Scratch-Built Kahuna Nui

Discussion in 'Ship & Watercraft Models' started by pashlispaht, Aug 3, 2008.

  1. pashlispaht

    pashlispaht Member

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    Greetings from the tropical paradise of Baghdad!

    I have been working on an idea of mine for a while now, and now that I have great success, I decided it was time to post my progress. I have a great interest in regular boatbuilding as well as card modeling, and I have aquired a small library of books on the subject. One type of construction in particular has intrigued me; cold-molding.

    Cold molding involves building the hull by gluing diagonally opposed layers of thin plywood or wood with epoxy resin over an inverted framework, thus resulting in a strong, light and non-flexible monocoque hull. It is called cold-molding because there was a similiar process at the time of it's invention that used glues that were cured at high temperatures in a giant oven, hence the distinction because cold molding was done at room temperatures with first resorcinol glue and later with epoxy resin.

    So what does this have to do with card modeling you ask? Well, one of the limitations with plywood construction is that true compound shapes were almost impossible to form with sheet plywood until this technique came along. As card modelers, we face a similiar dilemna in that certain compound shapes are very difficult to construct from a flat two-dimensional material. This limits the types of models that can convincingly be constructed and the types of hull forms that can be built. I wanted to see if the compound shape of a sailboat hull with all of its reverse-garboard and rounded bilges could be constructed using the cold molding technique. The answer has been a resounding success!

    I started by selecting a plan. Another test that I conducted was to see if a model could be constructed from a table of offsets such as what a naval architect would use to do the full size lofting from. This opens the possibilities of models that can be scratch built to the thousands. All you need are the table of offsets or an architect's three view of the lines of a hull and it was possible to use that as the basis for the mold that the hull was built on. But I am getting ahead of myself. First the subject selected - I selected a design by sailboat designer Mark Smaalders. On his website there are a number of plans and three views and I chose to do the "Kahuna Nui", a 38' on deck traditional full keel offshore sailboat. He does not yet have plans for this boat, but he had a picture of the lines on his site under "drawing board". Here is a drawing of a slightly smaller design called the "Kahuna" with almost the same lines and profile.

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    Here are the lines of the Kahuna Nui.
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    This, I printed and used a needle to transfer the lines to heavy card which was cut up to produce the inverted mold that the hull was built over.

    Unfortunately, by the time I had determined that my experiment would be a success, I had already covered the building mold with planking and had neglected to take photos before doing so. Here you can see some of the hull stations that were lifted from the lines, then cut out and mounted in a framework that the hull was planked on.
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    First step after building the construction jig was to strip-plank it. Numerous 1/8" strips of 1mm card were cut and then glued edge to edge over the construction jig. The card was very stiff and it was self-fairing so I did not have too much problem with the ribs showing through. I used a wider strip prior to planking as a fairing batten to check the fairness and alignment of the hull formers, and these were then made fair with a nail emery board.
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    Here you can see a close up of the planking and the transom.
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    Next step after the whole hull had been planked was to start laying down diagonal layers of 3/8" wide strips. These were from regular manila folders and they worked quite well. This is what gives the real boats constructed from this method their immense strength. Here you can see the first layer of diagonals down with the second layer started.
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    A view of the second diagonal layer. A third and final layer of horizontal planks will be applied but this will be for asthetics and I believe that it is not necessary for strength as the hull is already solid as a rock!
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    One important step is to "spile" the planks, or fit them in to the previous plank. Because the hull is curved and you are applying a two dimensional material to a compound surface, a gap will open between each diagonal strip.
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    To eliminate this gap, I use my trusty spiling tool -
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    and with one hand holding the strip in place a short distance from the last strip, I use my tool to transfer the profile onto the new strip.
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    This strip is then trimmed with scissors, glue applied to the hull where the strip will go, and then the strip pressed into place. Don't be stingy on the glue here, you are trying to avoid voids in the layers. This is almost identical to the process that would be used in the construction of a real ship, the only difference being the materials used. It is not difficult, and in terms of time needed, well if you are already a card modeller, then time should not be much of a deterrent! But truly, it is not that much more time consuming and is quite theraputic, cutting and fitting numerous small strips to reveal a voluptuous compound curved hull! More to follow...
  2. pashlispaht

    pashlispaht Member

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    Here, I have just about completed one side of the hull. My plan is to color it so the seams would not be visible. In reality, the diagonal lines are practically invisible, only this angle with the flash from the camera makes them visible.
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    My roommate said that it was difficult for him to visualize my model as a ship because it was inverted, I have flipped it over for this photo. Maybe it helps? Anyway, you can see how fair the hull truly is; you can run your fingers down the whole side and there are no seams or bumps to be felt. The diagonal lines are just that, lines. You cannot feel them at all. My original plan was to layer a third row of horizontal planks for asthetic reasons and if I was planning on finishing it in wood grain color I probably would. But since the lines cannot be felt, when I paint it they will not be visible at all so therefore I think that it will be complete with just two diagonal rows.
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    Now I have begun the other side. Only a couple hours of work and it should be complete too!
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  3. SEBRET

    SEBRET Member

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    this is very interesting. You show extreme attention to deatial in your work, im impressed.
  4. pashlispaht

    pashlispaht Member

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    I have just completed the skinning of the hull. A layer of 1/8" strips over the hull formers followed by two diagonal layers of 3/8" wide strips. I have trimmed the excess from the keel area and attached the transom skin, and the hull is ready for the keel to be attached.

