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Old 05-10-2016, 22:42   #46
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Re: Most efficient way to boil water on a boat

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Single cup immersion coil. Maybe not the safest or lowest electric load, but quick!
Just got to make sure one uses a good quality version and not some el cheapo Chinese junk. In college I had such cheap one melt down on me while still in the cup. It was fun to watch albeit a bit scary as it could've been a disaster had I left my dorm room for a minute or two.
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Old 06-10-2016, 05:09   #47
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Re: Most efficient way to boil water on a boat

My issue with it is that using your meager electrical supply to heat anything is about the worst possible use.
Reasoning is that it takes a tremendous amount of energy to heat water, and if money is an object I'd bet that propane and or Diesel is your cheapest source of energy.
Now if you have excess Solar well then use it as you please.
But I believe that most are undercharging their battery bank more often than not, and this of course leads to an early death of the bank, and batteries are a significant expense to most. So I hesitate recommending anyone use electricity to heat water based on the efficiency of doing so, I think they are better off pushing those amps into their bank than by heating a cup of tea.

Think of it as being frugal, that free electricity, may come at a cost.


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Old 06-10-2016, 05:43   #48
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Re: Most efficient way to boil water on a boat

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Originally Posted by a64pilot View Post
My issue with it is that using your meager electrical supply to heat anything is about the worst possible use.
Reasoning is that it takes a tremendous amount of energy to heat water, and if money is an object I'd bet that propane and or Diesel is your cheapest source of energy.
Now if you have excess Solar well then use it as you please.
But I believe that most are undercharging their battery bank more often than not, and this of course leads to an early death of the bank, and batteries are a significant expense to most. So I hesitate recommending anyone use electricity to heat water based on the efficiency of doing so, I think they are better off pushing those amps into their bank than by heating a cup of tea.

Think of it as being frugal, that free electricity, may come at a cost.


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I agree with being electrically frugal and we have always been that way.
We never draw our batteries below 12.4 (80%).

Solar panels make it easy to keep the battery bank full.

We had 500 watts on our last boat and the original batteries tested like NEW after 7 years.
The Surveyor told the new owner the Battery's test like NEW.

We are big fans of solar as they just work for you all the time without skipping a beat or making any NOISE. After a while you forget where the power is coming from. What's not to like about that.

Lots of cruisers complain about generators and wind turbines, but you never hear them complain about Solar. Why, because their is nothing to complain about.
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Old 06-10-2016, 05:52   #49
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Re: Most efficient way to boil water on a boat

And there's no such thing as a "hot water heater". if the water is hot, you don't need to heat it.
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Old 06-10-2016, 06:03   #50
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Re: Most efficient way to boil water on a boat

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And there's no such thing as a "hot water heater". if the water is hot, you don't need to heat it.

While we're at it, there's no such thing as "unsweetened tea."


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Old 06-10-2016, 06:08   #51
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Re: Most efficient way to boil water on a boat

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While we're at it, there's no such thing as "unsweetened tea."


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Haha! That's one of my personal pet peeves. That and "white coffee"...
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Old 06-10-2016, 06:33   #52
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Re: Most efficient way to boil water on a boat

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Originally Posted by a64pilot View Post
My issue with it is that using your meager electrical supply to heat anything is about the worst possible use.
Reasoning is that it takes a tremendous amount of energy to heat water, and if money is an object I'd bet that propane and or Diesel is your cheapest source of energy.
Now if you have excess Solar well then use it as you please.
But I believe that most are undercharging their battery bank more often than not, and this of course leads to an early death of the bank, and batteries are a significant expense to most. So I hesitate recommending anyone use electricity to heat water based on the efficiency of doing so, I think they are better off pushing those amps into their bank than by heating a cup of tea.

Think of it as being frugal, that free electricity, may come at a cost.


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+1. I'm happy to use a bit of extra propane in order to keep my battery bank SOC with a good reserve.
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Old 06-10-2016, 06:45   #53
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Re: Most efficient way to boil water on a boat

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Originally Posted by a64pilot View Post
My issue with it is that using your meager electrical supply to heat anything is about the worst possible use.
Reasoning is that it takes a tremendous amount of energy to heat water, and if money is an object I'd bet that propane and or Diesel is your cheapest source of energy.
Now if you have excess Solar well then use it as you please.
But I believe that most are undercharging their battery bank more often than not, and this of course leads to an early death of the bank, and batteries are a significant expense to most. So I hesitate recommending anyone use electricity to heat water based on the efficiency of doing so, I think they are better off pushing those amps into their bank than by heating a cup of tea.

Think of it as being frugal, that free electricity, may come at a cost.

What makes you think it takes an "enormous" amount of energy to heat a bit of water?

To boil half a liter of water from 15C only needs 0.05kW/h of energy. My battery bank has usable 5kW/h of power in it. So every time I make a couple of mugs of tea in the electric kettle, I am using only 1% of the usable capacity of the bank (0.5% of the nominal capacity).

This is a trivial amount of electricity, which your batteries hardly notice.

Electric kettle all the way for me. One of the best items of gear on board. It is useful to find a small one which won't use up a disproportionate amount of battery capacity due to Peukert. Many of them are more than 2kW, some close to 3kW. I found one which draws 900 watts, and it is fine for up to four cups of tea.

Propane is a PITA to source and haul, and around here anyway it's not cheap. On the contrary, I conserve gas. If you boil water on the stove, most of the heat is dissipated uselessly around the pot. Electric kettle is almost 100% efficient, I believe making up for the heat losses you have in converting burning diesel fuel to electrical power in your generator.

