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RMV vs SAC rate

Discussion in 'Shearwater Research' started by BlueTrin, Oct 10, 2019.

  1. foob

    foob Nassau Grouper

    # of Dives: 100 - 199
    Location: San Francisco
    Fine shearwater should let us choose which to display. And require us to input tank type if we want rmv.

    Everybody is happy heh.
    BlueTrin likes this.
  2. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    Every time the user has to enter something, especially if it is required, the more chance for an error...either because it was entered incorrectly or misunderstood as to what was to be entered. It is a trade-off.

    Long ago, I used a device to measure surface waves as part of my job. It was a 1m stainless steel sphere with electronics and batteries inside and an antenna sticking out of the top. The batteries would last about a year. The crusty old Dutch engineer who designed them and sold them welded the two hemispheres together before he shipped the device to you....he said within a year it would be lost or some ship would run it over so there as no reason to allow it to be opened to replace batteries, and once you could open it all the problems began. I convinced him to make me one I could open; I wasn't going to be using it in a shipping channel, and when used it was only for a few days to a week or two. I needed to be able to replace the batteries. He made it, I used it, and only forgot to connect the battery pack before deploying it once. Sometimes, the manufacturer is so intent on making some foolproof he forgets it might also be less usable.
    TrimixToo and BlueTrin like this.
  3. DeepSeaExplorer

    DeepSeaExplorer Solo Diver

    # of Dives: 500 - 999
    Location: North Florida
    SAC and RMV are closely related, but are not the the same thing.

    SAC is expressed at PSI per minute. It’s used to estimate dive time remaining during the dive, or to calculate RMV.

    RMV is expressed in Cubic Feet per minute. Mostly used for calculating how much gas is required for a dive, before the dive. However, SAC must be known to calculate RMV.

    So they’re interrelated, but not the same.
    rongoodman likes this.
  4. Mike1967

    Mike1967 Manta Ray

    # of Dives: 50 - 99
    Location: Victoria, Australia
    True but, there's other things that must be set right so what's the difference?
    I would like the option.
  5. BlueTrin

    BlueTrin DIR Practitioner

    # of Dives: 100 - 199
    Location: London
    I think that’s what @tursiops said as wel if you read the rest of his post.
  6. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    ...or bar per minute.
    ...or surface liters per minute.
    ScubaWithTurk likes this.
  7. Mike1967

    Mike1967 Manta Ray

    # of Dives: 50 - 99
    Location: Victoria, Australia
    Umm yeah, we agree.
    BlueTrin likes this.
  8. divezonescuba

    divezonescuba ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Houston, Texas
    Here is a response to my inquiry on this subject to Shearwater 2 years ago.

    For now we've decided to report based on pressure (psi) and not volume (cu ft) mainly because it keeps simplicity. We agree with your assessment that many technical divers do not find air integration attractive. Concurrently many recreational divers are attracted to the air integration feature and we want to keep things as simple and reliable as possible for them. That said, we always take feedback from customers like yourself seriously. Feedback always plays a role in decisions for implementing new features. Thank you for your note.
  9. FreeFlyFreak

    FreeFlyFreak Solo Diver

    # of Dives: 25 - 49
    Location: California
    I just calculate the RMV myself using the provided SAC psi and looking up the rated tank air volume and rated tank max psi.
    I then record it in the App under gas notes.
  10. Mike1967

    Mike1967 Manta Ray

    # of Dives: 50 - 99
    Location: Victoria, Australia
    Old school :)
    FreeFlyFreak likes this.

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