As our boats become bigger and we rely on more fancy toys to run them, electrical power has become critical to enjoying our boats. We rely on the GPS to find our way, the Auto Pilot to get us there, and the refrigerator to cool the beer when we arrive, we well as turning on the stereo, the lights, and in some cases, the TV and or the DVD.
We try very hard to sail, never turn on the engine and in the process depend on the energy stored in the ships batteries to run everything. When we do this, we keep in mind that we have to start the engine at the end of the weekend to at least motor out of the anchorage, as the wind will always be blowing in the wrong direction.
I think of the power, or energy stored in the ships batteries as money in the bank. As you use power, you are taking money out of the bank. As you are charging the batteries, you are depositing money in the bank. The difference on our boats is that there are no loans or credit cards! When the balance is zero, something does not work and the engine won’t start. That is embarrassing, annoying and expensive.
Melissa and I, with the exception of our vacation, will spend long weekends on the boat. I have engineered Indulgence so that there is sufficient electrical energy stored in the batteries for three days on the hook. That is enough for everything we do, including the refrigerator, lights, water pump and stereo. In addition, I have installed a starting battery, so that even if I use too much energy, I can always start the engine. The operation is simple, it is almost impossible to use the starting battery for anything other than starting the engine.
The one piece of engineering that you must understand is the concept of Ampere hours. A device that uses one amp for one hour uses a total of one ampere hours. If the device runs all day, it uses 24 ampere hours per day. In our bank analogy, this is the equivalent of an amount of dollars. I started by conducting an energy audit for the way we use our boat. We keep our refrigerator on all the time and that uses about 60 ampere hours per day. Lights, pumps and other miscellaneous stuff use about 40 ampere hours for a total of about 100 ampere hours per day.
To conduct the audit, shut everything off on the boat. Then turn on the lights and look at the ammeter. Multiply the number displayed on the ammeter for the amount of time that you have the lights on. Turn on other stuff that you use and approximate the amount of time that you use it. You do not have to be super accurate, estimates work very well. In addition, most of the ratings on lights, pumps, etc. will note how much current they use. You now know how much energy you will use doing a 24- hour period. That is the equivalent of how much money you will spend during the day.
How much money do we have in the bank? I have three 4D House batteries on Indulgence. Each is rated for 200 ampere hours. The maximum recommended discharge is half the battery capacity, ergo 100 ampere hours of usage per battery. Therefore, with three batteries, I have 300 ampere hours or three days of use. Your batteries will have ampere hour ratings. Again, it is not an exact science, approximations work.
Now comes the part about charging batteries or putting money in the bank. Indulgence is at a slip and plugged in with the battery charger on. Therefore, I start each weekend with fully charged batteries or the maximum amount of money in the bank. If you are on a mooring, you have to determine how much charge you are putting on the batteries when you run your engine. This can be noted by watching the ammeter, noting the amount of amperes and the time for that value. For most good marine charging regulators, as the batteries reach full charge, the current into them will decrease. Be careful of this as the regulators that are supplied as standard equipment on our boats tend to be inexpensive automotive type regulators and will not allow the batteries to reach full charge quickly.
Reader Feedback.....
The first is from Melissa Patterson and Jim Meador. As a result of having to replace batteries, they have constructed two spreadsheets that they use to conduct a power audit of electrical consumption on their boat Odyssey, a C380. Jim or I will gladly send the formulas to you on request. Here is a brief description of the spreadsheet. Jim has listed all items that use power, including all the lights, instruments, pumps, etc. Power consumption, watts and amps are listed and then multiplied by the amount of time used to get total consumption. The usage will change, if you are under sail or at a mooring, e.g., you do not use your autopilot at a mooring. He then totals the consumption and compares it to the installed battery capacity on the boat, calculating a comfort factor. Should you choose to use this, you should make sure the ratings numbers match the equipment on your boat, and the times for use match your individual usage. You will also need to match the battery capacity with your boat. The spreadsheet is terrific, and I strongly recommend it to all as they will be able to understand why the lights get dim after a few days on a mooring.
Warren Elliott wrote and reinforced the concept of a battery monitor or battery management system. Warren wrote, “… it provides direct amp-hour monitoring as well as much more accurate current and voltage measurement, as compared to the usual meters supplied with most boats. Also, an important reason for good battery management is to have sufficient energy remaining to start the main engine.” Warren goes on to say, “Three good backups, in the event of failing house batteries, are a separate starting battery, a Honda or similar portable generator and battery packs.”
I just thought of two more backups: the first are good friends near by with very, very long battery cables; and the second is good towing insurance.