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Author Topic:   Radio Frequency Kill Switch Failsafe
pcrussell50 posted 04-25-2010 02:41 PM ET (US)   Profile for pcrussell50   Send Email to pcrussell50  
Is there any basis for worrying that these new radio frequency kill switches might somehow fail into a nuissance kill? Further, what if you fell overboard, and the water contact closed and killed the motor just as designed. Then, you climb safely back aboard, so far so good. Will the now-wetted remote allow an engine start? These seem like basic design considerations to a competent engineer. For those who have [radio frequency kill switches], does the brand you have account for nuissance no-starts?


contender posted 04-25-2010 03:34 PM ET (US)     Profile for contender  Send Email to contender     
[Described a kill switch but it did not appear to be a radio frequency kill switch.]
pcrussell50 posted 04-25-2010 03:54 PM ET (US)     Profile for pcrussell50  Send Email to pcrussell50     
Perhaps I shouldn't have used the word radio frequency. I was referring to the wireless kill switches.


David Pendleton posted 04-25-2010 04:11 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
The Autotether system "works" because radio signals do not travel through water. When the fob is submerged, the receiver loses the signal and activates the kill switch. Once the fob is within range again (or out of the water), it will function normally. If for some reason the unit is malfunctioning, you can just remove it and revert back to your lanyard. The installation isn't permanent.
jimh posted 04-25-2010 04:31 PM ET (US)     Profile for jimh  Send Email to jimh     
The only wireless or radio frequency based kill switch that I have seen is an add-on unit. The actual operation of the engine kill switch is performed by the original circuitry in the engine. The add-on kill switch just replaces the mechanical portion of the lanyard that fits onto the kill switch itself.

From what I see, these add-on devices increase the complexity of the kill switch or safety switch quite a bit. In the OEM safety switch the system is very simple and based entirely on mechanical operation. In the wireless add-on, there are several new systems added on the original.

First, a new actuator is fitted to the kill switch. This new actuator contains some sort of solenoid or rod that will push the actuator away from the kill switch, duplicating what would happen if the lanyard pulled the mechanical interlock out from the switch. This device operates electrically and is apparently wired to a base unit.

Second, there is a base unit that connects to the new actuator to control its operation. This unit provides power to the actuator and in turn gets its power from the boat power distribution. The base unit also contains some sort of multiple receiver installation so that it can monitor for a signal from the new kill switch remotes or "fobs." This technology is apparently radio based; I do not know what part of the spectrum it uses.

Third, there is the new kill switch remote unit or fob. These are powered by batteries. These units apparently transmit a signal to the base to control the operation of the new actuator. The system apparently allows for multiple fobs to be active at any time.

In seems reasonable to assume the system was designed so that there has to be a signal detected from the fob by the base in order to indicate the NO-KILL situation. When the signal from a fob is lost by the base, this indicates a KILL situation, and the actuator is operated.

Another consideration is the logic used for the actuator. It would be most reasonable if there were some mechanical force, such as a spring, that was always trying to pop the actuator away from the original switch mechanical interlock, and this mechanical force had to be overcome by an electrical force supplied by the solenoid in the actuator. In this way, if the system failed, the new actuator would pop off the original kill switch. However, if the system operated that way, you would not be able to leave the new actuator in place when the power was shut off--it would pop off each time. That could become annoying. It would also require fitting the new actuator to the original key switch many times during normal boat operation.

Human nature tells us that safety systems which begin to interfere with routine operation of equipment often get tampered with to override them.

jimh posted 04-25-2010 04:35 PM ET (US)     Profile for jimh  Send Email to jimh     
I am also curious how the multiple fob systems work. If the logic of the system requires the base to always receive a signal from the fob, how does the base know how many fobs are in the system? Do you keep fobs that are not being worn in close proximity to the base so they do not send a false signal?
jimh posted 04-25-2010 04:36 PM ET (US)     Profile for jimh  Send Email to jimh     
Of course the most obvious nuisance factor with any system where a critical component is battery operated is a dead battery. I am curious about the battery used in the fob. Is it in a water-tight compartment? Is it simple to change?
David Pendleton posted 04-25-2010 05:35 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Yes, the battery compartment is water-tight. Both the fob and receiver use AA batteries, and all that is required to change them is a small screwdriver.

