COOLBOX GROUPTEST

There's nothing better than being on a boat on a warm summer's day. Except perhaps being on a boat on a warm summer's day with a chilled drink to hand. And even if your boat already has a built-in fridge, having a portable cooler to take them to and from the boat or the beach is well worth the extra investment. But what type should you buy and who makes the best ones? The first thing to decide is whether you want an unpowered or 'passive' cooler, which relies on ice packs and some form of insulation to keep the contents cool, or a powered cooler that actively chills your food and drinks. There are pros and cons to both types: unpowered coolboxes tend to be cheaper, lighter and more compact but less effective, especially when opened regularly; powered ones are bigger, heavier and more expensive but can keep things cool for as long as power is supplied to them. We put four of each to the test to see which performed best.

- Phil Sampson

While any passive cooler will do a good job provided it's packed with ice, how long it retains that temperature depends on how good the insulation is. To find out we started by pre-chilling each unit. For the passive coolers that meant placing two 1-litre ice packs inside for an hour.

The four electrically powered models were also given an hour to chill, but under their own steam rather than with ice packs. We set the target temperature to -1°C on Dometic's CFX2 compressor and CFF18 thermo-electric units. Both achieved their target comfortably within the hour. The TCX21 doesn't have a digital temperature display but is claimed to cool to 1°C. After running for an hour its interior temperature had dropped to 1.5°C, so that was its starting point.

Once cooled, we placed 33cl of chilled water (the size of a beer bottle) in a sealed container inside. We then monitored the heat loss - both inside the cooler and of the water - over 24 hours, with a 12-hour midpoint check. The ambient temperature of our test room was also monitored, and a second sealed 33cl container of water was placed outside the cooler to act as a control.

Our tests found that in every case the air temperature inside the coolers rose rapidly once their power sources (ie: ice or electricity) had been removed. Typically, around 10°C was gained in the first two hours. Thereafter, the rate of climb decreased as ambient was approached, although in 24 hours none of our coolers actually reached room temperature, generally undercutting it by around 2°C.