resizing/stretching a stitch and glue design

Discussion in 'Sailboats' started by luftspringaren, Jun 15, 2010.

  1. luftspringaren
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    luftspringaren New Member

    any thought on how to resize the hull panels if I want to make an existing stitch and glue design longer by 10 percent?

    (my thought was to leave all stations exactly as they are and just increase distance between them by 10 percent)

    :confused:

    -Yes obviously they need to be 10 percent longer, but along what axis?
     
  2. hoytedow
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    hoytedow Wood Butcher

    You can do it in paint on your computer easy.
     

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  3. messabout
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    messabout Senior Member

    It is possible to stretch a S&G design but the possibility for problems exist. You can probably get away with the S&G extension but it is not a sure thing.

    Your best approach is to build a form with moulds and ribbands. That way you will not have to endure the tedium and uncertainty of the panel layout. Simply space the station moulds 10% farther apart and use the ribbands to trace your panels. The panels will absolutely fit with that method. Best of all you will not need to drill a zillion holes and you will not have half a kilometer of wire to deal with. The old fashioned way, as described above, is faster and far more precise with the result.
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    Messabout is correct. It is easy to get a boat that is equally scaled in 3 dimensions, length, width and height, by just scaling up the planks in 2 dimensions, but merely stretching the planks in length will result in a boat that is longer but distorted, and some planks may not fit together with the others.

    Imagine a boat that is broad and stubby with planks that bend a great deal near the bow. Stretching the planks close to the bow will increase beam as well as length in this region. However as the planks become parallel with the centerline stretching the planks will increase length only not beam. In between the hull will be distorted, although for a very long and skinny boat with sharp stem(s) the distortion will be less.

    If you have the hull offsets you can do as Messabout suggests. Alternatively, if you prefer to stick with stitch and glue construction, the safest plan would be to input the hull shape into a program such as FreeShip, stretch it by using the scaling tool, THEN generate the plank developments which will now be correct for the boat you want.
     
  5. Chuck Losness
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    Chuck Losness Senior Member

    You should talk to the designer of the plans. He will be able to tell you what will happen when you stretch the boat. I did this with Sam Devlin's guppy design after talking to Sam. I initially stretched the entire the entire boat but didn't like the way the bow came out. Too narrow and fine forward. So I ultimately left the forward half of the boat as is and only stretched the back half. But you have to talk to your designer before you do anything. Otherwise you are going to waste a lot of time materials.
     
  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    If (and only if) the original hull design is symmetrical about the mid-point, it is possible to stretch the hull by inserting a cylindrical portion at the mid-point. It is important to note that the hull must be symmetrical viewed from the side as well as the top, for this to work.

    At the center of each panel, the top and bottom of each plank will be parallel, and extra length can be inserted here. It is not the most elegant way to do the job, but for a small amount of "stretch" it will not look too bad.
     
  7. pistnbroke
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    pistnbroke I try

    how long is the original boat ? making it 10% longer should not be a problem if its in the 10-15ft range ...make it up in card to see if you like the lines...why make any sort of frame ? Just cut the panels as defined in Freeship and pull it together with cable ties. Any gaps help the epoxy to hold better Square and brace if neccessary whilst you butter the internal joints between the ties and then pull them out. Use the internal furnature and shear line capping to brace the hull. Good photos at www.epoxy-resins.co.uk clik on the boat Morgan and go through the pictures to see what happens to the finished result if you if dont take out the ties and fair the external taping.. Also has the free design software Carene which you can then export to freeship to get good developed plates . Google Hannu's boatyard for more ideas.

    Addition
    Re reading your question it is how to make the panels of ply the right size .........Use Carene to get the basic boat shape /size you want then export to freeship to develop the panels and give you all the dimensions to draw up on the ply...if its 10% longer you want why not make the panels too long...just continue the lines aft or put a bit extra midships.... If we knew which boat it was it would help..... Stitch and glue fits where it touches !!!
     
