Why Shelly on a Boat?
Shelly makes compact smart relays and sensors that can work locally with Home Assistant. Some models can be useful aboard, but their power supplies and switching ratings differ. A DC-capable relay contact does not mean the device itself can be powered by a boat battery.
We run multiple Shelly devices aboard our sailboat. They control lights, monitor temperatures, and automate systems that used to require manual switches or expensive marine-specific controllers.
The Key Models for Marine Use
Choose a DC-powered model—not the Mini
The full-size Shelly 1 Gen4 accepts stabilized 12V DC or 24–48V DC power. Its DC switching limit is 10A at up to 30V. Those are different ratings: a 48V supply rating does not make it suitable for switching a 48V load.
Potential uses for a correctly selected, installed and protected relay include cabin lighting and non-critical controls. Our experience is with Shelly automation aboard; it is not a claim that we tested every current model.
- Control cabin lighting from a dashboard
- Retain local physical operation with the correct switch configuration
- Monitor activity without depending on a cloud service
Keep independent manual control for safety-critical equipment. A physical switch input is not a bypass around failed relay hardware.
Shelly H&T Gen3
Temperature and humidity sensor with an e-ink display. Battery powered, reports over Wi-Fi. We have these in the engine room, the lazarette, and the main cabin. The engine room sensor triggers a Home Assistant alert if temperature exceeds a threshold — critical for catching overheating before it becomes an emergency.
Shelly Plus Plug S
For plug-in shore-power monitoring, choose a smart plug rated for your country’s voltage, socket and load. Do not assume a European Plug S suits a US outlet, or that a plug-in relay can safely handle a water heater, air conditioner or charger.
The 12V DC Question
Correction: Shelly 1 Mini Gen3 and Gen4 are AC-powered devices, not native 12V relays. The full-size Shelly 1 Gen4 is a different product. Its 12V input requires stabilized power; a nominal 12V boat circuit changes voltage while charging.
Check the exact Shelly 1 Gen4 manual for power, terminals, contact ratings and installation conditions. Use appropriate supply regulation, circuit protection and enclosure; do not copy a wiring diagram from another Shelly generation.
Connecting to Home Assistant
Shelly devices connect to Home Assistant via the native Shelly integration — no MQTT configuration needed. Once they are on your boat's Wi-Fi network, Home Assistant auto-discovers them.
From there, you can:
- Build dashboards showing all your boat systems in one place
- Create automations (lights on at sunset, fans on above 80°F, bilge pump alerts)
- Log historical data — temperature trends, power consumption, switch activity
- Set up notifications via phone, email, or Telegram when something goes wrong
We run Home Assistant on a Raspberry Pi 4 with a Zigbee coordinator for additional sensors. The Pi draws about 3W — negligible on a boat power budget.
Reliability at Sea
The biggest concern with smart home devices on a boat is reliability. If your Wi-Fi router reboots, will your lights stop working?
A properly configured physical switch can still command a powered relay without Wi-Fi. That does not protect against loss of power or a failed relay. We have had good service from our Shelly devices aboard, but they are not a substitute for independent controls on essential equipment.
What It Costs
Price the complete installation: relay, any required stabilized power supply, protection and enclosure. Comparing the bare price of an AC Mini relay with a marine controller is not a like-for-like comparison.
The Bottom Line
Shelly plus Home Assistant can be useful and economical aboard when the exact hardware fits the circuit. Start with a non-critical application, verify the ratings and retain local control. Buy for compatibility first, not the smallest case or lowest price.
Related Articles
- Home Assistant + Shelly on 12V DC
- Best Marine Battery Monitor: Victron SmartShunt 500A
- AI Tools for Marine Navigation
The Shellys are the muscle; Home Assistant is the brain. If you haven't set that up yet, our Home Assistant setup guide for boats and RVs takes you from blank SD card to your first useful automation.
Choose compatible hardware
Confirm the power supply and load ratings before ordering. These are current hardware options, not a claim that every model was tested aboard.
