The engine that drives your bareboat - be it outboard, gasoline inboard or diesel - is fundamentally like its counterpart in a motorcycle, car or truck. Indeed, the larger marine diesel versions of these automotive power plants are frequently built around the very same engine blocks. But the engine propelling your bareboat creates unique demands.

Boat engines are run at nearly full speed as much as 90 per cent of the time. This is because an engine produces its greatest power in the higher range of revolutions per minute, or rpm's - and far more power is needed to push your bareboat through water than would be needed to drive a car down the road at exactly the same speed. Moreover, the two-cycle design used in many outboard engines operates most efficiently in that higher range of rpm's.

To cope with the strains of running full blast for hours, boat engines are made with many heavy parts, and this added burden means that the power plants of your bareboat are more than ever dependent on dirt-free fuel lines and a plentiful supply of cooling water. Therefore, the routine checking of fuel and oil filters, although important in a car, becomes an essential step in preventing serious damage to the engine of your bareboat.

Marine diesel engines, moreover, are constantly being knocked about as a boat slams into a wake or bounces over wind-driven chop - and motion and vibration take their toll. The buffeting that a marine diesel power plant sustains can knock finely tuned parts out of adjustment, back off important nuts and bolts, and snap fuel lines. Because your bareboat engines have this tendency to take themselves apart, a large portion of your bareboat operators preventive maintenance consists of nothing more than on occasional trip around the engine with a screwdriver and a wrench, trying connections, and tightening things up before some crucial part is lost in the bilge or damaged.

Your dependable marine diesel engines

Most bareboats are fitted with long running and reliable marine diesel engines. While these engines are fitted with the usual operational safety features and safeguards, it will still require you to take care of them, to ensure reliable performance during motor yacht charters and sailing yacht charters.

Marine diesel engines are heavier than petrol engines and produce less horsepower in relation to weight. However, they do have some very important advantages... there is no electric spark required to fire a diesel engine, as it relies on very high compression of the fuel to attain combustion...also diesel fuel does not have the same explosive potential as petrol and is very much safer to use.

Before starting your marine diesel

1. Check engine oil and transmission oil levels. This check must be carried out first thing every morning, before you start engines and while the engines are cold. The location of these check points will be shown to you during your bareboat briefing. Only top up the engine oil if the level is below the minimum level mark... never over fill the oil as this can damage the seals in the motor.
   
   Under normal operating conditions the engine and transmission oil should not require replenishment during a bareboat yacht charter... Should unusually heavy oil usage or loss occur, advise your bareboat charter operator by radio. Do not start or run the engine if obvious, abnormal oil consumption becomes apparent.
   
   
2. Check the fresh water system. The fresh water system is filled through the cap on top of the expansion tank... generally located at the front of your diesel engine. You need to maintain this level to within ½ inch (10mm) below the top of the expansion tank. This tank and filling point will be pointed out during your bareboat briefing.
   
   
3. Tie the tender up short - make certain there is no loose rope in the water that could foul the propeller.

To start marine diesel engines

Before starting ventilate the engine space... Explosive fumes from all sorts of sources can collect in the bilge of a bareboat. Make sure that the area around the engine (which can get hot and often has sparks involved) is ventilated before starting...If your bareboat has a blower, (a fan in the engine compartment) run it for five minutes and make sure that the cabin of the boat has been open for awhile, then check below for any gas or fuel smells before starting the engine.

To rid the bilge of any dangerous fumes, an electric bilge blower - placed close to the engine compartment's exhaust vent - should be operated for five minutes before starting up the engine and for a similar period after refueling.

Procedure on starting a marine diesel

1. Gears in neutral
2. Throttle lever back
3. Turn on ignition key
4. Press - on starting button, until engine fires - release button.
5. Set throttle lever to warm-up (idling speed) at 700-800 rpm
6. Warm engine to 170 degrees fahrenheit (76° celsius) before load is applied.

Once your engine starts, look for water: Most inboard diesel engines have water-coolant and exhaust exit holes or pipes visible from on deck... These are often in the transom. When you start the engine, confirm that water is coming out of the exhaust (usually a slow, pulsing flow) - this means the cooling system is working properly.

When manoeuvring, never go from forward to astern or "vice-versa" without pausing in neutral for a second of two. Changing gear straight through the box while your engine is running above idle speed can damage the gearbox.

If your engine is showing a high operating temperature you know you have a cooling system problem (often a plastic bag can be sucked into the intake)... If the temperature gauge is telling you there could be a problem avoid operating your engine at maximum throttle - doing so may cause overheating and you will have to stop the engine.

Watch the tachometer if you have one, and keep the rpm's below the engine's safe operating speed, until you determine the cause. If you have twin marine diesel engines shut down the problem engine.

Procedure to stop

1. Throttle levers right back
2. Gears in neutral
3. Idle engines for 2-3 minutes allowing the engines to start cooling.
4. Depress stop buttons and hold until engines stop, and buzzer sounds.
5. Turn off ignition keys -buzzer stops.

