What it is
SeaVectors displays nearby AIS vessels as ranked targets with on‑map labels, computes each one's closest point of approach (CPA) and time to CPA (TCPA) against your own course and speed, and raises a flashing alert and escalating alarm when a target crosses your configurable safety thresholds. A color‑coded risk legend highlights developing situations.
Want to assess AIS targets and collision risk directly alongside your chart and route?
The 30-day free trial includes the complete experience, so you can evaluate SeaVectors with your own routes and equipment before deciding whether to subscribe.
- Download SeaVectors on the App Store
- Get SeaVectors on Google Play
- Not ready to install? Open the lightweight web chart for a quick preview.
Why it matters on the water
AIS turns "is that ship going to be a problem?" from a guess into a number. CPA tells you how close you'll pass; TCPA tells you when. SeaVectors ranks the targets so the one that matters is at the top of the list, and warns you before a close‑quarters situation develops — day, night, or in reduced visibility.
Before you start
- An AIS source feeding SeaVectors: an AIS transponder/receiver with WiFi (e.g. Vesper, em‑trak) or a gateway/MFD relaying AIS, connected per module 06.
- Your own GPS fix, COG, and SOG — the collision math needs your motion vector.
- AIS targets are shown from a moderate zoom in; zoom in to see labels and tap targets.
How to read AIS
On the chart
Each vessel appears as a target with a label. Tap a target to open its detail — identity (MMSI), range and bearing, CPA/TCPA, and relative speed.
The risk tiers (the legend)
Targets are assessed into three levels and color‑coded:
| Level | Meaning | Default trigger |
|---|---|---|
| Dangerous (red) | Converging inside your danger thresholds. | CPA < 0.1 nm and TCPA < 5 min |
| Caution (amber) | Converging, approaching the danger ring. | CPA < 2× danger (0.2 nm) and TCPA < 1.5× danger (7.5 min) |
| Clear | Diverging, passing wide, or effectively static. | everything else |
Targets are ranked dangerous first (soonest TCPA), then caution, then the rest by range — so the top of your AIS list is always the vessel that matters most.
CPA = the closest you and a target will get if neither of you changes course/speed. TCPA = how long until that closest moment. A short TCPA with a small CPA is the dangerous combination.
The alarm
When a target goes dangerous, SeaVectors raises a flashing alert on the chart and, if enabled, an escalating audible alarm. The AIS instrument widget also reflects the highest current risk.
Configure your thresholds
Tune AIS to your boat and waters (defaults in brackets):
| Setting | What it does | Default |
|---|---|---|
| Danger CPA | How close counts as dangerous. | 0.1 nm |
| Danger TCPA | How soon counts as dangerous. | 5 min |
| Max targets | How many targets to display/rank (0 = all). | 15 |
| Max range | Ignore targets beyond this distance (0 = no limit). | no limit |
| Flash on danger | Flash dangerous targets on the chart. | On |
| Sound alarm | Play the audible alarm on danger. | Off |
Open‑water passagemaking: widen CPA and lengthen TCPA so you get earlier warning. Tight, busy harbors: tighten CPA and shorten TCPA (and cap Max range) so you're not alarmed by every passing vessel.
Tips
- Turn the sound alarm on for passages, especially at night or solo — the flashing alert alone is easy to miss.
- If the list is noisy in a busy port, set a Max range and lower Max targets to focus on close vessels.
- Remember AIS only shows vessels that transmit AIS — keep a visual and radar watch for those that don't.
- Cross‑check a red target's CPA/TCPA, then make an early, obvious course change — don't wait for the alarm to escalate.
Troubleshooting
- No targets at all → No AIS source connected (module 06), or your source doesn't output AIS; confirm with the raw‑sentence line in NMEA settings.
- Targets but no CPA/TCPA → No own‑ship fix or you're stopped; the geometry needs your COG/SOG. Also shown as "clear" when tracks diverge.
- Too many alarms in port → Tighten Max range / Max targets, or adjust CPA/TCPA for close quarters.
- A ship I can see isn't shown → It may not transmit AIS, or it's beyond your Max range / target cap.
Safety note
AIS is an aid, not a substitute for a proper lookout, radar, or the collision‑avoidance rules (COLREGs). Not all vessels carry or transmit AIS.