How to calculate outside hull dimensions

Discussion in 'Wooden Boat Building and Restoration' started by Insomniac, Jul 25, 2018.

  1. Insomniac
    Joined: Jul 2018
    Posts: 22
    Likes: 0, Points: 1
    Location: United States

    Insomniac Junior Member

    Hello,

    Working on a build of a scull boat I purchased plans for.
    I would like to calculate the outside dimensions/profile of the hull shape at various points along its length. Having these dimensions would allow me to make multiple supports to place the hull panels in while gluing them together. The idea is to have enough supports so it serves as a sort of mold to keep the panels in their proper place.
    I have line spans(i think that is the correct term) I used for lofting the hull panels. Would it be possible to calculate the hull profile at specific points along its length using these plans? Perhaps there is a way to create this boat from the line spans in a program such as Prosurf3 or Delftship, and then use the program to run those calculations? Of course, I would also need to know how to calculate the change in vertical distance from one point to the next so I can have each support placed at the proper height to ensure correct rocker along the length of the boat.
    Can anyone help? Would be much appreciated.
     
  2. TANSL
    Joined: Sep 2011
    Posts: 5,307
    Likes: 134, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Could you show us the information you have and an outline of what you want to obtain?
     
  3. messabout
    Joined: Jan 2006
    Posts: 2,839
    Likes: 151, Points: 63, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Sounds like the plans that you have are for a stitch and glue build. If the plans and the panel dimensions are accurate then you do not need interior or exterior frames to hold the shape. I agree that a building frame of some kind could be desirable.

    Perhaps you could consult the supplier of the plans to provide you with a body plan of the boat. With that, you can easily enough build suitable interior or exterior framing.
     
  4. Insomniac
    Joined: Jul 2018
    Posts: 22
    Likes: 0, Points: 1
    Location: United States

    Insomniac Junior Member

    Hi,
    Yes I can...
    The PDF uploaded shows the general design of the boat. The photo below shows the measurements I used to loft the hull panesl (I didn't include the whole pdf of this out of respect for the designer who sells this, so only one hull panel is shown). I have also attached a very crude drawing of what I am trying to accomplish. In addition to knowing the dimension to cut for each support, I would need to know the vertical height to place it at (assuming I reference all the supports from the same horizontal line) in order to assure correct rocker. Is this making sense now? Can this be figured out from the drawings I have of the hull panels? Perhaps the hull panels could be "lofted" into a design program so I could construct the boat that way and then figure out the dimensions for the supports with software?
    Thanks for the help! Screen Shot 2018-07-25 at 10.26.04 PM.png IMG_2215.JPG Screen Shot 2018-07-25 at 10.26.04 PM.png
     

    Attached Files:

  5. Insomniac
    Joined: Jul 2018
    Posts: 22
    Likes: 0, Points: 1
    Location: United States

    Insomniac Junior Member

    Thanks for the suggestion, I think you understand well what I am trying to accomplish. Yes, it is not entirely necessary but I do believe it could make the stitch and glue process much easier and I would like to give it ago. I attached a picture of the "hull panel offsets" used to loft the hull panels. Do you think I could accomplish what I need to with these measurements? I am thinking that having these measurements for the hull panels is kind of the same as having a body plan.....right?
     
  6. TANSL
    Joined: Sep 2011
    Posts: 5,307
    Likes: 134, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    @Insomniac, what you need can be done without problems but it would be necessary to have some cross sections of the boat, to know if they are drawn on the outside or inside and to know the thickness of the plates in each zone.
     
  7. DCockey
    Joined: Oct 2009
    Posts: 4,004
    Likes: 151, Points: 63, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Obtaining the 3D shape of a boat from the unrolled shape of the panels is very difficult to do on a computer.

    If you have a lines plan then obtaining the information needed to make female molds should not be a problem.

    @Insomniac If you don't have a lines plane you could build a scale model.
     
