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Thread: Documentation and Lifting Lines off an existing boat?

  1. #1
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    Default Documentation and Lifting Lines off an existing boat?

    Hello all,

    This is just a question of academic curiosity with no real project in mind. I'm looking for resources, literature, videos, etc., on the process of documenting, measuring, and lifting the lines off of an existing boat for the sake of making lines drawings of that boat. Any recommendations of such resources or a forum thread that my cursory search failed to find would be much appreciated? I have the Mystic Seaport's Lofting Manual and a number of books on design that I intend on sifting through when I get back home next month to jog my memory. I've done a scant bit of lofting while assisting a builder and I have some drafting experience but I'm always interested in learning more. The process of measuring an existing hull shape and then creating drawings of it in an efficient manner piqued my interest recently when someone asked me about how I would do as such without modern tech like laser imaging and the like.

    I hope everyone's winter projects are going well and thank you in advance,
    ~ Bryan

  2. #2
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    Default Re: Documentation and Lifting Lines off an existing boat?

    There are several methods using basic equipment. The basic kit methods will vary dependent on the type of hull form, what sort of ground she is on and whether she is level ford and aft and/or athwart ship.
    There is no one single best method short of the laser survey.
    It really is quite difficult to build an ugly wooden boat.

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  3. #3
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    Default Re: Documentation and Lifting Lines off an existing boat?

    There is a good book on the subject. It was freely downloadable off the net when I printed my copy some 6 or 7 years ago.

    Boats
    A manual for their documentation

    Published by
    Museum small craft association
    Editors Paul Lipke/Peter Spectre/Benjamin A.G. Fuller

    However if you are going to measure a clinker built boat with wide planks it seems to be better to measure to the upper edge of each plank rather than to theoretical waterlines as described in the book.
    Amateur living on the western coast of Finland

  4. #4
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by heimlaga View Post
    There is a good book on the subject. It was freely downloadable off the net when I printed my copy some 6 or 7 years ago.

    Boats
    A manual for their documentation

    Published by
    Museum small craft association
    Editors Paul Lipke/Peter Spectre/Benjamin A.G. Fuller

    However if you are going to measure a clinker built boat with wide planks it seems to be better to measure to the upper edge of each plank rather than to theoretical waterlines as described in the book.
    https://schoonerchandlery.com/shop/b...documentation/

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    Default Re: Documentation and Lifting Lines off an existing boat?

    Available free from our sponsor....https://www.woodenboatstore.com/prod...l_publications
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by TR View Post
    How does one download this? The site is set up for shipping actual books...can't find a download button.

  7. #7
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by lupussonic View Post
    How does one download this? The site is set up for shipping actual books...can't find a download button.
    Use this link.
    It really is quite difficult to build an ugly wooden boat.

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  8. #8
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Much obliged.

  9. #9
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by lupussonic View Post
    Much obliged.
    Thinking of lifting Kate's lines?
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Documentation and Lifting Lines off an existing boat?

    High time frankly.

    There have been a few models made along the years but a bit not quite right visually. I would love to have her lines in their own right, but have always thought that a model along with rig mock up would be a wonderful aid in instructing a crew on how to tack her efficiently.

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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by lupussonic View Post
    High time frankly.

    There have been a few models made along the years but a bit not quite right visually. I would love to have her lines in their own right, but have always thought that a model along with rig mock up would be a wonderful aid in instructing a crew on how to tack her efficiently.
    I have lifted the lines of several boats of about her size. 2 man days work to measure, then a man week or so to draw up.
    It really is quite difficult to build an ugly wooden boat.

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  12. #12
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    Default Re: Documentation and Lifting Lines off an existing boat?

    I will study the download in due course. But my (foggy) understanding is that one can start either from an internal centre line or an external centre line datum below the keel or from top of stem to stern post. Saggy string is your enemy.

    If you have any tips or experiential advice sing out.

    Should have added previously, the models made of Kate were of balsa and have been sanctuary to several generations of mice.

  13. #13
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by lupussonic View Post
    I will study the download in due course. But my (foggy) understanding is that one can start either from an internal centre line or an external centre line datum below the keel or from top of stem to stern post. Saggy string is your enemy.

    If you have any tips or experiential advice sing out.

    Should have added previously, the models made of Kate were of balsa and have been sanctuary to several generations of mice.
    I find it easier from the outside. No outfit, bulkheads, engine beds etc to get in the way. The actual method depends on how level she is. However I usually work from a straight edge longer than the boats half breadth that can be set up level athwarship at each measuring station.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by lupussonic View Post
    How does one download this? The site is set up for shipping actual books...can't find a download button.
    The download instructions are there on the page I linked to....place your order and instantly receive email confirmation with download link....then you have 3 days to download the item.
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Does anyone know if any of the free photogrammetry programs can generate useful measurements? Failing that, if the subscription types can be learned and used before racking up a bill that would pay to have someone else document the boat for you.

    https://all3dp.com/1/best-photogrammetry-software/ says that MicMac has editing tools that make it a 'feasible solution for metrology and site surveying'. So, did that say it can be used to generate offsets?

