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Old 13-07-2009, 17:21   #16
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Hi Nick/S/V Jedi,

An interesting point regarding the power needed to re-cool the portable fridge after being switched-off. Prima facie I'd be surprised if the excess required in the morning was equal to that forgone overnight. But it's worthwile keeping in mind. It would need a very controlled experiment to test it. As I said, it generally only goes up a couple of degrees overnight and seems to quickly regain the required temp. And in a temperate climate, most nights are cool.

Also, a few cans of cold beer in the box probably acts as a bit of a cool bank! So I guess I should keep up the beer supplies!

And ruined food? Not been a problem. None so far.

Max.
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Old 13-07-2009, 17:29   #17
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This book is great. Really helps to explain this well. Just a happy customer.
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Old 13-07-2009, 18:04   #18
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Max,

You don't need controlled experiments to test that; simple logic is all we need:

It doesn't matter how cool the night is. Even when the box would stay at temperature on it's own. This is because the compressor has a thermostat control and will only run when the temp gets too high. If the box only gains a couple of degrees during the night, the compressor will only run very shortly to compensate just those couple of degrees. In fact, the thermostat does just that; when you set it to 5 deg. Celsius, it will not start the compressor at 5.1 Celcius. My compressor starts at 7 Celsius and switches off at 5 Celcius. This is called the "hysteresis" of the thermostat and it prevents short cycling. In the real world: at night, the compressor runs the fridge down to 5 deg. Celsius and stops. During the night the box heats up to 6 Celsius... nothing happens. In the early morning the box hits 7 deg. Celsius and the compressor brings it down to 5 again.

When you would have the system switched off during the night and find the box at 7 deg. Celsius in the morning when you switch it back on, the result is the exact same but you did more work (switching, remembering).

In other words: the amount of heat (=energy) that creeps in during the night must be removed (costs x amount of energy). It does not matter if you do that step by step during the night or all in one go in the morning.

If you experience energy savings when turning the system off at night, this is because the box warms up much more than you think. A box that is held at 10 degrees C needs less energy than one that is kept at 5 C. If you want that, adjust the thermostat to that higher temp but, like I wrote before, your food will spoil quicker.

cheers,
Nick.
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Old 13-07-2009, 20:54   #19
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I'll answer as someone who is not a full time cruiser, but has done a variety of cruising over the past decade for cruises of 2 weeks to 3 months.

First, as Paul, said a lot depends on lifestyle. For me it also depends on the cruising environment. When I sailed on Lake Superior, I was happy to go without a fridge and saw the occasional bag of ice as a real luxury. It was a luxurious step up from activities like backpacking.

When I began to sail the Bahamas in the summer, my priorities changed.

I still am happy to live fairly simply but there are four luxury "upgrades" I can't imagine cruising without: A fridge, an autopilot and a real marine head (as opposed to a porti-potti.) and a bimini.

On my new used boat, I'll be hauling the anchor up by hand. It has pressure water, but I'd gladly go with a foot pump system. A hand held GPS is fine. The fridge is something however, I need to take care of. I'm even thinking of tearing out the oven and using a camp stove, so I'll have room for one of those pre built units there.

Ice worked fairly well for me on the Great Lakes, but as mentioned previously here, one is lucky to get three days out of it in warmer climates. I frequently go 10 or more without ever visiting a store. Obviously, passage makers go much longer than that. The other thing I was quick to discover is there is no better way to have your food go bad than to keep it in a wet, humid, enclosed icebox that is no longer cold. Of course this can also happen if you don't have the power to run your fridge.
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Old 14-07-2009, 03:28   #20
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Originally Posted by nautical62 View Post
... there is no better way to have your food go bad than to keep it in a wet, humid, enclosed icebox that is no longer cold. Of course this can also happen if you don't have the power to run your fridge.
The preferred Refrigeration temperature is somewhere between 35 and 38 degrees F (1.7 to 3.3 degrees C).
A unit, set at 38 Degrees, might come on at 38 Degrees, and shut off at 35 Degrees.

Bacteria grow most rapidly in the "Danger Zone" range of temperatures between 40 and 140 ̊F.

