ENERGY MANAGEMENT
& DESIGN

After two years on the boat and approximately 190 nights at anchor, I have learned a thing or two about conserving and producing electrical energy. Before leaving Subic I knew the 24 volt 70 amp Balmar alternator was not big enough to run the watermaker underway so in January 2008, I installed a large case Balmar 140 amp unit and rewired the electrical panel so the inverter could pull the watermaker and aircons, though not at the same time. Now we make water underway without running the genset and I can do a two minute back flush on the batteries alone.
However, producing energy with the main engine is only part of the equation and we found that while at anchor for anything longer than one night, we would have to run the genset an average of three hours in the morning to get the bank up to 80%. We were relying on the Victron 24/70/3000 inverter and though it is rated at 70 amps it was only averaging 54 amps going in. Some of the difference was the boat’s DC demand that would draw down the current from the high I have ever seen, 63 amps, to 54.
When some of the marginal sailors would hear this they would ask how we could possibly use all those amps. Most of them did not use that much at half the voltage. I started looking for ways to reduce usage and found it in the freezer. We removed all the perishable items from the chest freezer and put them in the freezing unit of the refrigerator. We then put about two cases of bottled water in the bottom of the chest freezer and covered that up with beer and soft drinks. We also keep a few bags of flour in there because it is prone to getting infested with bugs if we leave it out.
While underway we turn the freezer on and the bottled water in the bottom either freezes or almost freezes depending on the length of the passage. We also run the freezer when we run the genset. Sometimes if we are anchor for extended periods this is not enough to keep the refreshments icy cold so I either let the freezer run off the batteries some or simply take a few cans that are already cool, out and put them in the fridge.
This works quite well and coupled with cutting the inverter off except when we need AC, has cut our daily amp usage from 150 a day to about 100. That freezer really pulled the juice. Quite often the bank charge level at 5:00 PM is the same as it was at 10:00 AM because of the two 125 watt solar panels, especially if we are off the boat.
The other thing I did, while we were in Singapore this past February, was add a Victron 24 volt, 100 amp charger to the system. This unit had to be ordered and cost $2,000.00 US but has cut my gen-set run time down to two hours every other day which is better than I had hoped for. The two units in parallel put in an average of a little over 100 amps per hour when I run the batteries down to a low of 53% to 58% and a high of 83% to 88% and run the genset two hours.
The little round lights used in the salon that get hot and put out good light, pull nearly 4 amps at 24 volts where the LCD lights in the salon will not even move the battery monitor when they are cut on and off. These LCD lights don’t get hot but also don’t put out as much light. We use the reading lights for reading anyway so I may lookout for some LCD lights to replace the conventional lights to save some more energy.
The little fan I leave blowing on me overnight pulls one amp and cutting off the inverter cuts back the usage by three amps. Part of that I’m sure is the fact we have multiple flashlights, cell phone chargers, and laptops plugged into the AC circuit.
I think if you consult with any marine electrical engineer like Arild Jensen who I would recommend by the way, the first thing he will ask is how do you intend to use the boat. Therein is the big question because I’m not too sure most people realize how they will end up using the boat.
We had planned from the get go to do a circumnavigation and of course anchoring and passages are a big part of that. Had I done more planning from the beginning or consulted with Arild I may have saved myself a lot of trouble and headaches.
Also I would like to add that these GEL batteries that I began to lose confidence in when we left Subic seem to be performing within my electrical budget but probably will never take the rate of charge that an AGM battery would, so I have decided to live with them as long as they last. Which I understand could be longer than my cruising life.
For those of you who are wondering about the cost of fuel for a cruising power boat. In two years while putting 1,000 hours on the main engine and 332 on the genset, we have purchased $7,687.00 USD resulting in 3,112 US gallons of fuel. The boat has at least 1,000 gallons of that still onboard. The boat burns 1.66 gallons an hour underway and I’m guessing the genset burns about 1 gallon an hour or less under load.


Randal

Thanks for the Report and suggestions.

Other owners may wish to check the output of their Victron inverter/charger as the default charging voltage is not 100% output (70A) I bought the Victron interface so that I could program the charger and optomise the functions and I recommend this over the very awkward dip switch method.

For those not familiar with my boat, I had Arild Jensen review and design the electrical charging system from day 1 and I highly recommend his approach to the way I use the boat. One of my wishes was that the boat be able to run the electrical system off the alternators and inverter(s) when underway. This dictated 2 x 140A Leece Neville alternators on the main engine and 2 Victron 3000W x 24V inverter/chargers. With a bit of load management I can do all voltage intensive operations when underway and running aircon at the same time.

My watermaker is the same as Randals and 220V. A 24V watermaker would shed some load load off the inverters and free them up for other work.

Another wish was for rapid house bank charging. The battery bank is 800 AHr @ 24V AGM's with a Victron 100A charger plus the inverter/chargers. This set up pounds the batteries with a temperature limited 240A (100 + 70 + 70) on the chargers and 280 with the alternators. Do not try this high charge rate if you do not have AGM batteries.
I never see the full alternator output as they are degraded by temperature and limited by integral temperature sensors. This can charge the 800 AHr bank up PDQ and limits genset running time.

Perhaps too techie for most, but the new mod this trip is to use one of the virtual switches in the inverters to shut off the 100A charger when bulk charge is over, thereby shedding load off the genset so that I can use these amps for another high load device. This will allow me to run the genset fully loaded, and reduce run time.
A fairly simple mod using constant duty solenoids, however one could simply use ones finger and manually switch off the charger just as easily.
Given that I need to manually switch on the next load anyway the only advantage would be some fuel savings by reduced genset load if not bringing more AC load on line to replace that now not being used by the charger.

I have a domestic fridge and the normal draw is 13.5A with just it and the DC freezer running with the odd light and small DC loads. A fairly high load as Randal notes and the fridge and freezer are the main amperage hogs. This limits the amount of time the boat can sit without me starting the genset as I do not have solar or wind generation. I am considering using the other virtual switch to trigger a genset start/stop box if I need to leave the boat for longer than the batteries can keep the fridge and freezer alive.

My boat is a power hog, and I am in a tropical environment. In retrospect, a larger genset would be nice so that I can charge full on, run aircon(s) and high high loads all at the same time. If aircon is not an issue than the standard genset is fine.

It should be noted that my set up allows me to run the aft cabin 8000 BTU aircon overnight on the batteries - a nice feature in the tropics.

As Randal notes, the end design is all about how you use the boat so YMMV

Robert

Has anyone used the Isotherm SP freezer and fridge systems.

The use very little amps and would cut down on the energy usage.
The reviews are generally good, even in tropical waters.