The Offshore Voyaging Reference Site

A Conversation With Ocean Signal About AIS Crew Overboard Beacons

Steve Moore, Product Manager at Ocean Signal, gave me a call about the issues we raised in an article on problems Phyllis and I had found with their MOB1 crew overboard (COB) beacon.

(If you didn’t read that article, please do so now, otherwise this one will make no sense to you.)

Here’s what we discussed, along with a couple of other thoughts on water activation and AIS/PLB combo beacons.

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Roeland Pieter Marchand

Hi John,
Thanks for again a very important matter for sailors in general. As such I tried to share your Facebook notification about the MOB1 with the Dutch sailing forum “Zeilen”, which has more than 11,000 members, but they complain they cannot read it as being behind a paywall. Could you move this to the public part of your site?

Dick Stevenson

Hi Roeland,
It would be great to get the word out to a greater sailing community, but before John considers his answer, why not suggest to the members that they join AAC for a great series on AIS MOB beacons that includes observations of common installation errors that might make their unit non-functional (and fixes). Not to mention all the other benefits which make the membership fee so worthwhile.
My best, Dick Stevenson, s/v Alchemy


I also advise that you consider supporting a path that makes this post public so that it may be shared. It would likely attract eye balls that have never visited AAC, which is an opportunity to increase your subscriber base. Cheers

Scott A

John, just adding a voice of support for the paywall. For anyone who has ever purchased or rented anything boat related, membership to the site is a bargain.

Dick Stevenson

Hi John,
Thanks for all your work on this.

Bob McDowell

Good morning John
I, like Dick, would like to thank you for following up on this issue. We just bought our (adult) kids the AIS/MOB units as they are both sailing offshore a lot. It gives me peace of mind knowing they would have a second chance in a MOB situation.

Marc Dacey

Ditto, John and Phyllis. I constantly beat the drum for your site as being not only the only one I pay for, but which constantly provides me with more and better information than it costs me. This sort of drill-down is necessary to fully understand, appreciate and choose new technologies for the rather select group of people who go out of sight of land, and your comments, preferences and reviews have played an increasing role in not only what I choose to buy, but how I organize and run our boat.


Hi John,
thank you very much for your work on this. When I read your article in November, I recognized my MOB1 (bought 2016) were lacking the cap. I informed my chandlery (AWN, Germany). They weren’t aware of the problem but promised to clarify it with their supplier. And so they did: last week I received the two missing caps!


Thank you John. Your thoroughness is second to none. AAC is the only worthwhile dialog available to sailing man.

We purchased and fitted two MOB1s to Spinlock deckvests and have suffered many false alarms – i.e. activations due to displacement of the clip inside a closed jackets. I had put them down to packing, but now realise that our units dont have, and indeed didn’t come with, the protective “armed” cap.

Shame on OceanSignal for failing to widely publicise this critical fix for earlier units! The only reference to the protective cap on their own website is buried in their revised user manual. Sadly they have no news item to highlight it and no top-line product shots showing the cap. Again: shame on OceanSignal.

I’ll be contacting them today.

L’escale, Portsmouth

Scott Thomas

I just bought a Ocean Signal EPRIB1 class 2.
I am returning it because the instructions printed on its surface are illegible. Even the battery expiration date is impossible to read. A combination of extremely small letters and very poor quality of printing is at fault. If Ocean Signal can overlook this basic need then what else have they overlooked?
If you provided a way for me to attach picture I would.


I’m in the market for an EPRIB since I plan on venturing beyond the sight of land this summer. After a search of the site, I couldn’t find any discussions regarding these devices. Is there a post I’m missing, or is that something that hasn’t been discussed yet?
As always, it’s a joy to be part of this community.


Thanks for the verification that I wasn’t missing some thing. I’m journeying about as far as I possibly can “offshore” in my area: crossing Lake Erie. But it’s a passage out of the sight of land and it only takes 25-30 knots of wind to cause some nasty waves on that puddle! After reading about them, I think I’ll be getting a PLB. It’s much cheaper, more portable and uses the same technology as an EPIRB. The floating version of the ACR ResQLink is the model I think would work for my application.

Marc Dacey

For what it’s worth, that was my conclusion, and I went with an older version of a ResQLink on Lake Ontario. Just remember that it’s important to file a sail plan (called a “float plan” in the States) with the Canadian Coast Guard (and to “close” it on arrival via cellphone or VHF) and to register the PLB with the correct federal registry, ideally with a third-party contact who can confirm your plans. Make sure it’s a PLB that is comfortable to wear, can attach securely to your PFD (which of course you must always wear for this scheme to work) and which broadcasts a GPS string as well as the 406 Mhz beacon. It’s a good choice for solo sailing the same way the AIS beacon is a good choice with more crew/beyond the reach of SAR resources.

Dick Stevenson

Hi all,
Just as an aside, when talking with friends and acquaintances about joining AAC, if any resistance or griping about paying a fee: instead of arguing about how little the fee actually is in the real world, I tell them that they should join for a year and if they are unhappy with the benefits, I will reimburse them the years fee.
I have yet to take my wallet out for that reason.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Hi John, No worries. I was never worried, but it was just a way that occurred to me to get some with reservations over the hump, although for the life of me, I did not know why the hump exists: just that it did and was an obstacle.
My best, Dick


I can certainly understand why John could be/is disappointed if new members are not joining AAC. Now that we are new members of AAC, and see the value in the work done here, it is doubly puzzling. Just think of the froth & bubble that Patrons shell out for on Youtube, WAY more $$ each video than a YEARS subscription here, and it defies logic. Sorry John, the word about AAC has to spread, somehow.

