marine-inspection

name	marine-inspection
description	Marine inspection — hull surveys (class, flag state, PSC), thickness gauging (UT), coating condition, corrosion allowance, ABS/DNV/Lloyd's classification, IACS common structural rules (CSR), close-up survey requirements, SOLAS Chapter II-1, condition assessment program (CAP), dry dock periods, Enhanced Survey Programme (ESP).
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Marine Inspection and Survey — Complete Skill

Survey Classification and Types

Classification Society Surveys

Classification societies (IACS members): ABS (American Bureau of Shipping), DNV GL, Lloyd's Register, Bureau Veritas, ClassNK, RINA, KR, CCS, RMRS

Survey types: Annual survey: yearly; general overview; life-safety equipment; certificates validity Intermediate survey: 2.5 years into 5-year cycle; selected hull spaces; cargo holds Special (renewal) survey: every 5 years; comprehensive; full hull and machinery survey; dry-docking possible Continuous survey: major components surveyed on rolling 5-year cycle; no single large survey required

Flag state surveys: SOLAS: Safety of Life at Sea Convention (IMO); structural and life-safety MARPOL: Marine Pollution Prevention; protection of marine environment STCW: Crew training and certification Load line survey: Plimsoll marking; freeboard calculation

Port State Control (PSC): Inspections by port authority of flag state compliance; TOKYO MOU, Paris MOU, US Coast Guard Deficiency → detention → significant commercial consequence Common deficiencies: fire-fighting equipment, life-saving appliances, structural defects, certificate validity

Enhanced Survey Programme (ESP) — IACS

Applies to: oil tankers ≥ 10 years old; bulk carriers ≥ 10 years old; chemical tankers Requirements at special survey: Close-up survey of all web frames (bulk carrier); all cargo tank internal surfaces (tanker) UT thickness measurement at required locations; coating condition assessment Full structural survey: all spaces, including void spaces, ballast tanks, cargo holds

ESP scheduling: S1 (< 5 years): annual survey; selected holds/tanks S2 (5–10 years): intermediate survey with some close-up; UT in critical areas S3 (10–15 years): close-up mandatory in many spaces; UT extensive S4 (15–20 years): ALL spaces; every web frame; entire shell plating (representative) S5 (> 20 years): very intensive; owner may opt not to class-renew (scrapping)

Ultrasonic Thickness Gauging (UT)

Measurement Principle

Pulse-echo UT (most common for marine): Transducer emits ultrasonic pulse → reflects from back wall → return time t → thickness: t_thickness = v_steel × t_flight / 2 [v_steel = 5,920 m/s; t_flight = round-trip time]

Equipment: handheld digital thickness gauges (Cygnus 2+, Olympus 38DL+) Couplant: glycerin gel applied between probe and surface → eliminates air gap → good acoustic coupling Range: 1–100 mm (typical marine use 3–40 mm) Accuracy: ±0.1 mm for good surface condition Surface preparation: remove marine growth, heavy corrosion, paint to bare metal (or use dual-element probe for painted surfaces)

Measurement Grid and Reporting

Measurement points per classification (ABS, DNV): Shell plating: minimum 1 reading per plate in each strake; additional at areas of high corrosion Deck plating: uniform grid; longitudinals; girders Bulkhead plating: minimum 1 per plate; web frames Typical grid: 500 mm × 500 mm to 1,000 mm × 1,000 mm (denser at suspected problem areas)

Gross wastage limit (IACS): Substantial corrosion = wastage > 20% of original thickness Substantial corrosion → close-up survey required at next survey (or immediate renewal/repair)

Allowable diminution: Original thickness (t₀) from as-built records → allowable diminution d_allow from class tables Example (ABS bulk carrier deck plating): d_allow = 20–25% of t₀ Remaining thickness: t_remain = t₀ - d_allow [plate must be renewed if below this]

Areas of High Corrosion Risk

Bulk carriers: Cargo hold frames (bottom region): contact with cargo moisture → accelerated corrosion; common failure location Upper deck plating (stool areas): cargo spill → corrosion pitting Ballast tank webs: aggressive environment; coating breakdown → rapid corrosion

Oil tankers: Cargo tank bottom: sludge accumulation; H₂S from crude → sulfide corrosion Inert gas pipe internals: corrosion from sulfuric acid (SO₂ + condensate) Tank coating breakdown → amine-type epoxy coatings (IMO 15 years life target per PSPC 2006)

Deck equipment foundation plates: weld toes; moisture trap; corrosion fatigue initiation

Coating Condition Assessment

IMO Performance Standard for Protective Coatings (PSPC)

IMO MSC.215(82) — PSPC: Applies to: ballast tanks (new ships > 500 GT) and void spaces; cargo holds (bulk carrier 2009+) Target life: 15 years for coating system in ballast tanks Requires: surface preparation Sa 2.5 (ISO 8501-1 near-white metal blast); min dry film thickness (DFT) 320 μm (total two coats)

