Forming the 'Plug'
The Skeletal Structure
As I opted to use a plug rather than making a mould I needed a skeletal structure in order to form the general shape. From a 3D model I had taken slices to give several cross sections forming the ribs, which were threaded onto a piece of square dowel. A stiff enough material was needed to use for the cross-sections as cardboard just wasn't up to the job so I used some fluted signboard, using the templates from the true scale drawings to cut out the cross-sections. On smaller scale models the inter-space between these cross sections could be filled with foam and then sanded/cut into shape to give a solid model with smooth contours. I found another submarine project that did just that, see www.rvjunkie.com/sub. However as I couldn’t source large enough volumes of foam for this project I used modelling mesh to wrap the skeletal structure to give the overall shape, inserting sections of doweling between the cross-sections to add some more rigidity, where required
I had some great photo's of these stages but unfortunately I lost them when my so called waterproof phone lost in a fight with the Mediterranean and I lost all the internal data. It's a similar process to putting together ribs of a boat before planking or skinning the hull, just in this case the mesh and Mod roc are providing the skin.
With the skeleton in place it was ready to wrap in the modelling mesh, lightly bending the mesh into shape as close as possible and adding further shaped sections to add further contours and details. Remembering that this is forming the plug which will be pulled out at the end so anything can be used to give the shape. It only needs to hold its shape for Mod roc which will solidify. Tie wraps were also used to hold the mesh tight around the cross-sections, with more help from a hot glue gun.
With a general shape in place the Mod roc could be laid over the meshing. The Mod roc is already impregnated with plaster so all that is needed is to soak the strips in warm water for a few seconds and then it can be laid straight on over the mesh and I also added PVA glue to the water as I heard it adds a better finish. It’s also worth rubbing the Mod Roc to make sure the plaster covers the surface completely, otherwise the gauze will show through and may come loose. When each layer is added any dents and imperfections with the mesh shape will be more visible and I filled this in as I went with filler, sanding down and then adding further layers of Mod roc. It’s worth putting in the effort to get the shape and detailing right at this stage as it is far harder to rectify once Fibreglassed.
For the small details such as the front dive planes and the stern planes and rudder, foam was used, cut into the rough size and sanded and smoothed into shape. I used the same dry foam used for artificial flower arranging, www.oasishomeandhobby.co.uk, which is very easy to shape with a sanding block or a hot wire.
So with a good solid plug to start laying the Fibreglass onto, the skeletal structure can be removed to leave a hollow structure. Given the shape of the submarine is tapered at each end the only way to remove the innards was to cut the submarine in half and it’s easier to cut it now rather than after Fibreglassing. After removing the internals the two halves were simply put back together using more Mod roc. I left the meshing in place in fear of damaging the shell by trying to persuade it out, but knew it could be pulled out once Fibreglassed.