Types of Propeller Guards

Most Propeller Safety Devices can be classified into one of the categories below.

Propeller Guards – they are physical barriers designed to provide protection for the propeller, marine life, or people compared to open propellers on conventional inboards, outboards and stern drives. Propeller Guards generally fall into one of four broad categories: Cages / Screens, Shrouds / Rings, Deflectors, and Unique Propellers.

Marine Drives – several types of marine drives provide some protection from being struck by a propeller in certain situations.

Miscellaneous Propeller Safety Devices and Approaches – sensors, mirrors, and host of other approaches, including virtual propeller guards.

Propeller Safety Interventions Not Involving Devices – boater safety education, decals, warnings, and many more.

Below we provide a reasonably extensive list of devices and approaches in each of the above categories.

Propeller Guards

Cages / Screens

  • Conventional propeller guards that look like a cage or screen
  • Cages with rear screens that swing up when underway to reduce drag
  • Cages that swing up out of the water at high speed to minimize performance and handling impacts
  • Retractable cage guards

Vane Guards

  • Flattened vanes are used to form a barrier between people and the propeller
  • Some use hollow vanes that can be shaped like airfoils to reduce drag
  • Some affix the vanes to what might look like a conventional ring guard

Shrouds / Rings

  • An extended ring or duct is installed around a prop on an existing drive
  • Ring guards with rear screens that swing up when underway to reduce drag
  • A series of concentric rings, like Prop Guard from Prop Guard Marine, or the Thrustor from Marine Propulsion Technologies


  • Deflectors in front of drive or propeller, including drive skegs
  • Deflectors beside the propeller
  • Deflectors below the propeller
  • Deflectors behind the propeller

Unique Propellers

  • Ring around the propeller (ring is part of the prop, like RingProp)
  • Rounded leading edges of blades (Australian Environmental Safety Propeller and PowerTech!’s version of it)

Marine Propulsion Designs / Drive Types Providing Some Protection From Propellers

  • Inboard Water Jets (water intake in bottom of hull, nozzle is behind transom)
  • Centrifugal Water Jet Outboard (everything is behind the transom, intake is part of the drive)
  • Axial Pump Jets (ACT Marine)
  • Contra-rotating water jets (Contrapel – was not yet on the market in mid 2012)
  • Tunnel Drives
  • Ducted Drives
  • Kort Nozzles
  • Rim Driven Drives (like Brunvoll and Norpropeller’s Rim Driven Thruster RDT)
  • Partially submerged water jet (Hydro-Air Drive)
  • Riverboat paddle wheel drives, stern wheeler
  • Oscillating vertical fins (Voith Schneider Propeller)
  • Hovercraft
  • Airboat (big fan on the back)
  • Electric Drives – U.S Patent 6,676,460 senses people in the water and brakes the drive
  • Hazelton Propulsion – most often used on submersibles. Like a ring of variable pitch blades captured in a carrier going around the circumference of a submarine. Can be adapted to boats by extending round “pods”. U.S. Patent 3,805,723 for example.
  • Oars / Paddles
  • Exotic Drive Types not currently on the market
    • Pursuit Dynamics steam drive
    • Hydrodynamic Flushing Propulsion from Tyvik of Norway- nozzles shoot water horizontally perpendicular to the bow to reduce pressure on the front of displacement boats (could be a houseboat) and pressure on the back of the boat pushes it forward. Vestfold University students are working with Tyvik.
    • MagnetoHydroDynamic Propulsion (MHD) – not currently practical
    • Fishlike propulsion (MIT Robo Tuna)
    • Flapper drives (a flat sheet is “flapped” in vertical or horizontal plane)
    • Track drives (something looking like a snowmobile track puts its tread in the water)
    • Bowthruster Propulsion – something looking like a bowthruster sucks water all the way through the boat and pushes it out the stern
    • Rocket propulsion
    • Boeing low signature propulsion – expands and compresses a volume to expel water U.S. Pat. 6,860,770 and others

