CrewWatcher Versus AIS POB Beacon—Speed of Alarm Claim

While I was busy tearing marine journalism a new one, I happened upon a claim made by the manufacturer of the CrewWatcher smartphone-based person overboard alarm, see the above screen shot.

This is, based on my testing, and checking with Ocean Signal, simply rubbish, at least for the MOB1 beacon (and I suspect most others), which sends the first signal (and sounds the alarm on the boat) 15 seconds after activation, regardless of whether or not it has acquired a GPS position.

I suspect that the Dutch magazine came to their incorrect conclusion because in test mode the MOB1 does indeed wait until it receives a GPS signal—generally around 1 minute in our testing—before it transmits an alarm.

Anyway, in my never humble opinion, the “20x faster than AIS” claim is just marketing hype (quote a worst case without verification) and CrewWatcher should be ashamed for using it. Come on guys, we are dealing with safety of life here.

What Really Matters

MINIMUM homing signal coverage area for an AIS POB Beacon compared against MAXIMUM area for a smartphone-based POB Beacon.

And even if this claim were true, putting weight on it is a classic example of using the wrong criteria to make a safety gear decision. As I explain in my original analysis of the CrewWatcher, fast notification is near-meaningless when evaluating a beacon with an absolute maximum tracking range of 200 feet.

What matters most in Person Overboard (POB) recovery is finding the person again once they are no longer within visual range, something that will happen in most scenarios in less than 30 seconds. And at that point the CrewWatcher is pretty much useless, at least in comparison to an AIS POB beacon with a range of between two and five miles.

And while I’m blowing holes in CrewWatcher’s marketing, they also make a huge thing about a test done by the Dutch Coast Guard while totally missing that said test highlights one of the greatest weaknesses of the CrewWatcher:

The first test was conducted at a speed of 6 knots with the test observer at the stern deck. Once the MOB occurred the CrewWatcher app alerted the cabin crew most notably not by the audio alarm (which was drowned out by the combined 2400BHP engines) but by the visual change in color from green to orange.

(Emphasis mine.)

This is a benefit? For crying out loud, what it actually shows is that a beeping and flashing phone is a totally inadequate way to warn the crew that someone has gone overboard—something I pointed out in my original article.

Think about this for just a moment:

  • What if the remaining crew are sleeping?
  • What if the engine is on?
  • What if someone closes the CrewWatcher app?
  • What if the phone shuts down due to low battery?
  • What if the phone is on deck and the remaining crew below?
  • What if the remaining crew is deaf as a post like me?
  • POB incidents tend to happen during noisy manoeuvres like tacking or jibing.

A Much Better Way

Contrast that with an AIS POB beacon-equipped boat that can easily be set up so that when a crew member goes overboard:

  • A specific alarm sounds that can’t be confused with something else and is loud enough to wake the dead.
  • An alarm sounds on the VHF radio, too.
  • An alarm sounds on the plotter and, within one minute, the POB’s position is plotted, and then updated in real-time.
  • An alarm sounds on any other AIS-equipped vessels within a two- to five-mile radius.

And this gear uses a proven robust commercial quality protocol (AIS), not a phone. Further, AIS reception equipment is powered by the vessel’s system, and is in constant use for navigation and communication, so that any failure will be quickly noticed.

Bottom line, the CrewWatcher marketing page just proves, at least to me, what I have long believed: marketing can be absolute rubbish but still be dangerously effective. Reminds me of the Marlboro Man.

Further Reading


Please read my original article (Further Reading) before commenting so we don’t end up covering old ground again.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

19 comments… add one
  • Stein Varjord Mar 23, 2019, 7:36 pm

    Hi John.
    I completely agree on all the above, of course.
    As mentioned many times before, a favourite banter of mine is that the ocean is a very safe place to be, if we are reasonably aware, but often we relax our attention because we think we’re safe. Disturbingly often, the foundation for that feeling is an illusion. Lots of articles and comments on AAC have been dealing with the most important sources for such illusions of safety.

    Having jack lines along the side deck, or going on deck at night with only a “life”vest, or having a gadget that will help finding you if you fall overboard, but which actually doesn’t really help in a significant way, and which is also far from the best alternative.

