Steps when drawing lines plan

Discussion in 'Education' started by droussel, May 12, 2021.

  1. droussel
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    droussel Junior Member

    Hi!

    First of all, a disclaimer! This is totally because I am a never-ending curious kind of person and also because I'd like to try to do it purely for fun. The most I expect to do is most probably a balsa model. With that said, I am currently building a small Michalak Mayfly 16 and have been sailing a bigger keel boat for the past 15 years.

    To the question now! I probably have most of the books people recommend regarding book design, from Ted Brewer to Skeenes, passing by the Chapelle, Bolger, etc, books on design. I am fascinated by the subject.

    However, I can not for the life of me understand the process and steps involved when designing the lines plan. Like, if I start from a blank page, in what steps would I proceed and how do I make a point in one view match the line in the other view? I feel like I may have missed something in all those books and that I just can't get it; the actual way and mechanic of how to you make the drawing and have everything fit.

    Is there a book, a video, a tutorial, whatever, somewhere that explains this? And I'm not necessarily looking for super complicated yachts either; my main interest lies in small sailboats such as the one I am currently building, the John Welsford Navigator, the Goat Island skiff, etc.

    Thanks in advance for your time!
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Just think of the boat as fitting into a rectangular block, like a shipping container, establish the dimensions of your boat ( length, breadth, depth) and they become the dimensions of the block. All points within the block are then defined by the distance along the length, across the breadth, and height above the base of that block.
     
  3. jehardiman
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    jehardiman Senior Member

  4. bajansailor
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    bajansailor Marine Surveyor

    I think that drawing a lines plan by starting with a blank sheet of paper might soon become a lost art, with computers making it so 'easy' (relatively!) nowadays.

    I have a copy of this edition of John Teale's book 'How to design a boat', and I think he explains it fairly simply.
    https://www.amazon.com/How-Design-Boat-John-Teale/dp/157409050X/ref=sr_1_4

    Lets say that you want to design a round bilge boat around 16', perhaps a bit like your Mayfly.
    You would start off with a rough general arrangement drawing showing a side elevation, a plan view on deck (and / or inside if there is accomodation), and a midship section.
    Make sure that the 3 views all relate to each other with correct dimensions.
    You could then start on a lines plan - draw the side elevation view with your chosen waterline spacing - you will add the buttock lines later.
    Do a rough estimate for the Load Waterline (LWL).
    On your plan view you have a deck plan - you can now sketch in what looks like a nice LWL.
    The midships half breadth of the LWL can be measured from the midship section in your GA drawing.
    Now try adding a couple more sections, say one forward and one aft of midships, and another waterline.
    You will quickly find that the three views will most probably not be in agreement - so then you have to start tweaking - and this is a process of trial and error, and it can be quite frustrating.
    Once you have a couple of waterlines and a few stations drawn in, try a buttock line, and see how it looks - if it is not a fair curve, then you need to do more tweaking.
    Gradually add more waterlines, stations and buttocks as required - maybe try a diagonal as well. If that is not a fair curve, then you have to go back and do more tweaking again.
    Once you get your lines reasonably fair, then you could calculate all the section areas, run them through Simpsons rules, and calculate your volume of displacement.
    And then you might find that it is not enough for what you need..... as you should have also done a VERY rough estimate of how much weight is going in to the boat - and you might well find that at your intended LWL you do not have enough buoyancy to support all the weight you want to carry.
    Time to go back, and do some more tweaking....
    If you know (from basis / reference vessels) what a typical midship section coefficient would be for your boat then that is a useful start (this is the ratio of the midship section area, to the rectangle encompassing it).
    Similarly re a waterplane area coefficient (in relation to the length x breadth rectangle at the waterline).
    You could now calculate your prismatic coefficient - and if this is approx in the right ballpark that you want it to be, then that is a good sign.

    Totally confused now?
    If yes, then best to take J E Hardiman's excellent suggestion above, and read his recommendations!
    I also have a copy of Skenes (One of Francis Kinney's revised editions from the 50's I think), and I think he explains it fairly well there as well.

    Alternatively, how about getting a lines plan for an existing boat (maybe for a nice Whitehall design or similar?), and then applying the above procedure to this lines plan - but just copy the initial basics (Side profile, Plan view with the sheer line and the LWL, and the basic midship section) from this plan, and then start from there, re filling it in by yourself.
    And then you can go back later on (try not to cheat too often along the way, by referring back to the original full lines plan), and see how different it is from the drawing that you started off with.
    This might be less frustrating in the long run?
     
    Last edited: May 12, 2021
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    That definitely suggests you have to think in terms of it being contained in a rectangular block with the three axes being marked in gradations.
     
  6. Ike
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    Ike Senior Member

    The first thing you need to understand in order to draw a lines plan is the basics of Mechanical drawings, particularly orthographic (three view drawings) Here is a youtube that explains the basics. It's not boats, but the basic idea is the same.

    You need to draw the boat in three views. See the drawing below all the text. Profile (the side view) , Plan (view from above, Or below) and Body Plan, The view for the front and the back
    The view in the middle is the profile. The view immediately below that is the plan view. (if you draw if from above, showing where things are, like seats, cabins, helm etc, it's called a general arrangement.) And the view on the right is the Body plan. On the right of the body plan is the view from the front, and on the left the view from astern.

