"Larry W4CSC" wrote in message
...
On Sat, 06 Sep 2003 02:17:49 GMT, new guy wrote:

It's easier to visualize and any obstructions you need
to avoid are "ahead" of you coming at you, in the center of the screen
from the top of the screen, no matter where the boat is actually
pointing.

Targets behind and to the side may well be threats, especially in a
slow-moving sailing vessel. You need to watch the progress of a target
(either electronically or by some plotting method), if it stays on a
constant relative bearing - ie runs down a line from the centre of the
display to its first detection point, then it will hit you. Many sets
without MARPA allow you to put an electronic bearing line (EBL) on 1 or more
targets to monitor this. Of course this also applies to rocks; 'will I
clear that headland ?' is really the same question as 'will that ship hit me
?'

That's basically "it".

I would add that radar can be a great navigation tool. It gives a very
accurate range (less accurate bearing) which allows you to identify features
on land and produce an instant fix by drawing circles on the chart with
centres on the features and radius their distance off. The same procedure
will allow you to confirm the identity of a doubtful feature given a known
position or known features. You can also set up an electronic range ring in
advance of a tricky bit of pilotage and use it to stay a known distance off
land. Just remember that the return from a bit of land does not neccesarily
come from the point where the colour changes on the chart; at a long range
you may be seeing high ground miles inland. At closer range it may depend on
tidal height.

A responsible navigator uses every piece of information at his disposal.

Steve