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    Note the perfect wineglass shape of the hull.
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    Once I have built and attached the keel, I can remove the hull from the building jig and the hull should retain its shape. Kind of a different way to obtain a hull, but it allows hull styles and types of models that are not generally available through traditional types of kits. I also see this method being practical for tank turrets such as the JS-2 or T-55, or possibly for the bulbous bows on modern naval vessels, and for radar shelters. In short, anything that is rounded in such a way as to make construction from the traditional methods impossible or non-convincing.
  5. pashlispaht

    pashlispaht Member

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    The keel was actually a lot more work than I anticipated. I was originally going to make a solid structure built up of layers of card but I realized that I could more easily accomplish the task by building a hollow box type structure since the outside would be skinned anyway... It still took a considerable amount of time and involved a good deal of fitting to ensure that there was a good fit to the hull. The stem was made of laminated layers of cardstock, eight in all.

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    Once the keel had been fitted, the hull could be removed from the construction jig. This involved a lot of work with needlenose pliers to break the glue joints between the strip planks where a little glue had leaked out and had joined them to the hull formers. Next time I think I will wax the edges of the formers to prevent this from happening. Otherwise, the hull came off just like I had anticipated.

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    Here you can see the faint lines perpendicular to to the inside keel, those were where the hull formers had been. I used twenty formers lifted from the three-view which the hull rests on. The forward-most former remained inside the hull and the rest were designed to be removed. In the very bottom is the internal keel which served as an alignment device to ensure the hull formers were all on centerline when they were glued to the construction jig. To ensure that this piece remained rigid and did not flex around the formers, it was coated liberally with cyanoacrylate and sanded smooth once it had dried. The white glue used for the strip planking did not seem to stick to it either.

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    The completed hull is as light as an eggshell and as strong as a helmet. The excess material has been trimmed off and she is now ready now for gunwales and deck bracing prior to the installation of the decking (I think a boat such as this is quite female by nature. Just look at those curves! There is just something sexy about a wineglass shaped hull, and I could just stare at it for hours!). I suppose if I was really ambitious I could construct an interior for this vessel... Suggestions?
  6. Padre

    Padre Guest

    Great work, I would like to continue with the interior and sail!
  7. redhorse

    redhorse Member

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    I look at a lot of full size boat building stuff as well and this is on par with most of that. You have to build an interior now that you said it :mrgreen:

    I enjoy sailing and would love to see her all rigged out too. I like the Kahuna design, being partial to gaff rigs - a very pretty boat.

    Thanks for posting this, it's absolutely fascinating.
  8. pashlispaht

    pashlispaht Member

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    I am seriously thinking about making an interior... I am not sure what to include though. Not very much of it will be visible and I had considered making a skylight and portholes, but an interior would be infinately more challenging... I went back to the website I pulled the hull lines from and one of his designs is very similiar in size and general layout. Here is an interior drawing for a boat 32' on deck. The one I am building is about 38' feet on deck and a little over 12' wide.

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    I think I could probably work something out using this as a starting point. Scratchbuilding is considerably more difficult than building from a kit, but the "ooh" factor of a well done scratch built kit is definately worth it! I am always amazed at the level of skill that some modelers have and it is truly humbling to see the models that are created. As I am looking at this interior plan, the gears are starting to turn and I am visualizing how I can create each and every part...
  9. Loopy

    Loopy Member

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    Mighty impressive! Some fine building there, can't wait to see her rigged.
  10. pashlispaht

    pashlispaht Member

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    After a week of steady work, I have some progress to post. I completed the cockpit, the interior bulkheads, cabin sole, cabin sides, and began work on the mainmast. Most of it was straightforward, just measure three times, cut once! The bulkheads were perfect fits, working from the lofting drawings. It is so cool to take measurements from drawings, mark out the part, cut it out, and find that it fits on the first try!

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    The cockpit was straightforward, this will be planked with strips to simulate teak. One thing I found necessary to do was to make a ruler to match the proportions of this model. Since the length on deck is almost 40' I had to make sure that the proportions were correct for cabin height, cockpit dimensions, etc. in order to make sure that it would be sized to the human occupants. I did not make this model to any particular scale so I used some geometry tricks to first make a ruler that matched the model and this was particularly useful for building the cockpit.

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    The cabin sides and deck were fun to build and went pretty fast. I used a punch set to make the portholes in the cabin sides, and later I will punch out some clear film to make "glass" inserts for the portholes.

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    The mast took a while to build. It is about 26 cm total length and originally I planned to make it from wood, but I decided I could do it from paper. I used a piece of 3/32" brass rod as a mandrel, and I wrapped with several inches of copy paper. I used white glue for this because it would not stick to the brass once it had dried. After it had dried, I spiral wound a 1/4" thick strip of manila folder around the entire 26 cm length. This was quite fun, and challenging to ensure that the spiral wraps were tight and did not overlap. After this layer had dried I coated the entire outside in cyanoacrylate and wiped off the excess. This soaked a little into the paper and helped to stiffen the whole mast. Once the cyanoacrylate had dried, I sanded the excess off and removed the mast from the mandrel. The mast is about 3/16" thick and is quite stiff. Don't know how much use this technique might be to the audience, but at least I proved to myself that it is possible to make long thin structures from card...

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    This is the one week worth of progress! Should have the hull completely closed in and rigging started by next week.
  11. barry

    barry Active Member

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    Boat hull

    That's really beautiful
  12. birder

    birder member

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    Congratulations on this creative project! Must be rather satisfying to be doing this one, Pashlisphat