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Old 13-02-2017, 05:51   #1
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Actual power budget of cruising monohull?

I'm planning on installing solar panels on my Morgan 462 in the next 6-12 months, so am in the information gathering stage, trying to figure out what I need to know to make intelligent choices. As part of that I'm trying to put together a power budget, but have little real-world experience to draw on. Sure I can make some good guesses, but they are still just guesses.

There's a wealth of real-world experience here on CF that I'd like to tap into to come up with realistic numbers, knowing at the same time that our actual usage will inevitably be a little different. Does anyone have a power-budget they'd be willing to share that I could use as a reference? Preferably from a similarly sized vessel (46ft monohull) that is being actively cruised full-time? I would be most grateful for anything you're willing to share! Beer's on me...

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Old 13-02-2017, 05:56   #2
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Re: Actual power budget of cruising monohull?

Here's a link to a previous thread

StuM has a couple links to some worksheets in that thread.
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Old 13-02-2017, 06:38   #3
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Re: Actual power budget of cruising monohull?

Your guesses are what will be the most useful, If you have a smart gauge or an amp counter, then you can get pretty darn close, now people usually figure two budgets, one under sail and one not. The under sail is usually higher.
Myself I use a tremendous amount of power and my plan ended up being pretty simple.
I stuffed as much Solar on the boat that I could, and if its not enough, then we will have to go on a diet.
I have yet to see someone complain that they have too much Solar, be like complaining they have too much fresh water or money.

We are not cruising yet, but I plan on not having to be either the water or power Nazi, I think we will get along better if I'm not hovering over her telling her to not use so much water to rinse her hair out.


On edit, Solar or not, in my opinion you need another way of generating power, like a Honda 2000 or built in Diesel genset. I know you have an alternator, just I don't want to use the engine as a generator long term.
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Old 13-02-2017, 06:53   #4
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Re: Actual power budget of cruising monohull?

Check out this thread that talk about this question in some detail

http://www.cruisersforum.com/forums/...ge-172450.html
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Old 13-02-2017, 06:58   #5
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Re: Actual power budget of cruising monohull?

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Originally Posted by a64pilot View Post
Your guesses are what will be the most useful, If you have a smart gauge or an amp counter, then you can get pretty darn close, now people usually figure two budgets, one under sail and one not. The under sail is usually higher.
Myself I use a tremendous amount of power and my plan ended up being pretty simple.
I stuffed as much Solar on the boat that I could, and if its not enough, then we will have to go on a diet.
I have yet to see someone complain that they have too much Solar, be like complaining they have too much fresh water or money.

We are not cruising yet, but I plan on not having to be either the water or power Nazi, I think we will get along better if I'm not hovering over her telling her to not use so much water to rinse her hair out.


On edit, Solar or not, in my opinion you need another way of generating power, like a Honda 2000 or built in Diesel genset. I know you have an alternator, just I don't want to use the engine as a generator long term.
We use solar and our alternator for cloudy days or on passages. We can on reasonable sunny days go for weeks without having to use our engine driven alternator. The real key is to get your use under control. Our fridge is very well insulated and sealed and in the tropics we normally don't exceed 30 amp hours in 24 hours. I use a CPAP at night but it's also very efficient with a low draw. Our water maker is a Spectra, very efficient. We use tablets rather than our laptops for most day to day internet stuff as they require way less energy to recharge. To me it's about getting your daily use down as low as possible or further complicate your life with gensets which I really try to avoid.
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Old 13-02-2017, 06:58   #6
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Re: Actual power budget of cruising monohull?

The All-Important Energy Budget:
Energy Budget

Record of Daily Energy Use of 100 ah per day:

"Breaking In" New Wet Cell Batteries
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Old 13-02-2017, 07:11   #7
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Re: Actual power budget of cruising monohull?

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We use tablets rather than our laptops for most day to day internet stuff as they require way less energy to recharge.
This is something I've been meaning to ask - what kind of computing do people use, and do you make special considerations based on power consumption. I guess your comment answered that question!
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Old 13-02-2017, 07:22   #8
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Re: Actual power budget of cruising monohull?

We are just out full time for some months now. We have 380 watts of solar and a wind generator. 4 GC2 batteries. Honda EU2000.

