The Offshore Voyaging Reference Site

Which Lifejacket Auto-Inflator Should We Select?

In the last chapter in this Online Book, I discussed Phyllis and my lifejacket usage and our thinking behind it. As always, we got some great comments on other ways to use and think about lifejackets, and several people mentioned auto-inflation options.

I also wrote about the issues surrounding whether or not to fit an auto-inflator at all or whether to go with permanent-buoyancy jackets—none of this is by any means an open-and-shut case.

But assuming that we do decide to use auto-inflation jackets, the next question is, which of the two types should we choose?

  • Hydrostatic inflators from Hammar that trigger when the mechanism senses an increase in pressure as the wearer is immersed.
  • Dissolving-tablet inflators that do just as their name suggests when they get wet.

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Marcin Kołacz


One more worth mention difference is the storage – Hammar initiated PFD can be left wet to dry with your foul weather gear in cold or warm or even dump place on your boat. Even new and clever tablets type PFDs can self inflate out of the blue in that circumstances /don’t ask me how I’ve learnt this 😉 / so user need to give them some more everyday /or every watch rather/ aftercare and protect them for excessive moisture wich can be quite tricky on some boats, watch schedules and latitudes.



John, you wrote “But Hammar-type pressure releases can’t be disabled” – while this may be true with the current H20 product types I don’t see why this should not be possible, in my imagination even easier to lock/unlock than with a tablet-based solution where you have to remove and reinsert the tablet. I am sure that if enough demand is given Hammar will easily come out with a lockable kit.
While I don’t see any use of locking a self-inflator in normal on-board routine I can see the situations that have already been desribed elsewhere, mainly wearing the vest when boarding or riding in a rib.
I currently have a tablet based vest, but my next vest will be a hydrostatic one so I will be able to compare. I tested my current vest once, and it took approx. 10 seconds to inflate and to bring me to surface, after jumping from the board, mimicking a motion I believe would be similar to being suddenly thrown overboard by movement or a wave. If one believes the Hammar product desription it activates with 10cm (3″?) immersion depth, so I suspect it of being faster than a dissolving tablet.

Marc Dacey

I’m interesting in this having fallen off a boat with a tablet-type, and owning a set of new DeckVests, which we’ve yet to wear in truly challenging weather and which I can’t even recall what arming type they have. A question: can the Deck Vests go from one type to the other? If you want a Hammar type, is it an easy retro-fit?

Chris Hopkins

Hammer and Disolving table not interchangeable. One issue with the Hammer is the CO2 bottle is actually inside the life jacket so harder to check etc. Though not really and issue l guess. I’m just used to the ease of checking and changing the disolving table type where the hammers seems more complicated

Marc Dacey

This was my impression, but thanks for the confirmation.

Rob Gill

Hi John – nice to know a bit more about these lifesaving devices.
We have UML type auto activators for our Baltic lifevests that appear very similar to the Pro-sensor units pictured above. Ours have a blank that convert them to manual inflation mode.
We have these for our nominated “splash diver” who dons a wetsuit to take the lead in inflating the life raft and being the one who boards first, rights the life raft if required, and assists the followers in case of an abandon ship. The splash diver may also be needed for MOB recovery where the MOB is beyond self help.
In each of these cases, an auto-inflated jacket will most likely be an encumbrance rather than an assistance, and having the manual inflation option is preferable.

Marcin Kołacz

For jumping or working in the water and inflatable driving in hard weather I use apart from drysuit foam type PFD – model for firefighters water rescue teams. Very streamlined, crotchstraps and integral safety belt with chest and back clipping points /but te back point can be easily released in emergency by the swimmer using dedicated front buckle/ 80N placed with active swimming in mind, lot of pockets including dedicated back pocket for throwing line.
There is also model with additional manual inflatable collar bladder giving you total 80+150 N when you need it.