I too was curious about multiple fobs (the receiver supports up to four, IIRC). I asked the factory rep about this and will post what I learn when they respond.

contender posted 04-25-2010 09:46 PM ET (US)     Profile for contender  Send Email to contender     
Should not be a problem, it would just like having more than one garage door opener.(same thing just reverse it) You could set it up to stop 1,2,3,or 4 outboards at once.
The problem is it is a life safety feature device, do you want to depend on a electrical wave from a sender, or a manuel switch/wire that will stop the engine for sure every time? Your call...
jimh posted 04-26-2010 01:49 AM ET (US)     Profile for jimh  Send Email to jimh     
Contender--Sorry, it appears the system is exactly NOT like a door opener. The system is supposed to work on LOSS of signal, not on the ONSET of signal. The little fobs must be transmitting all the time. When they get too far away to be heard the system actuates.
jimh posted 04-26-2010 07:29 AM ET (US)     Profile for jimh  Send Email to jimh     
From a manufacturer of a wireless kill-switch system:


Q. How does the sensor work?
A. Inside is a wafer thin circuit board that “senses” when it’s submerged. Then it sends a radio signal to the control module


This unit sounds like it works, as Contender described, like a garage door opener. This means there fob or remote emits no signal until it is in the water. That means if there is a failure of the fob transmitter, the system fails to operated. If the fob has a bad battery, the system fails. If the fob sensor switch fails to detect water, the system fails. If the boat gets too far away from the man overboard (as could occur with a really fast boat) the fob may be out of range and the system fails. So many ways for the system to fail in this design.

This manufacturer also mentions:


[The wireless kill switch] technology is unique because it is the only one activated by immersion in water rather than “proximity.” Proximity requires constant reception from base to personal receiver, which, upon break in signal, sounds an alarm. This is usually achieved by distance. However, this signal can be broken in many other ways, such as low batteries or compromising line of sight (i.e., doors, towels, people, etc.). It is prone to false alarms.

jimh posted 04-26-2010 07:47 AM ET (US)     Profile for jimh  Send Email to jimh     
In the AutoTether system, the decision to activate the kill switch is based on proximity. Also, the base unit is powered by its own batteries. And the remote fobs have power switches to turn them on. More details about the AutoTether are found in AutotetherManual-RevMay09_000.pdf

David Pendleton posted 04-26-2010 01:00 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
I just spoke to Andrea at Autotether and learned that each receiver supports up to four fobs and 16 different channels. All fobs and the receiver must be set to the same channel.

I was also concerned about other systems in proximity to mine, e.g. when cruising or rafting with someone else with an Autotether installed.

As long as the two systems are using different channels, there is no conflict between the two.

The channel used can be set in the field by adjusting a DIP switch setting.

SJUAE posted 04-26-2010 02:56 PM ET (US)     Profile for SJUAE  Send Email to SJUAE     
Sorry can’t get excited about this type of product. I have enough problems with my phone Bluetooth connecting with my car every morning let alone did I immerse deep enough am I far enough away and another battery system to check.

At least the lanyard when attached stops you straying too far and has a physiological affect on your proximity. The wireless fob may by its function make you take more risk IMO.


David Pendleton posted 04-26-2010 04:16 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Valid arguments, all.

However, running my boat single-handedly often requires me to move away from the helm. A standard lanyard is just too restrictive.

Because of this, I never wore the lanyard and took my chances.

Now I have a system that will shut off the motor if I fall overboard and I can still move around the cockpit and deck. That makes it perfect for me and my boat.

SJUAE posted 04-27-2010 02:46 PM ET (US)     Profile for SJUAE  Send Email to SJUAE     

I agree if you are in the habit of detaching your lanyard on the odd occassion when underway and solo. Then having one of these is better than none.

I think I would also have a ACR PLB in my pocket :)

On a minor point I have 2 kill switches one for my ETEC main and another for my Yamaha kicker. This is deliberate as it's advised not to mix control wiring on different makes of engines.

So I would have to buy and maintain two Autotether systems as I am not wiring both engines to one switch.


contender posted 04-27-2010 03:57 PM ET (US)     Profile for contender  Send Email to contender     
Jim: your thinking/working of your fob is just the opposite of mine? Everything that you listed can happen to yours(factory fob) the same way but just the opposite, What happens if you are to far from the engine, quits. Battery gone bad, quits. Lose the fob engine does not start (what if you lost it overboard at sea?) The best is you can fall over board and the circut board will work, may and may not, Its electrical and water and electrical do not mix especilly salt water. The best system is the cheapest one Kill switch that grounds out the engine, no battery to go bad, does not get lost, does not break, and works probably 99.999% of the time.

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