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Originally Posted by lelandtampa
Probably a real stupid question but how does the tablet get a GPS signal other than cell towers?
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You can get GPS receiver gadget called Bad Elf that plugs into the charging port on an iPad, so you don’t need a cellular-capable tablet. It comes with a cord that lets you charge the tablet while using it. It picks up the Russian Glonass satellites in addition to the US & euro ones, so I typically pick up about 19 of 21 satellites that provides a positional accuracy of about 6’! When you combine that with the 1’ contours in the Navionics Sonar maps, I’ve found that the iPad/Navionics combo is a very accurate system. It’s allowed me to run my trawler with a draft of almost 5’ over 2000 miles through some pretty thin water with no problems! Although I have 2 chart plotters on the boat, they’re just backups for my iPad Pro that I’ve used for the entire trip! There have been several boats that went aground and had prop damage in one section of the Rideau canal in Canada recently because some buoys were in the wrong place, but someone recently posted on the Great Loop forum that if you had the latest Navionics Sonar charts, it showed the deep water well enough that you could navigate that area despite the mis-located buoys.
I attended a briefing on mapping software at the Great Loop Rendezvous in Norfolk in May presented by an editor from Waterway Guide. He said that the big GPS makers like Garmin and Raymarine are running scared because of the competition from tablets with mapping applications like Navionics and Aqua Maps which are not only much cheaper, but also more up-to-date and more accurate! The $400 Garmin charts are 6 months old when you buy them, while Navionics updates their sonar charts every couple of weeks, and their charts also include input from Waterway Guide on anchorages and marinas! However Garmin has bought Navionics, so it remains to be seen if they will start using it for their own chips or screw it up like they did to the Active Captain program used by many cruisers that they also bought a year or two ago!