Here we explain the basics of boat electrics and how the various components work together in a simple and understandable way. Our specialist knowledge should help you to identify weak points in your electrical on-board system and to address these yourself with manageable "do it yourself" measures before they can develop into major problems. With over 30 years of experience, we know about the typical problems and questions our customers have, and this enables us to offer you an extensive selection of high-quality products from well-known manufacturers, such as MASTERVOLT, VICTRON, etc. You will find that many things are easier than expected, so don't worry! If you do decide to consult a professional, it will be easier for you to understand what he or she has to say and things won't sound quite as technical.
In general, the electrical installation on sports boats, whether sailing yacht or motorboat, should meet the highest standards in terms of design, quality and operational safety. Any failure in the power supply can have serious consequences at sea - whether at home or away. Therefore it is important to check the electrical system and the energy management of your boat regularly at the beginning of the season and to renew it if necessary. Nothing lasts forever and the harsh sailing and weather conditions at sea, as well as high humidity and sea salt, place a much greater burden on the individual system components of your yacht than if they were only kept on land.
Each time a new electrical device is added or equipment installed, such as a bow thruster, electric windlass, chartplotter with radar, on-board heating, a new powerful marine entertainment system, a coffee machine or even a laptop charger, the energy consumption on your motorboat or sailboat increases significantly. This not only affects the capacity of the installed batteries, but also the performance of the charger used.
Not all boats have the same electrical on-board system. The equipment and wiring used on board a sailboat is different from that on a motorboat. This is because of the different way the respective type of boat is used. It's easy to understand when we look at the differences between cruising in a sail boat and riding a motor boat.
Sailing yachts start with fully charged batteries. In most cases the engine (the alternator) is only running for a short time during mooring manoeuvres. As soon as the boat is under sail and the engine off, batteries start to be drained by devices such as plotters, radios, etc. When the boat returns to the harbour and despite a short mooring manoeuvre with the engine running, the battery will be empty. Here the shore power charger must be powerful enough to fully recharge the batteries overnight. No one wants to start the next trip the morning after with batteries that are not fully charged!
Motor yachts also start with a full battery. However, on board electrical devices are constantly charged by the alternator while the boat is in motion. Only when the boat is at anchor (or in a harbour without shore power) do the electrical devices discharge the battery. Heading back to the harbour, as soon as the boat moves again, the alternator powers the equipment and charges the batteries at the same time. Your motorboat will arrive at the harbour with reasonably charged batteries and your shore power charger will have to supply less power to fully charge the batteries. It is clear from this example that when the alternator is running, it contributes significantly to the power supply, which means that less battery capacity is required and consequently a less powerful shore power charger is needed.
There are also differences in equipment and cabling on motorboats. For example, the way the alternator charging current is distributed on a yacht with an inboard engine is different from that on a sports boat with a powerful outboard motor.
1. Energy sources for the on-board DC power supply are primarily the boat batteries and the alternator (if necessary, optimised by a high-performance regulator, etc.), followed by a solar power system, wind generator, or fuel cell. Other, but less frequently used energy sources are wave and tug generators.
Nowadays, especially in times of smartphones and tablets, one of the first questions most crew members ask is about the power supply - a socket to charge the communication devices they bring with them. But many guests tend not to realise how different electrical requirements on ships are: if the shore power supply is disrupted and the boat leaves port, the crew will have to rely on other sources of power. Here, as in cars or mobile homes, the battery is the most important electrical component besides the alternator.
When the engine is not running and no other energy sources are available, such as a wind generator or solar power system, the boat battery is the only energy source to supply all electrical devices on board. Since most boats and yachts are equipped with extensive and high-quality navigation electronics, a weak battery would be a disaster and a complete battery failure would result in a real maritime emergency.
It is essential that the on-board battery provides a reliable power supply!
One important aspect here is the required battery capacity. We strongly advise against using just any "give or take" capacity. In practice, we have often seen situations where sailors have chosen a smaller battery with a lower capacity when changing batteries, simply because a new one no longer fits into a battery box due to different dimensions. There is a risk that the new battery will be excessively discharged, which will quickly lead to loss of performance and premature wear. Unless otherwise specified by the battery manufacturer, the maximum permissible depth of discharge for consumer batteries is 50%. For a 100 Ah consumer battery (lead acid type), only 50 Ah can be used! In data sheets, the depth of discharge is also referred to in short as DoD.
