Zero fossil fuel sailing


The goal for the environmental element of Sustainable Sailing has to be a zero use of any fossil fuel, at least for energy when using the boat. I don’t think we will be there in terms of all inputs for a long time yet (zero fossil fuel food supply or clothing or replacement parts as examples).

Starting point

When we bought Vida there were 4 fossil fuels aboard her.

  • Diesel: For the main engine providing propulsion when not sailing
  • Paraffin: For the hot air heating system (used batteries as well for fans)
  • Propane Gas: For cooking
  • Petrol: For dinghy outboard engine (some petrol was included, an engine wasn’t – but is the default for most cruisers)

Where we are at

So far we have removed 3 of these (Paraffin, Propane and Petrol). Two of these we have replaced with electricity (cooking and outboard engine) and we are confident that we will have enough solar power generation for these to be powered fully by renewable energy.

But here on the challenges get bigger. We haven’t replaced the boat heating system yet and we can only have hot water if we burn diesel in the main engine (which heats hot water as a side effect). We will be removing the current hot water system anyway as it is 42 years old, totally inaccessible and the immersion heater doesn’t work. It is less dangerous than the risk we had of paraffin leaking all over the engine compartment but it is a metal tank full of water right by the alternator that I can’t inspect. So it will come out.

So we need electric only heating and hot water. This is a significant challenge and I’m struggling to find examples of people who have done this at all and certainly not without running fossil fuel battery charging.

The main engine

So far I haven’t mentioned replacing the diesel engine with an electric motor. To reach zero that will be essential, but for the moment our plan is to simply minimise it’s use by a) improving sailing performance & our skills so that we use the engine less b) not relying on the engine for hot water heating or electricity generation. An electric motor will have it’s own battery bank. It will also have the potential to generate some electricity when you are sailing (water turns the propeller and the motor turns into a generator). So it can be possible (in some circumstances) to consider this a as a separate, self contained system (if like us you intend to keep motoring to an absolute minimum)

Challenges and calculations

However, there are more challenges. There are other significant electric uses and we need to limit the daily average electric consumption to the daily average renewable generation. At the moment we don’t know what the real levels of power generation will be (see the post on Solar generation for our current plans).

For the rest the calculations all get tricky because generation and consumption both vary according to the current climate/weather and activity (sailing or anchored). Unfortunately, in colder places in bad weather energy consumption will rise (as you want to stay warm and are less tolerant of cold water for washing) and solar generation will drop (less sun).

There are also significant differences between when you are sailing and when you are anchored (or in a marina or whatever).

  • Cooking: much less energy when sailing as tend to restrict hot meals and do simple one pot cooking.
  • Hot water: much less energy when sailing as showering will be tricky and so reduced, also little washing up
  • Lighting: Much more when sailing due to navigation lights and someone up all night long
  • Navigation: All instruments on when sailing. Particularly heavy users include Radar and AIS.
  • Autopilot: If using electronic (all we have at present) then a pretty high use when sailing

Other things will probably vary less when sailing or at anchor eg refrigeration and heating.

Contrary to what we expected it seems that the biggest challenges are not the high draw items (induction hobs, watermaker, windlass) that are run for small amounts of time but the things that need to run for long hours at a fairly constant draw (refrigeration, autopilot, navigation, heating). That is especially true if you can use high power systems when you are generating renewable energy with a fully charged battery bank.

Gaining freedom

One of the key advantages of heading for zero fossil fuels is the longer periods of independence possible as you don’t need to refuel. However, the three other key factors frequently limiting independence are:

  • Food: Not much we can do differently, however, if you choose you can stock up for longer periods if you are willing to sacrifice fresh food after a while.
  • Water: This is where a game changer is available. A watermaker (turns sea water into drinking water) can significantly increase independence and in many cases save money (as well as being higher quality and safer in many places). However, it uses a lot of energy.
  • Laundry: The two most common options seem to be a) laundromats (time consuming, quite expensive, reduces independence) combined with occasional hand washing when you run out or b) a standard home washing machine on larger boats.

The plans

I’m now going to review all the main electricity uses and what we are planning (or just thinking about). Of course at the moment many of these are provisional and will depend on what we find in the real world is possible in solar generation (and whether we go for other means of generation).


We are starting with 2 separate 1 hob induction cookers. We will have a gimballed tray so that one of these can be used safely when rolling around at sea. We are going for two separate hobs as this provides redundancy. It also means the gimballed tray is smaller. This way each hob is capable of 2,000 watts, when you have a double hob the total is less than 4,000 watts, either one hob is less powerful or both can’t be run on full power. We will look at other items in the more distant future if there is power to spare (oven, breadmaker etc).


