Raymarine ST50 plus Specifications download pdf (Page 26)

3-2

ST50 PLUS RADAR Operation and Installation Handbook

3.2 Radar Map

The radar display is a map-like representalion of the area in which the

radar is operating. Typically, the ship’s position is at the center of the

display or sometime may be repositioned or offset up to 66% of the

radius anywhere on the screen in the OFFSET MODE. The ship’s dead

ahead bearing is indicated by the heading line at the 0” bearing with

every revolution of the sweep trace.

Coastline contours are generally depicted in solid filled blue echo

areas. Other surface vessels, and channel buoys, are displayed as

smaller single echoes. The radar picture or map can be viewed in many

sizes or scales from own ship. These sizes are selected by the range

scale controls. Greater detail of radar echoes nearby own ship is

shown when using the short range scales. The best technique is to

start with using a longer range scale and then switching to shorter

ranges when nearby targets appear, or as the ship approaches the

coastline, harbor, or other vessels in the area.

Until the operator becomes familiar with interpreting the radar display,

every opportunity should be taken to compare the radars display

patterns with visual targets, such as other vessels, buoys, coastal

structures etc. Harbor and coastal navigation should be practiced

during daylight with clear weather conditions.

3.2.1 Map Orientation

In the RELATIVE mode, the heading line always appears on the Display

Unit at

0”

relative, and is coincident with the antenna beam passing the

ship’s bow. Thus the top of the displayed picture represents the

direction in which the ship is heading. All targets appearing on the

display are “Relative” to own ship’s position and heading.

The

EBL’s

give relative bearing data. When in the TRUE mode, EBL

readouts give true bearing to targets. The MAGNETIC mode provides

magnetic bearings to targets.

Acompass

input is required

inorder

to have magnetic bearings. AGPS

or Loran input is required in order to have true heading. Some GPS and

Loran units allow for the input of magnetic variation into them, which

in turn, will provide magnetic course information to the radar.

Section 3. Operation

3.2.2 Effect of Ship’s Movement

Radar Displays can be drawn in two ways to show the ship’s motion,

The displays are called “Relative Motion” and ‘True Motion” Display. In

Relative Motion, the most common radar display mode the appearance’

of the radar display changes according to the ship’s speed and course,

that is own ship is permanently fixed in position but radar echoes

(targets) move in relation to your vessel. With no movement of the ship,

a steady display of fixed radar echoes is shown. If the ship is moving

ahead on a constant course, echoes appearing at the top of the display

will move downward across the display. Your position will always

remain at the center of the display.

If your vessel alters course to the right, the displayed echoes will be

displaced by an equal amount in bearing in a counterclockwise

direction, and vice versa. These changes in the display pattern with

ship movement is an extremely important factor when plotting the

ship’s course and the courses of nearby vessels.

The True Motion Display Mode is very much like seeing your vessel

moving on a map or chart. In True Motion, the surrounding landmass

echoes will remain stationary on the screen. If your ship is moving at

a constant course and speed, you will see your position move across

the screen towards the edge of the display. Any other targets which

are underway will also be moving on the display screen at their True

course and True speed. All motion seen on the True Motion display is

“TRUE”. (meaning motion over the ground).

The ST50 Radar only operates in the Relative Motion mode.

3.2.3 Navigational Echoes

Echoes displayed on the radar screen may be large or small, bright or

faint, depending on the size of the object. The radar indication may not

be similar to an observer’s visual indication; a nearby small object may

appear to be the same size as a distant large object on the radar. With

experience, however, the approximate size of different objects can be

determined by the relative size and brightness of their radar echoes.

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Raymarine ST50 plus Specifications Page 26

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