Scuba Glossary: T - U - V


Tank Boot  –  Flat-bottomed, plastic, vinyl or rubber devices that fit over the rounded end of a scuba tank, allowing the tank to stand up.

TDI  –  Technical Diving International. Maine-based certification agency for technical aspects of recreational scuba.

Thalassophile –   (n) A person who loves the sea, oceans

Thermocline  –  Intersection between two layers of water of that are of distinctly different temperatures, usually the colder layer is deeper.

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Tissue  –  A part of the body characterized by specific characteristics, such as muscle, bone, or cartilage. The term is also used to refer to any part of the body with a specific half time for loading and unloading nitrogen or even a theoretical compartment.

Triangular profile  –  A triangular dive profile is one in which, after a descent at constant rate, and a short bottom time at maximum depth, the diver maintains a constant, slow ascent to the surface or first decompression stop. A plot of depth against elapsed time takes a triangular shape.

Trilam  –  Material used for dry suit shells made of a layer of waterproof rubber laminated between two layers of woven textile.

Trimix  –  Mixture of helium, nitrogen and oxygen, used for very deep diving.

TUP  –  Transfer Under Pressure: Transfer of personnel between hyperbaric environments, usually between a closed bell and a saturation system, or between a portable recompression chamber and a multi-occupant chamber.

Turbidity  –  The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that may be invisible to the naked eye, similar to smoke in air.

Turn the dive  –  Start the return on a dive which has reached the planned turning point in terms of depth, time, gas supply or distance.


Umbilical  –  Life support connection to a surface supplied diver or diving bell. Comprises gas supply hoses, a strength member and communications cable, and may also include gas reclaim hose, hot water hose and hoses for hydraulic or pneumatic power, and electrical and optical cables for ancillary equipment. Also refers to the power, control and instrument cable for a ROV.

Unbalanced Regulator  –  An unbalanced first stage regulator is affected by tank pressure. The tank pressure works to force the piston in the first stage open. As the gas in the tank diminishes, it is easier for the piston to be forced into a closed position. This makes it increasingly harder to breath from the first stage as the dive progresses. This is an older style regulator and has pretty much vanished from today’s scuba gear market.

Undertow  –  A subsurface flow of water returning seaward from shore as result of wave action.

U-Pattern Search  –  A U shape search pattern that requires on line. This type of search pattern is suitable over many different bottom terrains and is a frequently used search pattern. A search team swims along the bottom in a long straight line, turns 90 degrees and swims for a short length, and then swims another long length.

Upline  –  A fairly substantial natural fiber rope which is deployed from the bottom using a small lift bag to provide the equivalent of a shotline. The lower end is tied off to the bottom, usually on a wreck, and the diver ascends on the line to avoid being swept away from the site by currents. After reaching the surface, the last diver cuts the line and it sinks back down, Natural fibre is used so the line rots away over a few years.

Upstream  –  Against the flow. Moving against the current.

Upwelling  –  Upwelling is vertical water movement. This occurs when surface water is moved away (offshore) due to winds blowing from north top south and acting as a force on the surface waters. Because water from somewhere has to fill the space left by the offshore movement of surface water, water fills in from below, creating a vertical current of water.


Valsalva Maneuver  –  A method of manually equalizing the inner ear. The pressure on the inside of the eardrum is increased by closing the nasal passage (pinching the nose shut) and blowing gently, forcing air into the inner ear via the Eustachian tube.

Valve cage  –  structure or frame fitted to scuba cylinder to protect the cylinder valve or manifold and regulator first stage from impact damage and roll-off.

Valve drill  –  Safety exercise in which the diver shuts down, tests regulators and re-opens the manifold valves on a twin set in a specific order.

Valve guard  –  A protective structure or frame fitted to the top of a bulk storage cylinder to protect the cylinder valve from mechanical damage.

Van der Waals equation  –  Thermodynamic equation of state for a real (non-ideal) gas.

Vasoconstriction  –  The constriction of the blood vessels in order to reduce heat loss from the blood through the skin.

Vasodilation  –  The widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large veins, large arteries, and smaller arterioles.

Venomous  –  Having a gland or glands for secreting venom; able to inflict a poisoned bite, sting or wound.

Vertigo  –  A sign of ear barotraumas and should not be ignored. Causes may range from minor ear squeeze to perforation of the eardrum to inner ear barotraumas.

Viewport  –

  1. Glass or plastic window on a diving helmet or full face mask.
  2. Window on a hyperbaric chamber.

VIP  –  Visual Inspection Program. Standardized visual tank inspection performed by a trained equipment technician, performed annually.

Visibility  –  The distance a diver can see underwater measured in feet. Normally vertically not up and down.

Visual gap  –  Gap between guidelines which is small enough that each line can be seen from the other.

Visual inspection  –  Internal and external inspection of a pressure vessel as part of revalidation procedure.

Visual jump  –  The procedure of crossing a visual gap (q.v.) without the use of a jump line.

Viton  –  Synthetic elastomer suitable for oxygen service O-rings.

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