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Electrical preventive maintenance on yachts

Preventive maintenance for yacht electrical systems, navigation, and other automation and alarm systems is crucial for keeping a yacht of any size at optimal performance.

It consists of systematic maintenance checks of equipment, even though it has not yet given signs of wear or error. Vulnerabilities of systems, equipment and materials are considered, and the maintenance is planned in a timely manner in order to avoid serious repairs, and requires a good maintenance plan.

Specific systems that should definitely be focused on for preventive maintenance are:

  • Lights and lighting systems
  • Alarms and monitoring systems
  • Circuit breakers and switchboards
  • Generators, motors

It is recommended that a trustworthy and reliable electrical service company undertake these surveys. Among the services that could be conducted are:

Thermographic Inspection:

The thermographic inspection is a Non-Destructive-Test (NDT) that allows us to perform a safe and non-intrusive examination without contact with the inspected elements. This thermography reveals defective elements and bad connections that need to be repaired.

Thermal image: Thermal sensitivity / NETD: 50mK at 30ºC

Measurement: Object temperature range: -20ºC to + 650ºC

Results:Class A – ∆T>50ºK -> Excessive temperature, needs to be repaired immediately

Class B – 30ºK>∆T>50ºK -> Medium temperature, surveillance.

Class B – 5ºK>∆T -> Low temperature, normal status

Insulation resistance or ‘megger’ tests:

This survey reveals if the insulation resistance to earth for each core and for each core to core remains acceptable.

Risks of electric shock are much greater on a yacht than they are ashore because the high humidity and high temperature (including sweating) reduce the contact resistance of the human body. In those conditions, severe and even fatal shocks may be caused at voltages as low as 60V. A breakdown in insulation can cause live parts to become uninsulated and exposed creating a hazard if touched either directly or indirectly by a conducting object.

Insulation resistance is to be measured for all circuits and electrical equipment, using a direct current insulation tester, between live wires and earth and, so far as reasonably practical, between all live wires of different polarity or phase.

The minimum values of test voltage and insulation resistance are:

Rated Voltage Un V Minimum voltage of the tests Minimum insulation resistance MΩ
Un ≤ 250 2 x Un (LR) / min 500V (BV) 1
250 < Un ≤ 1000 500 1

Generating Plant Load test:

Load banks are devices that contain resistive, inductive and / or capacitive loads, which are connected to an electrical power source, having the ability to dissipate the power of this source. Unlike field charges, which vary according to many electrical parameters, load banks provide a stable and controllable load, that, connected to a power source, serves to test, support or protect the power source, using the yacht’s generating plant.

Resistive load banks, mobile and fixed, allow increases in values as low as 1kW, allowing testing of small and large generating systems. The fine resolution control ensures complete adjustment of the following parameters:

  • Generators AVR setting for adjustment of power factor and voltage.
  • PMS parameters setting. Generator starting and load sharing should be demonstrated during survey
  • AMS alarms setting

Other regular tests and Preventive maintenance to be done:

  • Fuses (correct rating) and circuit breakers (correct operation, without signs of deterioration)
  • Inspection of earthing connections. There should be no corrosion present
  • On metallic hulls, the earth connection to be direct to the hull. On wooden or GRP hulls, all earth connections including lightning wire, to be direct to a special earthing plate fitted to the outside of the hull. Otherwise, corrosion problems and EM interference problems could arise.
  • Motor overhauling. Motors should be megger tested and appropriately dried or re-varnished if readings are low.
  • Generators should be cleaned, and bearings checked and renewed if worn. The generator should be megger tested and appropriately dried or re-varnished if the readings are low.
  • Switchboards should have all connections tested for tightness; this should be undertaken whilst blacked out. Current injection equipment should be utilized on large breakers to confirm correct operation.
  • Batteries should be visually inspected and checked for operational status. If deteriorated capacity is suspected, a full discharge test could be conducted to measure the current capacity.
  • Yacht wirings and wiring inside electrical panels should be checked for general cleanliness and condition. Wiring should remain flexible without cracking of the plastic sheathing.

Jose Perez Alacreu


For further information:

+34 666314318