the required index R. Cross-flooding, downflooding openings and the final waterline all matter.

Worked example

A box pontoon 40 m x 10 m x 4 m floats at 2 m draft with KG 1.5 m. Volume = 800 m3; KB = 1.00 m; I = 40 x 10^3 / 12 = 3,333 m4; BM = 3,333/800 = 4.17 m; KM = 5.17 m; GM = 5.17 - 1.50 = 3.67 m. A slack double-bottom tank 6 m x 8 m with free surface i = 288 m4 would give FSC = 288/800 = 0.36 m, cutting GM to 3.31 m.

Traps

Forgetting that free surface is added to KG rather than subtracted from KM; computing areas with degrees instead of radians; applying intact criteria to a damage case; assuming permeability of 1.0 for machinery spaces; ignoring downflooding points above the damage waterline.