Raymarine e7D, Installation And Operation Handbook, Page: 129 / 270

Blind Sectors
Obstructions such as funnels and masts near the radar antenna
may obstruct the radar beam and cause radar shadows or ‘blind
sectors’. If the obstruction is relatively narrow, there will be a
reduction of the beam intensity, though not necessarily a complete
cut-off. However, for wider obstructions there may be a total loss of
signal in the shadow area. There may also be multiple echoes which
extend behind the obstruction. Blind sector effects can normally be
minimized by careful selection of the scanner site prior to installation.
Sea Clutter
Radar returns from waves around the vessel can clutter the centre
of the radar picture, making it difficult to detect real targets. Such
‘sea clutter’ usually appears as multiple echoes on the display at
short range scales, and the echoes are not repetitive or consistent
in position. With high winds and extreme conditions, echoes from
sea clutter may cause dense background clutter in the shape of
an almost solid disc.
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Rain or Snow Clutter
The radar can see echoes from rain or snow. Returns from storm
areas and rain squalls consist of countless small echoes that
continuously change size, intensity and position. These returns
sometimes appear as large hazy areas, depending on the intensity
of the rainfall or snow in the storm cell.
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Interference
When two or more radar-equipped vessels are operating within
range of each other mutual radar interference can occur. This
usually appears as a spiral of small dots from the display centre This
type of interference is most noticeable at long ranges.
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12.5 Radar display overview
With your radar scanner connected and the radar in transmit mode,
the radar picture provides a map-like representation of the area
in which the radar is operating.
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Item Description
1 Range
2 Waypoint
3 Data cell
4 Databar
5 Range ring
6 Target
7 Orientation
8 Ship’s Heading Marker (SHM)
9 Ship’s position
10 Motion mode
11 Radar scanner status
12 Range ring spacing
Additional functionality of the radar application includes:
• Color palettes.
• Adding AIS overlay.
• MARPA targets.
Typically, your vessel’s position is at the center of the display, and
its dead ahead bearing is indicated by a vertical heading line, known
as the Ship’s Heading Marker (SHM).
Note: If the cursor is placed over the SHM, the SHM will
temporarily be removed to help placing markers or acquiring
targets etc.
On-screen targets may be large, small, bright or faint, depending on
the size of the object, its orientation and surface. If using a non-HD
digital radome scanner, strongest target returns are displayed in
yellow with weaker returns in 2 shades of blue. If using an HD or
SuperHD digital radar scanner, stronger target returns show as
different colors from a range of 256 colors, providing better clarity.
Be aware that the size of a target on screen is dependent on many
factors and may not necessarily be proportional to its physical size.
Nearby objects may appear to be the same size as distant larger
objects.
Note: Colors stated above refer to the default color palette.
With experience, the approximate size of different objects can be
determined by the relative size and brightness of the echoes.
You should bear in mind that the size of each on-screen target is
affected by:
• The physical size of the reflecting object.
• The material from which the object is made. Metallic surfaces
reflect signals better than non-metallic surfaces.
Using radar
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