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 The design angle of the hull at the keel relative to horizontal when viewing the cross section, or the distance of rise from the keel to a defined point on the hull.

## Related Terms

1. A rate of rise or fall of a quantity against horizontal distance expressed as a ratio, decimal, fraction, percentage, or the tangent of the angle of inclination. 2. The rate of increase or decrease of one quantity with respect to another. 3. A term used in radionavigation to refer to the spacing between consecutive hyperbolas of a family of hyperbolas per unit time difference. If the gradient is high, a relatively small time-difference error in deter- mining a hyperbolic line of position will result in a relatively high position error. See also GEOMETRIC DILUTION OF PRECISION

Steepest slope a vehicle can negotiate in low gear; usually expressed in precentage of slope, namely, the ratio between the vertical rise and the horizontal distance traveled; sometimes expressed by the angle between the slope and the horizontal.

### PARALLAX

The difference in apparent direction or position of an object when viewed from different points. For bodies of the solar system, parallax is the difference in the direction of the body due to the dis- placement of the observer from the center of the earth, and is called geocentric parallax, varying with the body’s altitude and distance from the earth. The geocentric parallel when a body is in the horizon is called horizontal parallax, as contrasted with the parallax at any altitude, called parallax in altitude. Parallax of the moon is called lunar parallax. In marine navigation it is customary to apply a parallax correction to sextant altitudes of the sun, moon, Venus, and Mars. For stars, parallax is the angle at the star subtended by the semimajor axis of the earth’s orbit and is called heliocentric or stellar parallax, which is too small to be significant as a sextant error.

### RECTANGULAR COORDINATES

Magnitudes defining a point relative to two perpendicular lines, called AXES. The magnitudes indicate the perpendicular distance from each axis. The vertical distance is called the ordinate and the horizontal distance the abscissa. This is a form of CARTESIAN COORDINATES.

### OBLIQUE COORDINATES

Magnitudes defining a point relative to two intersecting non-perpendicular lines, called AXES. The magnitudes indicate the distance from each axis, measured along a parallel to the other axis. The horizontal distance is called the abscissa and the other distance the ordinate. This is a form of CARTESIAN COORDINATES.

### COORDINATE

One of a set of magnitudes defining a point in space. If the point is known to be on a given line, only one coordinate is needed; if on a surface, two are required; if in space, three. Cartesian coordinates define a point relative to two intersecting lines, called AXES. If the axes are perpendicular, the coordinates are rectangular; if not perpendicular, they are oblique coordinates. A three- dimensional system of Cartesian coordinates is called space coordinates. Polar coordinates define a point by its distance and direction from a fixed point called the POLE. Direction is given as the angle between a reference radius vector and a radius vector to the point. If three dimensions are involved, two angles are used to locate the radius vector. Space-polar coordinates define a point on the surface of a sphere by (1) its distance from a fixed point at the center, called the POLE (2) the COLATITUDE or angle between the POLAR AXIS (a reference line through the pole) and the RADIUS VECTOR (a straight line connecting the pole and the point)- and (3) the LONGITUDE or angle between a reference plane through the polar axis and a plane through the radius vector and the polar axis. Spherical coordinates define a point on a sphere or spheroid by its angular distances from a primary great circle and from a reference secondary great circle. Geographical or terrestrial coordinates define a point on the surface of the earth. Celestial coordinates define a point on the celestial sphere. The horizon, celestial equator and the ecliptic systems of celestial coordinates are based on the celestial horizon, celestial equator, and the ecliptic, respectively, as the primary great circle.

### DIRECT-CURRENT POWER SUPPLY

A power space relative to another without reference to the distance between them; may be either threedimensional or two-dimensional, the horizontal and set points.

### CRITICAL SLOPE

The maximum angle with the horizontal at which a sloped bank of soil of a given height will remain undeformed without some form of support.

### LAT

1) Lowest astronomical tide under any predictable astronomical or meteorological conditions. 2) Latitude - a small circle measured as the angle between a position on the earth's surface, the centre of the earth and the pole. 3) Parallels of latitudes are consequently north or south of the equator (0o) and are used to measure the distance from it.

### GREAT CIRCLE DIRECTION

Horizontal direction of a great circle, expressed as angular distance from a reference direction.

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