    But first you need to pick a scale. 1/2 inch to a foot, or 1 inch to a foot is good if you are using large drawing paper, Smaller scales for smaller sheets. (or metric if you prefer metric) You will need an engineers scale (ruler to non engineers) Everything on the drawing will be drawn to the scale. To draw curves you may need splines. Splines require weights (usually called duck weights because of their shape) which may be hard to find. This is where computers come in handy. Most CAD programs have a spline drawing function built in.

    All views are sliced up like a loaf of bread. First you need to establish a designed water line. This may be guess work at first but you can adjust it later. For the profile view the boat is sliced into an odd number of stations starting at the point where the waterline meets the bow. That's station zero. Draw a vertical line through that point. Then find the point at the stern where the waterline and stern meet. Draw another vertical line. Then divide the distance between the two into equal distances. In this case 12, but it's better if its ten or more because this distance is going to be part of the calculations for displacement.

    Anyway. divide it up and draw vertical lines through each point. Look at the plan view below the profile . Those same stations bisect the plan view. You can further divide the profile into waterlines, above and below the designed waterline. The waterlines show up in both the profile and the body plan. But in the plan view they are curves. The boat can also be sliced vertically length wise at equal distances from the centerline. These are called buttocks and in the profile they show up as curves, but in the plan and body plan are straight lines.

    You get the idea. The intersections of all these slices are used to create a table of offsets, so that someone who intends to build the boat can then redraw it full size, called lofting. I've seen this done on a 6oo foot ship and it's really spectacular to see it done. I did the table of offsets on a separate sheet and seem to have lost it or I would show it here. The books suggested above will show how to create a table of offsets.

    Of course now days all this is done with software like Delftship, and it does all the calculations as well, but you need to understand what the computer is doing. For that you need an understand of how mechanical drawings are laid out. A good way to do that is simply learn how to draw it yourself. so you're on the right track.

    Here is a sample (This a link to the full size drawing https://newboatbuilders.com/designs/OceScans03058.jpg)[​IMG]
     
    Last edited: May 13, 2021
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  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Ike said it better than me, it is really a genre of standard technical drawing as he indicates, with the three-views covering the three axes employed in the drawing, that are required to define a 3-dimensional shape. The hard part is knowing what the shape best be, rather than being able to define it accurately, but that is a necessary, though far from sufficient skill to be designing a satisfactory boat.
     
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  8. droussel
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    droussel Junior Member

    I think I have a bit better understanding but maybe I just need to take time this weekend and try my hand at it. I re-read Yacht Designing and Planning chapter on "The Lines" yesterday and I still just feel as dumb as ever I also have the John Teal book which I'll re-read relevant chapters tonight; maybe it will click this time around. I also stumbled upon Jim Michalak essays on design which seems to be quite well dumbed down for a neophyte such as myself: http://www.jimsboats.com/15jan13.htm.

    I think Ike and Mr Efficiency are into something though. My problem may simply be that I do not properly understand how the projection is actually done between the 3 views and how to visualise it. I'll start with a super simple shape, a little ugly PDRacer type of boat with a flat bottom and see if I can figure it out. I mean, if I can't figure out how to draw a box hehe

    Thanks a lot for your detailed answers, I truly appreciate you taking the time!
     
  9. droussel
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    droussel Junior Member

    Thanks to Ike who put me on the path of mechanical 3 views drawing, I think those little video is exactly what I wasn't getting. If my understanding is correct, in the case of a boat, I would start by drawing the waterline which is a common reference on all 3 views. The 10 stations are also there to create a common reference in all 3 views. Afterward, the process is "basically" the same as when this guys traces the red lines from its front view to its right view. Am I understanding it right?


     
  10. DCockey
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    DCockey Senior Member

    The order curves are drawn and refined depends on the type of boat and the constraints and requirements. A planing powerboat with accomodations and a firm overall length constraint might be approached differently than a sailboat for racing under a rating rule.
     
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  11. jehardiman
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    jehardiman Senior Member

    David is correct here, waterlines should be one of the last things drawn because, except with certain exceptions, they matter the least. They just are what is left...
     
  12. TANSL
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    TANSL Senior Member

    Amazing. Anyway, the first thing is to establish the baseline, as the OP does, and then to fix the coordinate origin.
     
  13. Ike
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    Ike Senior Member

    TANSL is right. I forgot a step. Establishing a baseline is first. Then all measurements can be referenced from the base line. The base line is arbitrary but vital. If you look at my drawing the line below all the views, with the stations marked on it, is the base line. It's just a reference point. Here's the same boat without the waterlines, buttocks, and stations lines, just a profile and a general arrangement, but all referenced from the same baseline.
    [​IMG]
     
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  14. Ike
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    Ike Senior Member

    Actually, I usually drew a preliminary hand sketch first on a small piece of drafting paper, but any will do, just to develop the idea and figure out roughly where everything would go, before I even laid pencil to drafting paper. And if you have never taken a drafting course (do schools still teach it?) it's really helpful because they taught all the basics. Back when I was a teen I took drafting courses in Jr High (some places call that intermediate school) , and several in high school, and one specifically on drawing boats (yeah, my high school had that in the 60's. Not so strange in Seattle) But I was never a very good draftsman. Thank God for Computers.
     
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  15. bajansailor
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    bajansailor Marine Surveyor

    @Ike that is a very neat little trawler yacht in your drawings above - did she get built?
    I never did technical drawing at school - my first encounter with it was at technical college 40 years ago. I am not a good draftsman, but I enjoy working on a board, and am trying to get to grips with some CAD now.
     
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