Glossary — I

47 terms starting with I.

• IACS Polar Class
  Seven-tier ice class (PC1–PC7) under IACS UR I assigning ice-going capability from year-round in all polar waters (PC1) to summer-only thin first-year ice (PC7).
• Iceberg
  Mass of glacier ice >5 m above the water, classified small/medium/large/very large by IIP.
• Icebreaker
  Vessel with reinforced bow, high-power propulsion, and ice-friendly hull form designed to break level ice and clear channels.
• IGF Code
  International Code of Safety for Ships using Gases or other Low-flashpoint Fuels.
• IMDG Class 1 (Explosives)
  IMDG dangerous-goods classification for explosive substances and articles.
• IMDG Class 2 — Gases
  Compressed, liquefied, or dissolved gases; subdivided 2.1 flammable, 2.2 non-flammable non-toxic, 2.3 toxic.
• IMDG Class 3 — Flammable Liquids
  Liquids with flash point ≤ 60 °C; classified by packing group I/II/III based on flash point and boiling point.
• IMDG Class 4
  Flammable solids (4.1), substances liable to spontaneous combustion (4.2), substances which emit flammable gases when wet (4.3).
• IMDG Class 5
  Oxidising substances (5.1) and organic peroxides (5.2); pose fire risk by yielding oxygen.
• IMDG Class 6
  Toxic substances (6.1) and infectious substances (6.2).
• IMDG Class 7 (Radioactive)
  IMDG dangerous-goods classification for radioactive material.
• IMDG Class 8 — Corrosives
  Substances causing severe damage when in contact with living tissue or other goods, including most acids and bases.
• IMDG Class 9 (Miscellaneous Dangerous Goods)
  Catch-all for substances dangerous in transport but not fitting Classes 1-8 (e.g., asbestos, dry ice, lithium batteries, env. hazardous).
• IMDG Code
  International Maritime Dangerous Goods Code — mandatory packaging, marking, segregation, and stowage rules for DG in packaged form.
• Immersion Suit
  A watertight thermal protective suit worn in cold water abandonment that significantly extends survival time.
• IMO 2020 Sulphur Cap
  Global cap on marine fuel sulphur content reduced to 0.50% mass on 1 January 2020 (0.10% in ECAs).
• IMO GHG Strategy
  IMO 2023 strategy targeting net-zero GHG emissions from international shipping 'by or around' 2050, with checkpoints for 2030 and 2040.
• IMO number
  The seven-digit unique + permanent identifier assigned to a ship by the IMO — remains with the hull for its entire life regardless of flag + name changes.
• IMO Number
  A unique seven-digit identifier assigned to a ship for life, used to track its history regardless of flag, owner, or name changes.
• Impressed Current Cathodic Protection (ICCP)
  Active corrosion protection injecting low-voltage DC into the hull via inert anodes; used on most large vessels.
• Inert Gas System (IGS)
  A system supplying inert gas (flue gas or nitrogen) to tanker cargo tanks to maintain an oxygen-deficient atmosphere and prevent explosion.
• Inmarsat-C
  Geostationary satellite system providing low-data-rate store-and-forward messaging and EGC SafetyNET broadcasts, recognised under GMDSS for Sea Area A3.
• Innocent Passage
  The right of foreign ships to navigate through a coastal state's territorial sea continuously and without prejudice to its peace or security.
• Inshore Traffic Zone (ITZ)
  The water between a traffic separation scheme and the adjacent coast, normally reserved for local and small craft traffic.
• Intact Stability Code (IS Code)
  IMO mandatory code for intact stability of all ships >24 m, including weather criterion and severe wind & rolling.
• Inter-Tropical Convergence Zone (ITCZ)
  A belt of converging trade winds near the thermal equator characterised by squalls, doldrums, and heavy rain, migrating seasonally with solar heating.
• Intercept
  In celestial navigation, the difference in minutes of arc between the observed altitude and the calculated altitude, used to plot a position line.
• Intermediate Fuel Oil (IFO)
  A blend of heavy residual and distillate fuel oil with viscosity typically 180 or 380 cSt, used as main engine bunker.
• Intermediate Survey
  A classification survey conducted midway through the five-year special survey cycle, typically around the second or third year.
• International Association of Classification Societies (IACS)
  A body of twelve major classification societies that collectively establish and promote uniform technical standards for ship construction and maintenance.
• International Convention for the Prevention of Pollution from Ships (MARPOL)
  The main international convention covering prevention of pollution of the sea by ships from operational and accidental causes.
• International Convention for the Safety of Life at Sea (SOLAS)
  The primary IMO convention setting minimum safety standards for ship construction, equipment, and operation.
• International Group of P&I Clubs (IGP&I)
  Association of 12 mutual P&I clubs sharing claims via a pooling/reinsurance arrangement covering ~90% of world tonnage.
• International Load Line Certificate
  The statutory certificate showing the maximum permissible draft (load line) marks on the hull — required under the 1966 Load Lines Convention.
• International Maritime Dangerous Goods Code (IMDG)
  IMO code governing the safe carriage of hazardous materials by sea, covering classification, packing, marking, and stowage.
• International Regulations for Preventing Collisions at Sea (COLREGs)
  IMO rules prescribing conduct of vessels to prevent collisions, including lights, shapes, sound signals, and steering rules.
• International Safety Guide for Oil Tankers and Terminals (ISGOTT)
  Industry standard guidance jointly published by OCIMF, ICS, and IAPH for oil-tanker / terminal cargo operations.
• International Safety Management Code (ISM Code)
  IMO code requiring shipping companies to establish a Safety Management System to ensure safe ship operation and pollution prevention.
• International Ship and Port Facility Security Code (ISPS Code)
  IMO code mandating security plans, officers, and assessments for ships and port facilities to prevent terrorism and unlawful acts.
• Internationally Recommended Transit Corridor (IRTC)
  Naval-monitored corridor through the Gulf of Aden with eastbound/westbound lanes for grouping and transit of merchant vessels.
• Intertropical Convergence Zone (ITCZ)
  A band of low pressure near the equator where trade winds converge, producing persistent convective weather and squalls.
• Iridium GMDSS
  IMO-recognised GMDSS satellite service using Iridium's low Earth orbit constellation, providing global coverage including polar Sea Area A4.
• Iridium GMDSS Service
  Iridium satellite service recognised by IMO since 2020 for GMDSS Sea Areas A1–A4, including polar regions.
• ISM Audit
  Internal and external audit of the Safety Management System under the ISM Code; underpins the DOC and SMC.
• ISO 8217
  International standard specifying marine fuel grades — distillates (DMA, DMB, DMZ) and residuals (RMA, RMB, RMD, RME, RMG, RMK).
• ISPS Audit
  Verification audit of ship/port-facility security plans under ISPS Code — initial, intermediate, renewal.
• ISPS Security Levels
  Three-tier security alert: Level 1 normal, Level 2 heightened, Level 3 specific threat — set by Contracting Government.