Towards the beginning of our work on Mahdee, we attempted to settle on an electric plan that would be simple and meet various performance goals. That proved much more difficult than expected. Two contradicting factors dominated the debate: the only DC-powered windlass motor that can lift our 500′ of 1/2 BBB chain and 120 lb anchor requires 36V (actually 32V, but almost everything designed for 32V may be run on 36V, so we will call 32V devices 36V for simplicity), and virtually all mobile and marine accessories use 12V (there are also some high power devices that use 24V). In addition to the 36V windlass, Mahdee also came with 3 high volume 36V bilge pumps and a 36V autopilot–all compelling reasons to have 36V, but not enough to exclude a 12V system.
It is interesting to note that when Mahdee’s original owner in 1931 had her built with two 10kW gensets and a large high voltage battery bank to support her 25kW electric drive, he wrote in Yahting magazine that if he were to do it all over again, he would get rid of the large battery bank and run the electric drive directly from the gensets and switch most electrics to 110V supplied by the gensets. The only battery would be a small 12V battery for starting the gensets and safety essentials such as nav lights for those rare occasions when a genset wasn’t available. It’s interesting to see that many problems remain the same over long time periods: batteries still suck and electric drive is great, but you need to run the electric drive directly from electric gensets because batteries suck.
The best thing to do with a newly acquired boat is to work with what one has and evaluate how it works. We already had 3 AC powered 12V battery chargers, so we used one charger for each of the three batteries in our 36V series. This approach has the benefit that each battery in the series can be different and devices with any of three different voltages (12, 24 and 36) can be used. This approach also has wonderful redundancy since any battery charger can be used to charge any battery should one or two chargers fail. With all three chargers working, battery charging may be done 3x faster than with a single 36V battery charger.
Mahdee also came with a 32V engine alternator which we haven’t yet used. So we must turn on a genset or plug into dock power often enough to charge up the 24V and 36V batteries in the series–the first 12V battery is charged when the engine is used. We have considered buying a balancer which could be used to charge the entire series when the engine is running, but we haven’t really needed that capability yet. When we re-launched boat, we bought some 12V instruments and a small AC inverter to power laptops and cellphone chargers. All was good, except that we needed a bigger 12V battery to extend the time between running the genset. Although batteries still suck, their prices have dropped since Moffat’s articles on Mahdee in the 1930’s and fuel prices are going up, so it makes sense to use batteries to enable the gensets to run as efficiently as possible.
At first, each battery in the series was a 100Ah AGM and our 12V battery was also the engine start battery. The need to keep that battery sufficiently charged to start the motor and power the windlass if we needed to quickly exit an anchorage really limited how much we could rely on battery power. Thus, the next step was to upgrade the 12V battery to a 400ah “main” battery and add a 100ah “engine start” battery. We designed the space to make it possible to further enlarge the main battery to 800ah, or to put in 400ah at the 24V level depending on how our power usage evolves.
Notice that I have made no mention of lighting. That is because until now, we have not had any DC lighting. We have used kerosene lamps, candles, and AC lighting on either an inverter or the genset. Then, last Fall, we started working and we’re on a dock that has shore power for our AC lighting. I wanted to re-evaluate our electric situation and invest in some green-tech to show my support for it.
On a classic yacht, it is hard to implement wind or solar power without it looking all wrong; but I decided to take another look at those technologies. It’s amazing what data is available out there, so to evaluate cost-benefit, I wrote a program that calculated the power I could obtain from a 135W solar panel. I used data from the nearby airport (less than 1 mile away) and imported cloud cover and visibility data. I used that to calculate the distribution of direct solar radiation and the diffuse radiation hitting the solar panel for every hour of every day for the last two years. The depressing result is that solar panels suck. More than batteries suck. Compared to what we pay for electricity at the dock, a $500 solar panel will save us a puny $8.50 a year in electricity. That equates to roughly a 59 year payback if one ignores the cost of capital. Hardly a wise investment especially since we would require many panels to meet our full electrical requirement, so we still require a genset. Remember here that we are professionally engaged and thus work aboard our boat; we can’t conserve our usage down to nearly nothing. Using the higher cost of electricity from a genset (both fuel and depreciation of the genset) as a cost basis helps, but even then, the payback is over 11 years. Solar data in San Diego, a more southern latitude, yielded a little faster payback as should be expected, but anywhere on the US West coast, the only way to make solar have a reasonable payback is to use reflectors. Think: big parabolic monstrosities. On a 1931 schooner, the need for reflectors is a deal breaker.
Although we are in San Francisco which is notorious for the wind, the wind turbine analysis was only slightly better–28 years payback based on market rate electricity at the dock and 5 years 3.5 months for genset electricity. If we were planning to spend most of our time at anchor, a wind turbine might be viable. But, similar to solar power, a wind turbine will not meet our full demand, so we will require a genset. It really sucks having a MBA married to an EE–between the cost analysis and performance analysis, we’re dead in the water every time. Yes, one way or another, a lot of things suck.
The additional need for heating forced me to consider another option–more efficient use of our gensets. The new larger 400ah main battery bank already moves us in the right direction by increasing the time between genset runs. In fact, our Honda EU2000i is pretty well loaded by our Xantrex 50 amp charger. With a 400ah main battery, we have 100ah usable and charging will max out the charge capacity of the Xantrex which means that we can recover our 100ah usage in a little over 2 hours. That is pretty efficient, but the Honda uses gasoline which we must buy in jerry cans and tote aboard–a logistics cost–and it does waste a lot of heat…
In contrast, our diesel Onan genset runs on our large main fuel tanks, but needs a load of about 4 kW to match the Honda in electrical efficiency. Right now, we can’t come close to that unless we turn on nearly every appliance on the boat at the same time. But, the Onan has water cooling and there is a lot of heat in that water. In places like Japan, people often install gensets like the Onan, but with waste heat capture systems. If you can use the waste heat, the electricity is basically free. Put another way, with waste heat capture, total fuel efficiency can exceed the electric grid and power utility efficiency. My rough numbers show that for an investment similar to the wind turbine, we can implement a waste heat capture system. We would need to have much bigger AC battery charge capacity to put a bigger load on the genset, but that is doable. And then we would have lots of heat energy available and a total equivalent energy bill at or below what we are paying at the dock–all while sitting at anchor somewhere. Somewhere cold.
We designed a flexible electric system on Mahdee that was not fully implemented. We are happily living aboard her. Depending on what we do and where we go, we now have several options that will increase the green-ness of Mahdee while allowing us to live a comfortable and productive existence. If we go South of the Mexican boarder, solar becomes reasonably viable as a power source with a lower logistic trail than the Honda. If we stay here, we may consider a wind turbine. If we go North, the genset waste heat becomes the resource to pursue. What electrical path we take, time and our actual physical path will eventually tell. That’s part of the fun of living onboard a boat.
