Cheap but effective coolbox daydream

[Greenheart]

Tenting in a lavish-but-low-tech way years ago, I found the only way to get a bottle of Champagne really cold for breakfast, was to roll one of those 10mm sleeping mats into a tube of thick, dense insulation around the room-temp bottle, then stuff a couple of T-shirts up under the bottle, and put a kilo of ice cubes on top...

...in the morning, most of the ice hadn't even melted! The T-shirts had absorbed any drips, and the wine was luxuriously chilly. Just as well, since the curious objects that were sold as 'cool-boxes' were hopelessly bad at living up to their name.

But looking ahead with my usual cheapskate instinct (the 'Champagne' was Spanish Cava ), I'm wondering if one of those feebly-insulated 20-litre cool-boxes could be re-walled internally, reducing capacity by perhaps half (still plenty of space for cold refreshment) with perhaps a grille at the bottom to let defrosted ice run away...

Now, I realise that temperatures on the clear nights I remember, will have dropped to a level which didn't really threaten to defrost my closeted breakfast-bottle...

...my question is how thick will insulation need to be (I realise the lid and floor would need just as much padding) to keep ice mostly frozen, through a long hot summer day?

And, is there a preferred type of foam? Polystyrene is my first thought but I've no idea what newer alternatives are available. And, is the colour of the cool-box critical?

 

[abraxus]

Not that much extra insulation I wouldn't think, if it's just for one day. I tend to find that it's not so much the insulation that's the problem but continually opening it and letting heat in.

Obviously I don't know how much of cheapskate you want to be, but when my fridge was giving me problems I found that coolboxes like some Igloo ones, or Coleman Xtreme kept ice mostly frozen for 2 or 3 days. In fact when I'm staying on the boat for any length of time, or have guests, then that's what I use for drinks. I throw in a couple of bags of ice, few bottles of fizz, some beers and it's good for a long weekend.

They're possible a little more expensive, but if you're going to buy a cheap one, plus foam, and then some sort of grill, there's probably not much difference.

 

[Murv]

+1 for the Coleman Extreme.
Used one a few times when camping, they stay cold for days.
Only problem is the thick walls, they're huge on the outside with little capacity inside. But, they work.

 

[Kelpie]

If you're re-lining an existing box, use polyurethane foam (Kingspan, Celotex etc) as it has twice the performance for a given thickness than polystyrene.
You could be really clever and do a u-value calculation to work out the required thickness...

 

[ytd]

generally powered coolboxes have really good insulation. So if you have power no need to buy ice. If you don't have power, the ice lasts for days.

 

[Cappen Boidseye]

generally powered coolboxes have really good insulation. So if you have power no need to buy ice. If you don't have power, the ice lasts for days.

When camping my Halfords bought powered coolbox worked really well, keeping my cans of Scrumpy Jack lovely and cool. When near power I used it's cooly thing to keep the drink and food cool. When away from power I just threw in a bag if ice cubes, which lasted for days. Next time I will pour the ice cubes into tupperware type containers, the instructions say not to fill it with water, bowever it seemed to survive several inches of thawed out ice-water without any ill effects, but I will try and stop the melt water getting up to any mischief next time I use it that way. I am also going to see if the new 130w solar panel has any chance of supplying the chiller with enough power, at least for part of the day. If I can get the fridge down to temperature while sailing through the day, I am not too worried about it warming up a bit overnight, as long as the next day can get it cooled off again.

 

[paul-essex]

we use this stuff in a lot of our jobs very good http://www.insulationexpress.co.uk/Product.asp?gclid=CJnGqNXfybwCFWjKtAodS1kA1w

 

[rotrax]

First Mate and I used to fish in Florida.

For a day out or a boat trip we had a small coolbox which held our food plus a bottle of frozen water and another of 60/40 fresh orange juice/water.

No ice of coldpacks, just the bottles.

Even in 30 degree plus temps the bottles had to be taken out for a while to get a drink.

When out for 36 hours plus, we had a bigger box-a cheapo 5 dollar K Mart polystyrene one-that kept cold for the duration.

 

[Greenheart]

If you're re-lining an existing box, use polyurethane foam (Kingspan, Celotex etc) as it has twice the performance for a given thickness than polystyrene.

Thanks, that's what I had in mind. Is a foil-lining best on the outside to reflect heat, or inside too? I hadn't planned to use the box for keeping things hot. I'm surprised that lots of boxes are dark colours, if white might have absorbed less heat.

I'd like to be able to pack fresh meat at 7am, good for cooking at least twelve July hours later, with icy cold wine & beer. I'm not looking for an electrical solution in the dinghy and I won't mind if the interior space is pretty tight...as long as it stays really cold despite the day being really hot. I suppose the solution may be to segment the interior, so it'd be possible to remove things without raising the temperature of the whole.