Coating condition ratings: Good: no or very minor rusting; no coating breakdown (< 3% breakdown for epoxy) Fair: minor to moderate rusting; < 20% breakdown; some running rust Poor: > 20% breakdown; general rust; or any mechanical damage requiring immediate action

IACS UR (Unified Requirement) Z17: Annual survey of ballast tanks (Class requirement independent of PSPC) If Poor: immediate repair or increase inspection frequency

Corrosion Allowance and Ship Structural Design

IMO IACS Common Structural Rules (CSR) — bulk carrier and tanker: Net thickness (t_net): structural design based on net thickness (after subtracting corrosion allowance) Corrosion addition (t_c): added to net to get gross (as-built) thickness CSR corrosion additions: 1.0–2.5 mm (depending on location and exposure) Example: inner bottom (double hull): t_c = 2.5 mm → if net t_net = 13 mm → gross t_gross = 15.5 mm

Wastage action limit (WAL): WAL = 80% of corrosion allowance consumed → renewal/repair before renewal survey Some class: WAL = t_c × 0.5 → repair trigger

Dry-Docking

Dry Dock Requirements

Bottom survey (below waterline): Every class survey (5 years maximum); or at intermediate survey if ESP not applied Inspection: hull coating, sea chests, propeller, rudder, underwater fittings, keel blocks contact

Propeller inspection: Cavitation damage: pitting on pressure face Blade tip erosion: check repair by grinding/re-machining within tolerance Propeller shaft seal: pull shaft if necessary (every 5–10 years depending on seal type) Shaft bearing clearance: measure; allowable clearance per ABS ≈ 0.001" per inch of shaft diameter

Rudder: Pintle and gudgeon clearance: maximum 1.5–3 mm (class dependent) Quadrant and steering gear: function test; hydraulic system pressure test Rudder stock: UT for cracks; cathodic protection (zinc anodes)

Sea chests and valves: Valves: open/close test; body pressure test; replace gland packing Cathodic protection: zinc anodes consumed > 50% → replace; verify anode mass and attachment

Docking Survey Measurements

Underwater hull form: Draft survey: before docking and after undocking (ballast condition) Light ship displacement: calculated from underwater volume to verify no excess structural weight Camber and hogging/sagging: hull girder deformation measurement

Keel clearances: Hull-to-dock floor: maintained during blocking; uneven blocking → stress concentration → structural damage Survey requirement: 150–300 mm minimum keel clearance during flooding/dewatering

Condition Assessment Program (CAP)

CAP (classification-specific; ABS, DNV): Voluntary or mandatory at older age; provides quantified rating (1–4: excellent to poor) Enables informed maintenance planning; supports sale/purchase surveys; P&I club requirements

CAP ratings (ABS): CAP 1 (≥ 90%): excellent condition; new equivalent CAP 2 (75–89%): good condition; some wear; sound for continued operation CAP 3 (60–74%): moderate; repairs needed before next class renewal CAP 4 (< 60%): poor; significant repairs or scrapping

Statutory Certificates

Main certificates for trading vessels: Safety Construction Certificate (SOLAS II-1): structural and watertight integrity; 5 years Safety Equipment Certificate (SOLAS III/IV): life-saving, fire, navigation; 5 years Load Line Certificate (ICLL): freeboard; 5 years IOPP (MARPOL Annex I): prevention of pollution by oil; annual + 5-year renewal ISM Document of Compliance: safety management system; 5 years + annual audit ISPS Certificate: ship security; annual + 5-year renewal

Annual endorsement: all major certificates endorsed annually by class and flag state

Standards

Standard	Scope
SOLAS (IMO)	Safety of life at sea — structural requirements
MARPOL 73/78	Marine pollution prevention
IACS UR Z10.1/Z10.2	Survey requirements for oil tankers/bulk carriers
IACS CSR	Common structural rules (hull design standard)
IMO MSC.215(82)	PSPC coating standard
ISO 8501-1	Surface cleanliness for coating (blast standard)
ISO 19001	Guidelines for ship inspection
ABS Rules for Survey	ABS-specific requirements (publication by ABS)

Output

Provide: ship type (bulk carrier/tanker/container/general cargo), age [years] and ESP stage (S1–S5), survey type due (annual/intermediate/special), key inspection areas (based on type and age), UT gauging plan (measurement density, grid spacing [mm]), wastage found vs. allowable diminution [mm] (pass/fail), coating condition rating (Good/Fair/Poor per IACS) and area of coating breakdown [%], dry-dock items (propeller clearance [mm], rudder pintle clearance [mm], anode depletion [%]), CAP rating if assessed (1–4), certificates due for renewal (type, expiry), repairs recommended (steel renewal [m²], recoating [m²], anode replacement), and applicable standard (IACS UR Z10, IMO MSC.215(82), SOLAS Chapter II-1).