12 Comments on “Should I Get A Dive Computer With Transmitters – 8 min”

  1. Chris Tilley

    Hi Steve and Vas this was interesting to listen to, I have the capability on my computer I just haven’t bought the transmitters.

    My main interest in them is seeing how my SAC rate is affected throughout dives without having to do a sac test which in itself is a little articifical. What are your thoughts on that? Useful or knowledge we’ll develop over time anyway? I particularly worry about getting lazy as Vas mentioned, if my computer tells me my sac why would I calculate etc which i find a good thing to do from a skills practise pov

  2. Vas Proud

    Hey Chris,

    Good to see you are still watching 🙂

    I think that anything that can help you plan a dive or feel good during the dive has to be a good thing.

    The question (for me) is whether the computer is the best or only way to do this. If you take the data from a dive and get yourself a SAC rate to act as a baseline (you know the average depth from the computer and the gas used from your ending pressure etc. – we cover that in a video actually). Now, when you plan a dive, you know some of the key depths of the dive – so you can know upfront what the gas you are using per minute would be for that depth. So as you progress along that level, you would be able to see if you are using more or less gas than anticipated.

    Of course you will vary the breathing rate during the dive based on factors like comfort level, exertion level and say getting cold – so I am not sure it makes too much sense to try to dig too deep and get to a minute by minute level of accuracy.

    Instead, if you think about the safety of using a gas rule like thirds or fourths, you will generate a turn pressure or “minimum gas” needed when you start your ascent. So you have a hard limit you can’t go over and you will also know when that should come (after how long) – so what I like (and I think we maybe spoke about) was having a “way point” at say half way through the bottom phase of a dive – so we know the gas we would have at this point as well as the gas to start the ascent. We can therefore see if we are ontrack or if we are likely to have to start an ascent earlier.

    So knowing the “live” SAC is not helpful to me – especially as gauges read BAR/PSI and not Litres, what is helpful is knowing when I am going to get to a key gas way point so it doesn’t catch me out.

    What is really useful to me is to generate a table for the typical tanks you use (say 2 x 12L) and take your SAC rate and turn that into “BARS every 5 minutes” for the main depths you will be at (10, 15, 20, 25, 30, 35 etc) and then add columns for higher and lower SAC rates. Now you know that every 5 minutes that passes at 20m, you will have used “x” Bar – so this is what tells you how you are doing. What then happens is that you will “see” your SAC rate based on data you collect on the dives and will need to look at the SPGs less and less. You will also start to tune into how your breathing feels to you and use this as a cue as well – I can tell long before I look at my gauges if I am feeling super relaxed and therefore having a lower consumption etc.

    But I honestly wouldn’t worry too much about “what” the SAC number is, but instead “when” am I likely to need to do something.

    Let me know how that sounds 🙂

    1. Scott Steinbright

      I totally dig that cylinder SAC rate table idea! Nice

      Is it true that in order for a computer to display the data from 2 transmitters simultaneously (like in a sidemount config.), the transmitters must have different sync rates? Oceanic appears to do this (grey vs. yellow transmitters), but Ratio computers don’t. What is your understanding on this?

  3. Vas Proud

    Hi Scott,

    Yes, this is what I have read and understand also. The frequencies used in underwater transmission are not very different to be reliable, so instead, some use a timing style of transmission to send data – this is why the transmitters need to be different for the two tanks (e.g Shearwater recommend one grey and one yellow for the Perdix).

    Ratio transmitters have a user configurable channel you can set them to (31 channels to choose) so the same physical transmitters can be used for the tanks – just with different channels set on them.

    Do take a look at the manuals for these,
    http://www.ratio-computers.com/support/support4/manual/EN_User_Manual_CC_Transmitter_2.0.pdf
    https://www.shearwater.com/wp-content/uploads/2017/12/PerdixAI_Operating_Instructions_RevA.pdf

    Do also note that both these vendors state that the transmitters should only be used in addition to a regular mechanical SPG!

    Let me know how that sounds. Cheers

    1. Scott Steinbright

      Thank you for the link to Ratio’s transmitter manual (I could have looked that up myself, I guess. Haha!).
      The Ratio system has an impressively rich set of features.

