I want to post a quick note on these tracking systems. After watching the various ships for a year (yes he is done) we realized that there are places around the world that they do not post the position on a regular bases. At first this was a little disconcerting when we lost track of the ship for a couple of days. Then it would show up near the next port. Our best guess is that there are places around the world where the shipping companies do not want the position posted. There is no sense giving the bad guys the latitude, longitude, speed and direction of the ship. We also found that one of the US coastal tankers did not report well.
I've often wondered why the shipping industry publically advertised the types of ships and their locations. In the continuing age of piracy I'm surprised. I'd almost rather not have it out on the net.
Just a quick little note on the way these tracking sites work...
SailWX bases its positions of ships on the weather reports sent from those ships at sea. This is public information that is published on NOAA's offshore weather maps. Every bit of information on that is recorded and sent in manually by someone onboard (usually the cadet, actually, if it needs to be sent during his watch). Weather observations are completely voluntary and if for whatever reason, the company or master doesn't want this information to be sent, it doesn't need to be. Since weather reports need not be sent when in port, or near land (even on coastal voyages - the idea is to get weather data on the high seas), these position updates will cease for a little while until the ship is at sea again. This is why your son/daughter's ship may "disappear" for awhile.
Marinetraffic.com is a network of AIS receivers positioned throughout different ports. AIS (Automatic Identification System) is basically a VHF-based transponder that all vessels of a certain size must have. It's a very powerful tool, whose primary shipboard use is for collision avoidance, but the technology has expanded to allow tracking of vessels in/near ports all over the world. The system requires no constant user input, except for certain data like the destination and ETA. Position, speed and course are provided by onboard GPS. Between ships, the data is (relatively) "instant", but if you notice on the website, each ship has a time-stamp, usually of a couple minutes or so. I imagine that the bandwidth required to have constant updating would slow the site significantly and increase costs. Since AIS is VHF based, the receivers used to feed the website can only "see" so far offshore until the signal is lost (generally 30-40 miles or so, depending on antenna heights). Just like the weather reports, transmission of your AIS signal can be disabled (receiver can stay on), if deemed necessary by the master.
In short, it's not so much that the companies are publicly allowing tracking of their vessels. What is happening is that a tool designed for safe shipping and navigation/collision avoidance is being "tapped into" and broadcast on the internet. There's really not much that can be done about it though, short of strict enforcement of disallowing these types of websites (which would never be legal/practical). Once the signal is out, it's up for grabs.
AIS technology is advancing every day and soon there will be satellite coverage which will allow reception of AIS signals anywhere on the planet, allowing companies to see (in "real time") where their vessels are.
IMO, the whole "terrorists might use AIS websites to plan attacks" thing is a little overblown. Shutting down the sites (like some people want to) would do little. AIS receivers are so cheap that anybody who wants to see what's in their area can do so for a few hundred bucks. The real protection has to come from the captain/crew to use discretion on when to disable AIS transmissions. When I was going through the Gulf of Aden a few years ago now, we were ready to do that, but never had to.