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Determining Air Draft (Boat height above water level)

Discussion in 'General Yachting Discussion' started by Zud, Oct 2, 2016.

  1. Zud, Oct 2, 2016
    #1
    Zud

    Zud Senior Member

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    Okay you gurus of Yachting,

    Easiest/accurate method of determining required air draft short of driving under the bridge and measuring the amount torn off of the mast/radar arch. Boat literature makes no sense...20'8" with TV dish removed but the light mast with radar is considerably higher on the boat and would be required/original equipment. How do I get a good measurement from top of radar arch to water level with all electronics removed??

    Thanks
    Zud
  2. olderboater, Oct 2, 2016
    #2
    olderboater

    olderboater Senior Member

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    Yes, the literature is useless. Others will have other ideas I'm sure, but here's how we did it. We measured a boathouse height from the water. Pulled the boat in, measured clearance. So our air draft was the height of the boathours opening less the amount we cleared it by. You can do the same under bridges that have accurate markings, note the word "accurate" as some don't, so I'd select more than one to check. We've double checked our boathouse numbers with bridges.

    Just as you need to know draft at different loads, make sure you take loads into account on air draft. This in addition to knowing it with all different equipment and height permutations.
  3. Capt J, Oct 3, 2016
    #3
    Capt J

    Capt J Senior Member

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    Just lay a fishing rod across the hardtop where you can lay the rod verticle with a bobber on it and drop it down till it hits the water, then take it on land and measure it......if something sticks up above the hardtop measure that from the hardtop to the highest point and add to your measurement.
  4. Zud, Oct 3, 2016
    #4
    Zud

    Zud Senior Member

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    I knew I could count on you guys !!! easiest and as accurate as need be. Will do ASAP
  5. Oscarvan, Oct 3, 2016
    #5
    Oscarvan

    Oscarvan Senior Member

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    For RV's I use a laser level and large telescoping height pole. (Home Depot or Lowes)
  6. C4ENG, Oct 3, 2016
    #6
    C4ENG

    C4ENG Senior Member

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    Could you use your docking plan or general arrangement drawings to calculate the air draft while using a pair of dividers and the measuring scale on the drawing for the vessel and then add it all up?
  7. Pascal, Oct 3, 2016
    #7
    Pascal

    Pascal Senior Member

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    Home Depot sells measuring tapes....

    J, Some of us don't fish and may not have fishing gear... :) You can still measure the boat, first from WL to deck, then the house, then the hard top or whatever. I thin measuring tapes are cheaper than a fishing rod and line, and lead :) most smart phones come with free calculator app so you can add up the various measurements :)
  8. Capt J, Oct 3, 2016
    #8
    Capt J

    Capt J Senior Member

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    A boat without even 1 fishing rod? Sacrilege! The measuring tape works, but I've found with all of the angles and stuff sticking out, sometimes harder to get an accurate measurment on some. EVERY boat should have a small plackard on the dash with the air draft.
  9. Pascal, Oct 3, 2016
    #9
    Pascal

    Pascal Senior Member

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    :) not a single fishing rod on this boat ... Hoping to keep it this way