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Looking to learn from my mistake...

Discussion in 'New Divers and Those Considering Diving' started by sonofzell, Jun 26, 2020.

  1. sonofzell

    sonofzell Angel Fish

    # of Dives: 0 - 24
    Location: Philadelphia, PA
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    Not so much heading as distance (or duration, based on suggestions above). The dive I was referencing actually seems to be the perfect example: Our nav directions were about as simple as they could be - we were swimming due East in specific distances. The 90/270 degree headings were easy enough to maintain, but the distances are where I was thrown off. The current we encountered was equally elementary; it seemed to be running almost directly eastward.

    The "planning adjustments" I was asking about are considerations to the effect of currents relative to distance measuring and gas planning. For example, if our baseline to travel 100 yards is "X" (time or kick cycles), how should that be adjusted to compensate for the propulsion/resistance of the current. Similarly, if we can estimate that it will likely take us "X" percent longer to travel the same distance with/against the current, it seems prudent to plan our turn time accordingly.

    The replies here have made it obvious that the missing component here is that baseline value, and I plan to work on establishing that as soon as our local quarry gets the green light on re-opening! As for the adjustments, it seems that some trial-and-error can be expected, but I already feel more confident having a plan for improvement with specifics that we can practice.

    As always, the collective guidance is sincerely appreciated - Thank you!!!
     
  2. wetb4igetinthewater

    wetb4igetinthewater Instructor ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Seattle
    4,641
    2,949
    113
    This is non trivial. So if you are going against the current, you will be exerting yourself more (thanks Captain Obvious!). How much faster will you consume gas? That only you can determine through trial and error. Would using a gas consumption rate 50%, 100% or even more be appropriate? I cannot speak for you. You know it will take more time, but how much more time going against the current? Even with perfect trim and in sidemount, we still have a lot of drag, so that current will exert a fair bit of force on you even if the current is small. If the current is behind you, obviously less time, less exertion, less gas consumption.

    I admit that the above paragraph isn't helpful. Sorry for being Captain Obvious.

    Again, if people have better suggestions for having good "rules" to use for estimating the impact on time and gas consumption, I'm all ears and I'd be willing to experiment with those rules on myself (as we have a fair bit of currents here).

    Again Captain Obvious here, I'd always adhere to min gas when diving, so if you make a mistake in the gas needed to get somewhere, you just have to ascend to ensure that you always have sufficient gas to ascend in the emergency scenario of catastrophic gas loss (first stage failing shut, burst disc failure, etc.).
     
    sonofzell likes this.
  3. -JD-

    -JD- Eclecticist ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Greater Philadelphia, PA
    722
    466
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    One more week! One more Week! ... Dutch is finally opening on the 9th.

    Interesting map; it is not one that I've seen before. May I ask where it came from?

    PSA: the dive slate that Dutch sells has several listed headings in the student area that (given the frequent viz conditions) will pretty much guarantee that you will miss your target if you navigate correctly. It was the cause of great personal consternation, shame, and finally hilarity during my NAV course. :facepalm::(:nyah: IOW I actually can do good compass swims when I'm given the correct headings. :cool:
     
  4. wstorms

    wstorms ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Netherlands
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    One of the tricks you can do to stop and hover every few minutes or so. Assuming there is a bottom or some other reference, you can see if there is current (you are drifting). Experience will tell you if this is much current or a little.
    In any case, if you do notice currents you can guesstimate how much more time you should take for the way back (and just to be clear; ideally you should start against the current, so current works in your favor on the way back).

    The simplest way to guesstimate is to simply observe the current and lower your turnaround time by a few minutes. This gives you more time for the return trip, and will help to keep you within the time limits of your dive plan. Usually it works out quite well for gas too. The stronger the current, the more time you take.
    Say you plan a 1 hour dive, 30 minutes out, 30 back. If there is a mild current, you turn at 25 minutes instead of 30, you can take 35 minutes for the way back. This is about 15% extra time for the way back.
    Strong current? you might have to turn at 20 minutes leaving 40 for the way back, about a third extra time.

    If you want to have a better estimate, you can use the bottom as a reference. Pick something you can recognize (wreck, rock interesting coral) and drift with the current for maybe half a minute, then turn around and time how long it takes you to get back to your starting point. Drift again to continue the dive. This gives you an idea on how much longer the way back is going to be (but note that currents can pick up and go down, even if you are still heading in the same direction). Remember that the longer you need to go against the current, the more fatigued you will be, so at some point your stamina might run out and you end up adding even more time on the return part. Be conservative.

    Regarding visiting a site for the first time; try to get some info from the local divers that really know the currents. You did ask for the navigation, so just remember to ask about the currents as well.

    Final thought: keep up the good work, you are asking the right questions to become a more experienced diver and seemed to have handled the situation really well.
     
    James79, wnissen and sonofzell like this.
  5. sonofzell

    sonofzell Angel Fish

    # of Dives: 0 - 24
    Location: Philadelphia, PA
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    I KNOW!!! Already got my fills and VIPs so I'm ready to hit it as soon as the gates open! =)

    That map was posted on divebuddy.com, but I admittedly found it via Google. Some comments on the original post suggest that the headings on this version are also less than 100% accurate.

    I have that slate as well and have found at least one of those mismarked headings LOL!
     
  6. wnissen

    wnissen ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Livermore, Calif.
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    I like this idea!
     
    wstorms likes this.
  7. wetb4igetinthewater

    wetb4igetinthewater Instructor ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Seattle
    4,641
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    One of the most useful comments I've read in a long time. Thanks for that!
     
    wstorms likes this.
  8. wnissen

    wnissen ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Livermore, Calif.
    454
    247
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    I agree, I have done the same thing to assess the magnitude of surge, but for some reason it never occurred to me to do it for current.
     
    wetb4igetinthewater and wstorms like this.
  9. -JD-

    -JD- Eclecticist ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Greater Philadelphia, PA
    722
    466
    63
    Whoops, my mistake - opens on the 9th.
     

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