The United States Food and Drug Administration set the maximum refrigerator contents* temperature at 41 Degrees Fahrenheit.

* Maximum Food temperature, not interior air temperature, which may fluctuate.

See also Glacier Bay’s excellent FOOD STORAGE pages:

Glacier Bay - Support

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Old 14-07-2009, 05:14   #21
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Nick,

Mmmmm. I see your point. You are suggesting that if I leave it on all night it will use (eg) a+a+a+a =y energy ( to keep it at a predetermined temp). If I switch it off and then on again in the am. it will use Y energy (in one go)?

Also the "hysteresis" (Boy, there's a new vocab!) issue is interesting. But when iI do turn on the unit in the am, it usually immediately registers a temp of about 6oC (before it drops to 4oC). (Perhaps the beer helps!). (PS; we do celsius here)

But I do understand that most people with eutectic motor driven compressors (the noisey sort) turn them on about twice a day, bring the temp down, then let it creep up during the next few hours before bringing it down again. So I've been operating like that.

I'll experiment next summer - its mid winter here now, so its only day sailing for the moment, and so the beer can be brought from home pre-chilled..

Regards,

Max.
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Old 14-07-2009, 07:58   #22
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Correction, amplification and a funny.

Correction: our Engel is rated at 2.5 amps 12v DC not 4 as I posted. I was thinking of our PUR Power Survivor 40E desalinator which uses 4 amps.

Amplification: the Engel has a variable thermostat so that it can be used continuously as a refrigerator or freezer. Setting it lower maintains a given temp and we have found that in cooler conditions a setting less than the max setting maintains freezer temps.

Funny: This past Feb we were returning to NC via the ICW from St. Lucie Inlet. Air temp was very cold. We usually ran the Engel at max all the time and the motor never turned off. During the trip north with the Engel controls set at coldest the motor actually shut off a couple of times each night for a week. So much for our sunny south!
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Old 14-07-2009, 08:30   #23
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Having a freezer/refrigerator gives us more flexibility in what we eat, when we eat it, where we go and how often we have to restock. We like the HT milk. We take it while cruising, but the normal milk is a lot more cost effective, if you already have the fridge. We store lots of meat, we use them to supplement what we would buy locally. Often times what they had available was not what we liked, or what we wanted to spend on it. We found often times that there were things we really liked locally and at a good price. We found ourselves stocking up on those. My wife likes vegs, so we tend to buy and eat those quickly. We supplement with cans so that not as much an issue. We do however make larger quantities, refrigerate and eat multiple times. This cuts down on heat and hassle in the warm climates. Cold drinks and ice just makes life so good! But, they are not essential to health.

So, "c". Or whatever you like and/or can afford!
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Old 14-07-2009, 08:44   #24
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soda bottle idea

Cosmos;


We have a a Coleman Stirling Cooler, and I was thinking of doing the same thing. I tried an experiment, putting four on-gallon ziplocks filled with water in to freeze overnight, which it did not. There was some partially frozen water, but from a stand still, it could not handle to load.

I have to re-try that experiment using some soda bottles. I'll also load some pre-frozen foods in there to simulate more real-world situations.

Have you ever had the water not freeze overnight becuase of high outside temperatures?

Our icebox is larger, about 4-5 Cu Feet, and most likely the insulation has deteriorated, as it is 25+ years old. I may remove it carefully, and rebuild it with new insulation. As always, time and money are the limiting factors.

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It does depend on what you want and size is not necessarily a constraint. Aboard our 25' Cruising sailboat (and our son's 27' cruising sailboat) we have an Engel MT35 portable freezer. The unit is about the size of a normal cooler and lives in the aft of the cockpit. My requirement is 1) Two trays of ice cubes per day 2) Two 1 lt. bottles of ice per day 3) Some miscellaneous treats.

