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Current: How fast is too fast?

Discussion in 'Advanced Scuba' started by ADeadlierSnake, Sep 10, 2012.

  1. TSandM

    TSandM Missed and loved by many. Rest in Peace ScubaBoard Supporter

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    For planning shore dives around here, I don't want to be in the water over .5 knot. For a fun dive without stress, half that.
     
  2. 1.3

    1.3 Registered

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    With or without a scooter?
     
  3. gcbryan

    gcbryan One Bad Hombre

    # of Dives: 1,000 - 2,499
    Location: Seattle
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    I don't plan to deal with any current but up to .5 kts is reasonable. If it's a drift dive and you don't have to do a lot of navigating then 3-4 knots is doable but doing any movement (even lateral) against the current just isn't going to happen. You're just along for the ride at that point.

    Losing your buddy and not being able to regroup is very likely if you're not careful.
     
  4. TSandM

    TSandM Missed and loved by many. Rest in Peace ScubaBoard Supporter

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    You can definitely handle more current on a scooter. I can remember a dive on Farnsworth Banks where we'd shelter behind the top of the pinnacle, then drive the scooters full-tilt into the current until they stalled, and then let the current flip us over and drive us back to the lee side. I don't know how strong that current was, but it was the strongest I've ever tried to fight. I'd guess it was at least 1kt and maybe more.

    In the PNW, it is best, even with scooters, to plan either for a drift or for the best estimate of slack you can come up with. Scooters are insurance, but a dive plan should never DEPEND on a scooter to get home. Scooters fail, and towing another diver, a scooter cannot work against the same amount of current that it can with only one. Dives like the Diamond Knot are planned as carefully as possible for slack, and scooters are insurance, and even that doesn't always work, which is why you live boat the dives.
     
    beaverdivers and Doppler like this.
  5. meagicano

    meagicano Contributor

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    How can you tell what the current is? I've never had this answered to my satisfaction.

    In terms of currents, we are lucky that even when the current is up, we have enough structures to hide in. We found this summer that we had to do a LOT of kicking while drifting, especially compared to previous years. Even on our more advanced dives the current wasn't as strong as it has been in the past.
     
  6. GrumpyOldGuy

    GrumpyOldGuy Contributor

    # of Dives: 200 - 499
    Location: West Texas/NH/CA
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    Keep in mind, surface current and current at depth can be very different. For surface currents, spot some debris in the water and follow it to judge speed if you are fixed (anchored). If you are piloting a boat, you can shift into neutral and get the drift speed right off the GPS. You can also compare the GPS speed to the water speed if you have good instrumentation.

    I have been on dives where it going one direction at one speed on the surface, different direction and speed at depth. Normally, there are in at least the same direction, but if you can hug the bottom without damaging it you may find yourself in a better situation.
     
    beaverdivers likes this.
  7. TSandM

    TSandM Missed and loved by many. Rest in Peace ScubaBoard Supporter

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    I don't have any idea how you measure current when you're underwater, but I know what my experiences have been, and what the current predictions said we should have been experiencing at that time. That's how I concluded that more than .25kt makes a dive stressful.

    BTW, I've done a 7kt drift. Except for the speed with which the sides of the pass went by, you had no idea you were going that fast.
     
  8. lowviz

    lowviz Solo Diver ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Northern Delaware or the New Jersey Turnpike
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    Fixed (holding onto the upline etc): watch something in the water column move past your body
    Drifting: gauge your body's progress past a fixed point on the bottom

    3 seconds to move 5 feet is very close to one knot.
     
    AfterDark likes this.
  9. Darnold9999

    Darnold9999 Contributor

    # of Dives: 500 - 999
    Location: Victoria BC Canada
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    For calculating when to get out of the water on a tidal change I want to be out of the water before the current is forecast to be 1 knot.

    For grins here is a site that I would not want to dive today :D as the daytime window is just too short. Great spot to dive, but you have to pick your times.

    temp.jpg
     
  10. Pedro Burrito

    Pedro Burrito Moderator Staff Member ScubaBoard Supporter

    # of Dives: 5,000 - ∞
    Location: Boussens, Canton de Vaud, Suisse
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    Estimating current is always interesting. 10 divers could get into a current and after the dive will give wildly different estimates of the velocity. I visited Cozumel at the end of March, 2012 and there were some very fast currents on some of the dive sites.

    A 1 knot current is 1.687810 feet per second or about 10 feet (10.12686 feet) in 6 seconds. In metric that is 1.852 kilometers per hour, 0.514444 meters per second or about 3 meters in 6 seconds.

    The current at Barracuda in Cozumel runs at about 6 nautical miles per hour at times. That's over 10 feet or 3 meters per second!
     
    beaverdivers likes this.

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