Diesel runaway
An engine that accelerates uncontrollably may be burning lubricating oil rather than metered fuel. The normal stop control may not work. Keep people away from rotating machinery and possible component failure. Use a purpose-built emergency air shut-off only if fitted and trained to do so. Never cover an intake with a hand. Prepare fire control and abandon the machinery space if unsafe.
Engine-room fire
Raise the alarm, stop engines and generators, close remote fuel shut-offs, stop ventilation if the fire plan requires it and deploy the fixed system as designed. Avoid opening the compartment and feeding the fire oxygen. Make a distress call when warranted and prepare survival equipment.
Major fuel leak
Stop the source if safe, close fuel valves, eliminate ignition sources, contain the spill and do not pump contaminated bilge water overboard. Notify the relevant authority when required.
Cooling hose or seacock failure
Stop the engine, close the seacock, use a soft plug or damage-control measure, pump the bilge and monitor the repair. A leaking through-hull is a flooding emergency, not merely an engine fault.
Seawater suspected inside a cylinder
Do not crank the engine. Cranking incompressible water can bend connecting rods. Close the relevant seawater path and obtain urgent model-specific assistance. Rapid preservation may reduce corrosion damage.
Loss of propulsion near danger
Shift from repair mode to seamanship early. Sail, anchor, warn traffic, call for assistance and put on lifejackets before the boat reaches a lee shore or confined water.