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PLBs Can Save Your Life

Discussion in 'Training, Practices and Equipment' started by letterboy, Mar 19, 2019.

  1. chillyinCanada

    chillyinCanada Solo Diver Staff Member

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    This would be awesome if it works.

    @Dan ?
     
  2. GJC

    GJC Solo Diver

    # of Dives: 100 - 199
    Location: Southern California, USA
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    Water, unlike air, is not compressible.

    A canister that flexes a tiny bit at depth will only slightly increase the pressure inside of an air filled container.

    A canister completely filled with water, that flexes the tiniest bit, will expose the contents to the pressure that is outside. Even if only the seals flex or compress a little, the contents are compressed.

    Unless the contents have an air pocket, and then the air pocket would compress the amount equal to the volume that the canister flexes. The resulting pressure increase would be partially absorbed by the compressed air. The pressure on the contents then gets complicated to compute. The big factors being the amount of flexion and size of the air pocket.

    I don't think it's a good idea to fill your canister with water. There is a risk of exposing the contents to the outside pressure and flooding the contents.
     
    Dan likes this.
  3. Dan

    Dan Orca

    # of Dives: 500 - 999
    Location: Lake Jackson, Texas
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    I don't get it. What would be the advantage of flooding the canister with water? You would still have bulky canister size. I would consult with the OEM technical support before doing something like that.

    I doubt it's going to work when I look to my PLB1 with winding spiral flat / blade-like antenna. That kind of antenna would be hard to seal a slot cavity, especially at the edge. If you submerge it in the water for a long time, say for an hour, water would eventually seep through the antenna compartment and get into the electronic. Nautilus fix that problem by putting a sealed cap over the spiral antenna.

    My PLB1 canister (2.5" OD x6" L) doesn't take much space in my BCD pocket. It is about the same size as my DSMB.

    25B46962-7A80-459D-AF29-A73B6227091A.jpeg
     
    chillyinCanada likes this.
  4. aviator8

    aviator8 Professional Photographer

    # of Dives: 25 - 49
    Location: Georgia
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    This is the real problem I see! How to do you calculate it

    To me the advantage would be this:
    1 An air filled pressure vessel is great, but if it fails everything in it fails catastrophically and the PLB is rendered ineffective.
    2 If it is water filled the failure rate could be mitigated and less likely to cause catastrophic failure in a seal breach.
    3 There is a side benefit of having drinkable water in an emergency unless there was a seal breach.
     
  5. aviator8

    aviator8 Professional Photographer

    # of Dives: 25 - 49
    Location: Georgia
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    Also I should say benefit 4. not having to by a high priced bulky pressure vessel. A diy solution may work fine
     
  6. DandyDon

    DandyDon Old men ought to be explorers ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: One kilometer high on the Texas High Plains
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    Leaks can happen, especially with old or ungreased o-ring, and that can ruin a camera or a light, but not likely with a PLB as it's water resistant.
     
  7. Dan

    Dan Orca

    # of Dives: 500 - 999
    Location: Lake Jackson, Texas
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    Do you think there is no air space inside the PLB? Also I know the housing of my PLB1 is just a thin plastic sheet, especially around the button. With water-filled canister, as you go down to 100’ depth, the water column crushing pressure would be transmitted directly on to the canister surface. Since the water inside the canister is incompressible, that pressure would then be transmitted directly onto the PLB housing and ended up flexing the PLB housing and turn on the red button. On top of that, now you have water pressure inside the canister pressing against the PLB housing to beyond its rated value.

    I tested this by putting my PLB1 in a soft case and taking it to 100’ depth. The red button turned on as the soft case crushed on the PLB1. See the red LED lights up in the picture, below.

    190E396B-8998-45F8-9345-BFC3740EBFAD.jpeg

    If you have air inside a rigid canister and the canister leaks underwater, as long as there is still air in the canister cavity, the PLB would still be fine. The pressure inside the canister would still be below the rated value since the air is compressible.

    Unlike the PLB1, Nautilus Marine Rescue GPS (MRG) alert buttons are placed inside the protective cap that would hold up to 425’ depth water pressure. That’s why you need a canister to take the PLB underwater beyond tge rated value. The PLB makers need to design the PLB with more rigid housing with buttons inside a protective sealed cap, just like the MRG.
     
    aviator8 and chillyinCanada like this.
  8. Dan

    Dan Orca

    # of Dives: 500 - 999
    Location: Lake Jackson, Texas
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    This makes sense. My canister is sealed by a big o-ring on top. Just imagine you fill the canister up to the brim with water at 1 atmosphere, close the lid so it traps no air . If you take it down to 100’ (30m) or 4 atmospheres, the differential pressure across the o-ring seal is going to be 3 atmospheres (44 psi). That 44 psi pressure is going to squeeze the o-ring flatter and pressuring the water-filled cavity towards 4 atmosphere. The flat polyethylene lid and bottom acrylic plate would also cave in.

    726B368D-BEE0-4E28-931B-4CE2648490DB.jpeg
     
  9. Joshua Young

    Joshua Young Angel Fish

    # of Dives: 0 - 24
    Location: Japan
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    If you’re just diving with a group, as well as a DM in a controlled setting, wouldn’t a PAB all you’d need?
     
  10. Dan

    Dan Orca

    # of Dives: 500 - 999
    Location: Lake Jackson, Texas
    5,671
    3,204
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    To avoid the alert buttons from getting pressed by hydraulic pressure at depth, Nautilus MRG has those buttons inside an o-ring sealed air cap.

    9C86C1D1-BDEB-4B13-B078-35CF6E26FC81.jpeg
     

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