All lights used more than occasionally are LED, a big help. Finding the sweet spot for the fridge is a biggie. All too often my Wife will accidentally turn the thermostat when digging in the fridge and then the damn thing will run the batteries down unless I notice it.

She is still working part time and runs her laptop maybe 20 hours per week. It's an old behemoth with a huge 17" diagonal screen (poor eyes). It sucks an amazing amount of power. She should retire at the end of this year and then we will be done with THAT.

The older Raymarine chart plotter draws a fair bit of power, it's important because it's on for so many hours. I tend to leave the VHF on when we are on the boat, that doesn't help.

Just my non-scientific observations.
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Old 13-02-2017, 07:30   #9
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Re: Actual power budget of cruising monohull?

I don't see how any real cruiser 'out there' could use one of those 'energy budget' spreadsheets. I have never spoken to someone who uses one.

It's a fudge, a guess, a stab in the dark and then you adjust what goes out by what you have (or can bare) going in.

Fill the boat with solar. You can't ever have too much solar. Many boats refuse as they think it unattractive. So that's a good time for me to stop advice to them. If you regard prettiness above a freezer and cold beer you are not going near my comfort zone.

Fill with batteries. 600amp hours is good if you can fit 500 watts solar. And a wind generator is great. But can be noisy. Using the main engine or generator can be WORSE as its loud and heats up the boat, tgats not a good thing in the tropics. A small Honda generator on deck will piss off the anchorage.

The electrical plan can never work as most things in a boat are intermitantky used: bilge pump once per month 15 seconds.
Anchor winlass 1 minute every 2 weeks.
Water pump 1 minute per day except if your have engine grease ... etc etc. Its all baloney to try to calculate it.

The big draws are freezer and refrigeration, but these are totally variable too: in the tropics getting a freezer down to zero F -18C is utterly impossible. The compressor just stays on chugging away, but set at 10F or -8C you only use 40% of elec consumed colder.

So I don't think a spreadsheet works. What does is filling the boat with solar and batteries.
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Old 13-02-2017, 07:43   #10
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Re: Actual power budget of cruising monohull?

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Originally Posted by a64pilot View Post
On edit, Solar or not, in my opinion you need another way of generating power, like a Honda 2000 or built in Diesel genset. I know you have an alternator, just I don't want to use the engine as a generator long term.
I beg to differ. I know more than a handful of folks who have circumnavigated on a wind generator and alternator. One of them was a merchant marine engineer who who installed his new Yanmar before he left and 15 years later had put 10k hours on it and it looked and ran brand new. Add solar to the mix, particularly like your setup, and chances are that Honda is just taking up space and making you carry more gasoline.

That said, everyone's energy budget is different. I have no auxiliary charging at the moment, have 210 usable amp hours, and that lasts me two to three days at anchor. The largest load is my 20 cf fridge/freezer. Under sail, an hour of running the engine every 24 hours keeps me in business, more or less. But I'm assuming when I add solar that my usage is going to change. Being solo, I usually have no one to police and I'm content with my budget, but if I have more power to play with I'll probably find a way to use it.

To the OP, you really need to draft your own budget, which should be easy to do if you have any time spent on the boat. It's simple enough to determine the draw of any individual load, and all you have to do is estimate how much time that load is on at anchor and under sail. Add it all up, add whatever cushion you feel appropriate, and you have your budget.

That said, I do agree that you can never be too good looking, to rich, or have too much solar. In a couple of months I'm doing a good sized refit and I'm going to cram as much solar onto the boat as is reasonably possible.

Don't forget that if you add a significant amount of solar you're going to want to look at your battery bank. If you can't store the energy, then piling on panels is basically a waste of money.
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Old 13-02-2017, 07:56   #11
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Re: Actual power budget of cruising monohull?

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Originally Posted by hpeer View Post
SNIP

All too often my Wife will accidentally turn the thermostat when digging in the fridge and then the damn thing will run the batteries down unless I notice it.

SNIP
This is only one reason why asking about others power usage will not really translate to how you use power. It is true the fridge/freezer will probably be the biggest power sink; but how it is used is also a huge factor in just how big a sink.

