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Waterproof GPS/compass for long-distance swimmer

Discussion in 'Electronic Design' started by _, Jun 7, 2007.

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  1. _

    _ Guest

    I coach a girl who does long-distance open-water swimming - like the
    Channel, that sort of thing.

    We think that some sort of GPS or at a minimum a compass would be a good
    tool for her to wear, both while training and while actually doing the

    One of the things we'd like would be some sort of feedback on direction.
    There are a number of issues/characteristics with this:

    Aural feedback may not work well. Bone conduction is a possibility, but
    earphones probably won't stay put for the length of time she will need the

    An led indication of course could work; maybe a tri-colour attached to one
    goggle (green ok, red veering left, yellow veering right, that sort of

    There is a bit of body-motion to consider. She could wear a belt with the
    unit in the small of the back, or on the head if it is not too large. The
    back would have mainly roll; the head may have a bit of yaw as well, so
    that might be trouble.

    Initial setting of the course would have to be worked out - if the unit
    were on the head, perhaps she could orient as desired, then press a button
    to fix that course.

    Course indications would need to be integrated over a short (~5 to 10 sec)
    period. It might be helpful if this period could be randomly varied
    within those limits, as some swims do not allow "pacing", and a repeating
    signal could be used for this - unless it were irregular.

    For training she often does multi-leg "loops", returning to a starting
    point several times. For that some sort of GPS-type distance logging,
    course & waypoint setting, etcetera would be a plus. This would also be a
    BIG plus for some swims where current is a variable.

    Waterproofing needs to be enough to withstand shallow immersion - say 30

    Battery life might be a factor, some swims can be more than 10 hours.

    Radio coms would also be a plus, but rather than get just a radio and have
    a guide give info, a self-contained unit would be much better.

    I can do small electronics, uc programming, and machining, but have very
    little knowlege of what building blocks are out there and their qualities -
    like how fine a resolution can you get from electronic compasses, what
    tricks can you get GPS to do, will these blocks work if under 2 feet of
    seawater, current draws etcetera...
  2. Donald

    Donald Guest

    GPS antenna will _not_ work in water. Spray is just as bad.

    The swimmer I have seen in the news are towing a small raft behind them.

    This is not a good solution for you ??

  3. A further observation: Is it really wise to have a long distance swimmer
    out in open water without an escort craft? That would be the logical
    place (and pretty much a no-brainer) for the location of any navigation
  4. _

    _ Guest

    Of course not - but that's not even a consideration; don't worry. For swims
    of any length there is a guide boat. What we are looking for is to reduce
    the small course variations that can occur, and if possible to track
    distance for training purposes.

    Another poster has said that GPS units will not work in spray - is this a
    guaranteed idea-killer? A unit mounted on the head would might be able to
    see satellites for some proportion of the time.

    A towed raft might not be oriented in the same direction as the swimmer,
    and compass heading would then differ.
  5. Rich Grise

    Rich Grise Guest

    Isn't it possible to simply tell her, "Follow the boat"?

  6. A small amount of water on the antenna will attenuate the signal, but it
    should still work. Otherwise no GPS unit would ever work in Washington
    State ;-)

    You'd probably have to mount the antenna high on the swimmer's back,
    where it would have a view of the sky but not be continually immersed as
    the swimmer rolls her head to take a breath.
    A GPS unit won't give highly accurate bearing information until it moves
    some tens of yards and can calculate the difference. Same for the track
    error. The swimmer could end up weaving quite a bit back and forth and
    not get a correction signal. A compass, on the other hand will give
    instantaneous course error feedback. What is needed is a GPS unit and
    some other instrumentation (to calculate drift due to currents, etc.) on
    the boat to calculate the preferred heading and some way to get that
    information to the swimmer, who carries a compass.
  7. ehsjr

    ehsjr Guest

    GPS on the boat, boat goes straight, swimmer looks at boat,
    swimmer goes straight.

  8. krw

    krw Guest

    Tell that to Ted Kennedy.
  9. _

    _ Guest

    Yes, but no.

    The boat will wander, too.

    The aim (pun yes) is to feedback course following on a very frequent (~5
    sec) basis.

    And lifting the head to see the boat *really* increases the effort of
    swimming; when you are going for 10+ hours a small percentage can make the
  10. Al

    Al Guest

    If I remember correctly, someone designed such an item for himself and
    described it in "Circuit Cellar" magazine. Look here for the archive.

  11. Ross Herbert

    Ross Herbert Guest

    I think Paul Hovnanian has adequately explained the problems
    associated with what you are trying to implement. In a practical
    sense, what you are looking for is a system similar to this

    While RaceFX was developed for positioning cars on a racetrack the
    makers say there is no reason why it could not be applied to other
    sports such as sailing - and a swimmer could be equated to a boat. My
    opinion is that the bulk of a suitable antenna/receiver would make any
    GPS system unsuitable for wearing by a swimmer, even if it did work as
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