If you haven’t been following the blog of Kosmos, the Nordhavn 40 that is circumnavigating, this could be a good day to start. On today’s blog (which lags by a few weeks the actual events), they are just starting their Atlantic crossing, traveling alone, with only three people on board.
And on a different topic….
My boat is back at the dock at the Salmon Bay Marine Center, after several weeks of work at the Delta Shipyard. Most of the major work is now complete, although there are a large number of small details that still need completed.
As you can see, it was snowing in Seattle!
While the boat was out of the water, we had the props re-pitched. I mentioned a few weeks ago that the owner of the second N68 did some research which indicated that with some tweaking of the prop pitch we might be able to pick up another 15-20% of fuel efficiency. This sounded overly optimistic, but I decided to have the ship yard take a look at my prop. After a bit of study, they decided my boat was over-propped. This added to my confusion, in that David, the owner of the second N68, heard from the experts that his boat was under-propped. Both of us puzzled over this one. We have roughly identical boats, bought from the same company, and yet the experts are telling both of us that our props need tweaking, and that the fix is the exact opposite for each of us.
We did send my props out for modification, and here is the report I received back:
Kruger & sons report
Report 1 – OSO Class 1 Initial Report Left wheel / Final report after adjustment
Marked Dia 38.5 Marked Dia. 38.5
Measured Dia 38.6 Measured Dia. 38.7
Mk’d Pitch 37 Mk’d Pitch 35
Pitch of wheel 36.45 Pitch of wheel 34.97
Report 1 – OSO Class 1 Initial Report Right wheel / Final report after adjustment
Marked Dia 38.5 Marked Dia. 38.5
Measured Dia 38.5 Measured Dia. 38.7
Mk’d Pitch 37 Mk’d Pitch 35
Pitch of wheel 36.46 Pitch of wheel 35.10
It is too soon to say whether or not the modification to Sans Souci’s props increased fuel efficiency or not, but the first indication is positive. All we have done at this point is a short test run, but here’s what Jeff wrote me afterwards:
“Ken: The sea trial went well. The wind was blowing S/E 25 knots so we have some wind. I went in the wind and with the wind and the engines did not change RPM. I had 1850 on the port and 1879 on the starboard. I have to compare my records but at 1350 I was burning 12 per hr. making 9.5 kts. I think it used to burn 13.5 per hr. at that RPM….”
I’ve now spent four days staring at Sans Souci’s electrical plans. I set what I thought would be some easy goals, but I’m not particularly gifted at studying electrical plans. My goals are: 1) to produce a simplified electrical diagram that I can use to quickly spin others up to speed on the system, and 2) To identify points in the system where I want to add additional current and voltage measurements, so that I can know how much power I have available at a glance. Currently, it is almost impossible to know power consumption around the boat.
This got me thinking about power management….
Power management on a boat is a daily part of life. I don’t want to make it sound tougher than it is, because after you’ve done it for a while, it becomes second nature. Roberta knows that before she starts the dryer she must say: “Is it ok to start the dryer?” There are a number of things around the boat that use a lot of electricity, for instance, the air conditioning, the water makers, the davit, the dive compressor, the electric stove, etc. Before any of these high-current items are started, I need to know about it.
I always have to be aware of where the boat is getting its’ electricity, the state of charge of the batteries, and the approximate electrical load. Mistakes can easily mean blown fuses or dead batteries.
This sounds simpler than it is. Sans Souci actually has four electrical systems; a 12 volt DC system, a 24 volt DC system, a 120 volt AC system, and a 240 volt AC system. Some of these systems have multiple sources of power. For instance, the 240 volt system can be fed five different ways: from two different generators, shore power (directly), our Atlas shore power converter, or our inverters. Each of these different power sources have different limitations, and I constantly need to keep the loads at appropriate levels. Overload means blown fuses, and under-loading a generator wastes fuel and can cause damage.
My electrical panel has digital gauges which help me know what is going on, however the gauges aren’t always easy to interpret, and it isn’t always me doing the interpreting. On our trip to Costa Rica we blew a lot of fuses. This can be fairly annoying when running at night and suddenly all the lights go out.
One of my goals for this winter has been to “idiot proof” the electrical system. I think that if it were just Roberta and I on the boat, this wouldn’t be an issue, but we tend to have a lot of guests and crew on the boat. Guests don’t generally read instruction manuals, and many have no fear of pressing buttons, whether they know what the button is or not. For instance, Sans Souci has electrical heaters built into the air handlers in each room. These electrical heaters use a HUGE amount of electricity, and using them can easily put the boat over the edge to tripping a shore power breaker. Once I tired of constantly resetting the breaker, I discovered that it was possible to lock out the heat strips. This allowed me to become master of the heat strips, and I could adjust the loads as needed to ensure that there wouldn’t be an issue.
