Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: how does this unit do when used with Navionics charts on an Ipad, for boating navigation?
Document: I purchased this Bad Elf GPS module with the intent of using it mainly for navigation on the water. (Chesapeake Bay and East Coast US waters)I have used it mainly with Navionics East Coast chart app for Ipad. It works flawlessly. I have an IPad 2, wi-fi. NO 3G, so I needed a stand alone GPS plug in.The Navionics app is not the only one that works.
This unit was all that was advertised. It was basically plug and play and worked great from the get go. I used it for the Foreflight app on my iPad for navigation as a private pilot and am really pleased with the function in the cockpit.
If you use your iPad as a personal navigation device or as a backup to your flight planning or navigation charts, Bad Elf is a must to insure great reception. Even works if you are sitting near the windows in the back of the bus!
Bad-Elf is the new paradigm in air navigation ... its that good. I expect that in the least, the Bad Elf GPS/iPad combination will put alot of downward price pressure on Garmin. When iPad software developers start geo-referencing instrument approach charts as a no-additional cost, routine capability, I'd say Garmin is just about done.Competition is good.
I have used the Bad Elf with my iPad for at least 4 months. I routinely use it with the Navionics and ForeFlight Apps. I've only had one issue with the connection (it was a little wobbly), but when I asked the folks at Bad Elf about it, they promptly replaced it! Since I use it with ForeFlight, I have the opportunity to check its accuracy with an FAA certified GPS.
I use the Bad Elf in my airplane to drive my navigation charts in geo sync mode. Plug it and it works..
This worked great on my iPad 1 and was used with Foreflight. Perfect for GPS navigation for the private pilot cross country flights.
If you have an iPad without a data plan (WiFi only), you will soon discover there is no GPS in the iPad itself. So, all of the cool navigation apps don't work or work very poorly. This fixes the problem. I used it on a cruise recently and had no problems tracking our location. It's simple to use and works very well.
This is a reliable GPS unit and I've used it quite often with my iPad. I am unable to use it with newer devices due to the connector change but can't fault the unit for that. Bad Elf has updated the firmware a few times and each time it seems to have gotten better.
The gps is exactly as described by most on this site. It plugs easily into the apple unit and gives you native gps. Not only that, it has its own battery for satellite memory; do not worry, this battery can be charged while the unit is being used and simultaneously charging the iPad/pod/phone unit. It is an excellent product. To raise this even more, the staff is helpful and patient and take the time to explain any problems you are having.
Answer: Hi Ester. That's the main reason I bought it. Wifi assisted gps on the ipad doesn't work in most places in our country and definately not off shore. This tiny little bad elf is brilliant. One thing you do need to be wary of though  ... make sure the gps remains firmly plugged in. I had someone on the helm for a while and she knocked the gps inadvertanly and went for half an hour not noticing that the arrow in the gps wasn't moving.