One of the most common questions about DC electric bow & stern thrusters is how long they can run continuously before overheating, and the answer is dependent on three main factors. In this article, we'll detail what those factors are as they relate specifically to Sleipner (Side-Power) thrusters. 

What Triggers the Thruster Motor to Shut Down?

All DC electric motors generate heat as they operate, and at a certain point of continuous operation they will overheat and begin to breakdown. For this reason, all of Sleipner's DC electric thruster motors have thermal-overload protection. In the case of their standard on/off thrusters, which are either on and operating at 100% power or off and dormant, they're protected with a bimetal mechanical "thermoswitch". This type of switch works by using metal which expands when heated, and when the metal expands to a certain point, it triggers a switch which shuts the motor down to protect it from any further heating. Because the metal doesn't always return exactly to its pre-expansion size as it cools down, triggering a mechanical thermoswitch multiple times may cause it to become more sensitive and shut the motor down at lower & lower temperatures.

In the case of Sleipner's proportional-speed thrusters, the thermal overload protection is done with an electronic temperature sensor which is programmed in the system's internal software to shut the thruster down when it reaches a certain temperature. This style of sensor does not become more sensitive over time. 

3 Contributing Factors to Overheating & Run Time

1. Voltage & Amperage