Over the Horizon AIS suddenly stopped or targets disappeared
Most likely, your chart plotter is filtering out far-range targets it determines as unimportant or of lesser importance when overwhelmed by targets to avoid CPU or display overload. Raymarine and many other chartplotters apply automatic filters after a few minutes after the initial target load.
Older chartplotters may struggle to load and track hundreds of AIS targets because they were designed to expect this volume, e.g. we received a report of a Furuno MFD that could not display more than 100 AIS targets. Garmin devices and the Navionics App have also been reported to display only up to 75 miles of AIS targets.
If you restart your Chartplotter and don't see any Over the Horizon targets load again after 5-10 minutes, please check the following:
Your GPS Status is Active, i.e. the DataHub GPS is connected, or your boat GPS is powered on to provide a location.
Did you change your PredictWind Forecast Account password? If you recently updated your password, please update it in the DataHub, then Save & Apply.
In the NMEA menu, please click the top menu Syslog tab. If the AIS Target refresh shows the status: "Success", it is working. Check the number of vessels downloaded, as this will indicate how many targets the DataHub is receiving before filtering to publish the unique targets only onto the N2K network.
If you see many vessels in the feed (hundreds+), try reducing the Target Age from 45m to 5 or 10m and reducing your Range to 25 miles or less. Next, please turn off your Chartplotter, wait around 5 minutes and turn it on again.
Duplicate VHF and Over the Horizon AIS Targets appear on my chartplotter or App
The DataHub filters out targets published by a VHF AIS transponder onto the N2K network already and does not publish them again with Over the Horizon targets reported. If you have connected your VHF AIS directly to your chartplotter or laptop App, and added the NMEA2000 or 0183 feed from the DataHub, duplicates will appear because the sources independently provide the same information.
If you have connected your VHF AIS to the NMEA2000 network and are still seeing duplicates, please check it outputs AIS targets onto the network, as some AIS transponders only send/recieve GPS position via N2K. Please also allow time for the DataHub exclusion filtering list to build up and for any duplicate targets appearing on your chartplotter to expire.
To resolve this issue, power off the AIS transponder, chartplotter and DataHub and close any App you are using. Then please:
Power on the AIS transponder and allow 5-10 minutes to acquire all local targets.
Power on the DataHub and wait 10-15 minutes for it to boot up, connect, download Over the Horizon AIS and build an exclusion list from targets on the N2K network.
After 10-15 minutes, power on your Chartplotter.
This ensures the Chartplotter's initial data load is only VHF AIS targets and Over the Horizon targets, excluding those the DataHub has filtered out. If you continue to experience duplicates after this restart process, please contact support, including details of all your devices, their model numbers and how they are connected.
I do not see VHF AIS targets on my chartplotter when I enable Over the Horizon AIS, I only see Over the Horizon targets
The DataHub downloads the OHA targets for your set radius area. It then looks at the active VHF AIS targets on the NMEA2000 (N2K) network and filters them out from the downloaded targets. The remaining downloaded targets are pushed onto the N2K network so the chart plotter can see both sets at the same time, VHF AIS targets and the filtered OHA targets.
It can happen that your chartplotter caches the DataHub call sign for a VHF AIS target even though the actual target being displayed is from VHF AIS. To understand why this might appear to be happening, it can be helpful to know the following:
There are two types of AIS targets:
Class A AIS is required for commercial cargo vessels larger than 500 tons, fishing vessels over 65 feet and all passenger vessels, regardless of size. Class A transmits with 12.5 watts of power with a typical range of 10-20 miles line of sight.
Class B AIS is intended for recreational vessels and is not legally required. Class B transmits with 2-5 watts of power with a typical range of 2-5 miles line of sight.
AIS position data is transmitted from vessels at a variety of rates:
Class A AIS send position updates every 2 - 10 seconds when moving faster than 3 knots, depending on their speed and rate of turn. When moving less than 3 knots, at anchor or moored, updates are sent every 3 minutes.
Class B AIS send position reports every 5 - 30 seconds when moving faster than 2 knots. When moving less than 2 knots, at anchor or moored, updates are sent every 3 minutes.
Vessel static information (the pop-up box with boat information) that doesn't change frequently, such as the vessel's name, call sign, size and voyage information, is sent every 6 minutes for both Class A and B vessels.
In the N2K data stream pushed by the DataHub:
The time to live in the DataHub filtered targets list for VHF AIS targets is 2 minutes. This ensures a smooth transition as vessels move out of VHF AIS range and into OHA.
Anchored vessels or vessels moving less than 3kt transmit every 3 minutes, so for these vessels, the DataHub will publish the target as an OHA target because the update frequency is longer than 2 minutes. This means in the pop-up box, they’ll look like a DataHub target even if they’re within VHF AIS range.
This is not an issue for the position of moving vessels because the update time is 2-30 seconds; however, for the pop-up box, because this is updated every six minutes, you may still see call sign as 'DataHub', even though the position information is being supplied and updated by VHF AIS every 2-30 seconds.
If you’d prefer not to see the DataHub call sign for OHA targets, uncheck the NMEA > Internet AIS > Mark AIS option and click Save & Apply.
My vessel appears as a ghost AIS target ~20m behind me. This is setting off proximity alerts, why?
We have received reports of some AIS transponders, notably Vesper, experiencing this. The AIS transponder does not publish an AIS target of your vessel into the N2K network, so the DataHub cannot filter it out before publishing Over the Horizon targets.
Please contact Support with your VHF AIS transponder model, MMSI and DataHub Serial number, which can be found under Services->Tracking. We can provide you with a unique key and steps to activate a fix for this.
My RayMarine Chartplotter displays AIS Target names with diamond question marks
We have received reports of Raymarine Axiom series Chartplotters displaying diamond-shaped question marks at the end of the target name. A fix was released in DataHub Firmware version 4.06. Update the DataHub Firmware to resolve this issue.
Over the Horizon AIS Time Zero does not show vessel dimensions
Over the Horizon AIS works with Time Zero however, you may find that vessel dimensions do not display for AIS targets in the App. PredictWind endeavoured to resolve this issue; however, it is not something we are pursuing further now. To avoid this limitation, please try Navionics, OpenCPN or AquaMaps.