Select Page

Boat batteries need to be kept properly charged, which means never allowing the batteries to discharge below 50 per cent of their total charge.

As well as the batteries themselves, keeping a boat’s charging systems in good shape will also help to keep batteries topped up to a higher level of charge. The output of standard alternators can drop to as little as one-third of the alternator’s rated output after only 15 minutes or so of engine running. However, a smart charging regulator will keep the charging rate close to the initial figure, thus re-charging the batteries in minimum time. These have a further advantage in that they charge batteries to as much as 95 per cent of capacity – compared to less than 80 per cent for a standard alternator regulator.

In addition to improving charging systems, minimising the power drawn from batteries will also extend their lifespan. This need not involve major inconveniences – changing to LED lighting, for instance, will significantly reduce daily current drain, and costs significantly less than replacing a battery bank that prematurely runs out of puff. It’s also worth ensuring the fridge has at least four inches of insulation all round. Unfortunately, many are lacking in this respect, which can put a huge strain on batteries.

Avoiding and identifying electrical problems

The diagnosis of many boating electrical problems is within the grasp of anyone with basic knowledge of electrical systems and a few key skills.

Battery state

At a basic level, one of the most useful diagnostic tools is a simple digital voltmeter. The voltage produced by a battery, when no load is being drawn from it, is a good guide to its state of charge. When fully charged, a 12V battery can theoretically hold up to 13.2V, although in practice 12.8V or 12.9V is a more likely maximum. At 12.5V, the battery has 75 per cent of its maximum charge remaining, and at 12.2V there’s 50 per cent of the battery’s total capacity left – the point at which the battery should be recharged.

boat voltmeter

If the reading drops to 12.0V, there’s only 20 per cent of the battery’s capacity remaining, and the battery will be (almost) fully discharged at 11.8V.  A battery that’s nearing the end of its life may still give reasonable voltage readings when fully charged, but only if no load is being drawn. Switching a couple of lights on will create a large voltage drop in a weak battery, whereas an example in good condition will show a drop of only 0.1 or 0.2V in these conditions.

The voltmeter can also be used to check that the alternator is producing charge. Standard alternators have their output capped at around 14.2-14.4V, although there may be a voltage drop of 0.5V, and occasionally more, by the time the charge reaches the batteries. If there is little or no increase in voltage across the battery when the engine is running, then it’s very likely that there’s a problem with the charging system that will need further investigation.

Battery monitors

Unfortunately, it takes a long time for battery voltages to settle when load is removed, or after charging, and while a reasonably stable voltage may be seen after a few minutes, it takes several hours for the voltage to completely stabilise. This is one of the benefits of more sophisticated battery monitors that give a precise indication at any time of how much charge there is left in the batteries.

Boat battery monitor

When properly calibrated, battery monitors can account for all factors that affect battery state, including calculating the total charge delivered to the batteries, and subtracting the total charged used by the boat’s systems. In addition to battery voltage, these monitors can display battery charge/discharge current; state of charge of the battery in Amp-hours (Ah) or in percentage of total capacity; and time to go until the battery needs to be recharged.

Additional information available includes the average depth of discharge, depth of deepest discharge; number of charge/discharge cycles and number of occasions on which an under-voltage alarm has been triggered.

Alternative charging inputs

With many boats running numerous electrical devices, keeping the batteries topped up on a long passage, or during a period at anchor, can be a challenge. However there are now many options that mean there should be no need to rely on the engine for this. In the past wind generators were the mainstay for the power needs of many long-term cruisers and still have their fans today. However, they also have a number of drawbacks – when sailing downwind, for instance, the reduction in the apparent wind speed means their output is quite low.

The cost of solar panels has fallen rapidly and they are increasingly becoming the primary means of charging on many boats. On passage this can be supplemented by further inputs from a towed generator, or from the type of hydro-generator that’s increasingly common to see on long distance racing yachts.

Sterndrive maintenance

Sterndrives are a popular form of propulsion in the powerboat market, but require a fair amount of care and maintenance. The main factors to be aware of are salt water corrosion, lubrication and regular inspection of the bellows, the condition of which is vital to prevent water from entering into the hull.

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.

Boating emergency – how to broadcast a MAYDAY emergency call

How to broadcast a MAYDAY emergency call   How to broadcast a MAYDAY emergency call if a vessel or person is in grave...

Common marine electrical problems

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.

Medical Emergency at Sea

How to deal with a medical emergency afloat   If you are planning a boating trip, it is important to have at least one...

Boat Engine Failure – what to check

Engine failure If your engine fails or is overheating there are a number of things to check immediately: • Air filter...

Essential Knots: Reef knot

Essential Knots: Reef knot Use: Tying two ends of rope together, often used for tying up a bundle of loose sail around the boom. Step...

Marine engine electrical system

The typical basic electrical system associated with a marine engine includes a dedicated engine starting battery, a starter motor, a charger in the form of an alternator, a solenoid and some engine sensors and instruments.

ColRegs Rule 14 – Head-on Situation

  ColRegs Rule 14: Head-on Situation (a) When two power-driven vessels are meeting on reciprocal or nearly reciprocal...

Rewiring a boat – overcoming the challenges involved

Skippers need to have a basic knowledge of boat electrics, to avoid potential problems and to be able to solve them when they happen.

Boat interior varnishing

Most boat interiors have a combination of varnished and painted surfaces including solid wooden joinery, plywood laminates with thin hardwood veneers and glass reinforced plastic. When making your assessment of what you are going to do, bear in mind that the varnishing process consumes a lot of time, especially if the existing surfaces are in poor shape.

The VHF DSC Radio jargon buster

AIS - Automatic Identification System This system is used by shipping. It allows another vessel or coast station to use...

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.

Wooden Hulls – Part 1

Traditional wooden boats have a plank on frame construction, a centuries old boat building method that is still in use today. Variations of the traditional method include carvel, clinker and strip planking, which all relate to the way the planking is attached to the frame.

Know your Navlights & Shapes – essential for all skippers

Know your Navlights & Shapes International Regulations for Preventing Collisions at Sea (ColRegs) Anyone who is...

Boat electrics inspection checklist

With the boat ashore, here are some recommendations for carrying out a boat owner electrics inspection. Safety is always paramount so remember to do the checks with the batteries off. Wearing a head torch helps, make notes as you go and only tackle a repair if you are 100% sure you know what you are doing:

Electric motors and hybrid systems

In recent years there have been considerable advances with the development of electrically powered propulsion in the leisure marine sector. This includes developments with inboard and outboard electric motors, hybrid systems, lithium-ion battery technology as well as solar, wind and hydro powered generators.

Tacking a sailing boat

Tacking is the sailing manoeuvre used to change a boat's direction through an oncoming wind. Tacking a sailing boat calls...

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.

Boat plumbing maintenance & troubleshooting

A boat’s fresh water system needs annual maintenance to keep it in good condition. Some boats have far more complex systems than others, with pressurised hot and cold water, associated pumps, an accumulator, calorifier and pressure valves, all to keep a boat owner busy.

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...

Top five windvane self steering installation questions

Top five windvane self steering installation questions answered by Sarah Curry of Hydrovane International Marine, courtesy of Viki Moore from Island Cruising NZ

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.

Boat gas system maintenance

There are correct types of hose for marine plumbing, sewerage, exhaust, cooling and gas and all hoses should be checked regularly for wear and deterioration.

Fire prevention on boats

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