Depth Sounder on a Stick

Discussion in 'Hydrodynamics and Aerodynamics' started by Asleep Helmsman, Dec 19, 2019.

  1. Asleep Helmsman
    Joined: Jul 2008
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    Asleep Helmsman Senior Member

    A friend of mine has a 40 foot Warram Cat

    We need to install a depth transducer. Sadly he decided to not do the through-hull method, so now we're stuck with using some kind of pole. We have a Transom mounted transducer, but there are no transoms on a Warram 40.

    If we build a poll that is shaped like a symmetric foil approximately 1.5 X 3.5 with a bulb at the bottom about 3" wide. It will penetrate the water about a foot.

    How much force would be applied at 6,10 and 15 knots. Approximate is fine guys I need to make a breakaway and want some kind of starting pint.

    Thanks
     
  2. BlueBell
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    BlueBell "Whatever..."

    < 1/8" plastic pins would work in a hinged break-away.
    But spring loading the pole might work better for you.
     
  3. bajansailor
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    bajansailor Marine Surveyor

    I think that many depth sounder transducers nowadays will work quite happily if they are located inside the hull (ie they do not need to be protruding through a hole in the hull), so long as they are in an oil bath, or are bedded down on silicon or similar, such that there is no air gap between the transducer and the hull.
    I appreciate though that Wharram cats have 'vee' shaped hulls and ideally the transducer should be reasonably vertical. However it should be possible to achieve this, perhaps by mounting it on a wee levelling plinth in the hull?
     
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  4. kapnD
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    kapnD Senior Member

    Transom mount transducers are “skimmers”, designed to be run trailing right at the waterline of a boat as it planes, and kick up if any obstruction or too much resistance is encountered. Most of them have plastic housings, and are not very robust unless mounted to a hard vertical surface, like a transom, so yours may not perform too well deeply immersed on a stick.
    Visit Airmar website, they make transducers for most all situations, and are suppliers for most major brands of depth finders.
    Photo is of a hydraulically retractable transducer I saw recently, this ducer was originally designed to be mounted below the hull. Ingenuity at work!
     

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  5. gonzo
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    gonzo Senior Member

    Mount it to the trailing edge of the rudder. It will be better protected from debris.
     
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  6. Asleep Helmsman
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    Asleep Helmsman Senior Member

    I was thinking of a 1/4th" nylon pin.
     
  7. BlueBell
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    BlueBell "Whatever..."

    Spring loaded is self resetting, in any weather, under pretty well any conditions.
    However, trailing edge of the rudder has promise.
     
  8. kapnD
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    kapnD Senior Member

    It will be adversely affected by the turbulence off the trailing edge of the rudder, unless mounted clear below the blade.
     
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  9. Asleep Helmsman
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    Asleep Helmsman Senior Member

    Thanks for all the input.
    In the end, he built the poll with a pivot, and used tie-wraps (zip-ties) as the break away.
     
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