Select Page

Most problems with marine electrical systems arise from four possible sources, a lack of maintenance, a poor standard of initial installation, insufficient battery capacity, or ineffective charging systems.

Water ingress is a frequent issue – salt water can corrode contacts very quickly. If connections are not scrupulously clean – or are loose – resistance will be increased, resulting in progressively reduced power. Contacts should be cleaned with wet and dry paper until the surface is shiny. Investigate any evidence of water ingress and eliminate the source. Also make sure you don’t confuse a battery that’s almost at the end of its life with one that is simply flat. The old battery may give reasonable voltage readings after charging, but these will fall rapidly when even a small load is drawn and the battery will soon be flat again.

  

Fault finding

This is essentially a case of using logic to eliminate as many potential causes of failure as possible. Occasionally a large dose of perseverance is needed to identify an obscure problem, but equally it’s really easy to overlook an obvious problem, so always start with the basics.

circuit breaker boat electrics

In the case of a non-functioning navigation light, for example, the first action should be to check the fuse or circuit breaker. If not the fuse or breaker, the problem is likely to be a defective bulb, so examine the old one. If it’s blown – shown by a break in the thin filaments within the glass case – it can easily be replaced.

If the bulb appears to be intact, a voltmeter can be used to measure the voltage at the contacts in the lamp unit. If there’s power at the switch panel, but not at the unit, you’ll need to trace the wiring and attempt to locate the break in the circuit. How easy this is to find will depend on the individual boat – some boats may have a number of joins in the wire. In any case, a boat with separate red and green pulpit lights will have a junction box somewhere near the bow, where the single supply from the distribution panel divides to take power to the two separate lamps. There will similarly be a junction somewhere for the feed to the stern light.

A meter can also be used on its resistance (Ω) setting to check whether or not a component is damaged. At the most basic level, electrical current must flow through the component in order for it to work. The resistance function of the meter passes a small current through the device being tested. If no current flows, it records infinite resistance (often shown as a figure 1 on the left hand side of a digital meter display), telling us the component doesn’t work. Note that components must be isolated from the boat’s 12V supply before testing for resistance.

Alternators

Most marine engines are fitted with a belt driven alternator with an output normally ranging from between 40 to 60 amps. The same belt often drives the fresh water circulating pump. The condition of this belt and the alternator itself are both critical to keeping the batteries charged.

Alternators themselves need very little maintenance but correct belt tension is important in order for the batteries to be charged properly when the engine is running.

  • Adjusting belt tension – alternators normally have a support bolt and link adjust bolt. Belt tension is adjusted by loosening these two bolts. The alternator can then be swung outboard as it pivots on its support bolt. The link adjust bolt is tightened first and then the support bolt. The belt should be tightened enough so that it can be depressed by 12mm or so when pushed down by your thumb.
  • Worn belt – alternator belts need to be replaced when they can no longer be tightened sufficiently. Always keep a spare, if not two.
  • Charging test – to test whether the alternator is charging correctly, follow these steps using the instrument panel voltmeter or a digital voltmeter connected to the battery terminals:
  1. Check the battery voltage without the engine running, this should read in the region of 12.5 volts.
  2. Start the engine and check the voltage at idle. It should remain the same.
  3. Increase engine speed to 2000 rpm. The reading should now be somewhere between 13.8 and 14.4 volts.

Alternator problems

The electronic components of alternators can quickly burn out if the electricity they generate is not being channelled to a battery. This would happen if the battery isolator switch has been turned off, which should never be done when the engine is running.

Like all components, alternators can become worn and ineffective. This will need some troubleshooting to determine if the problem is a problem with the wiring, batteries, regulator or the alternator:

  • Batteries not charging – if the batteries are not charging this could be either a wiring problem, battery failure, a faulty regulator or a fault in the alternator.
  • Batteries not charging enough – this could also be a wiring problem, loose alternator belt or the alternator.
  • Batteries over charging – this could be a battery problem or a faulty regulator.

In my experience I have found having an alternator serviced and repaired professionally is the preferred option after identifying that it has a problem.

