have a unit with adjustable intrusion alarm
features and MARPA (mini automatic radar
plotting aid) capabilities. And for the average
boater, a 4 kW unit will do the job nicely.
Although radar is a line-of-sight system,
its range is actually a bit farther than that.
Because atmospheric refraction bends the
beam slightly, a radar can actually “see” about
15% farther than a human observer located
at the same height. The location of the
antenna on the boat (mounting it higher
extends the horizon), the height of the target,
and the visible horizon all make a difference.
The height of targets located beyond the
visual horizon determines the actual radar
range. This distance (see Table 16-7) can be
calculated as follows:D=1 144. ( HH 12 + )
186 marine electronics installation and troubleshooting
waterline12.5 ̊12.5 ̊wedge orwashersforwardusing shims to
lower the
main beamWhen mounting a radar antenna on a powerboat, ensure that the 25-degree vertical beam is leveled horizontally and
not obstructed by structures on the boat itself. Adjustable brackets and shim kits are available from radar suppliers as
aids in leveling the unit (inset).tilted
radomeA proper radar installation on a 35-foot lobster boat. Notice the slight
downward tilt to the radome relative to the cabin top. When the boat is
running and its bow rises, this radome will be level, or parallel to the
water’s surface, which is the goal.