"The Joy of Radar"
I'm going to show you a little bit about radar. This page highlights the Radar/Chartplotter on our old boat, Arecales, but they all work the same.
Below is a car carrier coming up the river, we are in front of Caterpillar in our usual spot (Pier 1)
and below is the radar image of the ship, it has such a large radar signature that it appears to cover the whole width of the river. The range ring shows it at 1.89 miles from our current location. In this display Arecales is at the center with the bow up, and the stern down. Note that when you have radar the whole world revolves around you :-)
The car carrier is closer and now you can see the other ship that is anchored near us...
and here you can see both ships on radar. The range ring shows the car carrier 0.94 miles from our current location.
From our location the car carrier appears to be ahead of the anchored ship...
but in fact, it's still not yet even with it. Another thing you can see here is the South End channel behind the island. How can the radar see that? It sees the trees on the island, then it sees nothing, then it sees trees on the mainland. The gap between the two is the empty space between the two groups of trees. Note the same thing happens with the ships, you can see a gap between the ships for the same reason.
Now the car carrier is ahead of the anchored ship...
and you can see this on the radar.
And now the car carrier is abeam of the Arecales...
and there it is on the radar. Note that because the ship is taller than the trees behind it, the radar image obliterates the radar image of the trees (since the trees aren't getting any energy from the radar).
Here is one more example. Below are three blips on the radar.
and here is the view out the window. The three ships are anchored.
Can you believe that in the Navy they have a training course to teach people this stuff. Pretty easy isn't it?
Below is a good example of why you need radar.