We have a built in 2 cu ft ice box in the galley. We keep two 1 lt bottles (juice bottles like Ocean Spray) of ice in the ice box. Each morning we swap the partially thawed 2 in the ice box for the 2 completely frozen bottles in the Engel. This way we have fresh block ice every day. Power consumption is 4 amps at 12 volts. We have four solar panels providing a rated 460 watts per hr. Count on half that. Both ours and our son's Engles have run continuously since June 2005 and defrosted about every 6 months (takes 1/2 hr). Capt. Woody of Lats and Atts took the smaller MT 17 on his circumnavigation. And yes it will keep ice cream.
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Old 14-07-2009, 10:45   #25
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Well, I seem to be in the minority here; I prefer to cruise without a fridge.
Aside from the power consumption, a very well insulated top loading ice box will keep ice for up to a week, ( at least mine does). THere is abosultely no need to live on canned and dried food only. THere are lots of fruits and veggies that will keep very well if stores in bilges etc. Carrots, Tomatoes, cabbage, potatoes, oranges, apples, onions, pears, etc. THe only thing really not able to keep unrefrigerated is meat. Having cruised thru some very remote parts of the world, I would not to eat the meat there anyway . Mayonaisse and mustards, ketchups etc all keep a long time un refrigerated, if one uses clean utensils EVERY time. For meat Use an air dried ham, they keep for months.
It is interesting to note that Beth Leonard and Evans Starzinger when they built the boat after Silk did not put a fridge on board.
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Old 14-07-2009, 19:40   #26
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Rhosyn Mor,

So tell me where you get that block ice every week when cruising very remote parts of the world? I can't even get it in not so remote parts of the world.

We did all that ham/salami/cans etc. but that was in the days we still had a house; now that the boat is our house, we appreciate the same luxuries we had ashore and fridge, freezer, washer/drier & A/C are all part of our spoiled way of life.

What you are doing reminds me of my time in the army, or going camping with tents etc. All very nice but all way behind me ;-)

Now explain me how you get cold beers in the remote places??!!

cheers,
Nick.
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Old 14-07-2009, 19:44   #27
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We did all that ham/salami/cans etc. but that was in the days we still had a house; now that the boat is our house, we appreciate the same luxuries we had ashore and fridge, freezer, washer/drier & A/C are all part of our spoiled way of life.
It's a nice house too!
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Old 14-07-2009, 19:48   #28
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It's a nice house too!
Thanks Chris. Jedi's mother (original Sundeer) is now in the second slip from us... strange sight ;-)

ciao!
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Old 14-07-2009, 20:01   #29
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Cosmos

We have a a Coleman Stirling Cooler, and I was thinking of doing the same thing. I tried an experiment, putting four on-gallon ziplocks filled with water in to freeze overnight, which it did not. There was some partially frozen water, but from a stand still, it could not handle to load.

I have to re-try that experiment using some soda bottles. I'll also load some pre-frozen foods in there to simulate more real-world situations.

Have you ever had the water not freeze overnight becuase of high outside temperatures?

Our icebox is larger, about 4-5 Cu Feet, and most likely the insulation has deteriorated, as it is 25+ years old. I may remove it carefully, and rebuild it with new insulation. As always, time and money are the limiting factors.
A correction to my previous post: the rated power consumption of the Engel MT 35 is 2.5 amps. We've never seen it go over 2.0.

From a dead start it takes about 36 hours to freeze 1 gallon of water in the Engel. That is from their spec sheet and confirmed by my experience. Based on our experience I would say that you would need 1 lt ice bottle per cu ft of cooler.

Changing the ice bottles every morning means we start refreezing partially defrosted bottles not from scratch every time.

Keeping the freezer FULL of frozen stuff helps the Engel refreeze faster.

Keeping the ice box full of cold stuff helps the ice last longer. For instance, we have two 1 qt metal seltzer bottles that charge with small CO2 carts. When one empties we leave it in the cooler to stay cool for the next refill. If we took it out until we refilled it it would warm and stress the temp in the ice box when we put it back in.

Insulation is a critical factor. We have the insulating jacket marketed by Engel and it helps. Also we try to keep the Engel out of the sun in the cockpit which has Bimini, dodger, connector and full side curtains and awning. When in hot climates we double a large beach towel and lay it over the top of the Engel then wet it with fresh water. The evaporative cooling helps.
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