    I’m convinced that if I want to go on deck in rough weather at night, and have no harness or beacon available, (hypothetical) it is far safer to NOT wear a “life”vest. That will keep me very aware of my vulnerability. The fact is that even I, who nag about this issue, will change my behaviour by wearníng a “safety” item. This operates on another level than the logic. We can indeed compensate for those parts of our mind by actively repressing their influence, but we cannot remove the influence. Not possible. That means that this influence will ALWAYS add at least some carelessness or distraction to our behaviour.

    Even the best safety equipment will have this effect. However, with the best equipment, the safety contribution is far greater than what the aforementioned carelessness can outweigh. With a correctly arranged safety harness systems, we can actually be fairly careless in an otherwise risky situation without getting into danger. With an AIS beacon and a good vest, we should still use the correctly arranged harness system, but it’s actually quite probable that we’ll be found if we fall. It really helps a lot.

    So a question then: Will having the good vest and the AIS beacon make us use the harness less frequently? Yes, it most certainly will. Since staying on the boat is a great deal safer than falling overboard, even with a good AIS beacon and vest, this means having them does add a risk ingredient. However, it also reduces the risk in those instances where we would not have used the harness either way, or if the harness fails. It seems obvious that the net result of adding god vests and good AIS beacons must be a significantly reduced risk of POB fatality.

    With the Crewsaver and similar, the effect on behaviour is exactly the same as with the AIS beacon. However, their contribution to a POB getting saved is obviously waaay smaller. It will contribute a bit, some times, but what is the biggest influence? The minor safety contribution or the influence on risk behaviour?

    After many decades of observing myself and loads of other competent sailors, I’m totally convinced that using a Crewsaver and similar products will noticeably increase the risk of fatal POB situations.

    • John Mar 24, 2019, 8:27 am

      Hi Stein,

      Now that’s a really interesting way to look at safety equipment: does the item question add more real safety than it’s potential to produce false confidence in the user? And I would totally agree with your results of applying the test.

      The other point that this brings, up at least to me, is how morally corrupt the marketing of CrewWatcher is: to actively denigrate a much better technology in order to sell their own.

      • Stein Varjord Mar 24, 2019, 10:57 am

        Hi John,
        I think that’s a very good point that I should have noticed, but didn’t think of. However, I don’t think Crewsaver sees this issue the same way as described here. I think they should, but again, they’re just as human as me, making it hard to see that one’s own hope isn’t a conclusion of the whole issue. I think they mean well, but just manages to mess it up.

        “Kill your darlings” is one of the main rules in product design, but when killing a darling kills the whole product, it is hard to accept that it needs to be killed. The “darling” in this case was probably to help crew safety by using a cheap technology that is already available to most people. Great aspiration, but the mentioned available cheap tech just isn’t suited for the task. Not because it’s cheap or available, but just because it doesn’t do what it needs to do; reach far. “But it still does some good, right!?” I could have walked into the same trap….

        The test of real added safety versus real increased risk behaviour from feeling safety, is the reason I’m very critical to how “life” vests are brainlessly marketed by the authorities and others. I’m totally convinced that vests are the cause of more lost life in leisure boating than they save. Not because vests are a bad idea. They’re a very good idea, but only if used in the right context, with the right added equipment, like AIS, ect. Any safety issue is a two edged axe. We need a bit of awareness to chop the wood rather than our skull.

        • Marc Dacey Mar 24, 2019, 11:50 am

          Once again, I find myself nodding in agreement while admiring your fine writing, Stein.

        • John Mar 24, 2019, 5:10 pm

          Hi Stein,

          So true, the way we can all fool ourselves. That said, I still think that the CrewWatcher people crossed a bad line when they started implying that their product makes us safer than an AIS beacon, particularly since they got their facts wrong.

        • Stein Varjord Mar 24, 2019, 5:37 pm

          Hi Marc,
          I find myself blushing from pride, but also from shame over being so vain. Life is hard. 🙂

          Hi John,
          Sorry for using the wrong name. CrewWatcher, not Crewsaver, which is another (English) company making vests and more. I agree that attacking another product that is clearly superior, thus influencing customers into make the wrong choice, potentially increasing the risk of death, is indeed hard to defend…

      • David Ross Apr 1, 2019, 9:35 am

        Hi folk,

        It was refreshing to read Stein’s comments, I have held the same view for some years. Whilst trying to program and attach one of our AIS POB to a life jacket, the aerial popped out. The VHF and chart plotter went into full alarm mode, the cabin was a very noisy place. Having calm all the devices down ch16 piped up reporting an AIS POB in the harbour to the coastguard (Oh the shame) from another yacht. Whilst not planning to test the systems, I can say they worked quickly and effectively. By the time I could get through to the Coastguard (due to the ongoing incident) the RNLI had already had their lunch interrupted and had to be stood down.
        Just as an aside have you seen Duncan Wells’ MOB device (no association), so simple, so cheap so I fitted them.


