Sans Souci has arrived safely in Ensenada! Today will be spent doing various projects on the boat, clearing out of Mexico, taking crew that is leaving the boat to the airport, and swapping the sat tv from Sky-Mexico back to Directv. Jeff mentioned that the night-time approach to the marina was trickier than expected. The charts, as usual, were not much help, and showed him driving across land as he made his approach.
There has been a lot of discussion on my blog the last few days about electricity generation on boats.
Yesterday, I received this email:
ken, trying to keep this short and simple so hopefully it makes sense! freeing up space in engine room/lazarette. victron has an excellent article referring to this. batteries used with inverters means the generator used can be smaller and is now properly loaded at all times. my first thought is why not go further. hot water/ac/heating/fridge/freezer all have one property in common: they fluctuate between two values ie. hot water 100 to 140 in other words length of cycle time. one could create a simple algorithm to schedule each one in order. now you cut down significantly on how much ac you need. in the case of your boat: kabola thrown overboard. use heat strips and an inline heater for hot tub. a small generator needed now, no need for 2nd generator. atlas overboard, victron invertors can accept shore power anywhere in the world. pto on main engine used for redundancy and produce power while under way. hot water storage changed to hot water tank. some free space used add batteries.
then again i can’t find such a product anywhere or software program that would do this. – jon
I had somewhat the same idea when configuring the electrical system on Sans Souci. The boat has twin generators, but my vision for how I would use them, and how I’ve actually used them, is completely different.
On Roberta’s and my first Nordhavn, our 62, we hardly used our generators. At the time we sold the boat, we had under 300 hours of usage on each of the two generators. Given that we owned the boat for eight years, and cruised over 12,000 miles, this is very unusual.
Our standard practice was to run the boat off the batteries. There were a few ways the batteries were charged. If in port, then they were charged from shore power. If at anchor, they were charged by running the generator an hour a day. And, if underway, we had hydraulic alternators that acted as powerful battery chargers. So in other words, the only time the generator was used at all was if we were sitting at anchor, and even then, if we were moving from anchorage to anchorage each day, the engines and hydraulic alternators would charge the batteries, so there were many days when the generator wasn’t needed.
Our inverter capacity was not adequate to run the air conditioning. We could have run a generator while at anchor to have air conditioning, but never felt the need. In port, we did run the a/c from shorepower, but at anchor we normally just opened up the boat and enjoyed the breeze. The boat was in the Pacific NW for a few years, where air conditioning is not an issue, and in the Med for several years, where it is hot, but not so hot that we needed the air conditioning when at anchor.
We were very happy with our N62 and when working with Nordhavn to design the electrical system for our N68, we wanted to follow the same design theory. Recognizing that the N68 is a larger boat, we put in more inverter capacity. I forget what the inverters were on our N62; my guess would be about 6kw. On the N68 we put in a whopping 14kw of inverter capacity. We also put an auto-start feature on the 16kw generator. I had thought my plan was pretty clever. My plan was that I would have the 16kw generator monitor the batteries, and charge them if needed. With 14kw of inverter capacity, I would be able to run the boat off the batteries, and the generator would charge the batteries from time to time if it felt the need. With 14kw of inverter capacity, my belief was that I would even be able to run air conditioning, just in the master stateroom, on warm nights, off the inverters. Sometime during the night the generator might pop on for an hour to add some juice to the batteries, but I’d never have to think about it.
Jon mentioned in his email that running the boat off of batteries could even negate the need for an international power system. This is true, and we ran like this on our N62 while in Europe. Battery chargers are available that accept both US (60hz) and European (50hz) current.
Almost immediately, after taking delivery of our N68, I discovered that my plan was flawed.
One surprise we received was that the N68 turned out to be much larger than we expected. Although one might think that the Nordhavn 62 is 62 feet long, that isn’t completely true. Almost all N62s, including ours, had a “stern bustle” which extended the length from 62’ to over 68’. We thought of our N68 purchase as going from a 68’ boat to a slightly larger 68’ boat. We knew that the N68 would be larger than our N62, but we didn’t appreciate how much larger. As it turns out the N68 has 91% more sq footage, even though it is roughly the same length. And, even that statistic understates the difference in the boats. We knew we were moving to a bigger boat, but didn’t realize how much bigger. I’m not complaining, and as large as it is, no one has ever complained that their stateroom was TOO large. Because we’re living on the boat half the year or more, we enjoy having all the space we can get. But, with all that space comes a thirst for power.
I underestimated the power requirements of the boat, and much of the added power requirement comes from equipment I’ve added to the boat. I like electronics, and loaded up the boat with lots of things that consume power.
I also under estimated the need for air conditioning. Whereas we could “open up” our N62 and get fresh air through the boat, the guest staterooms on the N68 are downstairs, and tougher to bring fresh air into. Or, perhaps we’ve gotten more spoiled. More likely, the major factor is water temperature. Although it was warm in the Med, the water temperature was in the 70s, instead of the 90s we’ve now seen in Central America. Water temperature, and humidity, makes a bigger difference than I understood.
All of this is the long-way-round to saying: I designed the boat to run off of 14kw of inverter, and it has not worked out. We use the air conditioning more than we had thought, and air conditioning eats a lot of electricity. Also, and I don’t completely understand this issue, but 14kw of inverter capacity is different from 14kw of generator capacity. It isn’t an apples to apples comparison. When electric motors kick in (primarily pumps), they draw large amounts of current for fractions of seconds. Generators accommodate these brief power surges, whereas with my inverters (Outback) the sudden surges cause the inverters to stop inverting.
So .. there are a few issues here, that I’ve been thinking about. First is: do I need higher inverter capacity? Do I need a different brand of inverters?
My current thinking is that the answer to both these questions is “no”. I have been pursuing a strategy that doesn’t work on my particular boat. I do think that there is a place for what Jon is asking about, and what I did on my N62. But, that at some point a boat gets large enough that it doesn’t make sense to run it on batteries. Somewhere between the N62 and the N68 we crossed that line. With boats like the N68 and larger, particularly a boat that likes to run in the warm water climates that we prefer, and with all the electronic gadgetry that I tend to surround myself with, should not try to run on batteries. Actually, it isn’t just warm water cruising. Jon mentions heat strips in his email. We’ll be in the Bering Sea this next summer, where heating will definitely be an issue. I have not spent much time running the heat strips on Sans Souci, but thus far, my experience has not been good with them. They are an enormous power drain.
As I think about work to happen this winter, in preparation for our upcoming cruising, this shift in strategy may mean changes. To some extent, I’m already taking action. I mentioned yesterday that I am swapping one of my generators for a larger one. One major benefit to my new approach (“just run the generator when away from the dock”) is that it is much simpler. On a boat, simplicity is good.