We have referred to this collection of technologies by various terms in the past (Stealth Prop Guards, Sensor Based Propeller Guards, Virtual Prop Guards), today April 20, 2002, we propose the media, companies involved in this area, inventors, patent lawyers, patent offices, law firms, courts, U.S. Coast Guard, researchers and others refer to this group of technologies and systems in the future as Virtual Propeller Guards. We present an “official definition” of the term below.

Virtual Propeller Guard: A system composed of sensors, decision making capability, actuators and one or more outputs. The system detects potential collisions with objects near or soon to be near a submerged marine propeller about to be engaged or currently engaged. Objects detected may include people in the water, large marine life, floating or submerged debris and the ground. If a potential collision is detected, the system takes appropriate action(s) such as shifting to neutral, turning or braking the craft, slowing the craft, raising the drive, shutting off the engine or sounding surface or underwater alarms in a manner to prevent or minimize the severity of injuries to people in the water, people in the vessel, manatees and other large marine life, and to the propeller and drive. Sensors may scan the area to the rear of the vessel, beneath the vessel, around the vessel and in the vessel’s path. Other sensors may monitor the steering system, throttle position, shifting mechanism, engine, navigational charts, GPS and the position of swim ladders. Virtual Propeller Guard can be abbreviated as VPG or plural as VPGs.

Later comments

• The Definition of a “Virtual Propeller Guard” has since been extended to include devices predicting or anticipating an increased probability of a hazard or safety issue near the propeller. Swimming ladder switches and swim gate switches logically fit inside the definition of “Virtual Propeller Guard” as they help predict an increased probability of people being near the propeller. They are actually somewhat parallel to the people sensor based detection methods. Instead of detecting people and taking an appropriate action, they anticipate people may be in the danger zone and take the appropriate action.
• The many virtual lanyards that later entered the market also fit within the definition of Virtual Propeller Guards. They detect the possibility of the operator being ejected and at risk to being struck by the propeller and shut down the vessel.
• Operator Presence Systems (OPS) on vessels including the virtual lanyards mentioned earlier, plus traditional kill switch lanyard systems are Virtual Propeller Guards by the nature of their use.
• The definition of a “Virtual Propeller Guard” also includes “preventing the engaging of the propeller” and “preventing the starting of the engine” as actions a Virtual Propeller Guard system might select.
• In more recent years infrared detectors, computer vision, computation of a moving average (video image presence detection method), and neural network technologies are being spoken of with potential application to both detecting people in the water near vessels and Operator Presence Systems. As of early 2018 we have yet to see such systems enter the market.
• If you have any comments about the terminology “Virtual Propeller Guard” or its definition, please contact us.