As explained in the project details, there are three trackers on the boat. The RockBlock module which is connected to the Arduino-based controller is transmitting interesting data via the Iridium Short Burst Data service; such as the GPS position, the battery voltage, power consumption, temperature, wind speed, etc.In case the main hardware fails, there is another tracker called SPOT Trace that is transmitting only the current position via the Globalstar satellite network. It has an independent power source made of four NiMH AA batteries being recharged by two 6V / 50mA solar panels.
Because SPOT Trace may permanently turn off in case it loses power (for example, when the batteries completely discharge or when the connection breaks for a moment in rough ocean conditions), a timer 555 periodically sends short pulses to the SPOT Trace switch.
You need pretty good soldering skills to connect the wires to the switch. All soldered connections that may break off were potted with epoxy. Another great hack was to solder wires for an external battery source for two reasons – a larger battery capacity would provide enough power during a series of rainy days. Secondly, I wouldn't trust the micro USB connection.
For testing purposes, a vibration motor from a mobile phone was glued to the vibration sensor to ensure that SPOT Trace continuously reports position, even when it is not moving. It is not necessary for the ocean as the ocean waves are continuous and never stop. :)
The day before launch, I added a third tracker which is another SPOT Trace. However, it's powered only by non-rechargeable batteries. Based on the tracker power consumption when reporting position every hour, eight D cell alkaline batteries should last about two years.