Navigation With The Radar - Raytheon Pathfinder 1200 Instruction Manual

2.4 NAVIGATION WITH THE RADAR
2.4.1 Obtaining a Position Fix
The Model 1200 Radar is an accurate and reliable navigational aid for determining
your ship's position. Figure 2-4 shows examples of alternative methods of using radar
sitings from prominent navigational points which can be identified on a chart. A position
fix based on two or more navigational points will furnish a more accurate fix, especially
when the points approach 90 degrees apart from your ship's position.
2.4.2 Avoiding Collision
The moment a target appears on the screen, its range and relative bearing should be
noted. This is best done on a plotting sheet or chart.
As in visual observation, "a constant bearing indicates a collision course".
As soon as a series of plots indicates a closing range and no significant change in
successive bearings, positive action should be considered mandatory and "The Regulations
for Preventing Collisions at Sea" should be observed.
2.4.3 Determining Your Radar Line-of-Sight Range
When searching for distant targets, your radar line-of-sight range to the target can be
a limiting factor. Radar waves behave like light waves but they are refracted slightly more,
increasing the distance to the radar horizon slightly more than that to the optical horizon
(however, displayed range is correct). As Figure 2-5 shows, the radar line-of-sight range
is a combination of the radar horizon of your ship's radar scanner and the radar horizon
of the target.
The distance to the radar horizon from radar scanner of height "h" meters, under
standard conditions, may be calculated from the formula
Distance
(nrn)
=
2.23
v'i1
For example, a scanner at a height of 5 meters has a radar horizon of 5 nm.
A 5 meters cliff has a radar horizon of 5 nm. Therefore, under standard conditions,
the cliff should begin to appear on the screen when ship closes nearer than 5 + 5
=
10 nm.
2-7