Following feedback from VirCru users about the Geofence system we made some improvements. This is an explanation of how the system now works.

How It Works

The VirCru Hub has an integrated GPS receiver that provides a position fix once per second. Low power consumption is at the core of the VirCru system so to avoid the GPS using too much power we have a set of rules which dictate how the GPS receiver is used under different circumstances:

No External Power – VirCru Hub running from internal backup batteries

The GPS receiver is powered up for a few seconds every five minutes to get a position fix.

External Power Connected but not Charging

The GPS receiver is powered up for a few seconds every two minutes to get a position fix.

External Power Connected and Charging

The GPS receiver is powered up permanently

Whilst the GPS receiver returns a position fix within a few seconds of being turned on (called a hot start) this fix tends to be quite noisy/varied. Typically if the GPS receiver is powered up all of the time we get positional errors of up to 10m but if we are relying on a hot start to get a quick position fix to save power, we get errors of up to 70m. The GPS receiver needs to be powered up for a few minutes before these errors reduce and the position fix stabilises. These figures also assume that the hub is installed sensibly with nothing more than a bit of fibreglass, glass, wood or plastic between it and the sky.

In an effort to reduce the likelihood of false triggers from the geofence system, we previously limited the geofence radius to over 100m.

The Concerns

100m is a long way when your boat is at anchor. If being used for anchor drag detection, 100m could easily leave you stuck on a lee shore or allow your boat to collide with your neighbour before it alerts you.

The solution

We have now changed the VirCru system to allow the geofence radius to be set as low as 10m. If the radius is set below 100m, the VirCru Hub will keep the GPS receiver powered up permanently while the geofence is enabled regardless of the power supply. This will increase power consumption by a small amount (somewhere in the region of 0.3Ah per day), even in this setting even a modest domestic battery on a boat should last months. The app will warn you of this increased power consumption when you set the radius below 100m. Additionally, it will warn that ‘False alarms are likely when set below 30m’. The increased power consumption will only impact boats whose batteries are not being charged at the time (by shore power, wind, solar, alternator etc.) as the GPS receiver is permanently powered up when charging.

Timescale

This was implemented in the App update (Ver 1.5 9th May 2023).