[CliffordK (OP)]

It sounds like the individual container tracking is much easier to do when the containers are loaded onto a train than when in the bottom of a hull deep within a cargo ship.

If one can't really track the individual containers, then the system is not much better than using bar codes.

Would a local ship-board repeater help?

[graham.d]

A repeater would not help as it would still need to communicate with each container. This would be no easier than the satellite doing it. Ships themselves can be tracked though as well as any containers at the top of the stacks, so if the software is clever enough, it would know that these containers were on the same boat. I guess that the system only has to know the last position before it goes out of communication. If that position is on a boat or in a stack somewhere, that is good enough. It is probably more important to note if a container is somewhere it should not be i.e. misplaced or being stolen.

[imatfaal]

Some container vessels will provide power for chilling to containers (really not sure if the big ones can do this) - if they did that they could link up individuals to main GPS beacon; but that sounds highly unlikely. 

[graham.d]

GPS satellites are transmit only and there is no reason for the containers to know where they are if they can't tell the LEO satellite network where they are. In theory the containers could be connected to some master system but I don't think they are; they all just operate independently. All that is needed is for the system to know they are on the boat and then for the system to know where the boat is.  The containers don't have to communicate at all once aboard (even if they try to). I think this is how it works however I don't know much about the system software from my limited perspective.

http://www.satmagazine.com/cgi-bin/display_article.cgi?number=27078890

[CliffordK (OP)]

Periodically containers do wash overboard.  Although, I presume those are most likely those on top of the stack, revealing the next lower conex boxes that would suddenly show up on the net.

Assuming there is adequate power for the system, it would be easy enough to make a local ad-hoc network with each container communicating with other local containers.  Then you could, in fact, transmit reefer unit info to the bridge, as well as the company.

I suppose I would be leery of a system that would just assume there would be 100% tracking of containers as they are loaded onto a ship.  So, if a crane is moving a stack of a half dozen conex boxes, the bottom one would get not get missed.  And, there is never  a momentary system hiccup in which data isn't collected. 

As mentioned, if it is merely knowing when a conex box is loaded and unloaded, then one could simply track the boxes with bar codes and bar code readers that the transfer equipment would periodically pass.

[graham.d]

The idea is to track the containers on road, rail, sea, stored or stolen. Obviously the company who own the satellites are trying to sell this service which may or may not be flawed in some ways. There has been a fair investment in the concept so far though.