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.
Here are the lines of the Kahuna Nui.
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.
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.
Here you can see a close up of the planking and the transom.
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.
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!
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.
To eliminate this gap, I use my trusty spiling tool -
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.
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...
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.
Here are the lines of the Kahuna Nui.
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.
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.
Here you can see a close up of the planking and the transom.
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.
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!
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.
To eliminate this gap, I use my trusty spiling tool -
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.
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...
