If you have or become aware of any technologies that might be useful in reducing propeller injuries, or have any comments about this page, please contact us.
A couple days ago I noticed two Brunswick trim system patents from the 1970's that also include a "trail out" under low speed feature. They allow the drive to raise up and over obstructions struck at slower speeds. The "trail out" feature seems intended to prevent people from being ejected from the boat when striking underwater obstructions at slow speeds. That kind of approach (trim cylinder "trail out") under lower force impacts might be useful in reducing or eliminating blunt trauma which has been mentioned as an objection to cage type propeller guards. Plus the "trail out" system might also provide additional protection to the guard itself. It seems conceivable the concept might also work when the guard itself impacted the obstruction or person instead of just the leading edge of the drive. The Brunswick patents are U.S. Patent 3,999,502 and U.S. Patent 4,050,359.
Stopping circling boats does NOT require the wireless features needed by the pendants / tags associated with virtual lanyards and would thus be much cheaper. It could even just be sold as a separate inline "add on" to the fuel line. Small totally self contained unit with sensor to detect circling, a timer, a valve, and a battery. With some work, you might even be able to get by without the battery (wind it up or cock it, or solar power, etc plus I suspect people have integrated time delays into tilt switches using non electronic means in the past). The final result could just be a small block in an external fuel line with an arrow indicating direction of fuel flow and another one indicating which side goes to the inside of the spinning boat. Components might be cheap enough you could make it detect both ways to avoid the RH LH propeller and RH LH drive rotation issues. One might even be able to store up enough rotational energy from the circling to close the fuel valve creating a totally free standing, self acting unit.
There are some other possible variables to detect here, like capacitance at the steering wheel (a small boat is underway at above "x" miles per hour, but nobody has touched the steering wheel for "y" seconds).
In addition to tilt, centrifugal force, and steering wheel capacitance, other potential variables include steering wheel rotation position, steering cable position, drive steering angle, change in mass in the boat, etc. Systems like Brunswick's Smart Craft Gauges might give you access to some interesting variables for this purpose.
There are also a few patents for detecting operator presence at the operators station by infrared sensors and by sensors in the seat. This is sometimes called Passive Occupant Sensing.
There have also been a few instances recently of a very young child still being in the boat so it is not totally unmanned. You might consider that possibility in any alternative designs sensing presence in the boat.
Seems like this whole concept (unmanned circling boats stopping themselves) has been overlooked
too long.
2 August 2007 follow up - boats with GPS on board could monitor boat position over time (if
drawing out circles on the water pretty fast) and shut off the boat if it is circling wildly.
As I began to think about it further, I saw how it could be made from metal (no longer floats) using a "flap" at the bottom that points straight down when the guard is hanging vertically at the rear of the drive. This "flap" would create a planing surface that would rapidly bring the guard to the surface if the boat was going more that a couple of miles an hour forward, but leave it down over the propeller when the drive was in reverse or not rotating, thus protecting those in the water. Just as the floating version mentioned above, it would be self cleaning, and have minimal drag going forward. Plus the screen size (size of holes in the screen/cage) which has historically been limited due to drag (smaller holes mean more drag when going forward), could now be much smaller as it would only create drag in reverse which is at a slower speed and only for a small portion of the time, thus smaller "holes" and/or larger wire/rod diameter could be used, further increasing the safety and durability of these units. Yes some water would be flowing through portions of the screen when it is raised, but it has a much smaller cross section to the oncoming water and the water can much easier find a path around it.
The "hinge" would need to be kept clear so it could not be "bound up" and fail to let the cage back down.
This "hinged, planing guard" concept could be used on pontoon boats, party barges, and other displacement boats concerned about the boat being started in reverse when someone is in the water behind it. To better illustrate what I am talking about, I made a rough sketch. If anybody has any comments on this approach, please contact us.
9 Jan 2007 - Further thoughts on the guard above - a nice round, flat seat could be prepared for the flapping guard to come down against when it is pulled down (back to the toilet example - like a toilet seat comes down against the flat rim of the toilet.) This would provide additional strength and stability to the design.