    Some comparison between laser line scanners and photogrammetry, along with some of the difficulties getting a usable set of pictures: https://www.youtube.com/watch?v=0WTns1ItVss
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  16. #16
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    Default Re: Documentation and Lifting Lines off an existing boat?

    "Saggy string is your enemy." - lupussonic

    String stretches and sags. Welding wire does not. I made two standards on braced bases out of 2x4 lumber, counter-weighted them with cinderblocks, ran welding wire from one to the other, and tightened the wire by using a small bottle screw on one end. Using a laser level, I deduced that I could set up the wire to have less than 3mm of sag over 18 metres, and it did not sag over a ten-hour work day.

    The other thing I would like to mention (brace yourself, I am about to blaspheme...) is that accuracy in the lifted lines is variable, depending on the intent. If you are wishing to record the exact shape of the subject hull suitable for recreation of the hull as a replica to millimetre tolerance, then you need to get seriously anal about the process. If, however, you merely want the shape of the hull accurate to within an inch or so, with the intention of creating a set of lines for a modified hull based on the subject boat, or for calculating stability, then accuracy and its attendant fussiness can be a bit more relaxed. Also, the best method of taking lines can vary depending on the size and location of the boat, and the time available to take the lines.

    I work with another company to do existing-hull lines take-off and stability analysis using a laser-ranging photogammetry method. The hardware & software is around $70,000, and a measurement of your 15-metre (50-foot) hull and a lines plan from that survey will set you back around $5,000 plus expenses.

    I worked with a system a few years ago that was an add-on to Rhino that used multiple digital camera photos of the subject hull with stick-on targets applied to the hull surface. The photos were then processed thru the software and a 3D 'cloud' of datum points were created that when imported to Rhino could have surfaces wrapped around the points cloud to create an accurate 3D model of the hull. It was pretty slick, worked quite well, and cost around $3,000, plus the Rhino software.
    Hope for the best, but plan for the worst.

  17. #17
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    Default Re: Documentation and Lifting Lines off an existing boat?

    In the case of Kate.
    Get down and personal and squint along the keel. If it is not straight you will see it. You can then decide whether to harden up some wedges to straighten what was intended to be straight. Then use the underside of the keel as your base line, which can be extended out to the ford side of the top of the stem and to the extent of the stern by straight edges clamped to the keel and supported on legs at their outer ends.
    You will only need a string line to define the CL of the deck. Alternatively just measure the beam at each measurement station and halve it.
    It really is quite difficult to build an ugly wooden boat.

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  18. #18
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    Default Re: Documentation and Lifting Lines off an existing boat?

    I document boats with photogrammetry using Metashape, formerly Photoscan, software. https://www.agisoft.com/ The output is a colored point cloud and textured mesh, usually with millions of points available. My usual workflow is to import the mesh into Rhino, then slice it for lines and/or sample it and fit surfaces to create a 3D model. Almost any camera including cell phones can be used to take photos for Metashape, and the software automatically corrects for lens distortion. The subject does need to have a bit of visual texture so clean, glossy gelcoat usually does not work. However I've had good luck with painted surfaces, even recently painted, which are slightly dirty.

    The standard edition of Metashape is $179. I purchased a license in 2012 and it continues to be good for the latest updates.

  19. #19
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by mmd View Post
    "Saggy string is your enemy." - lupussonic

    String stretches and sags. Welding wire does not. I made two standards on braced bases out of 2x4 lumber, counter-weighted them with cinderblocks, ran welding wire from one to the other, and tightened the wire by using a small bottle screw on one end. Using a laser level, I deduced that I could set up the wire to have less than 3mm of sag over 18 metres, and it did not sag over a ten-hour work day.

    The other thing I would like to mention (brace yourself, I am about to blaspheme...) is that accuracy in the lifted lines is variable, depending on the intent. If you are wishing to record the exact shape of the subject hull suitable for recreation of the hull as a replica to millimetre tolerance, then you need to get seriously anal about the process. If, however, you merely want the shape of the hull accurate to within an inch or so, with the intention of creating a set of lines for a modified hull based on the subject boat, or for calculating stability, then accuracy and its attendant fussiness can be a bit more relaxed. Also, the best method of taking lines can vary depending on the size and location of the boat, and the time available to take the lines.

    I work with another company to do existing-hull lines take-off and stability analysis using a laser-ranging photogammetry method. The hardware & software is around $70,000, and a measurement of your 15-metre (50-foot) hull and a lines plan from that survey will set you back around $5,000 plus expenses.

    I worked with a system a few years ago that was an add-on to Rhino that used multiple digital camera photos of the subject hull with stick-on targets applied to the hull surface. The photos were then processed thru the software and a 3D 'cloud' of datum points were created that when imported to Rhino could have surfaces wrapped around the points cloud to create an accurate 3D model of the hull. It was pretty slick, worked quite well, and cost around $3,000, plus the Rhino software.