Fridges and freezers can easily become the biggest users of energy when in the tropics. We don’t have anything at present so will be fitting a keel plate based fridge condenser (most efficient) and in our refitted galley will be creating a new highly insulated fridge space. We will not fit a freezer.


The three most common types of boat heating system are:

  • blown hot air
  • fuel burning “stove” typically diesel or wood
  • hot water radiators

I’ve found no examples of any of these using renewable energy.

The most promising option that we are going to try (it will at least work while we are in a boatyard with mains power) is an electric radiant heat wall panel. These are 240 volt and can work with electric socket thermostats/timers. They claim to be highly efficient. There are far too many unknowns at present to know how viable this option will prove to be, all we can say is it is the most promising option with the fewest energy losses that we have found so far.

Hot Water

The two options I have found so far are:

  • A “standard” marine calorifier (hot water tank with immersion heater and often additional heating from the engine cooling water), with the immersion heater potentially changed from 240volt to 12 volt or powered from the inverter. These need an expansion tank.
  • A 12v all in one water heater tank from Whale.

Getting hard information to compare these is difficult.


Before we start living aboard we will be installing a watermaker to increase our freedom from expensive marinas or lots of time and labour carrying water bottles to and from the boat. As water becomes more expensive and scarce this saves money and reduces demand on a limited resource in poorer communities. We will need to build a system ourselves from parts (cuts the cost to about 25% of a ready packaged system), the downside of this is a higher power consumption. Likely to be restricted to times when we are at anchor with the sun out


Our preference is to combine a hand powered washing machine with an electric spin dryer as allowing us to avoid the need for laundromats while keeping energy use way below a washing machine. The key benefits are:

  • Time: finding and using laundromats/laundry’s is costly in time, money and location
  • Space: a standard electric washing machine is much larger, not portable and will require permanent plumbing.
  • More suited to boat needs. The hand powered washing machines are robust and give good results. A spindryer will get clothes much dryer than the washing machines typically installed on boats.


Vida has very poor internal lighting (eg just 2 12v lamps in the main cabin), none of the lighting is LED. So we will be able to get much brighter lights that are more reliable and use far less power.


Currently the masthead light doesn’t work. None of the lights are LED so we can save power and gain reliability.

In terms of instruments the systems are very old. We are not going to rush to replace them but they are not complete and are not connected together. The total draw is likely to grow a bit over time. Plenty more research to be done.


Vida still has an original working Necco autopilot. They are supposed to be effective although we don’t know how much power it will use compared to a more modern one. We need to add an external on/off switch as the original broke and has been bypassed (it isn’t safe to have to go below to turn the autopilot on or off in an emergency). The controls are very limited compared to a modern autopilot. You have to set the compass dial to the course you want. The two key features we will miss compared to modern ones are follow current course and tack.

The good news is that it is installed in a really good way. The drive unit is completely protected from the weather and has an excellent connection via a chain to the steering rods.

For the short term we hope that this will be enough. If it fails then I would expect we would replace it with another electric autopilot. I can’t imagine us not wanting to have one. However, in the long term if we are finding ourselves making long ocean passages then we will be looking hard at installing a mechanical windvane self steering system as they work well without using any electrical power at all. We would probably fit a Hydrovane as it doesn’t need any connection to the existing steering system (which would be tricky due to the layout and space constraints). A hyrdovane also gives the option of attaching a very small/cheap electric autopilot to it as a backup, it is also the only common system that also acts as an emergency rudder if your main rudder fails (one of the most common worst case scenarios when crossing oceans).


We are upgrading to an electric windlass to raise the anchor (more in future posts). The current draw when in use is large, however, it is not used for very long and so we are not concerned about the impact on our power capacity.


As we look at what other people are using we are clearly aiming at the lower consumption end of the spectrum. No big audio visual systems, no scuba tanks, no massive computer power for continuous high quality video editing, no air conditioning, no bow thruster.


Our goal remains to get to zero fossil fuel dependency. So we will change the consumption side to match what we can achieve from maximising the renewable generation side. That will not just affect the renewable generation we fit but also where we cruise. For example if we can’t generate enough renewable energy to stay warm and comfortable in a cold climate then we will move to a more temperate one. If we need to stay at anchor for a few extra days to fully recharge batteries then we will do so.

11 thoughts on “Zero fossil fuel sailing

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