The same Brunswick patent cites an aircraft patent that might be of interest to some. U.S. Patent #5,074,488 Aircraft Aviation Deactivation Apparatus issued 24 December 1991. The patent describes using infrared sensors to detect people near an aircraft propeller when the plane is on the ground and deactivates the engine. A bypass switch can render the system inoperable if needed.
Water Search With Dogs May 1992 NASAR Conference
The sonar head, a ceramic transducer projects a pulse of sound into a sidewall of a coal mine to determine how far it is from parallel tunnels. Due to the difference is sound travel speeds in air and coal, most of the sound is reflected when it hits air on the other side (open space in the other tunnel). The speed of sound in coal is used to determine the distance (thickness of the wall) and then control steering the continuous miner to maintain a constant wall thickness. Perhaps this type of sensing system could be used to reflect sound off human bodies?
Spacecraft conventionally use two thin, spaced aluminum walls for debris impact protection (called a Wipple Shield). Sparsely distributed wires made of shape memory materials could be thermally activated from compact containers to augment Wipple Shields.
Perhaps shape memory materials could be used to jump a guard out into position when it was needed from a stored container? You would only suffer the decreased performance and some of the other issues when it was deployed. If it could not be deployed in time with shape memory materials, perhaps explosives might be used (like an air bag). One would have to be careful not to do "bad things" to boat handling characteristics during and after deployment.
Bistatic Doppler Sonar can be used to detect swimmers in high security areas. The patent identifies frequencies of specific interest to eliminate false alarms. It also talks about using detection logic to decrease false alarms even further.
Development of Cognitive Sensors
Nasa Tech Brief
Vol. 26 No. 4. April 2002 Pg. 22
JPL New Technology Report NPO-30283
Inventors: Ayanna M. Howard and Edward W. Tunstel
Abstract is in printed version of Tech Brief's above
Full paper is online at http://nasatech.com/TSP
in the Electronic Components and Systems category
This paper "Cognitive Sensor Technology" develops the concept of a hierarchy of sensor classes with
different levels of intelligence. Sensors are grouped in three levels of increasing intelligence:
smart sensors, intelligent sensors, cognitive sensors. The design process for intelligence based sensors
is based on five main quantities.
1. Self Knowledge - the sensor must understand its propose and understand its operational functions.
2. Communication - the sensor must be capable of transmitting/receiving information (vs. raw data) to and from other devices.
3. Perception - the sensor must have the ability to recognize, interpret and understand sensory stimuli.
4. Reasoning - the sensor must be cable of making decisions based on perception of sensory stimuli and
5. Cognition- the sensors's intellectual process must subscribe to the process of knowing, which includes aspects such as awareness, perception, reasoning and judgment.
As the authors explored this cognitive sensors, they developed an optical recognition sensor using an imbedded micro controller and a gray scale CCD image sensor mounted on a gimbal platform. The optical recognition sensor responded based on the movement of a transitioning target (it located and tracked moving objects in its view). The intended application was in guiding rovers on space exploration. They discuss using the sensor to detect the safest traversable region for rover navigation based on rock distribution. The micro controller turns the camera to face the safest region and further explore it. An intelligent visual perception algorithm was developed for this application. This same approach might be used in Virtual Propeller Guards to identify people and floating debris near vessels.
This introductory level paper talks about using multiple sensor types to detect landmines, a situation not unlike the type of problems encountered trying to detect people in the water.
This article discusses the 2005 Toyota Crown Majesta which introduces a new Vehicle Dynamics Integrated Management system (VDIM) including a pre-crash radar system with both millimeter wave radar and a CCD camera for sensing. Several suppliers are investigating the combination of ranging and vision sensing with complex algorithms, frequently called Sensor Data Fusion, to compensate for the shortcomings in any one particular sensing technology. This technique (Sensor Data Fusion) certainly sounds applicable to sensing people in the water.
Using an array of sensors, including several already present in the Engine Control Module, its not difficult to imagine the system being able to determine what activity you are using the boat for. For example water skiing involves hard acceleration and results in a slower takeoff than would be without pulling a skier (if you sense boat speed and engine RPM and compare it to previous acceleration data you can tell if you are pulling a skier /wake boarder, etc or not. You can even sense when they release or fall off. The sensors could make decisions based on boat activity and the segment of that activity that you are currently in.