        • John Apr 2, 2019, 8:22 am

          Hi David,

          Good to hear that it all worked! And thanks for the link to the MOB device. I had not seen it before. Definitely something I will look into further.

          • Marc Dacey Apr 2, 2019, 10:59 am

            Duncan Welles, who is also an author of a decent boat-handling book, has a series of well-done videos on You Tube, some of which deal with his MOB retrieval kit.

  • Philip Wilkie Mar 24, 2019, 3:52 pm

    I have to second John’s comment above. Sailing while an apparently simple endeavour, is a remarkably complex thing to do really well. For someone like me starting out there are so many problems to solve simultaneously there is a real temptation to ‘deal’ to at least some of them with a pre-packaged solution that comes in bright red package and the word ‘safety’ on the label.

    • John Mar 25, 2019, 7:21 am

      Hi Philip,

      Good point. Getting started is indeed intimidating, so it’s only human nature to default to whatever seems easiest.

  • Timothy Hansing Mar 25, 2019, 12:04 am

    Hi John,

    My new 48 foot cutter rig cruiser was launched last week and to be clear, based on all the articles I have read over the last few years the best safety kit is as follows:

    1. Safety line down the centre of the yacht (don’t fall in strategy).
    2. MOB 1 fitted into the Spinlock life Jackets
    3. MOM Jonbouy attached to the stern area of the yacht.

    I just want to make sure !

    Many thanks for a great website.

    SV Tipsy Tuna

    • John Mar 25, 2019, 7:29 am

      Hi Timothy,

      I’m all good with that list. That said, so much of this is in the details and usage profiles so I’m always a bit uncomfortable labeling any strategy as best, or safest. For example, if the alarms are not right on the boat the MOB1 might not do it’s job, and if the chest strap on the Spinlock is too loose, it to won’t do us much good. And, added to that, there are a lot of other good AIS beacons and life jackets out there.

      So, to me, the key thing is that each of us has really thought about the reasoning behind any gear recommendation, rather than just the final conclusion.

  • Paul Padyk Mar 26, 2019, 12:13 am

    Hi John,
    Thank you again for your thoughtful look at the details. It is clear to me you describe systems from the point of view of inputs, process, and outputs. As an overwhelmed newby, I am grateful for such a starting position; and as an adult, I appreciate that my outputs will depend on the attention to detail I achieve. I can guarantee I have a much better chance at good outputs because of your insights, and those of the astute community cultivated here.

    • John Mar 26, 2019, 8:31 am

      Hi Paul,

      That’s it exactly. And the other thing I would add is think for yourself. I think that often people who are new to a sport don’t give their own reasoning powers enough weight and therefore get swept up in whatever the latest trend is. Clearly you are really thinking about this stuff, and that trumps pretty much everything else.

  • Petri Flander Mar 28, 2019, 3:29 pm

    That signal coverage illustration is excellent communication. One good picture is worth…

  • Megan Roberts Apr 22, 2019, 3:28 am

    Hi John, I know that this has been mentioned in an earlier article but I think that it is worth reiterating at this point that the mob alarm is not compatible with every VHF radio and in fact may not sound an alarm on the VHF.
    While generally happy with the device this was something I didn’t find out until after purchase .
    Thanks for some very useful articles.

    • charles starke Apr 22, 2019, 4:58 am

      Hi Megan
      I am not sure I understand the conditions or specific radio you are referring to, which will not respond to a MOB alarm. An Ocean Signal MOB alarm should be programmed with the boat’s MMSI. The boat’s MMSI should be entered into the VHF. Obviously, if the VHF radio is not DSC enabled with MMSI entered and GPS input, it will not respond. Are there any other conditions you are referring to? Thanks.
      Best wishes,
      Charles L Starke MD FACP
      s/v Dawnpiper

    • John Apr 22, 2019, 7:19 am

      Hi Megan,

      Absolutely, we have a complete chapter on the boat side of things:

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