We spent the last week motorsailing down the Intracoastal Waterway from Norfolk, VA to Oriental, NC and had a fine time enjoying the Albemarle and Pamlico sounds and rivers. We were navigating with a Raymarine chartplotter and the latest e-charts from Navionics, both of which are excellent nav tools.
We noticed on a fairly regular basis, but not all of the time, that the GPS position on the chartplotter was often 75 feet or so away from our actual position on the water. GPS normally has a 10-meter margin of error, and we were seeing more than double that distance. Was it the GPS, the charts or a combination of both? Interestingly, the 75-foot offset was pretty consistently to the west of our actual position, but not always.
Once you are aware of a GPS-chartplotter position variance, you can easily factor it in as you navigate as long as you have the ability to check the variance fairly regularly against real fixes. The variance won’t be there all the time and it can change direction. So, be vigilant.
The moral of the story is that in close-quarter navigation such as in the ICW, you really need to keep a good visual lookout for where you are in relation to the actual navigation markers. Plus, you really need to have paper charts for a tangible cross reference of the data on the chartplotter. On coastal runs or at sea, the small errors inevitable with GPS and chartplotters are scarcely noticeable. But in narrow channels, the variance can make the difference between running hard aground and smooth sailing.
Raymarine?? That is maybe the problem, I was ahappy user of their products for 21 years, new boat, new Raymarine stuff, including a now obsolete E120, some ST70, Airmar PB200 windsensor, A500 AIS, st7000 AP. You might think the Raymarine stuff would work together on their ng (=NMEA2000) -bus? NOPE! The Autopilot still connects to Seatalk, the AIS despite its Seatalk-ng has to be connected via NMEA0183-high-speed. the AIS 500 is supposed to work as multiplexer, but it does not as promised in the manual.
This company was bancrupt and purchased by a new owner, it might see brighter days again, but those poor guys who bought in the recent years are left with scrap. whatever I do, there is terrible overshooting (my cat has only 1.5 turns an the helm from hard to hard), the E120 quits connection to the GPS regularly as there are to many gps in the system, Airmar, autopilot, AIS, all have their own, but adjustable settings are limited. AIS is mainly controlled by a PC, few setting available on the plotter only.
I agree with blubaju I also have E120 and E80 Raymarine. Every component in my system has been returned to Raymarine more than once. My Navionics charts Platinum for the west coast will show me on land in Mexico and the Sacramento Delta area. I can’t rely on accuracy of the equipment. I just had to purchased new chart for Mazatlan, Mexico south and was unable to purchase Plat chart for the area as it was removed from the market you can only purchase the basic chart which now shows me to be on water and more accurate, but does not show a lot of anchorages and invalid depth information. I can’t mention any names but heard from a valid source Raymarine was purchased by Flir the night vision company. I used Raymarine in the past but their products now are poor and the support useless.