How do I know how much power I need on my boat?
There is no one single answer that is right for everyone! The amount of energy used on board has a lot to do with the equipment and the different ways the boat is used. It is therefore important to work out your own energy needs and choose the appropriate battery capacity based on those needs. Once you have done that, it might become obvious that some consumers have a high energy demand, which may require additional energy sources or you might have to think about how these consumers are used.
Can I use solar and wind energy as an additional energy source on board
Of course! Additional energy sources, such as a solar power system, wind generator or compact, low-noise fuel cell, can significantly improve the situation. However, due to the installation space available and limited space on board, it is very rarely possible to meet the total daily power requirement with wind and solar energy.
Solar modules for boats - an overview.
We have high-quality starter or complete sets for your solar power system and a wide selection of individual components, all from well-known manufacturers and suppliers, such as SUNWARE, SUNPOWER, SUNBEAM, PHAESUN, etc. Every solar system consists of at least one module, a charge regulator, fixing and installation material, such as glue, connection cables, module connectors, clamps, fuses and of course cable passages. The connection cables below deck must also be connected to the regulator.
Today, various types of solar modules are available to suit every need, whether they are stable high-performance panel modules or thin semi-flexible solar panels that can also be mounted on a slightly curved surface.
A charge regulator, often also referred to as solar regulator or just regulator, must be chosen to match the module output. It must be capable of processing the module output, but may be more powerful so that it is not pushed to its limit or can later perhaps handle the output of additional modules without damage.
Regulators are available in different versions, for example as standard PWM regulators or as efficient MPPT regulators, featuring one or two charge outputs, with integrated or external battery temperature sensor, with convenient LCD display or simple status LEDs, etc. As you can see, there is something for every need.
Our tip: Never connect a solar module to a maintenance-free battery without a charge regulator! When the battery is relatively fully charged, a module which is directly connected will be underused, which can cause the module voltage to rise above the permissible charging voltage, which then causes the battery to overcharge and gas.
2. The energy sources for a 230 V AC on-board network are inverters, power generators and 230 V shore power on the dock.
As a responsible specialist dealer, we must first inform you of the following before we go into detail here: In power engineering, 230 V is considered low voltage. This may make it sound harmless but should in no way be misunderstood. Compared to the low voltages in a 12 or 24 Volt DC on-board power supply system, 230 V is a very high voltage which can cause life-threatening personal injury and damage to property if it is not handled properly or if installation errors occur. There are clear national and international installation regulations which must be followed in order to prevent the risk of personal injury or damage to property. For this reason, only a person who has the appropriate expertise and is familiar with the installation regulations should carry out work on a 230 V vehicle electrical system. If you are unsure, contact a professional boat electrician on site.
If you wish to read more on the subject, you will find clear guidelines in the European standard EN ISO 13297, or in specialist literature, such as the book "Elektrik auf Yachten" by Michael Herrmann.
230 V shore power.
While you are moored at the jetty in the harbour, 230 V shore power is the most reliable source of alternating current. A long and sufficiently sized shore power cable is used to connect the 230 V AC to the shore power supply (shore power socket) on board. For this purpose, standardised CEE or similar plug or socket connections are used, whereby it is not possible to incorrectly connect the outer conductor (L or phase) or neutral conductor (N).
On board, power goes from the shore connection socket directly to the shore connection unit and from the shore connection unit, the 230 V AC on board is distributed to the individual power circuits. The shore connection unit is a fuse box, which is fitted with a Ground Fault Circuit Interrupter and Equipment Leakage Circuit Interrupter. These are abbreviated as GFCI switches or ELCI or RCCB. The "state of the art" is an RCCB shore connection unit with an additional fire protection breaker (AFDD), as this also detects sparking (arcs) on board, which occurs, for example, in the event of defective plug connections, cable breaks or insulation damage and is one of the most frequent causes of fire.
As soon as you leave the harbour, the alternator and the battery supply power to the DC on-board electrical system again. If you then want or need to continue to operate 230 V AC consumers on board, you can use an inverter. This converts the 12 or 24 V battery voltage into a 230 V alternating voltage. An inverter can be used to supply a single 230 V consumer. If required, its output voltage can also be fed into the AC on-board power supply. Safety note: Installation is a job for professionals!
