The best sailing app that I have on my iPhone is MotionX-GPS. It's only $0.99 for iPhone and $1.99 for iPad. I have so much fun with this app. At the start of a sail I can set it to track my path and when I'm done my sail I can view this track and if I choose share it on Facebook, Twitter or email.
I have one Facebook friend that always makes comments like "At what point did you decide to let a monkey take the helm?" or "go home Daryl you're drunk!"
You can view multiple tracks at once. These are 18 tracks from this summer's sailing. Pelican Lake where I sail is about 1 1/2 miles wide by 14 miles long with the marina at the north west end of the lake.
When I zoom in on these multiple tracks it's obvious how many short sails that I make close to the marina! I will often drive an hour to the lake to sail in the evening. Our wind almost always drops off to nothing at some point later in the evening. I don't want to motor very far to get back to the club.
MotionX also produces a .kmz file that can be opened in Google Earth.
You can set your speed and distance units to kilometers, miles, nautical miles or even feet and yards (for hiking or biking). Voice coaching can be turned on or off and set at different time intervals to tell you your speed, distance and elapsed time and other functions. If you're playing music through your device it can be set to pause when voice coaching is talking.
A lot of information is available when on route
or when looking at the details of your track.
You can mark waypoints or set them ahead of time by using Latitude Longitude co-ordinates. I set this waypoint by getting the co-ordinates from Google Earth for a spot where we had stopped for a beach picnic and spotted Golden Eagles.
I have navigated to a waypoint watching my sailboat track in real time along my route when it was getting dark and I could no longer see landmarks.
Any of the sailors that I know that use MotionX absolutely love it. One friend that I recommended MotionX to actually thanks me every time that we meet on the water.