Narrowboating on the Kennet and Avon Canal

A recently cancelled sailing event I was due to take part in left us with a free weekend in the diary. Given that my wife and I were celebrating a bumper wedding anniversary and the weather forecast was for fine weather, we decided to hunt around for a last minute canal holiday.

Sailing & Motoring in Fog

Sailing & Motoring in Fog You can only measure the visibility accurately if sailing & motoring in fog when you have...

Seacock maintenance

If seacocks are always left open and neglected they can eventually seize which will prove a serious threat to boat safety should a connecting hose fail and the seacock refuses to close. There are three main types of seacock – ball valves, cone valves and gate valves.

Essential Boat Buying Tips for First-Time Boat Owners

The first question that comes to mind when thinking about buying a boat is: what type of boat? There are more than 20 different kinds, of different sizes, for different purposes, and different pockets. So, your first step is to decide your boat type.

Essential yacht tender safety for skippers and crew

Essential yacht tender safety - the dangers inherent in using a dinghy to get ashore from a moored or anchored yacht are all too easily...

Avoiding personal dangers at sea

In order to stay safe at sea, we need to know the risks we are facing and to be aware of any personal dangers we could possibly encounter. Here are six of the most common potential dangers individual crew members should be aware of.

Anchoring – getting it right is not always straightforward

If you can set an anchor correctly with confidence and know your boat will be safe in a secure anchorage, then you can rest...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 10 – The Return Trip

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the final instalment of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

You Need To Understand The IRPCS ColRegs To Pass Your Yachtmaster, Master of Yachts and Coxswain Certificate of Competence

IRPCS ColRegs Rules of the Road at Sea and Yachtmaster Learning, understanding and remembering the International Regulations...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 2 – Weather

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the second of a 10-part post where solo sailor, Bernie Branfield, shares his first hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Seized fixings and fastenings

Maintaining a boat can be a rewarding experience but at times it can also be frustrating. A prime example of this is when you come across a seized fixing or fastening that refuses to budge. Read our tips on how to release and fix them:

A five day sailing cruise of the Solent, UK

Welcome to our virtual Solent sailing cruise – a five day sail in the south of England from Bosham Quay in Chichester...

Safe Skipper – crew management tips

Effective crew briefings are a vital part of the good on-board communication that helps everything to run smoothly on a sailing vessel at sea, whether it is cruising or racing.

Fractures, sprains and dislocations at sea

Moving about a boat at sea often results in a few knocks and bruises, but if a crew member has a fall or major bump and is in serious pain, they should be examined and treated accordingly.

Boat interior inspection and checks

While a boat is ashore, the most critical interior checks to carry out are those that concern the safety of the boat. This entails the integrity of all through-hull fittings and seacocks, the gas system and the electrical system.

Boat batteries

Under-sized battery banks are one of the key factors behind power failure at sea, as well as the premature failure of batteries, so make sure that your boat battery measures up to the use you want to put it to.

Liferafts

Liferafts should be stowed where they are ready for immediate launching. All crew should know the location of the liferaft and know how to launch, inflate and board it. They should also know what equipment it contains.

Pleasure craft safety equipment recommendations

Safety equipment is an important part of boat preparation and it is advisable for all pleasure craft skippers to check their vessel is...

Light characteristics – how do navigators identify lights at night?

How do navigators identify the different types of light around our coasts at night and what are their characteristics?Navigating at...

Seasickness – how can you prevent it?

Seasickness is a common problem at sea and affects both seasoned sailors and novices. What are the causes and symptoms of seasickness?...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 9 – Around the Azores

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the ninth of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Top 5 Reasons Why an Inflatable SUP Should Be Your Next Yacht Accessory

In this article, inflatable paddle board expert Jason Paul gives the top 5 reasons why an inflatable SUP should be your next...

How a propeller works

Have a look around any boatyard and you will notice quite a variety of propellers – some have two blades, some have three and others have four or more. While most propellers are completely rigid some have blades that fold.

Estimating and plotting your position at sea

This post covers how we go about estimating and plotting our position using traditional methods, when out of sight of land – covering Dead Reckoning, Estimated Position, Tidal Streams, Leeway and more…

Understanding your boat’s compass

Article submitted by Mike Rossiter, Certificated Compass Adjuster. Since the magnetic compass was first used by the Chinese...