Marcin Kołacz

Hi John,

I don’t know about Coast Guard, but British RNLI AFAIR use permanent floating vests with manual pneumatic additional float chamber and double chamber pneumatic vests with one chamber automatic and second manual for rescue swimmers and rib crew>

Henrik Johnsen

I´ll think the only right choise here, is to wear Lifejackets all the time… (when at sea a 🙂


The manually activated option of the auto-inflate vests we own caught in a crab trap I was deploying. It is a shock and is a potential design flaw. It has to be available but too available and it trips accidentally.


“You can’t have the cake and eat it”, or, as Goethe put it, when there’s light, there is shadow.

Bill Wakefield


We chose Spinlock Deckvest Pro 5D PFDs [circa 2013.]

We prefer the disolving tablet [UML Pro sensor] type for reliability, simplicity, rapid inflation, and cost and availability of spares.

Our pre-purchase bias for the Pro inflation mechanism was further reinforced by the following brief video Spinlock links from their website demonstrating resistance to ‘accidental’ [non-submersion] activations:

As you know, Spinlock sells manual inflation retrofit kits [i.e., manual only vs. manual optional] in case we ever decide that is better for given circumstances. [Not likely in our case.]

There are many other features we like about the Spinlock Deckvests, but I will confine this comment to the question you asked about inflation mechanism preference.

Cheers! Bill

Stein Varjord

Hi John.
As I’ve mentioned several times, I’m not happy with several issues related to vests, and especially self inflating ones. The topic here, of course, is just the auto release mechanism, none of the other issues. I have had two laundry threatening shocks from unexpected vest releases, salt tablet type, including once sitting next to it inside eating lunch. They move fast… In none of the cases had the vest been in unusually wet conditions recently, but in both cases the tablet was almost a year old, indicating that a year between changes might be too much. Either way, this has made me doubt the merit of salt tablets, but I’m probably not up to date. I’m still not sure how repositioning the water inlet can help much, though….

By the way, i have the impression that most users don’t actually change their tablets at all. I’ve heard claims that old tablets can get hard and thus extent release time a lot, even totally prevent it. I have no first hand experience with this, though.

The last time I did an offshore safety course, (mandatory for longish ocean races) is maybe 10 years ago, (I don’t do much ocean racing anymore) at Falck Nutec near Oslo. They also do safety training for the offshore oil business in the North Sea. In their courses they use auto inflating vests several thousand times every year. New ones, reused ones, and those their customers bring. They told me that about 20-30% of the vests do not satisfy the minimum of functionality required by the certification rules. The most common problem is that the self inflation is triggered to late or not at all. The second most common is that they don’t turn face up quick enough, which I think was max allowed 40 seconds. (?) The inflatable ones are generally far better than non inflatable ones in turning the victim, but only when they work….

Personally, I’ve removed the salt tablet, as I think it causes more danger than it contributes to safety. I agree that this must be a judgement every user must make, not a general guideline.


Hammar does sell a manual conversion kit,


Sam Shafer

My guess is:
“This conversion cap, when applied, voids any USCG approval for the device.”

Steve Hodges

I have and use either of two PFDs with integrated harness and Hammar hydrostatic release mechanisms, one by Mustang and the other a Spinlock. After several years in the Mustang, the Hammar mechanism broke through the vinyl view port. It still inflates and holds air, but a boat show price resulted in my buying the Spinlock offshore jacket. After many days in it, I prefer the Spinlock because it is more comfortable (for example, a little easier to sleep in than the Mustang has been), and the Spinlock has great gear pouch options for storing a headlamp, PLB, and snacks, and I can stow my knife out-of-way but accessible in the waist band. I’ve never had an inadvertent release with either PFD, despite some stomach-dropping, waist-deep wet work on the bow.

After jumping in with a Mustang (as a test) and feeling like my head was going to be popped off, I became an advocate of using crotch/thigh straps. I added them to my Mustang, and the Spinlock came with them. My conviction that using the well-adjusted straps is important was both tempered and reinforced (the well-adjusted part) by the 2013 Uncontrollable Urge accident which involved the filled chamber coming off the heads of several of the crew in the surf zone, including the one fatality. After reading the US Sailing report on this unfortunate incident, I prefer my Mustang for coastal races!

