Glossary — T

35 terms starting with T.

• Tail Shaft
  Aftermost length of the propeller shaft, running through the stern tube to the propeller; subject to bearing wear and torsional fatigue.
• Tailshaft Survey
  A classification survey of the propeller shaft withdrawn from the stern tube to inspect for corrosion, cracking, and bearing wear.
• Tank Cleaning
  The process of removing cargo residues and gas from cargo tanks using water, chemicals, or crude oil washing prior to loading a new cargo.
• Tanker Familiarisation / Advanced Training
  STCW Reg. V/1-1 (oil/chemical) and V/1-2 (gas) basic and advanced courses required for tanker crews.
• Tanker Management & Self Assessment (TMSA)
  OCIMF programme requiring tanker operators to self-assess and continually improve their safety management against 13 elements.
• TCPA (Time to Closest Point of Approach) (TCPA)
  The time remaining until own ship + a target reach their Closest Point of Approach — the primary time-window indicator for collision-avoidance action.
• Technical Superintendent
  A shore-side engineer responsible for overseeing planned maintenance, drydockings, and technical compliance of assigned vessels.
• Territorial Waters
  The belt of coastal waters extending up to 12 nautical miles from the baseline over which a coastal state has full sovereignty.
• Third Engineer (3/E)
  A junior engineer officer responsible for a watchkeeping duties and maintenance of assigned machinery and systems.
• Third Mate (3/O)
  The most junior certificated deck officer, typically responsible for maintaining fire-fighting and life-saving appliances.
• Three-Point Bearing
  A position fix obtained by simultaneously measuring horizontal angles between three charted objects using a sextant or compass.
• Time Charter
  Charter party hiring the vessel for a fixed period; charterer directs employment, owner provides crew/insurance/maintenance.
• TMAS (Telemedical Assistance Service) (TMAS)
  The 24/7 free international radio-medical advice service used by ships worldwide for medical emergencies at sea.
• Tokyo Memorandum of Understanding (Tokyo MOU)
  A regional port state control arrangement covering the Asia-Pacific region, established in 1993 with 21 member authorities.
• Tonnage Certificate
  A statutory certificate stating a ship's gross and net tonnage calculated under the International Tonnage Convention 1969.
• Tonnes Per Centimetre (TPC)
  The mass required to change a vessel's mean draft by one centimetre, used to calculate draft changes during loading or discharging.
• Tonnes Per Centimetre immersion (TPC) (TPC)
  The number of tonnes of weight that must be added or removed to change the ship's mean draft by 1 cm.
• Topside Tank
  Triangular tank in upper corner of a bulk carrier hold; carries ballast and reduces free surface of grain cargo.
• Towline
  Wire, fibre, or composite rope connecting tug to tow.
• Tractor Tug
  Tug with propulsion forward of midship — either Voith-Schneider or azimuth — towing from the stern.
• Traffic Separation Scheme (TSS)
  An IMO-adopted routing measure separating opposing traffic into lanes to reduce collision risk in congested waters.
• Transit
  Two or more objects in line with each other, used as a position line or to verify vessel alignment in a channel.
• Trim
  The difference between forward and aft draft; a vessel trims by the head if forward draft exceeds aft draft.
• Trim and Stability Booklet
  Approved booklet on board summarising loading conditions, hydrostatic data, and stability criteria compliance.
• Trim by the Head
  A trim condition where the forward draft exceeds the aft draft, reducing steering effectiveness and increasing wave-making resistance.
• Trim by the Stern
  A trim condition where the aft draft exceeds the forward draft, generally preferred for sea passage to improve propulsive efficiency.
• True Bearing
  A bearing measured clockwise from true north, used for chart plotting and unaffected by magnetic variation or compass deviation.
• Turbocharger (TC)
  A device driven by exhaust gas that compresses intake air to increase diesel engine power output and fuel efficiency.
• Turbocharger Surge
  An abnormal flow reversal in a turbocharger compressor, evidenced by a loud banging or barking noise, caused by sudden load changes.
• Turnbuckle
  A threaded tensioning device fitted in a lashing rod or wire to adjust and tighten cargo securing arrangements.
• Turning Gear
  An electric motor-driven gear unit that slowly rotates the main engine crankshaft for maintenance, cooling-down, or warming-through.
• Twenty-foot Equivalent Unit (TEU)
  Standard unit of cargo capacity equivalent to one 20-foot ISO shipping container, used to measure container ship capacity.
• Twistlock
  A securing device that fits into container corner castings and locks by a 90° twist to stack and secure containers.
• Two-Stroke Engine
  A type of internal combustion engine completing the power cycle in a single up-and-down piston stroke, common in large slow-speed marine main engines.
• Typhoon
  A tropical cyclone of the western North Pacific with sustained winds exceeding 64 knots, the regional name for a hurricane.