Overheating

Marine diesel engines are usually cooled by sea water... A pump (generally) mounted at the front of your engine, pumps seawater through the engine manifold, etc. A marine diesel does not run for long if this process is interrupted in any way. The most common problem encountered, when an "overheating" signal is detected is failure of the engine seawater pump impeller or blocked water intake. An impeller is easy to replace and spare impellers are kept on-board charter boats.

The first warning of your marine diesel overheating will be the engine alarm sounding or the needle on the temperature gauge rises. You will have already heard this alarm, when starting and stopping the engine. At the time of your bareboat briefing you will be shown that this alarm is in satisfactory working order.

If you hear the alarm, and it is safe to do so, immediately switch off the engine and investigate. The consequence of a badly overheated marine diesel engine is at best a blown head and more commonly a cracked head...both expensive.

Damage to a marine diesel engine through overheating is almost always a result of operating negligence.

Engine instruments

1. Revolution Counter - RPM. This allows you to select the speed or RPM (revolutions per minute) your engines will run.
   
   At your bareboat briefing you will be advised of the correct RPM for your boat, do not exceed these RPM during bareboat charters... Running your engine over the recommended RPM is not efficient and your engine will not burn off the increased fuel intake. This means you'll be exhausting unburned fuel at increased diesel costs, with little or no improvement in speed.
   
   This revolution counter also generally includes an hour meter which tells you how long your engine has run... These hours are noted at the beginning and end of each charter as 'used' engine hours determine the maintenance checks and services required.
   
   
2. Oil Pressure Gauge. If either gauge is not registering, or only showing very low pressure... notify your charter company.
   
   
3. Water Temperature. With engines operating at a normal cruise speed (RPM) your water temperature gauge should read approximately 180-190 F° (82 - 88 C°) (or as advised at your bareboat briefing).
   
   At temperatures over this start to pay careful and continual attention to your instruments and bring your engine speeds back.
   
   Once the temperature of either engine gauge goes over the designed running temperature you should hear the warning buzzer sound...If safe to do so, shut down your engine immediately... notify your bareboat charter company.
   
   
4. Ammeter. This tells you the rate of charge going into your battery banks...if any ammeter is not charging, notify your charter company.
   
   
5. Fuel Gauge. Your fuel gauge should accurately reflect the overall fuel position - at the start of each charter your fuel tank/s will be full - and will be refilled on completion of your charter.

The sturdy marine diesel

Diesel marine engines have a well-earned reputation for running smoothly with less care than other types of power plants. There are two reasons. Most marine diesels are built to heavy-duty specifications that help to ensure their durability; typically, a 50-horsepower diesel like the one below will run four times longer between major overhauls than a gasoline engine of equivalent power. In addition, a diesel engine is designed to operate without either a carburetor or an electrical ignition system. Consequently, it has fewer parts to wear out or break down.

Taking the place of a carburetor is a device called a fuel injector, which sprays precisely measured charges of vaporized fuel oil into each cylinder through a fine-gauged nozzle. The fuel vapour enters the cylinder just as the piston reaches the top of its stroke, compressing the air inside. This compression, which may reach as high as 500 pounds per square inch, raises the air temperature in the cylinder to about 1,000 F - well above the flash point of the fuel. Thus no electric spark is needed to ignite it

Despite it's rugged construction, the diesel is not entirely maintenance-free...your charter boat operator will see that crankcase oil is changed at regular intervals, as prescribed in the engine manual. Drive belts for the alternator and water pump will be checked for wear and proper tension following the procedure shown in the diagram... Adjusting Belts below.

The cooling system must be kept brimming with fresh water. In addition, the fuel system (outlined in blue, below) must be serviced periodically. Otherwise, specks of dirt and sediment in the diesel oil may clog the narrow channels in the fuel injector and nozzles.

To guard against clogging, a set of primary and secondary filters in the fuel lines trap minute dirt particles. The primary filter also removes water droplets suspended in the fuel - the result of moisture condensing inside the fuel tanks. This water accumulates in the bottom of the filter housing, which should be drained regularly during periods of normal engine use. In addition, after every 200 hours of operation, the filtering elements in both the primary and secondary filters should be replaced and the fuel pump cleaned.

In marine diesel engines, the fuel system (blue) and the primary filter (bottom left) extracts the condensed moisture and some dirt from the fuel.

A pump then drives the fuel through a secondary filter that removes any remaining dirt particles, and pushes it on to the fuel injector.

The cleansed fuel is led through the injection pump, which channels it in carefully timed, measure doses to the injector nozzles. The fuel injector's overflow line carries excess back to the tank.

Adjusting belts
Belts running off the drive shaft power the cooling and electrical systems. If the belts are too loose, the system will not work efficiently; if too tight, they will wear out, crippling the engine. Ideally, a belt should have from one quarter to one half an inch of play (dotted line) when pressed firmly with a thumb at the midpoint between the pulleys. This thumb test should be performed after every 50 hours of engine use, and the belt adjusted to the correct tension... shown at right.

If the electrical system's belt is slack, it should be tightened by moving the alternator along the slot in the mounting bracket. Loosen the mounting nut with a wrench and then take up the slack in the belt by prying the alternator away from the engine with a long sturdy tool, such as the wrench shown here. Secure the mounting screw and test the tension again to be sure that the adjustment is adequate.

The sea-water pump can be moved in the same way to adjust its belt.