Like most electric motors, the refrigerator will use a high current at starting the motor, after which the current will fall back to the level of continuous use. Refrigerators and freezers can be rated with the current they will use when the motor is running or have an average consumption per hour listed.
When you arrive on your boat, the refrigerator will have to run continuously for an hour or more, as it goes down to its normal operating temperature after which it will run intermittently. For more information about the boat freezer, you can visit https://kampetorpmarin.se/marin/kok-badrum/kyl-frys.html.
Image Source: Google
Typical small float fridges will consume around 4 to 5 amperes per hour, although the consumption can be as high as 12 amps when the motor is running, so the circuit is rated higher than this to cope with higher starting power.
Boat refrigerators are one of the few motor units on board that run on a more or less continuous basis. This means that when the engine stops, it will be one of the main users of the current and is the most likely cause of a flat battery if care is not taken.
Some refrigerators include a device in the control circuitry to warn when the battery voltage drops. In some cases, it will automatically shut down the refrigerator if this occurs, so as to prevent the battery from being deeply discharged.
It is possible to buy dual voltage refrigerators so that they can work on battery power and port power at sea. Another option is a refrigerator that can be powered with bottled gas or battery power.