Miscellaneous Propeller Safety Devices and Approaches

  • Propeller Risk decals – decals describing the risk involved with propellers are prominently placed.
  • Detect driver not at the helm and possibly overboard
    • Traditional lanyard
    • Wireless lanyard (CAST from MariTech)
    • Detect driver sitting down or present by weight in seat of use of infrared detectors
  • Folding Propeller (sail drive type prop could be folded flat when people detected nearby)
  • Mirrors near rear of boat viewable by operator (used by houseboats)
  • Video camera near rear of boat and display near operator (used by houseboats)
  • “Person in the Water” flags
  • Diver flags
  • Start up time delay – when starting the boat, an alarm sounds, then the boat starts several seconds later
  • Swim ladder / Swim Gate interlock switch – if swimmers lower the ladder or open a gate to get into the water, their boat will not start until the ladder is raised / gate is shut. (MariTech)
  • Sensors detect people going into the water (Turtle wrist watches or Maritech Virtual Lifeline)
  • Electronic pendants worn like wrist watches, or tags that can be detected when someone is near the propeller – these have been proposed, but not currently on the market.
  • Forward looking Sonar – EchoPilot
  • The use of “soft” propellers and energy absorbing materials has been proposed, but no appropriate materials have been identified.
  • The use of seat belts has been proposed, but creates problems with capsized boats.
  • Virtual Propeller Guards – sense people in the water near the propeller – Patent 6,354,892 (Brunswick infrared), 3,805,723 (U.S. Government uses “feelers” on a Hazelton prop on a submersible) and 6,676,460 are examples.
  • In late June 2005 I had the idea of fouling the prop when people were detected near it and the prop was being powered or about to be powered. Releasing a net, mesh, web, sheet, rope, chain, twine, string, fishing line, chemical compound or other materials that would cling to or wind up around the prop to slow the progress of the boat, and blunt the sharp edges of the prop before people were struck. More info is in our section on Fouling the Propeller on Purpose. This approach could be one of many possible actions considered by a system making decisions based on readings from sensors detecting people in the water (and perhaps their distance and direction from the prop) and sensors detecting boat variables (engine speed, boat speed, in gear forward / reverse, neutral, etc).
  • Inject air into the water from electric powered boats and sailboats to create noise (like power boats create noise) so swimmers and marine life can detect the presence of and direction of oncoming “previously quiet” boats. This system might reduce propeller strikes from electric boats as they become more popular. See U.S. Patent 6,976,891 issued 20 Dec 2005.
  • Cushioning devices that allow the drive to swing back some during forward impacts. They may reduce blunt trauma and allow survivability from cage type guard strikes at higher speeds. Two old Brunswick patents and a recent Teleflex patent describe systems that might reduce blunt trauma. They are further addressed in our report on the USCG proposed houseboat propeller safety regulation that was later withdrawn.
  • Alcohol testing interlocks similar to those used on cars (built in breathalizers, number panels like those used on car doors, alcohol sweat detectors on the steering wheel, alcohol ignition interlocks, etc ).

Interventions Not Involving Devices

Approaches other than the use of devices have been advanced as possible solutions or at least partial solutions to reducing propeller injuries. For example, the concept of educating boaters in safe operation of boats was advanced by the U.S. Coast Guard in their Preventing Propeller and Boat Strike Accidents. U.S. Coast Guard Boating Safety Circular No.76. June 1994. Pgs 1-2. Additional interventions that have been advanced by others are listed below.

  • Propeller Danger warning signs, warning decals, warning placards placed on boats, especially near the drives and boarding ladders pointing out the hazards of open propellers, their location, and how to avoid them when rotating.
  • Boater Safety Education – general boating safety education (including mandatory boater safety education) has been advanced in part as a means of preventing accidents such as man overboard, collisions, and others that often place people in the water that are then hit by propellers.
  • Propeller Danger Education – the use of flyers (such as the recent Coast Guard flyer on Propeller Dangers) and other vehicles to convey the danger of propellers to boaters and keep it in their minds.
  • Boating safety education provided to those renting boats, especially those renting houseboats in party environments.
  • Educating young children in school about the dangers of propellers with the intent they will convey that knowledge to their parents as well (SPIN tried it a few times in 2006).
  • Partial or total bans on the use of alcohol on board. This approach is advanced as helping prevent man overboard situations that lead to propeller strikes, reducing the number poor judgment decisions that lead to propeller accidents, and reducing the number of other accidents that lead to propeller accidents.
  • Focusing education strongly on sectors thought to be at larger risk such as PWCs, towed sports, rental boats, rental houseboats, youth operators, divers, etc.
  • Vessel design – placing propellers in places less likely to be exposed to people in the water, placing boarding ladders in places less likely to expose people to propeller risk, higher side rails, well designed and well placed handholds for boarding from the boarding ladder, longer boarding ladders making people more stable and keeping their feet and knees from swinging into the prop when they try to put them on the bottom rung, designs that force people out of bowrider bows when underway, designs that force people off the very front of a pontoon boat when underway, etc.
  • A State Fair type booth showing propellers chew up pumpkins or some other surrogate for people in a live demonstration similar the seat belt simulator used by those encouraging the use of seat belts often seen at large public gatherings. People participate by rolling the pumpkin down a chute to the water, it is drawn in by the stationary propeller and struck. The same process could be done virtually online in a educational setting, or just show an actual videotape of in on YouTube or a similar site. The demo could be combined with materials showing the many benefits of boating, but still bring attention to the need to be aware of the danger of propellers.
  • Public Service Announcements (PSAs) like USCG’s “Don’t Wreck Your Summer” PSA that was banned by the industry.
  • Increased presence of law enforcement officers, vehicles, and vessels.
  • Law enforcement presence in “Party Coves” and at major on water party / raft-up events around the country.
  • Prominent paramedic presence at major on water party /raft-up events around the country (just seeing their presence reels back some behaviors)
  • Limiting capacities on very busy lakes during holidays
  • On water versions of roadside crosses at fatality sites (these have been used in the past)
  • Prominently marking and enforcing swim zones

Maximizing Outcomes Once the Accident Happens

There are a whole world of paramedic response times, evacuation times, availability of life flight, proximity of major trauma hospitals, rescue communications, ability to supply and verify the exact accident location, ability to get rescue people out on the water, education and training issues that can vastly improve the chances of a propeller strike victim living and improve their ability to more fully recover. Many of these issues are particularly lacking in some popular third world diving, snorkeling, and party boat sites.

One particular area we are seeing is the challenges rescue crews face when trying to extract someone who has become entrapped or caught on a propeller. Rescuers have to try to keep the person’s head above water while trying to get them and/or their clothing off the propeller, or sometimes have to remove the propeller while the boat may be rocking in deep water. Some training in this situation may be needed.