Lines plan from measurements

Discussion in 'Boat Design' started by Rom, Nov 2, 2020.

  1. Rom
    Joined: Oct 2020
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    Location: UK

    Rom New Member

    Hi All,

    Looking at drawing up a lines plan of a 44' vessel from external measurements. In theory I have an idea how to do this but has anyone done it successfully? How many stations, waterlines, etc... do you use to get something as accurate as possible. Also were the measurements taken using simple, plumb-line and ruler/tape measurer or something more precise?

    Thanks,
    Rom
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Welcome to the forum.
    This has been done countless times, but success depends on how rigorous you are in taking the measures. Define as best you can the longitudinal profile and the deck line and I would say that with 7 cross sections, equally spaced, it would be sufficient, additionally, if the bow or stern are complicated, take some intermediate section in this area. If the boat has chine it would be advisable to also take the necessary points to define it.
    Very important: materialize the best possible reference planes to take measurements.
     
  3. Steve W
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    Steve W Senior Member

    I have taken the lines off a 40ft wood motorsailer. A customer had bought the boat out of storage and at some point all the ballast in the form of internal lead ingots had been stolen and the only way to figure out how much we needed was to measure the volume below the waterline. I only measured from the waterline down. I measured stations, waterlines and buttocks. I had the boat set up in a cradle and leveled to the existing waterline on a concrete floor and used plumb bobs to layout the stations and made up a stand with a laser to mark the stations and waterlines on to the hull, I don't remember how many stations I used as it was probably a decade ago. It did turn out very well as we ended up pouring an external keel of nearly 10000 lbs and the boat floated on its lines.
     
  4. DCockey
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    DCockey Senior Member

  5. Rom
    Joined: Oct 2020
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    Location: UK

    Rom New Member

    Thank you all for the advise. My only concern was the accuracy of just using a plomb line and tape measurer/ruler. What other tools have you guys used which would provide more accuracy? A laser?
     
  6. Steve W
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    Location: Duluth, Minnesota

    Steve W Senior Member

    Before computers what exactly do you think we used to loft out a boat full sized on the lofting floor. Of course its accurate enough. Iv'e lofted many boats old school, you can work to an accuracy of at least 1/16". We have a digitizer at work (that I would have no idea how to even turn on) that we use to pattern for foam decking that should be great for taking off lines.
     

  7. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    How accurate do you need the lines need to match the existing hull? What will the lines be used for? A major factor in accuracy is the care and precision of the person taking the measurements.

    I've heard of laser levels, cross levels and 3 line levels being used in various ways. Other methods for measurng boat hulls include using a laser total station, scanning with a laser system and photogrammetry.
     
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