Short answer
Keep control of the boat first. Identify which alarm is sounding, reduce load, and check gauges and exhaust-water flow. Stop the engine when the alarm indicates oil pressure or overheating and stopping is safe. Sail, anchor or call for assistance early rather than late, and record the readings.
You will need: Knowledge of your alarm panel, a written card at the helm
An alarm at sea is a seamanship problem before it is a mechanical one. The order below is deliberate.
The sequence
- Maintain control of the boat. Sea room, traffic, depth and crew come before the engine.
- Identify the alarm. Oil pressure, coolant temperature, charging and exhaust alarms mean different things and carry different urgency.
- Reduce load. Coming off the throttle buys time in most fault modes.
- Check gauges and exhaust-water flow. These confirm or contradict the alarm.
- Stop when required and safe. Low oil pressure and overheating both justify shutdown; judging when it is safe to lose propulsion is yours to make.
- Get help early. Sailing, anchoring or calling for assistance is much easier before the situation develops.
- Record readings and conditions while they are fresh. It shortens the diagnosis enormously.
- Do not restart until you understand the cause.
Prepare before you need it
Write the alarm meanings for your specific panel on a card at the helm, and make sure everyone who runs the boat knows which seacock feeds the engine and where the fuel valve is. Test the alarm self-check as part of pre-start checks.
The genuine emergencies
Runaway, engine-room fire and water ingress have their own procedures and are not situations to improvise. Read marine engine emergencies before you leave the dock, not after.