I use iNavx on an iPad 1 with the Bad Elf GPS add on.
I use the Scanstrut iPad case (Scanstrut iPad Case
) to make it waterproof and i can use it in the cockpit in the rain. Very accurate and the charts are free.
The iPad case also makes it non-skid and shock absorbing so I can leave it on the chart table and it wont slide off even with the rail in the water.