David Rinnan wrote:
Hi Bruce,

Thanks for all the information!

Just to make sure I understand this.. When you say "look at the way the
bearing data is generated" are you then refering to the GPS, in my case,
since I havnt installed a separate compass yet?


It is not about the GPS, he is talking about bearing as in the direction
the radar's rotating radiator or antenna is pointed (relative to the
center line of the boat). That bearing is the direction the radar pulse
was sent to and received from. If that bearing display is off, the
relative bearing to a radar contact from the boat would incorrect.

Does your boat have a flux gate compass? A boat with a radar system
and/or a autopilot really should have a flux gate compass for
determining the boats bearing when not moving. A flux gate compass
knows the bearing at all times (boat moving or not) and sends it to
other devices as a NMEA sentence.

If you do not have a flux gate compass your radar has probably been set
up to use the heading data from the NMEA sentences from the GPS. GPS
headings are only reliable when you are moving, they float around when
you are stopped and do not stay relative to the bow of the boat.

In the above I use heading and bearing as follows:

heading - the direction the boat is moving
bearing - the direction the bow of the boat is pointing

Some people will want to argue about the terms and their use but I'm not
likely to indulge in discussion about it. :) There are many different
definitions and schools of thought on some navigation terms and none of
them are wrong.

Jack

--
Jack Erbes in Ellsworth, Maine, USA (jackerbes at adelphia dot net)
(also receiving email at jacker at midmaine dot com)