I have an Engle in the salon and a Frigaboat in the galley. I try and never open the Frigaboat more than once a day; and only to transfer what I will use that day or the next to the Engle which I sometimes open multiple times a day. With 420 watts of solar charging a 430 amp hour battery bank I normally am dumping power after 10:00 AM on a sunny day; at which time I charge my computers, camera batteries, other toys, and sometimes use my electric rice cooker or other 120 volt toys.

On the other hand I have seen folks who seem to ignore energy saving habits and do things like unintentionally messing with the thermostat. Bottom line is you will need to personally figure out how much power you will use on your own boat, something no one can tell you in advance.
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Old 13-02-2017, 08:10   #12
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Re: Actual power budget of cruising monohull?

People have circumnavigated with no engine, much less electricity.
Electrical devices are a Luxury, you do not actually need them, but as I think they will make cruising much more nice, I want them.
Depending on battery chemistry, you may need to completely recharge them to 100% pretty regularly and or equalize them, that pretty much means something is burning a fossil fuel to do so, a Honda is the cheapest and easiest way to get that. I ended up with a built in genset.
My plan is to make water, wash clothes etc. twice a week, that may change to once a week, but either way on that day the generator will be started early in the morning and as much bulk charging as the bank can stand until I have the excess to make water and wash clothes, water made, clothes washed, generator off and the Solar will finish taking the bank to 100% charge, cause the generator spent an hour or two pushing as many amps as the bank would take early before there was enough Solar to do much.

I just couldn't see how cruising long term could be done on Solar alone, maybe if you accept battery bank replacement ever 24 months or so, or have Life-Po. Life-Po may be the game changer than makes a pure Solar boat more viable.
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Old 13-02-2017, 08:43   #13
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Re: Actual power budget of cruising monohull?

Hi David,

If you looked at any of the other threads linked in other replies you probably saw mention of this, but short answer, to get a realistic energy budget you need to look at what electrical items you use.

Generally the two big ones are fridge and autopilot. Depending on the size, quality of insulation, freezer or not, fridge/freezer could draw 25 to 100 amp hours per day.

Autopilot could be similar.

Most other stuff, lights (especially if LED or at least fluorescent), nav gear, etc will pull much less.

So get a list of all your electrical stuff and you can get a much better idea.
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Old 13-02-2017, 08:56   #14
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Re: Actual power budget of cruising monohull?

With a small refrig box and refrigeration, I'm gonna say 100-120 ah per day.
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Old 13-02-2017, 09:17   #15
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Re: Actual power budget of cruising monohull?

Quote:
Originally Posted by a64pilot View Post
People have circumnavigated with no engine, much less electricity.
Electrical devices are a Luxury, you do not actually need them, but as I think they will make cruising much more nice, I want them.
Depending on battery chemistry, you may need to completely recharge them to 100% pretty regularly and or equalize them, that pretty much means something is burning a fossil fuel to do so, a Honda is the cheapest and easiest way to get that. I ended up with a built in genset.
My plan is to make water, wash clothes etc. twice a week, that may change to once a week, but either way on that day the generator will be started early in the morning and as much bulk charging as the bank can stand until I have the excess to make water and wash clothes, water made, clothes washed, generator off and the Solar will finish taking the bank to 100% charge, cause the generator spent an hour or two pushing as many amps as the bank would take early before there was enough Solar to do much.

I just couldn't see how cruising long term could be done on Solar alone, maybe if you accept battery bank replacement ever 24 months or so, or have Life-Po. Life-Po may be the game changer than makes a pure Solar boat more viable.
I see a lot of boats that generate all their energy from solar. I think it all boils down to finding a balance between consumption and generation of energy. A simple boat with a fridge and LED lights, modern electronics (but no fancy stuff like a washing machine, microwave etc.) should be able to find a way to get by on solar alone (with an engine alternator for exceptional circumstances). I just don't see the need for a generator unless you have committed to "having it all" on your boat, regardless of the energy it consumes. Then yes, I agree that you need a generator. I for one have everything I need aboard and, after my upcoming solar upgrade to bring the total to 365w in panels, will be more than self-sufficient. One thing is certain- it's a lot cheaper (and perhaps easier!) to reduce your consumptio than it is to increase your energy generation!
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