Chris Cartwright

***I posted the information below to Sailing Anarchy and also contacted Ocean Signal

This was before someone referenced your site. In my case I felt the issue was a magnet coming dislodged from the triggering tab; but in my case also I did not have/was not supplied one of the clear plastic clips. I have one now. Thanks for all of this. There is now a reference to your articles in Sailing Anarchy for greater awareness.

I was testing the ability of my Spinlock Deck Vest to hold air.

I unzipped and manually inflated (because I didn’t want to waste a C02 cartridge). During inflation I saw the antenna of my MOB1 pop up (and thought shit what a dumba$$) as I forgot to about its automatic deployment with inflation. As I quickly went to disarm it I realized it never activated.

Normally when the grey plastic tab is pulled away, two small magnets on the backside of the tab are also pulled away and the device switches on. (internal magnetic switch I presume)

One of the small magnets that is glued to the backside of the grey plastic tab remained attached to the MOB1 so when the plastic tab was pulled away the device did not activate.

This sees like an incredibly rare events as the sweeping motion of the plastic tab should have dislodged the magnets anyway. Perhaps because I inflated manually and it happened very slowly…….

I am posting this to remind people with this device to be aware of how to manually activate it (the tiny red button); which is seen once the grey plastic tab pulls away. This also should trigger a DSC alarm, which unless you have gone to the added steps of programming in an MMSI number won’t happen. Only an AIS MOB alarm happens automatically.

The device is approximately 3 years old. The test function is perfectly normal. It has never been immersed. This MOB I installed myself (not a factory installed one from Spinlock); although I don’t think this would play any roll in the malfunction as the plastic tab was pulled away with inflation as it is designed.

David MacDonald

YAfter a great sail from Dublin to Belfast yesterday, we arrived at midnight in the pouring rain at our anchorage. While getting the snubber fitted my deckvest with MOB1 suddenly inflated. A great test of both, as far as I was concerned. My lume-on lights illuminated; the dsc on vhf started squawking; the chart plotter started beeping; and an MOB icon appeared on the screen. Everything worked just like it is supposed to. And I had just bought rearming kits, as the uml expiration date was looming, so no loss of that!

We figured out how to shut everything off (not immediately obvious) and took some moments to think about what would have happened in a real MOB. My one observation following is that the MOB1 as attached to the inflation tube did not seem as secure as I would perhaps like. I believe it could be possible to dislodge it while looking to access the whistle or sprayhood strap. Both are attached to the inflation tube as well. On rearming I have made sure that the MOB1 is below the whistle as I think it will be less likely to be inadvertently dislodged. I may also look at attaching an additional lanyard to ensure the MOB1 and vest stay together.

And even better, the next morning I spotted the clear plastic “Armed” cover at the bottom of the anchor locker!

Jean-Louis Alixant

Hi All,
We’ve owned six MOB1s since 2018 and 2019. They were initially fitted on Spinlock DeckVest 5D and now on Vito’s. I read all manuals and findings, spoke with OceanSignal, studied John’s posts with great attention as well as the comments, we test and train – but I continue to learn!
Following our last annual inspection of PFDs and associated equipment in November, I got in touch with OceanSignal to verify the state of the art and latest recommendations regarding the MOB1. I shared the details with John of what this latest annual exercise taught and reminded me; he suggested I posted as a comment. Here’s a summary:

1. OS’s recommended tape for self-activation
The tape with one loop and one flat end is the “preferred and current fitting option“.

2. MOB positioning and tape tightness
Like most, the bladder of a Spinlock PFD gets thinner around the neck. Make sure that the activation tape has maximum effect my locating the MOB1 as low as possible down the blow tube such that the tape will find itself across the largest bladder diameter available, rather than slipping to the narrower part. Tightness: the “lose enough for one finger but tight enough to prevent two fingers” guidelines sounds very approximate on paper, but is amazingly accurate in practice.

3. DSC matters – check it out
Be sure to activate the DSC option of the MOB1 if your country regulation allows it (the screen programming using OC’s online App is easy and works well). That was not allowed in France when I bought the units, but regulation changed and so I programmed all the MOB1’s to send a DSC Individual Alert to our fixed VHF’s MMSI.
During the extensive tests, it turns out my onboard AIS had failed in the three days since I had last sailed. DSC was the only alert I received, AIS failure is not theoretical. A MOB1 has two radio alert possibilities, best to use them both.
Another point in favour of DSC to me is that the way AIS MOB devices interject their messages into the otherwise organized stream of shared AIS exchanges could *theoretically* delay transmission, especially in more crowded areas (where the chances of rescue should be higher). I would expect DSC to be the first alert, and every second counts.

4. What is being transmitted
After less than 15s warm-up, the unit starts transmitting DSC and AIS, even though at that stage it has no valid GPS position: this raises the alarm so immediate action can be taken. It will continue to do so every minute or so. Once a valid GPS fix is obtained, AIS and DSC transmissions will continue every minute until the battery dies or the device is powered off.

Sorry for the long comment if it is all known to many of you, but I share hoping that it might help someone.

Stay safe,

Michael Jack

Hi, John. The Ocean Signal combo MOB1/PLB is out. Any chance you will be giving it a look over? I am curious if you will change your mind about it as I am on the verge of buying a PLB and am wondering if the combo is the way to go.

Michael Jack

Haha, what else is Christmas for, John 🙂 Have a great one and thanks for all the hard work.