Hello everyone and welcome to my first (official) post on this blog!

When sailing, power (i.e. electricity) is paramount for security (radar and AIS to see and be seen in the darkness of the night, GPS, auto-pilot, radio, etc.) and comfort (fridge, lights, windlass, internet, charging your phone, etc. – the never ending list)

During our first 4 summers on board, we improved several times the electrical systems on Soledad. By improving, I mean we managed to get a better autonomy AND more comfort at the same time. “Better autonomy” was the goal, and to achieve that there are 4 different aspects of the electrical system you can work on:

  1. Energy production (Maximize it!)
  2. Energy storage (Maximize it!)
  3. Energy consumption (Reduce it!)
  4. Energy losses (Reduce them!)

The first season on board: discovery

The first summer we spent on Soledad, we (sadly) discovered that after leaving the dock, our autonomy was quite short. By the end of a normal day, the batteries would be flat. The previous owner had left a note saying: “Run the engine at least 2 hours a day.

A “normal day” (for us) comprise a bit of motoring (leaving/entering the anchorage), 4 to 8 hours of sailing (navigation electronics + auto-pilot + radio), fridge all day and lights at night (plus the fresh water pump, charging phones/handheld devices, computers, etc.)

What if you want to sail for 2 days in a row ? Or stay at sea for 4 days ? What if you just want to enjoy the silence and not disturb your neighbors at anchor?

At that time, the only way to produce energy (outside the marina) was to run the main diesel engine with it’s 80 Amps alternator when the batteries were flat. This, from our point of view, is less than ideal. Burning diesel is so nosy (and so 20th century 🙂

The second season on board: solar panels and reducing consumption

For energy production, we installed 2 solar panels (flexible, 120 Watts each, in parallel) with an MPPT (best efficiency) solar charge controller. After considering wind generators, hydro generators (and all “free energy” videos on YouTube :-), we found it to be the best solution for us. After 3 years, it proved to be really the best thing to have. Those solar panels are silent and powerful (during the day, that is). You only need to clean them from time to time. The 2 panels also help to keep the helms protected from the sun.

On the consumption side, we changed all existing halogen lights (typically, 15 Watts each) to LED lights (1 or 2 Watts). It was a drop-in replacement, and was really worth it. This includes all lights down below the deck, but also the navigation lights and the mooring light (just a few LED bulbs, drop-in replacements).

Reducing the losses is a difficult task… but, by reducing the electricity going through the wires, you can reduce the losses: cut the power by 2 and you reduce the losses by 4.

To validate the effectiveness of the changes, a proper battery monitor was installed, a Victron Energy 602S (it can monitor both the service bank and the engine battery).

The third season on board: further reducing the consumption

The fridge (a compressor run by an electric motor) is, by far, one of the biggest electricity consumer on board – the fridge works 24 hours a day. The sealing of the fridge’s thermal insulation has been check and fixed, as a first step. Then, an electronic controller has been fitted on the Danfoss compressor (the one that comes with most boats, the BD35F). This controller as a proper temperature sensor and is able to detect when the batteries are fully charged (or when the sun is shinning hard on our solar panels or the main engine is running) and makes the compressor work harder during that period of time, in order to store more “cold”. It then reduces the compressor’s load when the battery’s voltage gets lower. This device is quite difficult to find (check below) but adds a welcome bit of intelligence to the compressor.

The fourth season on board: big changes

For the fourth season, we renewed all 3 battery banks. But putting a smaller battery for the windlass, we were able to squeeze in one extra battery for the “service/comfort” bank – while still using the original battery anchoring points.

We now have 5 batteries (instead of 4 previously):

Engine: 54 Ah (starter battery)
Windlass: 54 Ah  (starter battery)
Service 3 x 90 Ah = 270 Ah (deep cycle)

Why a 3rd battery in the service bank? Because with only 2 batteries, the panels/sun would have them completely charged up by 11 am. With 3 batteries, we can use more electricity during the night and still recover the next day, around 2 pm. Let’s not waste the gift from the sun!

We chose to stick to lead-acid batteries. That’s a well-proven (and the cheapest) technology. Moving to another battery technology would have implied a new solar charger (or maybe to simply reconfigure it), a new shore-power charger, a new charge controller for the engine alternator, etc.

Massive changes for the 4th season have been done on the navigation system.

The auto-pilot on Soledad works with an electric motor directly linked to the chain used by the two wheels to control the rudder. We replaced the autopilot compass (SIMRAD FC40) with a gyro-compass (SIMRAD RC42). The auto-pilot has also been completely reconfigured carefully (or configured? Had it been ever configured properly?). As a result, the pilot is now working less, much less – like 25% less, thank to better data it gets from the gyro-compass and to a sane configuration.

The AIS (SIMRAD AI50) on board was nice, but it had several issues: it has an always-on screen, it was not installed properly (no antenna for transmissions – funky commissioning) and it was not on the boat’s navigation network (yes, really funky). You don’t really need a screen for your AIS, what you want are loud alarms when there is a risk of collision.  It has been replaced by a brand new AIS (VesperMarine XB-8000, much more than AIS in fact) with a nice antenna spliter (Navico NSPL-400). We selected this one for its low power needs : it is basically always on (for VHF, AIS or FM radio), so power was an important criteria.

