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GPS Chartplotter Update

Update?  Well, sort of.  I have a small and old hand held Magellan GPS which has graced the cockpit seats many times.  Unfortunately, it chews through batteries like mad.  It is also lacking a solid mount, although I suppose I could remedy that problem.  I'd like to have something hard-wired into the boat's electrical system, with a solid mounting on the pedestal to make it convenient for the helmsman.

Although they are very sexy, the new large touch screen units are not what my old boat needs.  They won't fit the pedestal very well.   They are also too high tech.  Yes, I said it.  If I had a more modern boat I'd probably think about one, but it just throws the aesthetics for me.  I'm looking for something small because I don't want it to be a visual anchor.  I'd like it to mount in the ~ 8 inch area between the pedestal support tubes so that it can be viewed just above the binnacle compass.

From a feature perspective I have no worries.  The features I care about have been part of every GPS unit built in the last ten years.  It needs to be able to output NMEA signals so that my VHF's DSC capability is enabled.  I expect to be able to plot a series of waypoints, see my latitude and longitude, and speed over ground.  A nice feature would be the ability to synchronize with a computer, but it's not essential.  My preference is for an internal antenna, but I can work with external if need be.

Considering these requirements it became obvious that I was looking at low-end units, and I immediately found two which stood out:  The $479 Standard Horizon CP180i, and the $449 Garmin GPSMap 431 (Pre-loaded with US Inland Lakes - I'm on Lake Ontario).  The next bump up in price brings me to a $699 Garmin 531 which adds screen resolution.  It's hard to justify an extra $100 for screen resolution when my current hand held unit seems to be working fine, but it's worth keeping in the comparison just in case another feature jumps out.

Feature Comparison
  Standard Horizon CP180i Garmin GPSMap 431 Garmin GPSMap 531 Garmin GPSMap 541
 Adv. Price ( $479 $449 $599 $699
 Dimensions 4.4"H x 7.1"W x 1.7"D5.0"H x 5.7"W x 2.7"D 5.9"H x 6.4"W x 2.9"D 
 Antenna Internal Internal (ext optional) Internal (ext optional) Internal (ext optional)
 Screen Resolution 320 x 240 240 x 320 234 x 320 
 Screen Dimension 5" 4"  
 Power Consumption 520mA max @ 12v 15W max @ 13.8v 15W max @ 13.8v 15W max @ 13.8v
 Waterproof????  IPX7 IPX7 IPX7
 Cartography C-MAP by Jeppeson NT+/MAX Garmin Garmin Garmin

Mounting Location
My intent is to mount the GPS on the pedestal immediately behind the binnacle compass.  Since I'm looking down, I anticipate that the compass will not block the screen significantly.  There are a number of options for raising the mount point a bit to mitigate this situation as well.  When reading the installation instructions for each unit I discovered a unique requirement that Garmin lists:  The unit needs to be mounted 20-38" away from a compass (distance depends on the model).

I did some Internet surfing and found that people don't seem to pay much attention to this requirement.  People seem to mount the GPS on their pedestals all the time, and very few report any detectable issues.  However, I wonder how many people have really measured deviation at all compass points?  I tend to think the issue is minimal at best, however, knowing that Garmin says, "don't do it" puts a huge negative mark against the Garmin units.  Based on this, I'm leaning heavily towards the Standard Horizon CP180i.