Electrical (AC)

There are a few reasons to provide AC power aboard. Generally this revolves around appliances although it seems that each year more and more appliances are appearing in 12 volt form.When we bought Maringret she did not have any AC facilities. (Note: as Maringret is presently lying in Europe the AC system installed was 200 volts. When we sail into waters where shore power is 120 volts we will have to make some adaptions.

The benefit of having electrical tools to use once we started our refurbishment of Maringret was immediately obvious. The first thing we did was to purchase a marine grade extension cable whose plug matched those in our marina. That allowed us to run this big thick orange cable up and over the deck, down into the saloon and constantly trip over the cable. But it did solve the problem and to be honest, our present (final?) solution is not that very different from the big orange cable. (In fact the big orange cable is part of the new built-in system). We grew our installation in steps, partly because we weren’t sure how best to approach the problems and secondly as we found out how we lived and worked in the boat and where the provision of AC power would be most beneficial.

Below are the rough phases we went through:

  1. As mentioned above, we made do with a cable running from the dock, over the deck to the cockpit and then through the companionway.
  2. We installed a permanent, waterproof, marine grade male fitting in the anchor locker as high up under the deck as possible, as far out towards the hull as possible. A hole was drilled under the mounting plate, through the bulkhead, coming out high up under the deck, in the fore peak. The forward cabinets in the fore peak totally block access to this making the fitting very awkward indeed (we didn’t remove the forward cabinets which would have greatly facilitated the installation). The cable was lead alongside the starboard side of the forward lockers and terminated in the same old orange extension – but now it looked much better from the outside as the lead from the dock disappeared into the anchor locker. Inside we had a permanently installed extension cable (it even had a marine fitting on the end) which when we weren’t using was coiled up and stored in the fore peak. The lead was long enough to get to the companionway when we stretched it out fully.
  3. After we fitted the Dickinson heater, it made sense to have an AC outlet next to there under the starboard bookcase. We drilled a hole through the forward bulkhead at the level of the bottom of the shelf behind the backrests in the fore peak – this comes out behind the backrest in the saloon about 15cm (6 inches) above the shelf. We ran the cables to the fixed AC power point, we had no breaker or isolation switch at this point. Also at this point we no longer had a thick orange cable running across the fore peak cushions, through the forward companionway and across the saloon floor.
  4. About this time we purchased a 75 watt inverter in order to charge the laptop aboard. 75 watts is not much so we could alternatively power a 20 watt Ikea halogen light (they make an excellent work light by the way). Our inverter stayed at this level for a couple of years. In talking to other boats we started to think of sourcing enough AC for ourselves in order to run kitchen appliances (mainly a 160 watt Braun mixing stick and a 150 watt beater) and smaller tools (such as our faithful 125 watt Dremel drill and our 75 watt sewing machine). We ended up purchasing a 300 watt inverter, which once again is not very big compared to what other boats are running. As a guage, our power tools require the following wattages:
    jigsaw 370 watts
    drill 400 watts
    angle grinder 780 watts
  5. It was at this point that we started to consider running one set of delivery wires for the AC with a switch to select whether shore power or the inverter was to supply the AC. We also decided at this point that we wanted a 3-way switch so that the circuit could be isolated from either power source. We bought a 3 pole, triple throw rotary switch so that all 3 wires for the AC are switched and we can select sharper, inverter or to have the boat AC circuit totally isolated from either.
  6. The final phase was to run out power points as needed. We don’t have one in the fore peak as we use it exclusively for storage; one in under the bookcase on the forward bulkhead in the saloon, one under the starboard book shelf at the rear of the saloon (immediately adjacent to the wet locker), one on the rear of our electrical circuit box at the starboard side of the entrance to the basement, and the last one is mounted inside the galley cabinets (mounting it inside the cabinet minimises the chance of cooking liquids splashing into the outlet, and by mounting it about 5cm above the surface the chance of spilt liquids fouling the contacts is also minimized). We have never decided whether to provide a power point in the aft cabinet of not. The cable was run under the starboard bookcase in the saloon, through the bulkhead into the wet locker, across the wet locker and through the dividing wall into the head, along under the head cabinet, through the cockpit forward bulkhead into the starboard cockpit locker where it cuts across the corner of the locker and through the partition into the basement. It skirts the exterior of the basement and exits into port side cockpit locker where it runs through the bulkhead into the galley and terminates there. Should we decide to install a power point in the aft cabin then we would simply take it through the dividing partition from the basement.

The schematic below shows our present system (the bottom circuit line simply shows the locations where power points have been installed):

Further anticipated changes (not shown) are:

  • integrate a polarity checker into the system so we can check the correctness of the sharper prior to switching on any appliances;
  • when Maringret enters 120 volt sharper waters we will need to get a 2:1 transformer to convert the 120 volts into 220 volts.
    Rewiring the boat outlets and replacing our electrical tools and appliances would be prohibitively expensive.

One of the main sources we used for designing our AC electrical installation was Nigel Calder’s “Boatowner’s Mechanical and Electrical Manual.” Based on the advice given there, we did not tie our AC ground to either the ship’s DC ground or the anodes and engine block. The reason for this that the chances of the electrical supply being incorrect in some of the less thorough marinas is about 50% as they might hook up one wire or the other. In addition there is the possibility of them actually substituting the ground wire for one of the “hot” wires. If the AC and DC grounds were the same and therefore the outer anode was attached to the AC ground, then in the event of a neighboring boat having a different wiring coming aboard, 220 volts could be applied through the water which although vary bed for any hull fittings aboard could be fatal for anyone in the water. So as a result the ground on our AC circuit is isolated and electrically floating with respect to the boat. If the sharper is incorrectly wired then we will bring that aboard and face the consequences (note that there are very inexpensive polarity testers available), if the ground supplied is faulty then we will have a faulty ground. And of course when using the inverter there really is now ground in a true sense as the inverter box only has DC positive and negative going into it.

Click here for a description of Maringret’s DC power system.

We certainly learned the usefulness of having access to electrical items aboard. As many marinas now bundle electricity into their daily rates, it makes more sense to use electricity you have paid for as opposed to generating your electricity in another manner. By wiring the inverter into the same distribution circuit, we can now operate up to 300 watts of tools in remote locations. For short tasks we can do this off the house battery without starting the engine. Should power be needed for longer then the angine alternator has no power running the 300 watt inverter and recharging the batteries at the same time.

We have had no problems. An inverter rated at 300 watts is too small to handle most power tools which range from 800 watts and up but for now we are settled in with our 300 watt inverter.


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