    Great information, thank you. That's another topic I've been interested since I took my stability exams, that is designing with specific stability criteria in mind. It's another passive interest as I'm not likely to use the knowledge. Thank you again.

  20. #20
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Sorry to have started a topic and then disappear. I was at sea for a couple weeks with my regular job and then got busy when upon returning home again. I have just had a moment to sit down and read these through.

    Thank you so much to everyone for the information. The book on boat documentation downloaded successfully. Given the names of those involved in the creation of the book I am surprised I haven't seen this before. Only a couple weeks before I posted the original question I had been talking to Walter Ansel at a gathering and had asked him this question. However, I wasn't very clear with my question for if I had been I'm sure he would have brought up his father's involvement in said book. Oh well, here the answer is now.

    Thank you again for all of the replies.
    Bryan

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    Default Re: Documentation and Lifting Lines off an existing boat?

    Regarding laser photogrammetry and taking lines... I've done quite a bit of work with inexpensive depth-sensing cameras for interactive installations in museums and similar environments. Based on that work I've wondered about the feasibility of taking lines using a simlar setup. A stereo optical or IR depth-sensing camera can be purchased for under $500. Mount one on a tripod and collect point cloud data at several points along the hull and I would think you could get a pretty decent set of lines. You certainly wouldn't get the same accuracy as with the $70,000 setup, but with a little work to correct for noise in the depth data, parallax errors and similar factors, and to stich together multiple images into a single cloud, I think you could get very, very close for a tiny fraction of the cost.

    Of course you would need the ability to write the necessary software since I don't know of any off-the-shelf programs that would do it. I'd probably write something based on OpenCV, with a custom converter to output point cloud data in a form that could be imported into Rhino or a similar 3D modeling program. Somewhat like the setup that MMD describes, but using depth data rather than optical data and stick on targets.

    Not that I need another project but it would be an interesting challenge. Hmmmm.

  22. #22
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    Default Re: Documentation and Lifting Lines off an existing boat?

    I was looking at this kind of thing a year or so ago and happened upon virtualSFM.It seemed promising but I couldn't get it to work and yet there are examples on youtube of projects that have used it.It was devised for an academic project and I suspect that having completed the work it was meant for, it was abandoned.

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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by cstevens View Post
    ... I've done quite a bit of work with inexpensive depth-sensing cameras for interactive installations in museums and similar environments. .....
    Are you referring to devices such as the now discontinued Microsoft XBox Kinect? I looked into using those for boat shape documentation a few years ago when they were popular and software was available but it appeared the accuracy would not be as good as photogrammetry with Photoscan (now Metashape).

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    Default Re: Documentation and Lifting Lines off an existing boat?

    Quote Originally Posted by David Cockey View Post
    Are you referring to devices such as the now discontinued Microsoft XBox Kinect? I looked into using those for boat shape documentation a few years ago when they were popular and software was available but it appeared the accuracy would not be as good as photogrammetry with Photoscan (now Metashape).
    Yes but the technology has come a long way in the last few years. The first generation Kinect camera could only capture depth data at 640x480 resolution using IR. The ZED stereo optical camera that I used most recently for an installation at the MoPOP Museum here in Seattle can capture depth data in HD (1920 x 1080) resolution. I'm not sure how the ultimate accuracy would compare to Metashape but I expect that the underlying algorithms are pretty similar. Although I also suspect that the depth mapping algorithms in the ZED camera SDK are optimized for speed over accuracy, given that their primary market is AR/VR and computer vision for autonomous robot control. Metashape is designed to process far more data and produce a denser point cloud, but that takes a lot of GPU processing time which would be unfeasible for a vehicle trying to respond to the environment in real time.

    At CES in January I saw an interesting demo from Intel. They used a drone flying a predetermined pattern to completely map the entire structure of a stone bridge and then used photogrammetry to create a detailed 3D model of the bridge, complete with every crack and flaw. They are planning to use this technique to monitor the condition of bridges and other structures more accurately and with less effort than the manual inspection process currently in use. The accuracy was pretty amazing. They didn't talk about the processing power or amount of time needed to produce the 3D model from the many thousands of images captured by the drone, but I'll bet it was not cheap or quick.

  25. #25
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    Default Re: Documentation and Lifting Lines off an existing boat?

    You can avoid string sag by hanging one end over a smooth pivot point or small pulley and hanging a weight.

  26. #26
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    Default Re: Documentation and Lifting Lines off an existing boat?

    Whether using string or wire, sag can be minimized but not eliminated. For a given wire size and tension, there are calculations to determine the amount of sag at any point along the wire, but I have never used or learned them. Can't remember the terms to even search for them. Caternary might be one.

    Catenary led to cable sag erro, which led to: https://www.spaceagecontrol.com/calccabl.htm

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