There is a free app called OVITALMAP (it runs on several devices including the iPad) that we found very useful when close to any land. It uses Google images
and you need to zoom in to any area that you may be interested in while you have cell or wifi
connection. The app then saves those images
and you can use it while offline to navigate. You can turn on tracking and it saves the tracks for you.
We have used this app while navigating in areas where the charts
are bad and are able to zoom in and see the passages thru very shallow water
. On several occasions we used the app in conjunction with Inavx
charts and the charts showed us ON LAND but ovitalmap images showed our track within the gps
accuracy of the ipad that we used. We use the Inavx
on the iPad for planning and general navigation but when we get close to anything we turn on ovitalmap and can see with better confidence. We have used the saved tracks to follow thru very narrow twisty paths thru reefs
in less than ideal conditions knowing that we had previously been safe in that area.
There is a small upgrade fee that allows more track saving space but I don't remember the coast.