boat motor

How does a boat engine work



The pollutant development of internal combustion engines is determined by the correct air-fuel mixture setting and in two-stroke engines by the correct mixture ratio (fuel / oil)
decreased. Water, fuel, air and gas ensure the safe operation of an internal combustion engine
Oil filter.
As boat engines come after the type of fuel
Gasoline and diesel engines and according to the working procedure
Two and four stroke engines in question.
In addition, the boat engines can be divided into inboard and outboard


In the case of a gasoline engine, a gasoline-air mixture is created in the carburettor outside the combustion chamber
manufactured. This mixture is sucked in, compressed and passed through the spark plug for combustion

The gasoline-air mixture poses a risk of explosion and fire in the ship,
the ignition system is sensitive to moisture and wetness (engine stops),
high fuel consumption.

High performance with low weight


In a diesel engine, air is sucked in and heated up considerably. Diesel oil is injected into this hot air.
The diesel oil ignites in the combustion chamber and drives the piston.

Great weight, soot development

Explosion-proof, low fuel consumption, no ignition system, low-maintenance, long service life


So that the engine does not run hot, it must be cooled. Two common ones are used
Cooling systems, single-circuit cooling and dual-circuit cooling.


Sea water is pumped into the engine by means of an impeller pump, injected into the exhaust pipe through the exhaust sea water injection and discharged with the exhaust gases.


There are two circuits, an inner and an outer circuit. The outer cycle is that
part of the system on the seawater side and is used to cool the inner (motor-side) system. The
the external cycle is an open system, the internal cycle is a closed system.

External system:
Sea water is sucked in by means of an impeller pump and cools it in a heat exchanger
Engine-side system coolant. The sea water is eliminated with the exhaust gases.

Inner system:
The coolant flows through the engine and its own cooling water tank. In the heat exchanger this is
Coolant cooled by the external system.

Fresh water is used in the internal circuit, to which antifreeze can be added.
Deposits (salt crystals) caused by extraneous water are prevented. By a thermostatic
The engine controls the heat exchange between the inner and outer circuit
quickly reaches its operating temperature, which is kept constant.


Before starting

Before starting an engine, the following measures must be taken:

  • Turn on the main power switch,
  • Open the fuel and cooling water valves,
  • Vent the engine compartment with bilge (petrol engine),
  • Set the transmission to “neutral” and
  • Check the cooling water (dual-circuit cooling).

After starting

After starting, the following can be observed:

  • cooling water flow,
  • oil pressure and charge control,
  • Engine noise and exhaust gases.


The first signs of malfunction in safe engine operation can be:

  • Unusual and strange engine noises,
  • vibration,
  • discoloration of the exhaust gases,
  • Illumination of the charge control or the oil pressure control and the corresponding acoustic warnings.

Discoloration of the exhaust gases

The color of the exhaust gases can be black or white in the event of a fault.

If the exhaust gases turn black, incomplete combustion occurs due to:

  • dirty air filter,
  • poor fuel quality,
  • misaligned injection pump.

If the exhaust gases are white, water evaporates through:

  • Condensate in the exhaust system when the engine is still cold,
  • cracked cylinder head,
  • defective cylinder head gasket.

The charging control lights up

The battery charge control lights up during operation due to broken cable connections.
This can have the following causes:

  • oxidation,
  • loose or broken connections.

The oil pressure indicator lights up

If the oil pressure is too low, the oil pressure indicator lights up. Causes can be:

  • clogged oil strainer,
  • oil level too low,
  • clogged oil filter,
  • defective oil pump,
  • defective oil pressure valve or
  • defective display device.

Engine will not start

If the engine does not start, the following errors can be the cause:

  • starter speed too low (battery too weak),
  • no fuel in the tank,
  • air in the fuel line,
  • Incorrect operation of the cold start aid on the diesel engine (possible preheating too short),
  • Defective starter motor.

If none of the errors mentioned are present and the engine still does not start, then should
the following parts of the fuel system are checked:

  • fuel tank,
  • fuel shut-off valve,
  • fuel hoses,
  • fuel filter,
  • carburetor (petrol engine)

Starting difficulties can also occur due to condensation in the tank. It is therefore important that the fuel tank is filled up when the engine is not used very often.

In many cases, water separators are built into the fuel line, in which the condensation water collects.

If the motor stops while engaging, the following causes are possible:

  • foreign bodies in the propeller,
  • The gear unit runs hard due to defective gears, bearing damage, thick oil or
  • a bent propeller shaft.

If the parking device is defective, then a diesel engine can be shut down by interrupting the
Shut off the fuel supply or by closing the air intake pipes.


After the engine has been switched off

  • close the sea cocks and the fuel valve and
  • turn off the main power switch.


Fixed-wing propellers, folding propellers and controllable pitch propellers are used on yachts with built-in engines. A distinction is made between right-handed and left-handed propellers.

Right-hand propellerWhen the machine is moving forwards, it turns to the right when viewed from the rear in the direction of travel.
Left hand propellerWhen the machine is moving forward, it turns to the left in the direction of travel, viewed from the rear

The propeller not only provides the desired propulsion, but also flows into the rudder blade with built-in motors. The better the flow against the rudder blade, the more effective it is
Rudder effect, because only a rudder blade affected by a flow causes a ship to change course. If there is no flow against the rudder blade (initially when driving backwards), the wheel effect occurs
carry, a lateral offset of the stern. The stern is generally shifted to port when the vehicle starts reversing with a clockwise screw. Conversely, the stern is shifted to starboard if the vehicle reverses with a left-handed screw.
This effect and the type of propeller installed must be taken into account when mooring and stopping. So the folding propeller only develops its optimal efficiency at a higher speed.
With two screws there is no wheel effect due to the counterrotation of the propellers and you can turn on the spot by letting one propeller work forwards and the other propeller backwards.
The propeller must be protected against electrolysis with zinc anodes, so-called sacrificial anodes on the propeller shaft. Used anodes must be replaced in good time.

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