Electrical (AC)

An AC (shorepower) system had been retrofitted to Maringret. Various issues required a re-working of the installation.

A 2-breaker AC system had been installed and allowed the AC circuits to be switched:  off; shore power;  generator. We had sold the generator and installed 2 inverters in parallel.

We bought Maringret with a 3 kW diesel generator fitted. As our soft energy system meets all our needs we had little use for the gen set. Being another diesel engine it was something else to service, change the oil, replace filters. It worked very well, started at the touch of a button and so we were able to sell it on eBay to a narrow boat. This freed up one circuit on the AC selector switch which we could use to handle an inverter.

We learned on the Maxi that although modified sine wave inverters can operate most tools and appliances they do not get along well with computers or entertainment equipment. The price premium between modified sine and sinusoidal (i.e. full sine wave) inverters was such that it was worth buying two inverters: a sinusoidal model which was big enough to handle the computer and then a larger modified sine wave model which was large enough to run our power tools (click here for more details).

Following this strategy we had to be able to have the inboard AC circuits select from the following:

  • off
  • shorepower
  • inverter (sinusoidal)
  • inverter (modified sine wave)

In addition we needed to be able to switch the polarity on the shorepower if the dockside feed had reversed polarity.

We wanted to move the electrical panel from its location under the companionway. We had a number of reasons for this:

  • the sill on the companionway on the HR 41 is not very high and on occasion water has entered this way. On one occasion water was running down the bulkhead under the companionway and covering parts of the AC system. Admittedly this was because we had had the cockpit sole up and not yet sealed it down but nevertheless we resolved that the last thing we wanted under the companionway was an electrical system.
  • the AC outlet for the galley had been placed immediately above the sink which had seemed quite dangerous to us.
  • once the AC panel was removed then we could regain full use of the galley countertop.
  • we also felt that it made sense to separate the control functions (such as the selector switch) and the operational functions (e.g. the breakers and RCD) apart and mount them in different areas if it was beneficial.

We decided to relocate the AC control panel to immediately aft of the nav station. We had a piece of sheet aluminum powder coated black and cut out to handle the following:

  • AC supply selector switch which had a polarity reversal indicator light
  • polarity reversal switch
  • sinusoidal inverter power switch
  • modified sine wave inverter control panel
  • controls for the AC powered charger for the bow thruster batteries
  • speaker switches (they had to go somewhere and we didn’t want to put them on the master breaker panel for the DC circuits)

The breakers we put immediately in front of the nav station, mounted behind the settee back rest. Although they need to be accessible they are usually only dealt with when there is a problem to resolve (e.g. blown breaker). On the other hand the control circuitry is constantly interacted with as the AC system is managed.

There are 2 16A circuits side by side, they are logically configured as:The assumption is that the 240 VAC dockside supply is 16 A. became:

One design goal was to have 2 points of failure for AC supply in any area of the boat. The saloon and aft cabin have power points on both circuits so if one breaker blows there is always a power point operable on the other side of the room. In an emergency situation this could be critical by saving time to diagnose and reset the blown circuit.

The AC system is physically configured as:

To the best of our knowledge there was no AC system fitted to the boat at the factory. The existing AC system on Maringret had been fitted after all joinery had been completed. While we had the galley ripped out we decided to take advantage of running AC cables and providing power points where they were needed rather than where the completed joinery would facilitate them.

We placed double outlets at each end of the cupboard behind the stove, the power points are mounted at the top of  cupboard, behind the sliding doors so the power points are taking space that is the last to be filled and so the cables do not lie on the counter where they may encounter liquids.

The AC outlets that had been placed throughout most of the rest of the boat seemed to be quite workable. We re-ran new cables between the power points and placed the cables in conduits for safety.


We sized our AC loads for inverter as follows:

For operation on 120 VAC the system is configured:

  • Most of our fittings were domestic units, the exception being the Blue Sea AC source selector switch.
  • By moving the power points as high as possible the AC use became much safer (the previous outlet had been near the counter level and immediately over the sink!).
  • We had to be careful so that the battery charger could not be run from the inverter which ran off the same battery as the charger was charging. The solution to this is integrated with being able to supply 120 VAC to the battery charger.
  • Having a battery charger like the Sterling 50A model which accepts any AC voltage from 80 to 400 made the installation much easier.

After 1 year everything is working well. We will not fully test the 120 VAC operation until we reach that portion of the world.

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