traditional designs and traditional methods

Discussion in 'Sailboats' started by chandler, Dec 5, 2005.

  1. RHough
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    RHough Retro Dude

    Those are the same people who's first reaction to MOB! is to start the engine and drive back.

    It's amazing. I had several people tell me I had no idea how GPS works after I told them that their GPS did not tell them how fast they were going through the water ... they wanted to use the "more accurate" GPS speed as an input to calculate True Wind from Apparent. I'm the idiot? :(

    I have gadgets on my boat, but I know how to navigate without them.
     
  2. h_zwakenberg
    Joined: Nov 2005
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    h_zwakenberg HullDrag/32 programmer

    same here.

    During my years as a delivery skipper, I had the opportunity to get to know quite a few yacht owners. Most of them weren't in tune with their toy. Also, GPS lured them into taking on journeys they never would have before GPS was around.
    Don't ask them whether they know their HO-tables, they just don't want to face up to reality....

    bye
    Hans
     
  3. gonzo
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    gonzo Senior Member

    I like to design with paper and pencil. Computer programs do calculations faster and easier. I find a computer screen too small to see the curves accurately.
     
  4. Roly
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    Roly Senior Member

    ????

    It's amazing. I had several people tell me I had no idea how GPS works after I told them that their GPS did not tell them how fast they were going through the water ... they wanted to use the "more accurate" GPS speed as an input to calculate True Wind from Apparent. I'm the idiot?

    Firstly, I am a beginner and thus somewhat confused.
    I don't understand the bold statement above.
    Surely you must input boat speed relative to land (via GPS) so the wind speed relative to the boat (apparent wind speed) can be adjusted to true wind speed? (relative to land)
    Is this VGM, the component of boat speed parallel to the true wind (relative to land)?
    Can anyone point me to a good book that deals with this?
    Thanks.
     
  5. gonzo
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    gonzo Senior Member

    And how does this relate to designing boat by hand?
     
  6. RHough
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    RHough Retro Dude

    The wind that a boat sails in is relative to the water not the land. The only time a GPS gives boat speed through the water is when there is zero current (never). The only way to get true wind speed and angle relative to the boat is with a knotmeter.

    The only time GPS ground speed is relevant is when you need to tell gonzo when his fresh supply of paper and drafting materials will get to the loft. :)
     
  7. chandler
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    chandler Senior Member

    Thanks for getting back to the subject Gonzo, and in turn I will try and keep my politics to myself.
     
  8. nero
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    nero Senior Member

    when the screen gets too small, print a hardcopy.

    As for seeing the lines and curves it takes awhile to learn. Flipping views between several obliques helps a bit.

    Some of what the lines truely represent become understood after building the model ... and the first boat. The beautiful surfaces I got out of TouchCad enchant me while looking at my partialy built hull. (loose too much time just looking at it)

    Without nurbs in a modeling/marine program, I would have never realized this design.
     
  9. gonzo
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    gonzo Senior Member

    It is cheaper to loft full size than to build a model. As for a hard copy, it would mean printing one after every change. Also, the printer would have to be of very high quality and work on mylar. Any other material is too unstable.
     
  10. nero
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    nero Senior Member

    only meant to say that you can print out the lines on a letter or A4 piece of paper inorder to "see" the curves better. 300 dpi works well for this.

    I only do a print when I get confused or want to compare one design to another by laying them on a light table "or up against a glass window"

    By building a model, the form of the design can be touched and seen. Less imagination work for the mind. On computer my catamaran looked fine. On the first one-hull model, I felt the bow stood to tall and would catch too much wind. When I went back to the program, I could understand much better what the lines were representing.

    For building the model a cheap printer is accurate enough. Paper and glue sticks work well to stick plans to part stock.

    For the full size, I use simple XY coordinates and a drywall square and Al straitedge. Using a 50 mm Y space and measuring with a metric tape (starting at 10) to the nearest half mm, the accuraccy is better than what I can hold with a jig saw. No 'lofting' process as described by in the tech books is needed. By keeping the control points low on the mesh, and resizing the profile by scaling and stretching to a control curve, the form remains fair. This also reduces a need to 'loft'.
     

    Attached Files:

  11. gonzo
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    gonzo Senior Member

    I disagree with that. It is not possible to see small imperfections on a print that small. The thickness of the line when lofted full size can be up to 3/4".
     
  12. gonzo
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    gonzo Senior Member

    Half models have been used for a couple of centuries. It is the precursor of lofting.
     
  13. chandler
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    chandler Senior Member

    I agree, my lines drawing@ 3/4" seemed fine. I made a half model using waterline lifts and the hull became obviously too fine. By the way Gonzo, what do you think of 5' of freeboard at the bow of a traditional 33' french fishing lugger, sail of course.
     
  14. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Nero: What sort of boat(s) are you building? I'd love to see and hear more. I'm inclined to get TouchCAD, but haven't gone beyond fiddling with the demo.
     

  15. nero
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    nero Senior Member

    My boat is 14.5 meter wood/epoxy catamaran. For the model I printed out at 1:10 scale. At that scale my lines print at .35 point thick. A mistake will show up easily. Then I can zoom in to an effective scale to correct my mistake. A line width mistake is 3.5 mm at full scale. A 2 mm mistake is 20 mm which is unacceptable. When building my 1:10 scale model, I had a couple of forms off a bit. The problems was my lack of craftsmanship and not design related. On the full size hull forms, I had one that was off 5mm. The form was not set correctly, After some repositioning, it was correct.

    Maybe, I am/was just lucky. I don't do this for living.

    Gonzo is correct that a full-scale, accurate-lofting will guarantee error free plans. A full size print out would do this also, but many times this is too expensive.

    Printing out lines also lets you see relationships between lines. For example in the photo I posted, between each line there is constant depth. Therefore the seen width between each line is realitive to each line. If there is a hump in the line or one form line in a series is tighter to one side of it's partners then the curve is changing unfairly ... not smooth.

    Must also state that I measure diagonaly the master sheet of plywood to make sure it is square. Also I hook the tape and mark the 50 mm grid lines on each side (ref. from the same end). After measuring all the X points, I connect the dots by freehand with a drafting pencil. Then I eyeball the line, correct it and ink it.

    Nice thing about software is that the line/surface is automatically fair by the program ... if you are using the program correctly. smile
     
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