The circle of death is a hazardous phenomenon experienced by

motorboat A motorboat, speedboat or powerboat is a boat that is exclusively powered by an engine. Some motorboats are fitted with inboard engines, others have an outboard motor installed on the rear, containing the internal combustion engine, the ge ...

s. A circle of death can be initiated if the boat operator releases the steering mechanism while the boat is still powered, which means the

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

is still turning. The force of the rotating propeller blades incurs a force known as steering

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of the ...

, causing the motor itself, which is mounted on a swivel jointed mechanism, to turn sharply into the direction of the blades. This causes the boat to cut sharply to the opposite direction, which can throw the operator and any passengers overboard. The boat then begins spinning in circles, oftentimes around the ejected passengers, who are in danger of being struck by the spinning propeller over and over again. The most common preventative safety recommendation, aside from simply ensuring maintained control of the wheel while the vehicle is in motion, is the installation of an automatic

kill switch A kill switch, also known as an emergency stop (E-stop), emergency off (EMO) and as an emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usual manner. Unlike a normal ...

References

{{reflist Motorboats Nautical terminology Maritime disasters