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The interval between the moon’s transit (upper or lower) over the local or Greenwich meridian and the following high or low water. The average of all high water intervals for all phases of the moon is known as mean high water lunitidal interval and is abbreviated to high water interval. Similarly the mean low water lunitidal interval is abbreviated to low water interval. The interval is described as local or Greenwich according to whether the reference is to the transit over the local or Greenwich meridian. When not otherwise specified, the reference is assumed to be local. When there is considerable diurnal inequality in the tide separate intervals may be obtained for the higher high waters, the lower high waters, the higher low waters and the lower low waters. These are designated respectively as higher high water interval, lower high water interval higher low water interval, and lower low water interval. In such cases, and also when the tide is diurnal, it is necessary to distinguish between the upper and lower transit of the moon with ref- erence to its declination.

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A valve attached to a water column or drum for checking water level.


A vertical tubular member connected at its top and bottom to the steam and water space respectively to a boiler, to which the water gage, gage valves, high and low water alarms and fuel cutoff may be connected.


Test valves on a water column used to verify the water level when the gauge glass is out of service.


One of three valves mounted on a boiler or water column within the visible range of the gauge glass and used to check the water level.


A pipe leading to the bottom of an oil or water tank, for guiding a sounding tape or jointed rod when measuring the depth of liquid in the tank.
Sounding pipes in the engine room are normally fitted with deadweight cocks and screw caps. Caps and cocks should be closed at all times, except when sounding tanks.


The effect that due to the depth of water, the speed of the vessel and shape of the vessel's hull causes the vessel to sink deeper in the water especially in shallow water and at high speed. The vessel becomes sluggish in responding to the rudder.


A caisson having a chamber filled with compressed air at a pressure equal to the pressure of the water outside.


A device for measuring the speed of water currents in which a perforated disk, which rotates with the current by means of a propeller, is placed in the path of a beam of light that is then reflected from a mirror onto a phototube.


A device for obtaining ocean bottom cores up to about 4 feet (1.2 meters) in length; consists of an upper tube, main body weight, and tailfin assembly with a check valve that prevents the flow of water into the upper section and a consequent washing out of the core sample while hoisting the corer.


The highest velocity at which water is permitted to pass through a structure or conduit without excessive damage.

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