Discusses use of cooperative multi-sensor technologies to detect fires. Different types of sensors reporting values vs. just an alarm are used to make decisions, resulting in fewer false alarms. Photoelectric sensors, ionization sensors and heat sensors are used in unison to make a more accurate decision. A similar process (with different types of sensors) could be used to detect people near a propeller in a virtual propeller guard system.
Since most "reverse" accidents occur at very slow speeds, just detecting the presence of people and shifting to neutral or killing the engine might be effective. When moving forward at moderate to higher speeds the prop could be "fouled" when needed. The system might even try to wait till the boat slowed down some or make decisions based on the distance to the person and speed of the boat (time til impact).
Wonder if that is something you could shove backwards down the water pickup inside the drive?
"ON THE WATER - Coast Guard Will Cast its Nets Upon the Waters to Corral Suspicious Boats" a 10 Aug 2005 San Francisco Chronicle article reports the Coast Guard is using nets to entangle propellers of boats entering high security areas. "The nets, known as the Mark 11 Static Barrier Running Gear Entanglement System, were the subject of a 320-page environmental review by the Coast Guard." The nets are made from 1/2 inch thick "Spectra" rope, "a fiber stronger than steel that doesn't deteriorate in water. As a boat passes over it, the net wraps around the propeller, stopping the vessel." The article reports the Coast Guard currently fires a similar net at "fleeing vessels to ensnare them".
This product might be used to "foul" the prop on purpose as a prop guard in the manner listed above?
3 Jan 2006 entry - the full 320 page environmental review published in June 2005, discussed above is available from the docket as a 160MB pdf file. It is docket item USCG-2005-21833-2. This document mentions two other systems of this nature. One is the "SeaSpider" a commercially available compressed air launched entranglement device for deployment from a pier, security boat or ship. The second is the "Aerial Compressed Air Net System (A-CANS) RGES, a helicopter launched entanglement system.
3 Jan 2006 entry - Mark 11 Static Barrier Running Gear Entanglement System (RGES)
Port Security, Maritime Security, and Homeland Security Blog
Thursday, December 22, 2005
This blog provides several articles on the Coast Guard's net fouling system and a great graphic of the system catching an outboard motor.
15 Aug 2005 while contemplating other ways to foul the prop today, we encounted a news report in the Roanake Times dated 14 Aug 2005 in which a tow rope "got caught in the propeller and stopped it", stopping a circling riderless boat after everyone had been ejected. This towrope may have prevented one or more of the four people in the water from being struck by the propeller. We momentarily later encounterd another report of perhaps the same accident indicating the driver (a teenage girl) became entangled in the tow rope and was injured by the propeller. The entanglement of the tow rope may have still prevented injuries to others, or perhaps worse injuries to her.
We began to develope the list below of materials that might be used to foul a prop:
We will also soon begin a list of ways those items might be delivered to the prop.
Additional thoughts, it would be best to limit the diameter of the "fouled" prop since a larger diameter would provide a larger cross section and impact more people? Their might be a tradeoff in slowing, stopping rotation, "padding the prop" and size?
19 Aug 2005 Fed BizOpps reported a proposal request for "Portable Entanglement Net" as a combined solicitation (from U.S. Coast Guard and related agencies) dated 18 August 2005.
It included reports they have "developed various devices to entangle the propellers of small outboard or inboard/outboard (IO) powered craft (length over all up to 40 feet, total power up to 675 HP using one or more outboard or I/O engines) that do not comply with orders to stop." The system called "Running Gear Entanglement System" (RGES) consists of a header-line with U-shaped loops of rope suspended below it. They alos have an existing It has been proven effective, but must be deployed by dragging it in front of the vessel to be stopped. There is also an existing MK 10 version that can be fired from a canister on a Coast Guard vessel (shot out in front of the fleeing vessel). The request for proposal is for a more portable system that can be hand-fired and reloaded quickly and used from small craft such as CG rigid hull inflatables, port security boats or utility boats (UTBs). They report the "USCG has found that it's relatively easy to fire a net into the water such that the net affixes itself to the lower unit. The difficulty has been in getting the net to entangle the vessel's propeller blades."
