I have just come across a AIS app for both Android and iPhone. There are several similar apps around that pick up the location of shipping, which we have used before when on a charter. Fog descended on the approach to Cowes and a combination of the Navionics mapping app and an AIS app not only showed us the way in bit also emerging ferries and other shipping. ( The yachts own nav system was not so hot...).
This new app called Boat Beacon, shows the position of other vessels as you'd expect but also act as an AIS transmitter for your own position. It means you must turn it off when travelling back home up the motorway otherwise some strange positions will be reported.......
Very useful for poor condition or on a night passage.
You can also add data about your vessel such as type, Sail. Motor etc., length, MMSI details and more.
I will give it a good this season - at £6.00 it's worth a trial.