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Diesel Marine Propulsion Engines & Marine Generating Sets

How Much Electrical Power Do I Need?

These guidelines will hopefully assist you to calculate the size of generating set you require; and therefore the cost involved. There are two major considerations when choosing a generating set:

  1. What size do I need?
  2. How much noise does it make?

1. What size do I need?

It might sound obvious, but you need enough electricity to power the electrical equipment that you currently have on board – but remember, you might also want to think about an additional amount of power you will need for additional items you add over the next few years.

There will be a difficulty in answering this question when compared to your normal house that has a 100 Amp supply as standard. A normal house will be unlikely to use this much power (23kW); the general impression is that there is as much electricity as you can afford. In a normal house you can walk in the front door and walk around switching on all the electrical items you want, it will be almost impossible to use 23kW. However there is no such standard with generating sets; you can buy very small generating sets that have enough power to drive a hair dryer on an intermittent basis, or larger sets all the way up to power stations. The only problem is that the bigger the generating set the more money it will cost.

When calculating the size of your generating set on your boat, your life style is an important consideration – if you wish to be able to walk on board and switch on everything at once then the calculation is straightforward, just add up the maximum ratings on the appliance labels/nameplates and you have the size required. However; if you are able to change your life style slightly and moderate/schedule your electrical power requirements by considering and limiting which appliance you are switching on and possibly using one machine after the other (say the washing machine first, then the tumble dryer) – then you can happily install a considerably smaller generating set.

Can we therefore assume that you wish to buy a correctly sized generating set for your current and possibly future needs without spending excessive amounts of money.

There are a few things that you will need to know:

  • Electrical Power is measured in Watts. One thousand watts 1000W = 1kW (kilowatt). An electric kettle is about 2kW / 2000 Watts. The measurement of Electric power in watts combines the electrical current measured in Amps multiplied by the electric flow in Volts 1 Watt = 1 Amp x 1 Volt. The mains voltage is normally 230V (AC, alternating current, single phase, 50 Hz) in the UK.
  • All electrical equipment should have a label somewhere on the item ‘the appliance makers’ label that is generally hidden on the back or underneath, and will include/detail all the information you require. Normally included are the kW, or W, or Amps, this figure should refer to the ‘ Stated Load’ i.e. maximum possible load, with the electrical item operating at maximum electrical consumption.
  • Many generating set manufacturers quote the electrical power output in kVA. Therefore to select the size of generating set you will need to understand that kVA and kW are related to one another by the ‘power factor’. The relationship of kVA to kW is based on a normal convention of a 0.8 power factor; so that kVA x 0.8 = kW, (or kW/0.8 = kVA). This means that a 20 kVA set = 16 kW. Things can become more complicated with electric motor starting for air conditioning systems; so if you have air conditioning you need to send us full details so we can help with the calculations.

On board your boat there are two sets of electrical equipment to be considered:

  • 230V AC – The mains powered items similar to those you would use on land where they are powered from the domestic mains. This is 230 volts AC (Single Phase, 50 Hz) supply
  • 12V DC – The items that are powered from your batteries. Usually 12 or 24 Volts DC

Electrical Appliances

Electric Cooker: If you wish an electric cooker you need to consider the physical size and power when buying – a standard kitchen oven will generally have a 4kW oven and 4 hot plates from 1 kW to 2 kW each, totally about 10kW maximum possible load, and if you wish to switch everything on at once you need to allow for 10kW continuous loading. However it may be that the oven is set at 180°C and 2 hot plates are set at low and medium (all thermostatically controlled) switching in and out, so the actual load may only be 6kW or less. A full Sunday lunch may push the loading up for a few hours.

Air Conditioning: Varies considerably dependent upon the size of motor yacht/wide beam and the air conditioning system can vary from 2 kW, up to 20 kW. You do need the exact details of the installation and the manufacturer will supply you with starting current and running current details – if in doubt please ask us for help.

Electric Kettle: Is powerful 1.5kW to 3kW, but only tales a couple of minutes to boil.

Fridge & Fridge/Freezer: If a mains powered fridge is selected it will need continuous power. This is normally via an inverter powered by your battery bank otherwise you would have to run your generator set continuously. Most fridges on boats are small and powered directly from the batteries. The generator set will have to power your battery charger or inverter charger and this should be taken into account when sizing. Usually the batteries are also charged from your main engine driven battery charging generators too.

Washing Machine, Washer/Dryer & Tumble Machine: These require from 1kW to 3 kW each and the cycle can take from 1 hour to 2 hours on load.

Hot Water: We would always recommend that you fit a calorifier for hot water, heated by the engine cooling system when the engine is running. This gives you ‘free’ hot water.

