Engines and systems rarely fail without warning. Two minutes of checks each morning and an eye on the gauges prevent most breakdowns.
1 · Daily checks and starting
Before you turn the key
What should I check on a yacht's diesel engine every morning before starting it?
Check the oil with the engine stopped and the boat level (milky oil means water in it: do not start), coolant in the header tank, about 1 cm of give in the belt, raw-water seacock open, strainer clear, bilge dry, gear in neutral.
A diesel has no spark: it needs fuel, air and compression. Each morning check:
Oil, engine stopped, boat level. Milky oil means water in it: do not start.
Coolant in the header tank, engine cold.
The belt: about 1 cm of give under your thumb.
Raw-water seacock open, strainer clear, bilge dry, gear in neutral.
Preheat a cold engine for 10–15 seconds, start, and look for water at the exhaust at once. With the key at ON, the oil and charge lights and the buzzer are normal until she runs. Shift at idle, pausing in neutral. To stop, idle a few minutes first; never use the battery isolator.
2 · Cooling and alarms
Water at the exhaust, or stop
What do I do if little or no water comes out of my yacht's exhaust?
Stop the engine and let it cool: seawater is what carries the heat away. Check the strainer first, then the impeller for broken vanes, and never open a hot coolant cap.
Seawater carries the heat away: seacock, strainer, impeller pump, heat exchanger, then out with the exhaust. If little or none comes out, or the temperature alarm sounds, stop the engine and let it cool. Never open a hot coolant cap.
Look at the strainer first, then the impeller: find any broken vanes. A strong flow with the temperature still rising points to low coolant or a broken belt. If the engine will not fire, crank with the seacock closed, or water fills the exhaust and floods it; open it as soon as she runs.
Sign
Meaning
Oil pressure alarm
Stop at once, check the oil
Charge light on
Not charging: check the belt
Black smoke
Overloaded or short of air
Blue smoke
Burning oil
White smoke
Normal on a cold start
3 · Fuel
Clean, free of air, and enough
How do I bleed air out of a yacht's diesel after running out of fuel?
Bleed the system: open the bleed screw and work the lift-pump lever until fuel runs without bubbles. Air gets in when the tank runs dry, or when a low tank lets the pickup suck air under heel.
Fuel runs from the tank through the water separator, the lift pump and the fine filter to the injectors. Water sinks to the bottom of the separator bowl: drain it. Dirty fuel makes the engine surge and stop: drain the separator, change the filter.
After running dry, or when a low tank lets the pickup suck air under heel, bleed the system: open the bleed screw and work the lift-pump lever until fuel runs without bubbles.
Range is usable fuel divided by hourly burn, times speed; the burn is litres refilled divided by engine hours. Easing the revs stretches it. At the fuel berth check the cap says DIESEL, switch off engine and electrics, and fill slowly with a rag at the breather.
4 · Under power
Prop walk and the pivot point
Why does my yacht's stern swing sideways when I put the engine astern?
That is prop walk: in astern the propeller kicks the stern sideways before the boat moves, to port with a right-handed propeller. So berth port side-to, and turn short to starboard.
In astern the propeller kicks the stern sideways before the boat moves: prop walk, to port with a right-handed propeller. So berth port side-to, and turn short to starboard. With sternway on, the stern follows the wheel.
Going ahead she pivots a third of her length from the bow, and the stern swings wide. A catamaran spins on the spot: port engine ahead and starboard astern turn her to starboard.
Vibration and lost speed mean a fouled propeller: stop, and clear it with the key out. Milky saildrive oil, or seawater on its diaphragm: report it. If the wheel goes slack, fit the emergency tiller; press Standby to take over from the autopilot.
5 · Electrics
Two banks, read in volts
What voltage means my yacht's battery is full, and when should I charge it?
Read it at rest: 12.7 V is full, 12.2 V is half and needs charging, below 12.0 V is deeply discharged. Between 13.8 and 14.4 V it is charging normally.
A starter battery and a house bank: at anchor run everything from the house bank alone, and the engine will always start. A flat starter battery: parallel the banks, start, then separate them. Never open the isolator with the engine running: it destroys the alternator.
Volts
Meaning
12.7 at rest
Full
12.2 at rest
Half: charge
Below 12.0
Deeply discharged
13.8–14.4
Charging normally
Above 14.8
Overcharging: stop, ventilate
Budget in amp-hours, amps times hours, and use only half of a lead-acid bank. Watts divided by 12 give the amps an inverter draws.
Replace a fuse like for like. A breaker or shore-power RCD that trips again at once is protecting you: find the fault. Connect the shore cable to the boat first, the pedestal last. Run the engine when you use the windlass; breaker off before hands go near the chain.
6 · Water, heads and bilge
Every hull fitting has a seacock
Is a seacock open with the handle along the pipe or across it?
A seacock is open with the handle along the pipe and closed with it across. If a hose leaks, close it; if the fitting itself breaks, hammer in the softwood bung.
Fresh water: tank litres divided by the crew's daily use. A pump that runs on while the tap spits air has an empty tank; one that cuts in with every tap closed has a leak.
The heads take only what you have eaten and a little paper. In harbours and bays the Y-valve stays on the holding tank; empty it at a pump-out or well offshore, where rules allow. Close the heads seacocks at sea, or the bowl can siphon full when heeled.
A seacock is open with the handle along the pipe, closed across it. Leaking hose: close it. Broken fitting: hammer in the softwood bung. If the bilge pump keeps running, taste the water: fresh is a tank, salt is the sea.
7 · Gas and the outboard
Small systems, firm rules
In what order should I turn off the gas after cooking on a yacht?
Switch off the solenoid valve at the bottle first, let the flame die, then close the burner. Bottled gas is heavier than air, so the gas locker drains overboard and its drain must be clear.
Bottled gas is heavier than air, so its locker drains overboard and the drain must be clear. A solenoid valve at the bottle shuts the supply: after cooking switch it off first, let the flame die, then close the burner.
Outboard
Answer
Fuel
Four-stroke: plain petrol, no oil
Will not start
Kill cord on?
Cold
Choke out, in as it warms
No tell-tale water
Stop: no cooling
Runs, then dies
Open the tank vent
Practice questions
Questions from this topic, as the app asks them. Open one to see the answer.
Cold start
Air temperature 7 °C
Engine cranks well but does not catch
Puffs of white smoke at the exhaust
Early April in Croatia, you turn the key straight to start. What do you do differently?
Crank for a full minute without a break
Open the throttle fully and keep cranking
Spray easy-start into the air intake
Hold the preheat 10–15 seconds, then crank
Show the answer
D. Hold the preheat 10–15 seconds, then crank
Glow plugs heat the chambers so a cold diesel fires; ether with glow plugs can wreck the engine.
All 100 questions of this topic are in the app: practice by topic with the reason after every answer, your mistakes brought back, and a timed mock exam. Free, no sign-up, in the browser or in Telegram.