If an inverter is used to feed into the AC on-board network, it is essential to ensure that shore power and inverter do not feed into the 230 V on-board network simultaneously. For this reason, powerful inverters often have an automatic mains priority circuit, also known as a transfer switch by some manufacturers, which immediately disconnects the inverter from the AC on-board power supply if 230 V shore power is available and then connects it to the on-board power supply. For devices without this priority switch, manually operated or automatic electronic inverter changeover switches (transfer switches) are available. Depending on the model, an inverter suplplies either a clean sinusoidal or an inus-like trapezoidal output voltage.
Sine wave inverter.
Sine wave inverters are used when the connected devices comprise sensitive electronics, such as chargers for smartphones / tablets / electric toothbrushes / razors, medical equipment, heating systems, microwaves, coffee machines, etc. Trapezoidal inverters are more cost-effective due to their lower circuit complexity and are best suited to supply ohmic loads, such as simple filter coffee machines, hair dryers, kettles, but also for simple machine tools, etc.
The connected devices determine the minimum output power the inverter must supply, i.e. how many watts or VA.
In our experience, people often don't think about where an inverter gets its energy from, i.e the battery, and when the engine is running, also the alternator. For powerful 230 V consumers, the battery must supply very high currents and is therefore quickly discharged.
Does it make sense to operate the inverter and the shore power charger at the same time?
The simple answer is, no. If the inverter was powerful enough, this would be possible, and although modern devices use highly efficient switching power supply technology, losses occur during voltage conversion in both devices, which ultimately discharge the battery - there's no such thing as a perpetual motion machine!
Our expert tip: If an inverter is supplying the 230 V electrical system, the shore power charger must be disconnected from the 230 V mains or completely switched off!
Generator (AC generator).
If you are far away from shore power and are looking for a reliable, resilient energy source for your 230 V on-board power supply that is not fed by the battery, you may consider an AC generator. Generators are available as mobile units with an integrated fuel tank and are available with different power outputs. These mobile generators can be used to supply individual consumers and can also feed into the 230 V AC vehicle electrical system. Large yachts are often equipped with permanently installed diesel generators with an output power > 3.5 kW. 230 V generators must also not feed into the AC on-board power supply system at the same time as shore power or inverters, but must be separated from each other by means of suitable manual or automatic changeover switches.
3. Charging technology on board - As described in section 1, batteries and the alternator are the primary energy sources on board. When the engine (the alternator) is not running, only the battery supplies power to devices in an on-board DC system. Batteries are energy storage devices, at some point they will be empty and need to be recharged.
When we ask our customers "how do you charge the batteries on board", we often get the answer " It' s very simple, with the alternator and shore power charger". This is correct to a certain extent, but when we then ask "how many batteries are on board" and "what are the batteries used for", we see a questioning look on their faces, and when we continue to ask "how does the charging current get from the alternator to the individual batteries", they often say: "You should know that!" Actually, there's no way of knowing this, because the boating equipment is very diverse and so is the use of the available batteries:
There are small boats with only one battery, which is used both to start the engine and to supply the consumers. When the engine isn't running, there is a risk that the active consumers (e.g. radio and cooler) could discharge the battery too much and prevent the engine from starting.
To prevent this, shipbuilders and owners have fitted their boats with two batteries that are used alternately. When one battery is discharged, the system switches over to the other. All they've done is basically increase their battery capacity. Nevertheless, the risk of not being able to start the engine because both batteries have been discharged is still there.
As a logical consequence, most boats use two or more batteries, with each battery serving a single purpose: the starter battery is used for starting the engine only. It is always sufficiently charged, because the energy taken for the starting process is replenished after the engine or alternator has run for a short time. The consumer battery supplies all other electrical devices on board with power. Even if the consumer battery is excessively discharged, the engine can still be started thanks to its separate starter battery, allowing the alternator to recharge the empty battery and continue supplying power to the devices. Larger yachts often have additional batteries for powerful bow and stern thrusters or winches, which reduces the drain on the consumer battery and also has installation advantages (short connection cables require smaller cable cross-sections).
Charging with an alternator and charging current distribution
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