I’m approaching this whole issue of idiot-proofing from many different angles. One thing I noticed was that when running our smaller generator (the 16kw), along with the air conditioning, it didn’t take much additional load to blow fuses. We prefer warmer climates, so this effectively locked us out of running the 16kw generator. To ease this problem, I upgraded our generator slightly, to a 20kw. I also swapped our air conditioning chillers to units that would start up with no spike in current demand. Electrical motors tend to use double their operating current, for a brief instant, while starting up. Most power sources are designed to accommodate quick spikes in demand, but I could never get this to work reliably, and I ultimately decided that the best way to deal with spikes is to eliminate the spikes.
Actually, when we built the boat, I did some customizing that was supposed to have made the electrical system simple. Sans Souci has 14kw of inverter capacity, which I believed would be adequate to run the entire boat, exclusive of air conditioning. In fact, my original plan had been that I could even run a limited amount of air conditioning off of the inverters.
However, this was my first experience with a chilled water air conditioning system, and I did not understand the current requirements. The minimum required power for any air conditioning on Sans Souci is around 7kw (Chiller plus Circ Pump plus Raw Water Pump plus Air Handler). I have a large battery bank, but it isn’t large enough to run the air conditioning for long.
With a little bit of math, I can quantify how long I could run the air conditioning off of batteries.
My battery bank of 1,500 amps, at 24 volt. With a bit of math, this equates to 18kw of stored power, implying I could run the air conditioning nearly three hours. Wrong. For maximum battery life, the battery bank should never be discharged more than 50%. In other words, I have only 9kw of stored power. Well.. unfortunately, wrong again. The process of converting power from 24 volt to 240 volt “eats” some of the power. In other words, 9kw in the battery equates to only 8kw by the time it gets converted to 240 volts. If nothing else on the boat were running, I could run the air conditioning for a little over an hour off the batteries.
The bottom line on this discussion: Realistically speaking, air conditioning cannot be run off the batteries. Period. When the air conditioning is running, a generator must be running. I have said a few times over the past few months that Sans Souci is an “Generator Always On” boat, and this is the reason why.
Given this, I asked the technicians to move the air conditioning off the inverter circuit.
When I think about power on Sans Souci, I mentally divide the world into “with air conditioning” and “without air conditioning”. If the air conditioning is going, then I MUST be on a generator or hooked to shore power. If the air conditioning is not running, then power management is completely different. I really want to run the boat off the inverters, with the generator kicking in ONLY when the batteries need charging.
That last half of that last paragraph needs some explaining.
When the air conditioning is not running on Sans Souci, we really don’t use a ton of electricity. Our “normal” load is only around 3kw, and with my switch to LED lighting, I’m expecting that I might shave a full 1kw off of this. There are plenty of spikes along the way, such as when someone fires up the microwave to make popcorn. But, on average, I think we can get the normal burn down to around 2kw per hour. You may recall that back a few paragraphs I mentioned that we have 8kw stored in the batteries. This implies that sitting at anchor, I need to run the generator every four hours, to keep the batteries charged properly. I can lengthen this time by allowing the batteries to drop lower than a 50% charge, but this ultimately shortens the battery life.
Running the generator all the time, even without the air conditioning, is a flawed strategy. We have been doing this on Sans Souci, and it doesn’t really make sense. Let’s look at what happens, and why I say this. Let’s say that I have a load of 2kw, and start a 20kw generator (my smallest). What happens? The answer is that under-loading of a generator by 90% is very hard on the generator. The generator’s life will be shortened. Not good. Historically, we’ve solved this by turning on everything in sight. We turn on the electric heaters, we turn on the air conditioner, even if it isn’t needed, whatever. We need to get the generator load up to at least 50% or more. The downside to this strategy: It narrows the “head room” of available current, increasing the need to do power management, and wastes fuel. My generators burn 1 to 2 gallons of fuel per hour. This translates to money and range. My 20kw generator burns over a gallon per hour of fuel, which isn’t a huge amount, but it does add up. It can easily cost $75 per day, just in fuel, if the generator is run around the clock. This is real money, perhaps not by government standards, but certainly by “Ken” standards.
My latest thinking is as follows (for power management when not running air conditioning):
I have auto-start on my 20kw generator. In other words, it has a mode where it will run only when it perceives a need to be run. I’m thinking I’ll just leave the generator in auto start mode, and forget power management. Without the air conditioning running, I’d have a heck of a time overloading my 14kw of inverter capacity. I’ll just tell the generator to constantly measure battery voltage, and kick in when the voltage seems to indicate that the batteries are in need of charging. My guess is that this means “every three to four hours.”
That said, there are some strange exceptions I’m trying to sort out.
Battery charging on my boat confuses the heck out of me. My house battery bank can be charged many different ways, and there doesn’t seem to be any central brain (except my own) that regulates the charging. The batteries can be charged by: My hydraulic alternators, my main engine alternators, the inverters and a manual electric battery charger. While underway, my main engine alternators put out over 2kw each! This power goes first to the starting batteries, with any extra feeding the house bank. It is possible that my generator never needs to run while I’m underway. I also have the hydraulic alternators which can add another 8kw in battery charging while underway. Before we get underway again, I want to develop a better understanding of the battery charging. With so many devices that are trying to charge the batteries simultaneously, I don’t understand how they don’t get in each other’s way.
Perhaps you can see why I am taking the time to study my electrical plans. This can all be very confusing!