Immersion Heater: This is generally a personal decision – if hot water is required then there are alternatives. A solution is an immersion heater and it is normally mains AC powered and 2.0kW, requiring either a shore line, Travel Power or a Generating set.

All electrical items will have different sizes and ‘Stated Loads’. Add your actual figures into the table below to establish the maximum possible load. The next column refers to the ‘considered’ load; this is a figure in kW that you have calculated/guessed/considered to be a reasonable figure to use for this calculation. A ‘multimeter’ that measures amps can be very useful in understanding how many amps are being used and when they are used during the cycle of the machine. This form can be ‘downloaded here’ and printed to create your list.

Appliance or Load - 230 Volts ACUsual kW LoadStated Load (Max.)Considered Load
Electric Cooker5.0 - 10.0 kW
Kettle2.0 - 3.0 kW
Water Heater (Immersion Heater in Water Tank)3.0 kW
Washing Machine1.5 - 3.0 kW
Tumble Dryer2.0 - 4.0 kW
Washer / Dryer1.5 - 3 kW
Microwave0.5 - 2.0 kW
Food Mixer0.5 - 1.5 kW
Toaster0.5 - 1.5 kW
Vacuum Cleaner / Hoover0.5 - 1.5 kW
Coffee Machine0.5 - 1.0 kW
Electric Drill0.2 - 1.0 kW
Fridge (If Mains Powered)0.1 - 0.4 kW
Electric Blanket0.05 - 0.2 kW
Hair Dryer1.0 - 2.0 kW
Television and Video / DVD Player0.1 - 0.3 kW
Battery Charger / Inverter Charger0.2 - 3.0 kW
Air Conditioning System2.0 - 20.0 kW
Additional 10% or 20% for next 5 years?
Total Load

A few notes and comments that may help:

Having establish two possible total kW figures you now need to consider your life style.

Can we assume that when on board your boat you are prepared to use your large electrical appliances in sequence? This would mean that the washing machine is followed by the tumble dryer and not used at the same time. Also, can you leave the washing to later, after you have finished cooking? Do you have air conditioning and can you turn it off while cooking? A big Sunday lunch will require a lot of power.

Another important consideration is the size of your battery bank. If you have an inverter you can have a discussion about the generating set size related to the size of your battery bank. Suggest you talk to a battery specialist who can guide you, as batteries are expensive and have a limited life span, needing replacement after a period of time – possibly 5 years. This form can be ‘downloaded here’ and printed to create your list.

Maximum Load PossibilityConsidered Load
Cooking - Electric Cooker, Kettle, Microwave, Food Mixer, Toaster
Washing - Washing Machine, Tumble Dryer, Washer/Dryer
Base Load - Fridge (If Mains Powered), Immersion Heater for Hot water, Freezer, Battery Charger / Inverter Charger
Vacuum Cleaner, Coffee Machine, Electric Drill, Electric Blanket, Hair Dryer, Television & Video / DVD Player
Air Conditioning System
Additional 10% or 20% for next 5 years?
Maximum ‘Considered’ Total Load at any particular moment

These different views of your life style aboard your boat will provide a reasonably accurate idea of how much power you will need. The most difficult question now becomes: ‘What is the maximum electrical Load (kW) that I will need at any one particular moment during the day’.

Cooking takes place over a period just before your lunch (possibly 11.00am to 1.00pm) or dinner (possibly 5.00pm to 7.00pm), when – during the day – will you need your cooking power?

Washing and drying takes place over a possible 2 hour period. Can this be arranged before or after you cook; alternatively if the timing coincides with cooking you will need to add the power requirement for cooking to the power required for washing and possibly doubling the size requirement for your generating set.

Base Load may take place continuously over the whole day. However heating hot water takes a lot of power and you may put this on a timer – so it does not clash with other power requirements. You will have to add this figure to the other major load requirement.

Air Conditioning – This can vary from 2kW to 20kW or more, depending upon the size. This power requirement also varies during the season and usually requires hot summer days; also this varies during the day when you may be sitting down to a meal at midday. Don’t forget that the air conditioning is frequently used during the evening/night when you are trying to sleep. Adding the power requirement for air conditioning to your existing load requirement has to be carefully considered as the motor starting load may require such a large set that the other loads may become almost inconsequential. Air conditioning has to be carefully calculated and considered. Please talk to us about your air conditioning.

Basically, the choice is yours, what comfort level do you want and how much extra is the next size larger or smaller – generally the difference is not that much.

If you buy a generating set that is too small you will suddenly become very aware of the electrical power you need, it is generally safer to err on a slightly larger size that allows for a safety factor and any electrical items you may purchase in the future. It may therefore be better to spend a little time talking to other people and getting the size calculation correct before you buy.

