"Wayne.B" wrote in message
...
On Tue, 27 Dec 2005 00:11:51 GMT, Gene Kearns
wrote:

Anybody know of a GPS with this capability?

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Some of the better sailboat systems like Ockam or B&G offer direct
digital readout of current direction and speed. They are calculated
numbers based on observing SOG vs speed through the water, and COG vs
magnetic compass heading. The instrument system resolves all the
vectors and spits out the numbers. It is fairly slick but requires
constant calibration and cleaning of the speed sensors which are
mechanical flow transducers in through hull fittings.

My Furuno Navnet, integrated chart plotter/GPS/RADAR, displays a
heading vector and a separate COG vector on the RADAR screen. It has
an electronic compass sensor to provide heading information. Since it
knows your heading, it can also overlay chart data with the RADAR data
which can sometimes be useful. It needs heading information to rotate
the chart into the proper orientation. I find this function
particularly useful for quickly determining whether a RADAR target is
a NAVAID such as a buoy, or another boat.

I had very mysterious readings for a while until it was discovered that the
electronic compass (I think it's called a flux gate compass) had been
mounted in the engine room about 6 inches away from the electric motor for a
washing machine. If I deviated more than 10 degrees off course, the boat
marker would swing around so it appeared we were doing 19 knots in reverse.

Another neat feature of the overlays (haven't tried it yet though) is that
you can set up the Raymarine system to automatically command the autopilot
to change course if the radar shows something big and solid (like another
boat) on a collision course and within a programmed range. I am sure the
Furuno system has something similar. I briefly had an Egg Harbor with the
Furuno setup and never really learned the system. I find the Raymarine to
be much more intuitive.

Eisboch