Third Class Marine Engineering

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Third Class Marine Engineering

• Electrical Systems
• 3ME7

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AIMS

• Describe a basic electrical system associated
  with a small marine diesel engine installed in a
  typical SCC power boat.
• Identify all major components and explain their
  construction and function.

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What you should have already completed

• HEALTH AND SAFETY GENERAL
• 3 ME 1
• HEALTH AND SAFETY WORKSHOP
• 3 ME 2
• INTRODUCTION TO MARINE ENGINEERING
• 3 ME 3
• ENGINE CONSTRUCTION
• 3 ME 4
• ENGINE CYCLES
• 3 ME 5
• MECHANICAL SYSTEMS
• 3 ME 6
• QUESTIONS ON PAGES
• 13, 19, 25, 31, 39 AND 45

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Electrical Systems

• The majority of SCC motor boats have similar
  electrical systems fitted to them.

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The main electrical system components

• Battery
• This provides the stored electrical energy for
  the electrical system. It is usually a lead/acid
  type. It will be covered in detail in 3 ME 9.

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The main electrical system components

• Starter Motor
• This is fitted with a pinion which engages with a
  toothed rim on the flywheel to turn the engine.
  As soon as the engine starts, it over-runs the
  pinion and causes it to disengage. The starter
  can be either a pre-engaged starter or an inertia
  type starter motor.

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The main electrical system components

• Alternator/Dynamo
• This charges the battery, and is driven by a belt
  off the engine. The rotating internal parts
  generates electricity and send it to the battery
  which will continually charge whilst the engine
  is running. If there is a heavy demand on the
  battery, it will discharge its charge, and render
  the starting circuit inoperable when the next
  attempt to start the engine is made. A small red
  light or negative indicator on the engine start
  panel will indicate if the system is not charging.

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The main electrical system components

• Alternator
• Dynamo

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The main electrical system components

• Voltage Regulator
• This regulates the voltage at 12 volts, and is a
  usually a sealed component

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The main electrical system components

• Wiring loom
• Electricity is transferred from the different
  electrical components through terminals to this
  loom of insulated wires. The wires are colour
  coded to identify which components supply each
  other. The wiring loom is earthed at various
  points to prevent components becoming live, to
  reduce the chance of electrocution or electric
  shock.

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The main electrical system components
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The main electrical system components

• Fuses
• These protect the various components and
  electrical circuits from electrical defects.
  Fuses are coded by colour and must be the correct
  size for the circuit. The different types of Fuse
  will be covered in Class 2.

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BASIC DIESEL ENGINE ELECTRICAL SYSTEM
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Materials used in electrical components

• Insulators
• Materials which dont allow current to flow
  freely. (High resistance). eg. Plastic, wood,
  air, rubber, glass.

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Materials used in electrical components

• Conductors
• Materials which allow current to flow freely.
  (Low resistance). eg. Metal, water, carbon.

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OBJECTIVESYou should now be able

• Identify all major electrical components and
  understand their purpose
• Provide examples of insulators and conductors
• Answer the question on page 49 of your task book

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Next Time

• You should have completed the questions on page
  49
• Basic Electrical Knowledge
• 3 ME 8