Electrical Layouts



The general arrangement of the electrical system is one of our more important decisions.

Native electricity for Fir is 400 volt, three phase, AC, 60 cycles. Nearly all of our large motors and critical pumps operate at 440 volts three phase.  Step-down transformers then produce 110 volt single phase electricity for lights, outlets, and small motors.

At issue is whether new generators and inverters ought to produce 440 volt three phase or 110 volt single phase.  440 volt systems will be more complicated in some respects and are more expensive.  110 volt power generation is better supported but it would not support many of our systems (including a number of our emergency systems).  Moving to 110 volts would require a major rewiring.

We decided to maintain our existing system and only add generators and inverters able to produce 440 volts.. This continues support for our three phase motors.  And, it allows us to maintain the existing wiring and transformer configurations.


The general idea behind a load calculation is to list all electrical loads and estimate what percentage of the time each device is expected to run. Generators are best utilized when the load is about 80% of the generator's capacity. One can imagine that in most systems, the load varies between 50% and 100% of generator capacity. In this case, demand variances my fit well within the parameters of a generator set.

The challenge with Fir is that her loads are so dynamic.  This ought to be the expected result of decreasing her passenger load (passengers and crew) from over 75 to as few as 5.  Fir's energy demand  can vary by an extraordinary amount. At rest in a warm climate location, she can power all lighting and required system with about 4KW of which solar power is a major contributor. Running the systems required to operate the boat constitutes another 15KW.  The emergency systems increase this to 24 KW.

We want a small utility generator set that is able to handle all the current draw at anchor and offer some recharging of house batteries. Smart battery systems will attempt to draw and store enough current to keep the generator at 80% production.

Total load is facet of the calculation. Another has to do with what systems are required to respond to unanticipated failure. Fir is dependent on electricity. In order to start her mains, she must have enough electricity to run the air compressors and lubrication pumps. In order to have a redundant system, at least one of the new generators must have a standing capacity to operate all the equipment required to start the mains. We want to be able to start the mains and run the emergency systems even if one unit fails. 

110 Volt Wheelhouse System

The existing Wheelhouse is powered by 110 volt alternating current. Aside from changing the incandescent bulbs to LED, we are not replacing the existing system.  We are running the old system through our new junction board so that all electricity passes through one location. The revised system is better organized, it allows for simple modifications, and it provides test points for locating problems. Our only modification is to reorganize the wires.

24 Volt Wheelhouse System

Fir had DC current at some point in her past. But, the 1988 refit removed these systems in favor of AC current. 

We want to add DC systems for a couple of reasons. Firstly, many of the more energy efficient systems like LED lighting are based around DC current.  Secondly, computer controls (distributed electrical systems) for DC current are much less expensive than similar systems for AC current.

We are adding 50 amps of 24 volt service using a Simplex power supply. This power supply is supplied by the inverter circuit in the Wheelhouse so it is protected against power losses. 

The main use of our 24 volt system will be to run the lights supplied by McDermott Light and Signal. This includes all of our navigation lights and many of our deck lights.  

12 Volt Wheelhouse System

Most new electronics are run by 12 volt direct current (DC). We have added a Simplex 100 amp 12 volt power supply. This power supply supports our electronics.  In addition, we will use this current for some of our monitoring systems.


Between the Wheelhouse and the old Wardroom is a crawlspace about 36 inches tall.  This area is accessed by two hatches in the floor of the wheelhouse. This is where much of the old wiring of the boat was run.  

We built two DIN rail connection points in the crawlspace.  These are simply DIN rails mounted to plastic (non conductive) boards.  Mounted to the DIN are pass through blocks that take the electrical supply on the bottom and connect to the load on the top.  The idea is to run all the wires into a relatively small space.