SeaTalk Standards Overview

Overview

• SeaTalk is a proprietary 1-wire serial protocol developed by Raymarine (originally Autohelm) for interconnecting marine instruments and autopilots
• All devices on the bus can both transmit and receive — a true multi-master network
• Connects chartplotters, autopilots, depth sounders, wind instruments, GPS units, compasses, and more over a single 3-wire bus
• Three versions: SeaTalk1 (original), SeaTalkNG (modern), and SeaTalk2 (a video/display bus, not a general instrument network)

SeaTalk1 — Physical Layer

• 3-wire bus: Red (+12V power), Yellow (data), Shield/Bare (ground)
• Daisy-chain or spur topology; devices can be tapped at any point on the bus
• No terminators required
• Spur runs up to ~6 m; longer runs possible on the backbone
• Power and data share the same cable — easy to install but vulnerable to voltage drop on long runs

SeaTalk1 — Electrical & Data Characteristics

• Data line idles at +12V; logic is inverted relative to RS-232 (a "1" bit pulls the line low)
• Speed: 4,800 baud
• Collision detection built in — a device monitors what it sends and backs off if it detects corruption
• Message structure: command byte (with a 9th bit marking message start) + attribute byte + 0–8 data bytes

SeaTalk1 — Common Data Types

• Depth below transducer (feet, meters, or fathoms)
• Boat speed through water (from paddlewheel/impeller)
• Apparent and true wind angle & speed (from masthead unit)
• GPS position (lat/lon), heading (fluxgate compass), water temperature
• Autopilot status, course, mode, and alarms
• Trip and total log distance

SeaTalk1 — Wiring & Practical Notes

• Power can be injected anywhere on the bus
• Voltage drop on long runs can cause instruments to reset or behave erratically — keep runs reasonable
• The bus is not electrically isolated; a fault on one device can affect others
• Avoid ground loops; corrosion in connectors is a common cause of intermittent data loss
• Label wires carefully — looks simple but gets confusing in real installs

SeaTalkNG (Next Generation)

• Modern Raymarine network based on NMEA 2000 / CAN bus — electrically and logically compatible with NMEA 2000
• Backbone + drop cable architecture with T-connectors; terminators required at both ends
• Powered network (12V on backbone); plug-and-play proprietary 5-pin connectors
• Much higher data rates and support for more complex devices than SeaTalk1
• Raymarine sells SeaTalk1 –▶︎ SeaTalkNG gateway adapters for backward compatibility

SeaTalk2

• A video/control bus for Raymarine display heads — not a general instrument network
• Not used for instrument data; rarely encountered outside Raymarine display installations

Compatibility & Bridging

• SeaTalk1 ↔ SeaTalkNG: Raymarine gateway adapter required
• SeaTalkNG ↔ NMEA 2000: adapter cable required (same protocol, different connectors)
• SeaTalk1 ↔ NMEA 0183: converter required (eg, Actisense USG-2, NASA SeaTalk converter); translates to standard sentences such as $IIDBT (depth) and $IIMWV (wind)
• Software bridges: open-source tools such as SignalK or OpenSkipper can decode SeaTalk1 via a simple RS-232 interface and resistor voltage divider
• Avoid mixing standards without proper interface boxes

Common Problems

• Voltage drop –▶︎ instruments reset or behave erratically
• Corrosion in connectors –▶︎ intermittent data loss
• Mixed systems (SeaTalk + NMEA 0183) without proper converters –▶︎ no data sharing
• Incorrect grounding –▶︎ noise or data errors

Quick Comparison

• SeaTalk1: 3-wire shared bus, 4,800 baud, multi-master, proprietary, simple — still on millions of older boats
• SeaTalkNG: backbone + drops, CAN bus, high speed, NMEA 2000-compatible with adapter
• SeaTalk2: video/display bus only — not an instrument network
• If your SeaTalk1 system is working, maintain it; if upgrading, go to SeaTalkNG or NMEA 2000