      The only time I use a transmitter is during OW classes and that’s always in a single tank config. with an SPG.
      Using transmitters in a doubles or sidemount setup never really appealed to me because of the additional “catch point”, the durability of the transmitters, and knowing that some of my dive buddies have experienced connectivity issues in the past (older computer systems). But it looks like they’ve developed the communication technology a bit.

      Thanks again 🙂

  4. Brock Morrell

    Thanks Steve and Vas for this video! I had been curious to see if Steve’s thoughts had changed over the last few years.

    I’ve been using the Air Integrated Sensors (AIS) with my Teric for about 18 months now. The additional data like SAC after the dive is nice to have but not need to have. The absolute biggest benefit I have found was in low viz and dark environments, the ability to have the information immediately in front of my eyes at a moment’s glance. The display on the Teric is definitely easier than shining a torch on my spg.

    I do still keep two spg’s with me (or close by) when out diving. At the start of every dive, while pre-breathing, I watch the Teric display to ensure that it is changing with my breath. If there is a problem, I can remove the AIS and replace with SPG. If I’m on a dive and experience a failure of the AIS, I end the dive and replace with SPG. I should also point out that both my AIS (left cylinder / right cylinder) are still on a 6″ hose, just as my SPG would be. In my opinion, this reduces the potential stress / accidental damage on the AIS, and eliminates potential hose routing problems at the 1st stage.

    I am in the process of adding a Perdix AI as my back-up computer. Shearwater has confirmed that both the Teric and Perdix can communicate with both AIS sensors at the same time. If my computer fails, the other computer will still display the information.

    This may not work for everyone but I am happy with this set-up. Thanks again for the new video.

  5. JOSE FRANCO

    Hello, guys.

    Definitely, food for thought. My Perdix provides a ton of information revealing that one can hardly know enough; SAC rates are just the tip of the iceberg. When I started diving a few years ago, I was taught that it was ok to “evolve” towards new technologies to find support/redundancy, but that one should never replace the “classics”, such as depth and pressure gauges or compasses (not to mention dive tables). Today, it is common to see fellow divers substituting them completely with dive computers.

    In the case of sidemount, I have seen a variety of set up’s around, such as the one appearing (approximately, on minute 6) of this video; teaming pony spg’s on one side of the first stage with transmitters on 6″ hoses on the other; or even with no SPG’s at all (transmitters only; either connected directly to the first stage or on 6″ hoses).

    How would you advice (or not) to set up Apeks DST first stages utilizing both, SPG’s and Shearwater transmitters?

    Saludos!

    1. Steve Martin

      Hi Jose, Thanks for feedback I also agree that teaching dive tables now is just not needed. Time is much better spent having the diver learn the real skills they need in the water and if they are only learning over a few days then honestly learning tables will not improve their diving underwater. In the video you watched there is a photo of a HP fixed angle adaptor, I would suggest that for having the transmitter work with your DST first stage, or a short flexible HP hose, you just want to aviod clutter around the valve handwheel and chest area as much as possible. I would still have the SPG pointing down and not sticking up in the air. Cheers, Steve

  6. Keith Seiser

    Using AI in the past I found that multi tank monitoring was just that monitoring. No matter what tank you had selected the computer ran off of sensor #1 for all calculations #2,3,4 was a remote reading of others tanks and not used in any calculations of the computer wearer. If that has not changed then when using AI the only useful data when selecting other sensors is PSI and nothing more. Gauges seem to be much more reliable in that aspect.

  7. Rob Bulman

    Hi Guys,
    Love the new video’s. For over the last year-and-a-half I have been diving sidemount with two Shearwater transmitters with the Teric and Perdix and both of them displaying the air pressure on the home screen. I have the transmitters on a short 4 inch high pressure hose in the traditional spot you would put the SPG, but for a backup on the top side high pressure port I have a little button SPG, it only takes up about an inch so you don’t even know it’s there but it’s just nice to know is there but I have never is it. With those transmitters just make sure you have good batteries in them you’ll never have an issue.
    Thanks Rob.

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