Inflatable life jackets and MOB1

We have had our inflatable life jackets for 3 seasons now and even though they still show green on both functions, I want to repack them and check that everything is OK. We have never tried to jump into the water to see how MOB1 works when you fall in. It was lucky that we did, MOB1 came loose from the life jacket and sank to the bottom. Read about how I modified our other MOB1 mounting to prevent this in the future

Still happy, not aware of the lost MOB1

Since we would be replacing cartridges in the life jackets, I took the opportunity to swim with them to see how they work in real life. The vest I tried showed green, ie that it still works as it should. Navigation system and AIS are running so that we can obtain an AIS position from the life jacket on the chartplotter. We are also ready to contact the authorities that we are only testing our MOB1 AIS.

The vest inflates as soon as I get in the water. It was fully inflated before I came to the surface again. The image suite below is about 3 seconds long and in one of the images you can see how MOB1 has come loose and is in the water at my left arm.

There was no AIS position on the chart plotter and that was explained when I got on the boat again. MOB1 was not on the life jacket any more, it had come loose and sending from the bottom of the sea! I do not know if it came loose when the life jacket was inflated or if it had come loose before I jumped into the water. Regardless of when it detached from the vest, it should remain at the vest and not end up in the sea.

Luckily, it was only 5-6 m deep by the boat and after 20 minutes of diving I found it on the bottom. When I was going to put it back, I did not find the transparent piece that makes MOB1 fold out the antenna and start transmitting when the vest inflates. It is not stuck anywhere and when it comes loose it ends up in the water and becomes impossible to find.

I do not know if MOB1 come loose before the vest was inflated or if it came loose during the inflation. Regardless, it should be secured to the life jacket along with the transparent plastic piece.

The life jackets was controlled by me when we launched the boat at the end of November last year and then MOB1 was fixed in the holder on all the vests. During a check I made of the other life jackets after the test now, MOB1 was fixed in the holders on all vest. I could not see any damage to the holders or MOB1 devices, so I think it’s most likely that MOB1 came loose during the inflation of the life jacket.

MOB1 was installed according to the instructions that came with the purchase. I have contacted Ocean Signal and asked them to comment on the problem. I have not received any reply from them other than that they have received my message and that they should contact me as soon as possible.

Update:
In the instructions that came with MOB1 when I bought them in 2018, there is no instruction that MOB1 should be tied with the included strap. In the updated instruction that is available to download from Ocean Signal, there is instruction that MOB1 must be tied to the vest.

Instruction that came with the purchase 2018

New instruction downloaded from Ocean Signal

In this version from 2019, they have added a step about tying MOB1 in the life jacket on page 8 of the instructions.

How I modified the mounting

To avoid this the next time a life jackets is inflated, I changed the mounting of our MOB1 so as not to lose any parts. On the one hand, I have attached the MOB1 itself with a strap to the life jacket. Then I drilled a hole in the transparent plastic piece and fastened it to the life jacket with a thin string. The pictures below show how I changed the assembly of MOB1.

Test of AIS in MOB1

When we were to test the AIS function in MOB1, I activated it with the Test button. When I did it in the cockpit, no position was displayed on the chart plotter. MOB1 indicated no errors. What could be wrong? I tried to go away some distance from the boat before activation of the MOB1, then the position on the chart plotter was visible. Maybe our plotter does not show the AIS position if it is to close to the boat. Another thing I noticed was that it took quite a long time (about 1 minute) for MOB1 to find its position when I was sitting in the dinghy. I can imagine that it can take even longer time if there are big waves.

Up next

Before we start sailing, I thought I would write an article about time and position when long-distance sailing. These are obvious things but not always as simple as it may seem. The time is not the same everywhere on earth and there are several ways to indicate a position on the globe