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An area on a filter screen where no filtering occurs. Also known as dead area.

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The bright area on the phosphorescent plan position indicator screen resulting from the brightening of the sweep by the echoes.


The clogging of filtering medium of a micro screen or a vacuum filter when the holes or spaces in the media become sealed off due to grease or the material being filtered. Also, insertion of blind flanges into a pipeline for isolation purposes.


The relationship of flow per unit area to differential pressure across a filter medium.


Measurement of the largest opening in the mesh of a filter screen; determined by the pressure needed to force air or gas through the screen while it is submerged in a liquid.


An electric filter consisting of a lattice network whose branches have L-C parallel-resonant circuits shunted by quartz crystals.


Fairing lines added to a vessel's body plan. They take the form of straight lines (usually three in smaller craft) drawn diagonally from the centreline, to strike the area of the waterline. The projection a line drawn from the series of intersection points found (of diagonal & waterline) along the hull, gives an indication of the likely water flow across the structure.


A pump intake-line filter in which the fluid is below atmospheric pressure.


  1. Having freedom of motion interfered with by collision or entanglement; entangled; the opposite of clear. For instance, a rope is foul when it does not run straight or smoothly, and an anchor is foul when it is caught on an obstruction.
  2. A breach of racing rules.
  3. An area of water treacherous to navigation due to many shallow obstructions such as reefs, sandbars, or many rocks, etc.
  4. Foul the range: To block another vessel from firing her guns at a target.


An area of hills situated at the base of a range of mountains.


An officially designated offshore area for the burning of chemical waste by specially equipped vessels. The depiction of incineration areas on charts (in conjunction with radio warnings) is necessary to insure that passing vessels do not mistake the burning of waste for a vessel on fire.

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