Because our Tracking Devices end up in boats they can spend long times away out of coverage, unlike their vehicle mounted cousins We have given considerable thought to this and all our units will store your location when they cannot send it back to the server.
What this means is on a crossing from say Plymouth to France there would be a short area of no coverage. What someone watching would see is the vessel going out into the channel and then at some-point it would stop reporting and remain stationery on the map. As soon as it picked up a cell-site on the other side, it would fill in the gaps and continue reporting. This would show in the reports just the same as if it had not been delayed and so you would still have the complete route and the true times at each point.
Another difference between our boats and cars is change of direction vehicle trackers tend to report in every X seconds when moving and every Y seconds when not (X is usually 2-5 Mins and Y 30-120 Mins). Our devices are programmed in the same way but we add another dimension 'Direction', we can configure the unit to send an extra fix if the boat changes direction (Tacking) by more than 35, or 90 degrees. We can even configure them to update based on distance travelled (ideal for slow moving boats).
Of course there is a lot more features geared toward use with vessels, but all you really need to know is we are the boat specialists!