Regarding choosing between the hydrostatic and dissolving PFD release mechanisms, some interesting and relevant commentary here, especially comment 11:

Sam Shafer

While watching the replay of the Volvo Ocean Race Start from Auckland, the leg jumper goes in and his vest does not inflate. Don’t know what kind it of infiltrator was on the life jacket but it is a Spinnlock. You can clearly see it get submerged a few times.


This was a voluntary jump in a float suit so it might quite well be that the inflator had been disabled.
If not, and if it was a hydrostatic mechanism, you can see that he was floating with the lifejacket well at the surface – the Hammar mechanism needs at least 10cm submersion to activate.
Anyway you can’t use this video to prove that auto-inflators don’t work.

Marcin Kołacz

Hi Sam,

Probably Hammer and jumper hasn’t dive deep enough – I can believe this, as with thick polar fleece middle layer underneath my drysuit /really thick – Admirality Bay, King George Island/ I haven’t use pfd of any kind during work. One only need to release excessive air from drysuit – if it migrate to lower part of your suit you may find yourself in some trouble.

Hans Himmelman

One point I believe that has not been brought up, is with travelling on airplanes with inflatable vests. The airline industry regulations are not standard worldwide . They continue to change the rules based on the level of terrorist activities. The issue is the compressed air cyclinder . When I am travelling with my inflatable vest ( which is the dissolving tablet activation type) I am able to remove the cylinder from the vest and store it separately, therefore eliminating the risk of security taking the whole life vest when all they want is the cylinder. I can always buy another cylinder .With hammar type vest it is not possible the remove the cylinder without disarming the firing mechanism therefore requiring that a new mechanism at great expense. So travelling with the hammar vest one runs the potential risk of losing your vest to security.

Marc Dacey

This is true. I took my Stearns vest to the USVIs and was not stopped with it as hand luggage leaving St. Thomas. But as I connected at Philadelphia for Toronto, the mall cops insisted I dump the cylinder. The application of this rule seems capricious and random, meaning I will have the Spinlocks on the boat only, and if I do deliveries, I’ll take a lower-quality PFD. I guess the terrorists have won!


This wouldn’t do away with the possibility of the airline refusing to transport the pressure cylinder. The last time a flew into Turkey I had a security agent scan all my baggage after they noticed the (removed) cylinder, but I could convince the plane captain (!) that this wouldn’t give any security issues, still I had to remove the cylinder from the baggage, it has been stowed somewhere by the flight personell and handed back to me after arrival.
Fortunately on my next delivery there are brand new Pro vests on the boat so I don’t need to carry mine 🙂

Marc Dacey

True, John, I have the “Pro” (cylinder) type, but I’d rather lose said cylinder from the Stearns than the Spinlock. It’s the wayward assumption that a PFD is some sort of bomb on one leg of an air journey, yet perfectly fine to carry as carry-on luggage while “armed” (and I use the term advisedly) on another leg I find annoying. I have heard some people who do deliveries request that the skipper buy them a cylinder at the pick-up point so that they needn’t have theirs binned at the gate. The skipper gets an extra cylinder for the next crew.

Michael Jack

Just doing some research on this and it seems that now the Spinlock 6D only has the (new) “Pro Sensor Elite Automatic Inflator [which] replaces the Pro Sensor Automatic Inflator late in 2018”. As far as I can tell, only the Spinlock VITO has the Hammar inflation system now (with no option for the Pro Sensor). The VITO may be more appropriate for offshore sailing anyway but I will be going for the 6D for now.

Michael Jack

Thanks, John. It is a pity the VITO doesn’t have the Pro Sensor option. I would be inclined to buy those when I truly start sailing offshore next year (this year will just be pottering around the Baltic).

Michael Jack

Go to know, John. Thanks.