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.

How to trim a genoa sail

I recently had two new sails made by Sanders Sails, based in Lymington UK. The first to arrive was the new genoa and it took me a little while to get to know it and learn how to adjust it correctly. Here is an aide memoire for getting to know how to trim a genoa so that it will deliver the best performance.

The give-way hierarchy – sail boats and power boats

Who gives way to who at sea? Even seasoned sailors sometimes get this wrong and in a crowded harbour this can easily lead to a collision or at best considerable embarrassment for a boat that mistakenly thinks it has right of way over another.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 3 – Preparations

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the third 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.

How to ensure your boat is in proper working condition

In this article Eva Tucker from Volvo Penta presents a handy check list of all the things that you need to check regularly in order to make sure that your boat is in a seaworthy condition. Including maintenance, safety gear and electrical checks.

Safety at sea principles

Safety at sea is not as simple as just spending money adding shiny new emergency equipment such as liferafts, danbuoys, distress flares, EPIRBs and so on.

Keel maintenance and repair – Part 1

Keels are designed to act as underwater foils that generate lift as the boat moves through the water, counteracting the leeward force of the wind and enabling the boat to sail closer to the wind. Keel maintenance and repair is essential for the performance of your boat.

First Aid Afloat – jellyfish stings

  Wherever you are boating in the world I am sure you will be using a pilot guide to aid your navigation. Often in the...

Keeping boat records and doing checks

A boat’s records should provide information about maintenance schedules, when major work was done and when equipment was replaced or added to the boat. Without this information you are left guessing when things are likely to need replacing in the future and also what the costs are likely to be.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Getting to the Start

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the start 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.

Essential Knots: Clove hitch

Essential Knots: Clove hitch Use: Tying a rope to posts, bollards, rings or a guardrail. Step 1. Make a turn around the object and lay...

Essential Knots: Round turn and two half hitches

Essential Knots: Round turn and two half hitches Use: Tying a rope to a pole or a ring. Step 1. Pass the end around the object. Step 2....

Competent crew skills: mooring lines

Mooring lines are used when arriving or leaving a berth. One of the most important competent crew skills is to know how to...

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...

Wooden Hulls – Part 2

It is important to ensure the essential hull maintenance of a wooden boat is done, even if you are paying others to look after your boat for you. The priority is to prevent rot from taking hold. The protective layers of paint and varnish over wood are far more critical than on GRP boats, where the topsides are painted more for cosmetic reasons.

Safety Equipment Checklist for Boats

Safety Equipment Checklist for Boats   Liferaft line attached The liferaft will not work unless the trigger line is...

Antifouling for leisure boats – Part 3

Antifouling is one of the least pleasant boat maintenance jobs to do, but it has to be done. The very worst job of all is removing the old antifouling as this can get seriously messy and is very hard work.

Peer to Peer yacht charter – How can you monetize your boat?

There is a growing trend in peer to peer yacht charter. How does it work? People already rent rooms, cars and bikes from one...

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.

Saildrive maintenance

There are less maintenance tasks to carry out on a saildrive transmission than on a traditional inboard shaft drive system with its associated stern gear. However, there are a few critical things that require maintenance, as recommended in detail by the engine manufacturers, and should be adhered to.

How to improve a yacht’s upwind performance

There are several ways to improve the upwind performance of a sailing yacht. Read on for some useful tips including headsail reefing, heavy weather jibs and motor sailing.

Nautical paper charts – a reminder of the basics

The nautical chart is an indispensable tool for navigation. A chart is a graphic representation of an area of the sea which might also include coastlines, estuaries and islands. All cruising leisure boats should carry up-to-date paper charts.

Sailing to windward – how to take advantage of wind shifts

For most sailors, sailing upwind is the most exhilarating point of sail as you tack your way to your destination. Sailing to windward is a bit like zig-zagging your way up a mountain road through a series of hairpin bends – great fun but also calling for concentration and hard work.

Cutless bearing replacement

Cutless bearings can last for many years but if the propeller shaft is out of alignment they will wear through more quickly. If you have noticed a clunking sound when motoring then it could be a worn cutless bearing that is causing the problem.

Tips and advice for staying safe on a sailboat at sea

Here we focus on how to stay safe on a sailboat at sea. We cover key things to ensure you have on board before you set sail as well as covering the most common cause of incidents on sailboats and how to deal with them.

Fire prevention on boats

  Fire prevention on boats - common causes of fire: • Smoking below decks • Galley cookers • Build-up of butane or...