There are various options for cooling a fridge... All use a compressor, but there are 3 different options for cooling the compressor... Air, water or water via a keel plate.
Air is the cheapest, but heat transfer in air is very inefficient, and not recommended for hot climates.. So it would work fine in the UK, but if our long term plans come together, would be very heavy on the batteries as we head south. Its how a domestic fridge or freezer works
Water is much more efficient, but needs a pump, plus holes in the hull to take water in and out... So i can install it, but can't use it until she's lifted and i fit seacocks.
The final option uses a second compressor to a special plate that fits on the keel. Its about the same efficiency as a standard water cooled system, but without the pump is much quieter and uses less power.
We think we'll go for the water cooled version and perhaps convert to a keel cooled version later as we can afford it.
The seperate fridge freezer is quite clever... The cold plate is in the freezer, and then a small hole between the freezer and fridge compartments is fitted with a fan to 'spill' cold air over to cool the fridge. Each is fitted with a thermostat to keep it at the right temperature... Neat huh?