Knowledge Base
rate gyro
A special kind of gyroscope that measures rotation rate around a fixed axis.

relative bearing
Bearing relative to heading or to the vessel.

relative wind
The speed and relative direction to from which the wind appears to blow with reference to a moving point (also called Apparent Wind).

The maximum variation between repeated measurements under the same conditions.

The smallest change that a sensor can measure.

rhumb line
A line on the surface of the earth making the same oblique angle with all meridians. A rhumb line is a straight line on a rhumb (or Mercator) direction.

rhumb lirection
The horizontal direction of a rhumb line, expressed as angular distance from a reference direction. Also known as Mercator direction (see Mercator Map Projection).

RMA sentence
Recommended Minimum Acceptable Sentence, a composite sentence recommended by the NMEA 0183 standard to insure interoperability between talkers and listeners and to insure that all data considered necessary for navigation is sent by a particular navigation unit.

The anchor line and/or chain.

Rotation around the X-Axis. In a vessel, roll is rotation about the axis defined by the vessels fore-and-aft center line.

In general, cordage as it is purchased at the store. When it comes aboard a vessel and is put to use it becomes line.

A planned course of travel, usually composed of more than one navigation leg.

route system
Any system of one or more routes and/or routing measures aimed at reducing the risk of casualties during a voyage which may include such items as traffic separation schemes, recommended tracks, restricted areas, inshore traffic zones, etc.

RS-232 interface
Standard serial interface for PC-type computers.

A vertical plate or board for steering a boat.

To allow a line to feed freely.

running sights
Lights required to be shown on boats underway between sundown and sunup.

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