Heat on board: 12 tips for keeping food cool without electricity
YACHT
· 23.06.2026
Photo: Nils Theurer
It can’t keep food fresh during the day, even in hot weather: a sleeping bag as a cool box. The other tricks you can use in hot weather work better.
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When the sun is beating down on board, the cool box quickly becomes a power issue. With a few simple tricks, drinks and provisions will stay cool for longer, even without shore power, a running engine or a large battery bank.
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Summer heat on board is doubly troublesome for crews: drinks get warm, fresh food goes off more quickly, and the cool box uses up power just when you want to save the on-board battery for night-time sailing, lighting and electronics whilst at anchor. Particularly on small yachts or minimalist boats, simple passive solutions can help before the on-board battery suffers.
The key is not to let food get unnecessarily warm in the first place. Anyone planning a sailing trip should consider provisions, packaging and storage space as a whole. In addition to these cooling tips, the following will help: Provisioning plan for the holiday sailing trip and the Checklists for a summer sailing trip during the preparations.
What actually kept things cool in the mini-test
In a small series of experiments, the various methods were tested using a liquid at exactly 30 degrees Celsius; the aim was to cool half a litre of the liquid in each case. 450 grams of ice cubes lowered the temperature in the bottle to 1.4 degrees within two hours; after 24 hours, it had returned to room temperature. 350 grams of ice mixed with 100 grams of salt cooled the liquid more quickly: to 0.6 degrees in an hour – but it also warmed up again more quickly. Standard ice packs cooled the liquid to 15 degrees; after 15 hours, they were on a par with the first two methods: a viable option. As predicted, the 440-gram Easy2Cool cooling pads reached their lowest temperature of 8.3 degrees after seven hours and maintained it for a long time; after 24 hours, the temperature had risen back to 19.3 degrees.
Whether it was a towel, a sock or a clay pot: all the evaporators struggled to cool the air; after 24 hours, the temperature was one to two degrees below the ambient temperature.
Key points at a glance
Ice cooled most quickly when salt was added, but the effect did not last long.
Cooling pads took longer to take effect, but kept the temperature low for longer during the test.
Evaporation using a towel, a sock or a clay pot resulted in only slight differences in temperature.
Good insulation is often more important on board than even the most spectacular cooling trick.
If you take care of your food whilst shopping and storing it, you’ll need to chill it less later on.
Insulate first, then cool
Photo: HerstellerKeeping food cool on board is always a faff. It’s better and easier not to let them get warm in the first place. Cooler bags or standard cool boxes usually provide poor insulation; polyurethane insulation offers a more robust and durable solution. For example, the Icetime range from Campinggaz (10, 23, 28 litres, from 40 euros) >> available here*
Thick walls and a seal make all the difference
Photo: Photographer: Ata TaefiModels with a rubber lip seal and thick polyurethane insulation are even more effective: Dometic (13–110 litres, from 69 euros >> e.g. available here*) and Peli (19–51 litres, from 240 euros) offer a range of sizes. Despite having walls five centimetres thick, the food-safe Dometic products are quite light: for example, the 33-litre box weighs just 5.7 kilograms
If electricity is an option after all
Photo: YACHT/Lars BollePortable, compact compressor-based cool boxes are the first choice if there is no built-in fridge on board. They are essentially compact fridges; here is one from Dometic with a 40-litre capacity from the CFX-3 series (>> available here*). In tests, the PLB40 battery was able to keep food and drink at a constant temperature of seven degrees Celsius for just under four days at an outside temperature of 20 degrees
Anyone wishing to use active cooling on longer cruises should take power consumption, battery monitors and charging profiles into account. Further suitable solutions and ideas can be found in the YACHT articles on Cool boxes with vacuum insulation and to Solar life hacks for small boats.
Cooling pads: slower, but more enduring
Photo: Nils TheurerYou can find them at the dentist’s, in chemists or as promotional gifts: Gel pads* consist mainly of water and propylene glycol. This is said to be harmless to health even if the sachet leaks. However, it is advisable to pack food in bags and tins, if only because of the mess that can be caused by any leakage
Cooling elements: leak-proof, robust and easy to stow away
Photo: HerstellerCooling packs* in rigid, stretchable plastic containers are often easier to handle (and leak-proof). Those with handles are much easier to label – for example, with a tag for the communal freezer at the harbour – as well as to carry and stow (photo: Coleman/Camping Gaz ice pack, from 3 euros)
Evaporative cooling: only a minor effect
Photo: Nils TheurerThanks to evaporative cooling, the first few minutes after coming on board from a swim are cool, even in the intense heat. It is only once you are dry that radiant heat regains the upper hand. This effect is utilised by wrapping a sock or towel around drinks – it is most effective when there is a breeze as well.
Clay pot: simple idea, poor test result
Photo: Nils TheurerThe clay pot method is also based on the principle of evaporation: two containers act as transpiration chambers; an intermediate layer of sand moistened with water regulates the supply of fresh moisture. Perhaps we did something wrong whilst making it: our amphora fridge was struggling
Ice and salt: quick to cool, quick to melt
Photo: Nils TheurerAll you need for ‘black ice’ in a bottle is salt and ice cubes: in our mini-test, we replaced 100 grams of ice with salt – the endothermic effect cooled the contents to 0.6 degrees very quickly, but after four hours, ordinary ice cubes had caught up. The process cannot be repeated; the brine must be discarded
Lowering food: use cold water
Photo: Nils TheurerEven at a depth of ten metres, the Baltic Sea is often barely 15 degrees in summer. Whilst that is slightly warmer than a fridge, the temperature is still low enough for the butter to retain its shape. Simply place the food, packed in waterproof wrappers, into a bag or net with a weight to keep it down, and lower it into the water.
Self-cooling barrel: a specialised solution for beverages
Photo: HerstellerHow long does it take to chill a fresh Pils? 45 minutes using the self-cooling beer keg for 10 or 20 litres. Once a valve is opened, surface evaporation causes a layer inside the thick wall to freeze, cooling the beer. The 20-litre CoolKeg costs 40 euros. The Tucher brewery sells Pilsner, Helles and wheat beer nationwide.
Thermos flask: Cold drinks stay cold for longer
Photo: Gunkel, FridtjofWhat keeps things hot also keeps them cold: The DIY store’s Thermos flask* performed well in the test. The liquid, which was 6 degrees cold at the start, was only 13 degrees warm after 24 hours. Stainless steel flasks are suitable for use on board. They are also available with a wide neck, for example for ice cubes. A nice winter craft project: make a holder for several flasks
What really helps on board, and which cooling tip is just a myth? Share your experiences in the comments.
