Power Consumption

By Michael (Nod) Crook

Service Manager, Multihull Solutions

I have recently spoken about power consumption at our Open Day at our Gold Coast Sales Centre.  The topic was well received and started a very open discussion on different experiences and preferences on how to best power a catamaran.  The following items were discussed and may be worth considering:


When setting up a new boat or re-fitting a recently purchased brokerage boat, the equipment required can vary significantly depending on the purpose for which you have bought it.  For example:

Day Boat

  • Requires small refrigeration, which is switched off after use
  • Basic instrument fit with low power consumption
  • Has plenty of engine running  and battery charging when in use
  • Can be fully recharged after use



  • Requires battery capacity for overnight use


Coastal Cruiser

  • Extra refrigeration/freezers
  • Power generation for increased periods at anchor



Blue Water Live Aboard

  • Power conservation to reduce unnecessary fuel use.
  • Power generation for ocean passages (solar, hydro or wind?)
  • Battery capacity for long periods of auto helm and instrument use



Is the boat going to be berthed or moored when not cruising?


When berthed, all systems will run off the shore power or through the 12v system which will be charged through the battery charger. Fridges can be left running at all times.

(You need to beware of power outages on the dock as these can flatten house banks if left unattended. A small back up solar fit would be a good addition to reduce the risk of this)


If the boat is permanently moored you might want to focus on a good size solar fit to recharge the house bank. A wind generator  might also be an option depending on the location.


 When commissioning a boat for clients I am often asked how much power I think they will consume. It is a very difficult question to answer. It depends on which of the following category they fall into:

 Power Conserver

Some people are very power conscious and like to minimise the amount of power they consume.

Carefree Power user

Others like to move aboard their multihull with the expectation that it is a floating apartment and everything is at hand and should be working. This type of client needs to have plenty of power generation fitted to the boat, to ensure they are not disappointed.


 Some simple first steps for everyone to minimise power consumption are as follows:

  • High current draw electrical items.

Picture2It is now common place that most boats are running 240v inverted power from the 12v house bank when disconnected from shore power. Try to prevent or limit the use of electric jugs, hair dryers, toasters, irons etc. If you do want use some of these, first check the wattage of the appliance.  Some are much lower than the standard.

  • Only operating necessary items.

Switch off lights when not in use. Do not leave instruments on unnecessarily. Ensure fridges and freezers well stocked and try to keep opening to a minimum.

  • Change all interior lighting and navigation lights to LED.

You will be surprised how much this reduces your consumption

  • Regulating your fridge and freezer thermostats.

Once the appliances are stocked and down to the correct temperature, you can save a lot of power by setting the thermostats correctly.

  • Solar Hot Water.

I have added this as a means of reducing consumption. I have only fitted this to a few boats due to its difficult and relatively costly install. Once fitted, it works very well. For remote cruising where engine running needs to be at a minimum, this is a great option. See the below diagram of a suitable set up.



 Alternators and Smart regulators

The alternators on most modern engines are usually the fastest way of recharging the house bank. Keep in mind that once on the water, engine running is usually the only way of making hot water.  With this needing to be a done a couple of times a day, the alternators are a great way of  charging.

Some people option to fit a smart regulator to the alternator to increase the output and decrease the recharge time. I have seen mixed results in trying to set these up, especially with catamarans, where 2 alternators are running together. I recommend asking a good marine electrician to review the system and assisting with this install.

Shore Power and Generator

The shore power and generator are used to charge the house bank via the battery charger.  Some boats have relatively small chargers and it may be worth upsizing the charger if you run the generator regularly while on the water.

For owners running air conditioning the generator run time may be all that is needed to keep the house bank full.

Wind Generators

These are another form of 12 volt power generation. Keep the following points in mind:Picture5

  • Wind generators can be ineffective  in sheltered anchorages. They are great for passage making though.
  • Beware of some of the cheaper units on the market. They can be very noisy with low output.
  • Wind generators can be very expensive to mount on some multihulls. With very big roachy mainsails the generator needs to be mounted a long way aft. It also needs to be set very high  in some cases to be clear of accessible hard tops.


Solar panels have decreased dramatically in price over the past 10 years. With lots of available roof space on most multihulls, solar is also relatively cheap to install.

WhenPicture6 calculating your generation from your solar fit, remember that there are only a few hours in the middle of the day when the system will be working at its optimum output. Solar output will also drop dramatically as soon as there is any overcast weather.

Shadowing on the panels is also worth trying to avoid as this will reduce the output of the system. For big installations it might be
splitting the system into 2, with 2 separate regulators. This will reduce the effects of partial shadowing over the whole system.

There is no noise and no maintenance with a solPicture4ar install.

I have installed both glass and flexible panels. The glass panels are well priced an
d have a good lifespan. However you cannot walk on them and the install can sometimes be harder. The flexible panels can be installed virtually anywhere and are easy to fit.  The lifespan of some of the flexible panels can be reduced in harsher climates.

Hydro Generators

These are an option for people doing long passages under sail. I have not installed enough of them to comment.


Most conversations about batteries are concerning the house bank and its capacity. When deciding on your house bank capacity you need to consider the following:

  • With the boat fully operational, how long do you need thPicture9e bank to run all systems before you recharge it? This may be just overnight? With making hot water, running air conditioning and vessel relocation, the boat may be fully recharged without consciously needing to assist
  • As an alternative to the standard Maintenance Free Lead Acid or AGM house bank, Lithium Ion batteries are becoming more popular and accepted for cruising boats. They have a much biggerPicture8 percentage discharge, a much faster recharge time and they are lighter than the equivalent capacity standard batteries.  They are much more expensive to install, but some manufacturers are claiming the battery life may exceed the life of the boat? This has yet to be proven as far as I’m aware.


This is a brief overview of items to consider. Please do not hesitate to contact me directly if I can help answer any further questions you might have in setting up your multihull.

































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