2. How much noise does it make?

Generally if you ‘live aboard’ then you will need a generating set in an acoustic enclosure. Noise is a very personal thing but when moored up in the middle of nowhere you will find that even the smallest noise travels a very long way at 10.00pm in the evening. Noise becomes an extremely important issue when living right next to the generating set. An alternative we can offer is good quality ‘Sound deadening’ material at reasonable prices.

Generators typically supplied by Beta Marine Ltd

Small Narrowboat: With only interior lighting, a television, microwave and a fridge, you need a suitable domestic battery bank and an inverter that is charged by the propulsion engine during the day, possibly a Travel Power 3.5kVA.

Narrowboat 60 foot: With 3kW Washer/Dryer, TV/Video player, 0.2kW DC Fridge, 2kW Electric Kettle, Microwave, Shower pump, inverter charger – we often supply a 3.5kW or 5kW Travel Power mounted on the propulsion engine. If you have the space – maybe a small BetaGen.

Wide Beam/Dutch Barge: With small electric cooker, 2kW Washing machine, 3kW Tumble dryer, 2kW Immersion heater, 0.5kW Fridge/Freezer plus television, video player, battery charger – such customers often specify a 1500 rev/min BetaGen 7 or BetaGen 10.

Sailing Yacht 25 to 35 foot: With 0.2 kW DC fridge, microwave, electrical navigation equipment, lighting, water pumps, inverter charger – we would recommend a suitable domestic battery bank and possibly a Travel Power driven by the propulsion engine.

Sailing Yacht +60 foot: With 0.2 kW DC fridge, electrical navigation equipment, lighting, water pumps, battery charger (possibly air conditioning) – customers have taken BetaGen 4/2 or BetaGen 7.

Power Boat 34 foot: With Air conditioning, small electric cooker, 0.2 kW fridge, electrical navigation equipment, lighting and water pumps – maybe a BetaGen 7 or 10

Power Boat 40 foot: With Air conditioning, small electric cooker, 0.2 kW fridge, electrical navigation equipment, lighting, water pumps, battery charger – perhaps a BetaGen 10 or BetaGen 11.

You will probably also have 12 volt DC (direct current) electrical loads. These are usually powered from the domestic battery bank and battery charger (or inverter charger):

  • Interior electric lights
  • Fridge
  • Navigation lights
  • Anchor winch
  • Domestic water pumps
  • Navigation equipment
  • Fans for diesel heating system and ventilation

Beta Marine Ltd offer the following:

1500 rev/min Generating Sets: are the ones to choose for long life and steady reliability with lower noise levels but they are slightly bigger and more costly. They generate 230 volts AC 50Hz electrical power. We also offer Generating Sets: 60Hz, 1800 rev/min.

Generating Sets: 50Hz, 1500 rev/min
Generating SetMax. kVA Output 4 Pole
@ 1,500 rpm - 1 Phase
Max. kVA Output 4 Pole
@ 1,500 rpm - 3 Phase
KilowattVoltsMax. Load
BetaGen 77.2 kVA-5.7 kW230 V24 Amps
BetaGen 7-7.2 kVA5.7 kW400 V8 Amps
BetaGen 109.7 kVA-7.7 kW230 V33 Amps
BetaGen 10-10.1 kVA8.0 kW400 V11 Amps
BetaGen 1110.7 kVA-8.5 kW230 V36 Amps
BetaGen 11-11.2 kVA8.9 kW400 V12 Amps
BetaGen 1212.3 kVA-9.8 kW230 V42 Amps
BetaGen 12-13.0 kVA10.4 kW400 V15 Amps
BetaGen 1414.0 kVA-11.2 kW230 V47 Amps
BetaGen 14-14.5 kVA11.6 kW400 V16 Amps
BetaGen 1716.0 kVA-12.8 kW230 V55 Amps
BetaGen 17-17.3 kVA13.8 kW400 V20 Amps
BetaGen 2119.8 kVA-15.8 kW230 V68 Amps
BetaGen 21-21.1 kVA16.8 kW400 V24 Amps
BetaGen 2625.3 kVA-20.2 kW230 V87 Amps
BetaGen 26-26.2 kVA20.9 kW400 V30 Amps
BetaGen 3332.0 kVA-25.6 kW230 V111 Amps
BetaGen 33-33.5 kVA26.8 kW400 V38 Amps
BetaGen 4038.5 kVA-30.8 kW230 V133 Amps
BetaGen 40-39.6 kVA31.6 kW400 V45 Amps
BetaGen 4944.0 kVA-35.2 kW230 V152 Amps
BetaGen 49-49.5 kVA39.6 kW400 V57 Amps
Generating Sets: 60Hz, 1800 rev/min
Generating SetMax. kVA Output 4 Pole
@ 1,800 rpm - 1 Phase
Max. kVA Output 4 Pole
@ 1,800 rpm - 3 Phase
KilowattVoltsMax. Load
BetaGen 77.1 kVA-5.7 kW120 V47 Amps
BetaGen 7-7.8 kVA6.2 kW220 V16 Amps
BetaGen 109.8 kVA-7.8 kW120 V65 Amps
BetaGen 10-10.5 kVA8.4 kW220 V22 Amps
BetaGen 1111.2 kVA-8.9 kW120 V74 Amps
BetaGen 11-12.3 kVA9.8 kW220 V25 Amps
BetaGen 1213.5 kVA-10.8 kW120 V90 Amps
BetaGen 12-14.6 kVA11.6 kW220 V30 Amps
BetaGen 1415.0 kVA-12.0 kW120 V100 Amps
BetaGen 14-15.2 kVA12.1 kW220 V31 Amps
BetaGen 1717.3 kVA-13.8 kW120 V115 Amps
BetaGen 17-18.7 kVA14.9 kW220 V39 Amps
BetaGen 2120.0 kVA-16.0 kW120 V133 Amps
BetaGen 21-22.0 kVA17.6 kW220 V46 Amps
BetaGen 2627.0 kVA-21.6 kW120 V180 Amps
BetaGen 26-27.5 kVA22.0 kW220 V57 Amps
BetaGen 3336.0 kVA-28.8 kW120 V240 Amps
BetaGen 33-38.0 kVA30.4 kW220 V79 Amps
BetaGen 4043.0 kVA-34.4 kW120 V286 Amps
BetaGen 40-46.0 kVA36.8 kW220 V96 Amps
BetaGen 4947.0 kVA-37.6 kW120 V313 Amps
BetaGen 49-50.0 kVA40.0 kW220 V105 Amps