  8. BlueBell
    Joined: May 2017
    Posts: 432
    Likes: 32, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Simply make your supports out of webbing that conforms to the hull shape.
    But why?
    Contact Colin Angus, the designer, and ask him, he'll set you straight.
    You did buy the plans from Colin didn't you...?
     
  9. SamSam
    Joined: Feb 2005
    Posts: 3,782
    Likes: 139, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    How do the plans suggest assembling the panels?

    You would need to keep all the supports in line so there is no twist one way or the other from support to support, looking from the ends.

    The thickness of the supports would have to be taken into consideration as only one corner will be touching the hull, unless the cutting of the supports was done at the precise angles of the hull surface relative to the centerline at that precise support station.

    Any solid support would have the possibility of introducing unfairness in the lines.

    Sounds like a PITA.

    The webbing idea from BlueBell sounds good. Supports maybe being two posts with a small diameter adjustable "rope" or string between them. Put the panels in loosely stitched and adjust support ropes and stitches until you're happy, and then go from there.
     
    BlueBell likes this.
  10. Insomniac
    Joined: Jul 2018
    Posts: 22
    Likes: 0, Points: 1
    Location: United States

    Insomniac Junior Member

    If you have a lines plan then obtaining the information needed to make female molds should not be a problem.

    Thanks for your reply! Any resources you could suggest to help me figure out how to create the molds from a lines plan? Also, not sure exactly how I would make use of a scale model.....though I should probably note that I have already built the boat once, so I have a full size model. Problem is that I lofted the panels myself (my first time doing this process) and the final result is ok but has some odd bulges in spots and is going to take a lot of work fairing. I want to do a second build and make everything more precise using the cnc. Stitch and glue took me FOREVER......so I want to try a different method, hence the supports. The idea is that with enough supports the alignment will come naturally and I can use much less stitches....but perhaps my thinking is flawed.
     
  11. Insomniac
    Joined: Jul 2018
    Posts: 22
    Likes: 0, Points: 1
    Location: United States

    Insomniac Junior Member

    Interesting idea to use webbing, I hadn't considered that. Sounds like a great idea for the traditional stitch and glue method. I am trying to streamline my process though for my second time building the boat.
    Yes I purchased from Colin Angus. I considered contacting him but I try to avoid bothering him too much so thought I would see if I could find a solution on my own.
     
  12. Insomniac
    Joined: Jul 2018
    Posts: 22
    Likes: 0, Points: 1
    Location: United States

    Insomniac Junior Member

    Thanks for your response! You make some good points here. Cutting will be done on a CNC so I expect the angles would be precise, assuming I am able to figure out how to do the calculations correctly.
    I don't understand how a solid support would introduce unfairness, would you mind elaborating? I am thinking that if I do everything very precise on a CNC, then everything should line up right.....but I must be missing something here?

    Also, whats a PITA?
     
  13. TANSL
    Joined: Sep 2011
    Posts: 5,307
    Likes: 134, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    No, what you say is totally correct.
    Additionally, comment that CAD programs usually have an "offset" command that creates a curve parallel to the original curve the distance you want. So, having a cross section of the hull, for example on the inside, it is very easy to obtain the exterior, at a distance equal to the thickness of the shell.
     
  14. rwatson
    Joined: Aug 2007
    Posts: 5,599
    Likes: 222, Points: 63, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    This was attempted some years a go, and I believe I found a partial solution.

    Let me dig it out, and we can discuss the methodology.
     

  15. rwatson
    Joined: Aug 2007
    Posts: 5,599
    Likes: 222, Points: 63, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    I am very disappointed. The archive of articles only goes back 3 years.

    If there isn't some sort of archive, it means we have lost a huge amount of valuable information.

    You can reproduce the station plans by triangulating the dimensions in CAD from the flat panel dimensions.

    If you still want to find out how its done, I can dig out the drawings I used to prove the method.

    Edit - found them. Quick illustration attached

    ReassemplePanels.png
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.