Tackle - Any combination of ropes and blocks that multiply power. The equipment on a vessel used to perform working tasks on the vessel.

Tank Washing - The cleaning of a vessel's tanks. It is divided into two types of activities:

Water Washing - The use of a high-pressure water stream to dislodge clingage and sediment from the bulkheads, bottom, and internal tank structures of a vessel.

Crude Oil Washing - The use of a high-pressure stream of the crude oil cargo to dislodge or dissolve clingage and sediment from the bulkheads, bottom, and internal tank structures of a vessel during the discharge operation.

NOTE: Regulatory agencies require that a vessel's tanks be inerted before this tank cleaning method is used.

Tender (TO) - A master tenders his vessel when he advises the charterer or supplier that he is ready to load.

Time-Charter - The hiring of a tanker from a shipowner for a period of time. As operator, the shipowner is paid on a per-day basis and is responsible for providing the crew and paying operating costs. The charterer is responsible for paying the voyage costs, save for certain specific exceptions such as loss of time arising from tankers breakdown and routine maintenance. See "Voyage Charter" and "Bareboat Charter".

Thieving - Determining the amount of water at the bottom of a tank of oil.

Ton - Typical unit of weight measurement used on tankers. See Long Ton, Metric Ton, Short Ton.

TMSA - Tanker Management Self Assessment. This is a self-assessment program for tanker operators, developed by OCIMF (Oil Companies International Marine Forum). TMSA is designed to motivate and reward high quality and continuous improvement in tanker operations.

Tonnage - See Deadweight, GRT and NRT.

Tonnage Tax - Taxes, fees, harbor dues etc. paid on the vessel based on a tonnage calculation.

Tonne - Metric ton.

Tons Per Inch Immersion (TPI) - The number of tons required to change a vessel's draft one inch in the water. TPI varies with the draft and it's values can be found on a vessel's deadweight scale. The metric equivalent is known as TPC (Tons per Centimetre)

Tonne- mile - Quantity transported multiplied by average voyage distance. Also Ton-mile.

Topping-Off - 1) the operation of completing the loading of a tank to a required ullage. 2) Filling up cargo tanks which were only partially filled at the loading port because of port or canal draft restrictions. The filling up occurs outside the loading port via lightering activities, or at another loading port.

Trim - The condition of a vessel with reference to it's longitudinal position in the water. It is the difference between the forward and after drafts expressed in feet/inches or meters/centimeters. Trim forward is called 'by the head' and trim aft is called 'drag'.

Trim By The Head (By The Stern) - A vessel is said to trim by the head (or stern) when its draft forward (or aft) is greater than aft (or forward).