AIS transponder basics for cruising yachts

Overview

AIS (Automatic Identification System) broadcasts your position, course, and identity to other vessels and shore stations. Most cruising yachts use Class B — lower power than commercial Class A but sufficient for coastal and Baltic traffic.

What you transmit

Data	Use
MMSI	Unique radio identity — register with flag state
Position / COG / SOG	Shown on other AIS displays and some chartplotters
Vessel name	Must match registration where possible

Installation notes

• Antenna — dedicated VHF-style antenna or splitter with low-loss filter; splitters reduce range
• GPS input — internal or NMEA feed; wrong GPS = wrong AIS plot
• Silent mode — some units support transmit off in sensitive areas — know local rules

AIS does not replace radar or visual watch — small craft and fishing buoys may not appear.

Pair with marine VHF and Baltic weather.