3000 rev/min Generating Sets: are more economical to buy, but you will need to consider that they operate at a faster speed and will be noisier. They generate 230 volts AC 50Hz electrical power. We also offer Generating Sets: 60Hz, 3000 rev/min.

Generating Sets: 50Hz, 3000 rev/min
Generating SetMax. kVA Output 24 Pole
@ 3,000 rpm - 1 Phase
Max. kVA Output 24 Pole
@ 3,000 rpm - 3 Phase
KilowattVoltsMax. Load
BetaGen 4/24.0 kVA-4.0 kW230 V16 Amps
BetaGen 6/25.7 kVA-5.7 kW230 V24 Amps
BetaGen 6/2-7.7 kVA7.7 kW400 V11 Amps
BetaGen 11/211.2 kVA-8.9 kW230 V38 Amps
BetaGen 11/2-12.1 kVA9.7 kW400 V13 Amps
BetaGen 22/222.0 kVA-17.6 kW230 V75 Amps
BetaGen 22/2-23.1 kVA18.5 kW400 V26 Amps
BetaGen 25/224.8 kVA-19.8 kW230 V85 Amps
BetaGen 25/2-25.9 kVA20.7 kW400 V30 Amps
Generating Sets: 60Hz, 3000 rev/min
Generating SetMax. kVA Output 24 Pole
@ 3,000 rpm - 1 Phase
Max. kVA Output 24 Pole
@ 3,000 rpm - 3 Phase
KilowattVoltsMax. Load
BetaGen 4/24.0 kVA-4.0 kW120 V33 Amps
BetaGen 6/25.7 kVA-5.7 kW120 V47 Amps
BetaGen 6/2-8.4 kVA6.7 kW220 V17 Amps
BetaGen 11/211.3 kVA-9.0 kW120 V75 Amps
BetaGen 11/2-12.5 kVA10.0 kW220 V26 Amps
BetaGen 22/222.0 kVA-17.6 kW120 V146 Amps
BetaGen 22/2-24.0 kVA19.2 kW220 V50 Amps
BetaGen 25/228.0 kVA-22.4 kW120 V186 Amps
BetaGen 25/2-30.0 kVA24.0 kW220 V63 Amps

Travel Power Generators: are fitted to the propulsion engine and are very compact. There are two options 3.5kW or 5.0kW (and generate 230 volts AC 50Hz electrical power).

12 Volt DC: electrical power is from your batteries, you can have a large ‘domestic’ battery bank that will provide 12 volts for all 12 volt appliances – fridges, electrical navigation equipment, lighting and water pumps and can also power an inverter for 50Hz AC for a television etc.

We can offer both heat exchanger cooling, or alternatively keel cooling normally for canal boats. If you have any doubts at all, please ask and we will try to help. Correctly sizing the generating set is your responsibility – and we do not accept any liability if you use these guidelines. Beta Marine Ltd also produce much larger generators up to 1000kVA for seagoing ships etc.

Generating Sets Downloads

If you have any questions please do not hesitate to contact us.
Beta Marine Generating Set Output – 50Hz Information.
Beta Marine Generating Set Output – 60Hz Information.

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