  8. messabout
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    messabout Senior Member

    When I was mouthing off above, I failed to mention that the suggested method of construction is still a glued but not stitched boat. It has no chine logs or other longitudinals except possibly in the bottom. I have built several boats this way and it works very well, saves a few pounds of boat weight, and retains a very clean interior.

    The drill goes like this.....Build the moulds and attach the ribbands in the usual way. Plane the ribbands as needed. Now you can lay the ply sheets over the framework and trace the cut lines exactly by using the ribbands as guide. Use some spay adhesive ( contact cement) on the ribbands. Place strips of wax paper over the sticky ribbands. install the sides or strakes in the conventional manner but do not fasten the ply permanently to the framework. Plane the surfaces at the chine and transom so that you have a reasonable fit for the bottom. Now you are ready to glue the bottom in place. The glue joint will be narrow at this time but it is adequate for the job until later. You can fasten the bottom down with nails or staples not sunken completely into the surface. You are going to remove 'em later.

    Now you have a boat with sides and bottom. Use some tape and epoxy at the outside of the chine joints. The boat is getting a little stronger now. Pretty soon you will want to remove the boat from the form and turn it over. It will be a bit twisty at this point. Build one or more frames that fit over the outside of the boat. Crawl under there and screw them in place before you take the hull off the form. Now the boat will not lose its shape and the designed rocker will stay as planned. The frames are also good for holding the boat in place and upright when you are working on the inside. Do the usual epoxy paste fairing of the plank intersections and apply tape. Apply inwales, side decks or other members that will progressively stiffen the hull. Remove the outer frames when you are satisfied with what you have built. When you have removed the hull from the framework you still have a perfectly good form for building another boat.

    All this may sound like more work than the S&G method. It is definitely not more work and it goes just as fast or faster than the S&G method. In the end you will have a boat that is more accurately built than you could hope for while using all that damned wire and holes and stuff.
     
  9. pistnbroke
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    pistnbroke I try

    well it all depends on how big the boat is ..if its up to about 15 ft then cutting the panels with measurements from Freeship and holding with cable ties ..not wire is much faster than your frame method ...well and the frame must be a good accurate job so personally I will stick with the computer .... I dont like tape on the outside of the chines just one layer of glass and epoxy over the whole outside..saves all that filling and sanding ...Epoxy likes gaps and that gives it strength....
     
  10. messabout
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    messabout Senior Member

    Pistonbroke; a large part of the total time for S&G is laying out the panels. The layout must be close to perfect and if there are several panels involved the whole bit becomes tedious. I have no problem with doing a three piece flattie the cheap and dirty way, but when it comes to a more complex 5 or 7 panel layout the whole S&G thing is too much tedium for common sense. The more panels you have to layout the more opportunities for error and even if the error is minor the shape of the boat will not be as the designer (or computer) had intended.
     
  11. pistnbroke
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    pistnbroke I try

    problem with this post is the original poster hs not told us anything about the length and number of panels he is using,,,,,I find the panel marking quite quick if you have got good dimentions from Freeship......its waiting for the epoxt to go off I dont like .....
     
  12. tom28571
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    tom28571 Senior Member

    No one has addressed the main question he asked.

    Assuming that this is a simple single side and single bottom panel hull:

    When viewed in profile, the station lines are all vertical. Looking at the panel layouts, the orientation of the station lines is not obvious. I think this may be the "what axis" question he refers to. If the flare in the side panel varies along its length, the length of the sheer and chine lines will vary by differing amounts. Therefore the station lines on the panel layouts will no longer be parallel.

    Does anyone know a simple way to make this expansion without relying on a computer solution?
     
  13. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    Duplicate the widest frame and put it in at the same spacing as the original frame. Stretch all the panels to match the stretched portion. Some sanding and fairing might be required to get a nice fit.
     
  14. tom28571
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    tom28571 Senior Member

    Not sure I understand what you mean but there are no frames in a typical S&G hull.
     

  15. pistnbroke
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    pistnbroke I try

    Why are we bothering to try to help someone who cannot even come back and give us some more details on the boat he is trying to build?

    Perhaps he is on holiday it is august ........
     
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