wrote:

Can someone direct me to to an explanation of the differences among
these three? I'm a coastal blue-water sailor with limited money to
spend but a willingness to spend where useful. I have a 24 foot
Wayfarer Islander and I'm considering buying a 28" Abbott cruiser.

Thanks in advance!

Here is a good place to find all the answers.

http://gpsinformation.net/

I'd briefly describe the three as follows:

non-mapping - Entry level GPS, shows your position in "white space" and
everything is relative to the fix location. This is the one that will
make you wish you had bought a mapping GPS.

mapping - Has a built in basemap with roads, towns and cities, maybe
even marine or aeronautical details. This is starting to get seriously
useful, you can see where you are relative to places you know and can
picture mentally. The primary purpose of the basemap on a mapping GPS
is to give you just enough detail to entice you into buying one or even
several of the optional detailed mapping packages (highway, topo,
marine, etc.) so you can get more detail.

chart plotter - Generally, a mapping GPS optimized for marine use.
Bigger display and many more controls and features. Has a basic marine
built-in basemap that may include some fixed and floating navaids.
Again the basemap serves to make you aware that you need to buy more
optional chart packages to have enough detail to navigate safely and
with confidence. From this port, the options become pretty complex and
myriad as far as the media used for detail charts, the way it is
packaged for sale, etc.

A good idea is to look at the long term use or direction you think you
want to go before you buy one. If you're pretty sure you want a color
display, buy it to begin with. If you want to travel moderate distances
or get a lot of use out of detail maps without a PC around, look for a
model that uses SD or microSD cards to expand the detail map storage
memory.

For more details and discussion on the two major brands of consumer
grade GPSr's and satnav in general, check out these newsgroups:

alt.satellite.gps.magellan
alt.satellite.gps.garmin
sci.geo.satellite-nav

Jack

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