To get the GPS position on the NMEA network, we had to turn on the GPS/Chartplotter (a good old SIMRAD CP31 from 2007), slow to use (slightly better than a minitel) and producing a lot of heat (= losses). Eventually, we got rid of it and installed a dedicated external GPS (SIMRAD GS25), eating much less energy and providing better data from GPS, GLONASS (and soon Galileo!) positioning systems, up to 10 times per second.

Better navigation system, less energy!

Oh yes, I almost forgot about the new internet/NAS/wifi/computer/22″ screen installation; more on that in dedicated post, most probably.


After 4 iterations, the current electrical set up on Soledad is now able to produce more electricity than needed while anchored. While sailing, we have almost enough energy to use the auto-pilot full time (if needed): no problem at all for short passages (2 or 3 days). Long passages should be fine, as long as someone stays at the helm some hours every day, or by running the engine for a couple of hours every 2 or 3 days.

Stuff we recommend

Here are some links to the various stuff we are happy with, for your information. We provide links for your (and our) convenience only ; we are not affiliated to any of these vendors.

For our solar panels, we got in contact with watt-u-need (from Belgium). They are really helpful guys (online help is available and effective), we recommend their services.

Our Victron Energy MTTP charge controller is no longer manufactured. If we were to buy a new one now, we would choose a Victron Energy BlueSolar MTTP charge controller.

Another link here to the Danfoss compressor’s controller (Smart Energy Control by Isotherm/Indel): SmartEnergyControl. This little device deserves to be known!

Our VARTA lead-acid batteries are good, especially the slow discharge ones (VARTA LFD90). Last time I checked them, they were still 90% full after 5 months without charging. For the engine, the VARTA C30 have enough power for the task in a tiny package.

For monitoring our batteries, we would choose the the BMV 702 from Victron Energy (602S is no longer manufactured).

For many changes on the navigation systems, we found very good deals on ebay. We were able to sell most of our retired devices on ebay or hisse-et-oh.com.


We’re looking forward to hearing your recommendations ; what else could be done to further optimise energy in our next iteration?

11 thoughts on “Power on board our sailboat

  1. Great information and a logical progression. Thank you.

    Harold Redden
    Perseids Catalina 42 mkII
    Annapolis MD, Chesapeake Bay


  2. for house bank a larger capacity can be obtained by using 2 6v batteries in series if you have room try the L-16 size also an upgrade to a high output alternator (200 amp) with a switch so you can turn it on when bulk charging is needed and turn it off when engine is being used for propulsion


    1. Hi wewhite74, thanks for your input!

      Looks like L-16 form factor batteries would not fit there (under the chart table’s seat). Also, it may be hard to find them in Europe…

      A high output alternator (w/ switch) is definitively a good option to turn the main engine into a genset at will…
      This article looks interesting : http://www.pkys.com/alternator_installation.htm
      Unfortunately, to take advantage of the high output, you need large battery banks: charging 3 banks at 66 A, means that you must have 3 banks (660 Ah each) to charge them at C/10, or more likely, large loads to feed (like a watermaker, the windlass, or an high power inverter, etc…).
      Most probably, you also need to install a stronger/better charge regulator.

      I’ll keep this option in mind ; maybe one day we’ll need to use frequently a big load on the network.
      Thanks again, your comment made me had a good look at alternators 🙂


  3. Muy interesante el post!!!!!! pensaba que hablarias de la desaladora que montamos…. espero que la nombres en otro post. No sabia que se necesitaba tanta electricidad.


  4. I am also in the ptocees of trimming the fat from my power budget and adding storage and better generation
    have a small solar (40w) with mppt. have a dual alternator with a variable load on the 2nd on for better use, have about 1000 AH total in 3 banks (starter grp 31, windlass grp31 , and house 4 L-16 2 parallel 2 series)
    added new LED lighting throughout also have a charger to charge my electric outboard from my house bank


    1. “trimming the fat” is a good (and affordable) way to tune the system. IMHO, that’s the first thing to do. It also helps to compare the different consumers on board and say “oh, wait,… Are we really going to spend that much electricity for this?”. Producing electricity is not trivial, so it better be used for important stuff first. Yes, LED lights are fantastic: I can read at night as much as I want – that is (at least for me!) pure luxury. OK, that AND cold beers any time.

      To reply to your other comments: trimming the sails does help (a lot) the autopilot. Usually, I steer myself, trim sails and when I am happy with the balance of the boat, I turn on the auto-pilot (in “wind” mode). Yes, a windvane is a must have for long passages. It can steer the boat for days (weeks!) without sipping a single watt. Equally important, it can act as an emergency/spare rudder. The windvane ranks high in my “must have” list 🙂

      Again, our idea was to avoid large loads on the electrical system (no electic watermaker, no inverter) to keep the whole system compact/simple and as much “stock” as possible. Most probably, we’ll have to change it again for long passages (i.e. ocean crossing), but that’s not part of the plans for now 🙂


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