Similar calculations with regard to microwave ovens vs. gas oven.

For me it's a no brainer. YMMV of course.
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Old 06-10-2016, 07:04   #54
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Re: Most efficient way to boil water on a boat

Creating heat as opposed to movement say is energy intensive,
For example, we all know that the kinetic energy in an automobile at highway speed is tremendous, enough to completely demolish a building for example but when you come to a stop all that tremendous amount of energy is converted into heat, and yet nothing catches fire (usually )

Its not boiling water so much, its creating heat that takes a bunch of energy, moving heat is more efficient than creating it.
No I am not abdicating a compressor based water heater, but they are more efficient, although I don't understand the though that electric resistance heat is nearly 100% efficient, maybe what they are thinking is that nearly 100% of the heat is transmitted to the water?


So what I am saying is using your battery bank to create heat may not be the best use of it, but concede that is of course dependent on other things, like if you have excessive power and availability and price of propane, for me it's easily available and dirt cheap as we don't seem to use much of it, but we are not full time either, usage rate will increase then of course
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Old 06-10-2016, 07:49   #55
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Re: Most efficient way to boil water on a boat

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Originally Posted by a64pilot View Post
Creating heat as opposed to movement say is energy intensive,
For example, we all know that the kinetic energy in an automobile at highway speed is tremendous, enough to completely demolish a building for example but when you come to a stop all that tremendous amount of energy is converted into heat, and yet nothing catches fire (usually )

Its not boiling water so much, its creating heat that takes a bunch of energy, moving heat is more efficient than creating it.
No I am not abdicating a compressor based water heater, but they are more efficient, although I don't understand the though that electric resistance heat is nearly 100% efficient, maybe what they are thinking is that nearly 100% of the heat is transmitted to the water?


So what I am saying is using your battery bank to create heat may not be the best use of it, but concede that is of course dependent on other things, like if you have excessive power and availability and price of propane, for me it's easily available and dirt cheap as we don't seem to use much of it, but we are not full time either, usage rate will increase then of course

"100% efficient" is somewhat deceptive -- yes, that's talking only about conversion of electrical power to heat, and getting the heat into the water. It leaves out the tricky bit which is making electricity in the first place out of heat.

Diesel engines without turbos are about 30% efficient I think, which means 30% of the heat in the diesel fuel is converted into mechanical energy. Then you lose some more converting mechanical energy to electrical energy.

So maybe 20% of the energy in the diesel fuel, makes it through all these conversion steps and into your cup of tea as heat?

But still, a lot of the heat in propane burned in the stove is lost. Different with different stoves and different pots, but I would be surprised if this is ever more than 30% efficient or so.

So considering the cost of propane per BTU compared to the cost of diesel fuel per BTU (difference of about 5x over here), you're probably equal or even ahead, making your tea with the electric kettle, cost wise.

But that's not why I do it -- we're talking about trivial sums. I use the electric kettle because it's easier and neater and doesn't put combustion products into the cabin. In my particular case, my batteries don't notice the power used. YMMV.


For whatever it may be worth, my next boat will have no gas system at all, and will have all electric cooking. I don't like gas on boats at all, as you may know from my other posts. I think it is inherently dangerous, and a PITA to keep reasonably safe. It's a PITA to source and haul gas, particularly when you cruise in different countries which all have different standard bottles, as I do. It's also an entirely different system to keep up. Electric induction cooking is really efficient, and electric convection ovens are fabulous. Add a couple more batteries in place of the gas system, and it seems like a no-brainer.

And even better if you're using lithium batteries, which my next boat will have.

I don't have solar, and don't plan to have it (sailing performance is REALLY important to me, and I don't want the windage). But with LiFePo with its huge acceptance rate, you can use a generator really efficiently, and there is no longer any need to keep the batteries topped up (lithium batteries don't even like that), and no need to worry about leaving them at low charge. All this will make is much easier to use electrical power for anything -- like cooking.
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Old 06-10-2016, 08:05   #56
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Re: Most efficient way to boil water on a boat

The question about what constitutes "efficiency" still has not been answered. Many have hinted at the various ways that it could be defined. In particular, my guess is that the original "efficiency" ratings are only taking into account how efficiently the heat source converts non-boiling water into boiling water.

This ignores how efficiently the original fuel is converted into heat. Turning electricity into heat is notoriously inefficient. Turning propane into heat is exactly the opposite. Then we get into all of the issues already brought up about how you get the propane or electricity in the first place, how you store it, how expensive it is, and so on.

Bottom line is that without a whole lot more information about what "efficiency" really means in the original post, the numbers are pretty meaningless.
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Old 06-10-2016, 10:03   #57
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Re: Most efficient way to boil water on a boat

We are trying to sail as close to the sun as possible so that we will never want to boil water.
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Old 06-10-2016, 10:16   #58
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Re: Most efficient way to boil water on a boat

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We are trying to sail as close to the sun as possible so that we will never want to boil water.
Alternatively, learn to like coffee and tea made with lukewarm water. Instant will be most successful.
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Old 06-10-2016, 10:22   #59
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Re: Most efficient way to boil water on a boat

It's easy to carry a seasons supply of gas. Cheap and always ready. We use a whistling kettle and make 2 Lt of Green tea at a time. Have it hot, warm, cold...... Works for us.
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Old 06-10-2016, 10:22   #60
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Re: Most efficient way to boil water on a boat

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........... Bottom line is that without a whole lot more information about what "efficiency" really means in the original post, the numbers are pretty meaningless.
The entire thread is pretty meaningless.
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