bigjimslade wrote:
...The great mystery for me is the shell and how to make allowances for that on the frames. Let's say the frames are laser cut out of plywood and the shell would be formed by wood strips. How much wood would there need to be? So how much would I need to offset the frames to accommodate the shell?
I have a book from NIP about building a large scale model of a RN battleship that is built plank on bulkhead. Yet the book leaves out the key subject of how much to offset the frames for the shell.
I asked in another forum for guidance and just got a run around. For me to do this kind of thing, I would need real guidance on how the shell should be created, how thick it would be, and how much I need to offset the frames.
I think I can help. Please bear with me, long answer follows based on a 1/192 scale plank-on-frame USS
Missouri I built in 2002-2003.
Bottom line up front - just the opinion of one guy:The
sides of the frames were given a design offset of 3/16 inch. The top of the frames where the frames meet the main deck was given a design offset of 1/8 inch.
Be advised that the shell thickness question can't be easily answered by modelers because there are a lot of variables that have to be considered to build a plank on frame hull that is 55 inches long and 6 inches wide. So, it is best if you as the model designer decide the frame spacing and shell thickness and provide those dimensions to the modeler. Guidance on how to do that for a 1/192 scale Iowa hull follows.
Keep in mind that the size of the modeling market making large scale plank-on-frame models with access to specialized tools like a laser cutter and the skills necessary to use those tools is comparatively very, very small. Since those kinds of models are individually made by hand by modelers with very specific skills that were earned from the school of hard knocks, each modeler is likely to have a very different opinion as to frame spacing and shell thickness required in making a battleship hull 55 inches long and 6 inches wide. Their opinions will be dependent on a host of variables including the skillset of the modeler, the frame spacing chosen (and longitudinal bulkhead arrangement connecting the frames), and the materials and tools the modeler has available to him/her. One modeler might say, "make it 1/8 inch". Another will say, "make it 8 mm". Neither will be wrong, even though they are very different.
So here's one opinion based on a 1/192 scale Iowa model made using the plank-on-frame method. The model is now 20 years old and the hull is as strong today as it was when first built.
The hull of the 1/192 scale
Missouri I built back in 2002-2003 has a structure composed of:
-
28 frames of 1/8 inch aircraft grade plywood commonly used in building R/C aircraft. The frames are shaped and spaced generally according to the drawing by Tom Walkowiak shown below.
-
3 longitudinal bulkheads (one centerline and two straddling the centerline bulkhead 2 inches away for hull stiffness). The longitudinals are also 1/8 inch aircraft grade plywood.
- The
frame and bulkhead skeleton is sheathed in 1/8 inch balsa which was sanded to shape so slightly thinner than 1/8 inch in some places.
- The
balsa sheathing is covered in fiberglass cloth and epoxy resin approximately 1/16 inch thick for strength and rigidity. Once fully hardened, the fiberglass became the outer hull shell, not the balsa. The balsa was only used to establish shape of the shell. The fiberglass resin was bead-filled with "micro balloons" to make the resin easily sandable for final shaping and to reduce weight.
- The fiberglass was sanded smooth then sprayed with automotive sandable gray primer from a rattle can. The thickness of the primer is negligible and can be ignored.
- Real hull shell raised plating strake detail was made by masking and spraying more layers of primer replicating the raised strakes. That thickness is also negligible.
- The
main deck (structural deck) is 1/8 inch aircraft grade plywood. The deck is not covered with fiberglass or otherwise treated. The plywood main deck is overlaid with 0.40" thick grooved Evergreen polystyrene sheet simulating the real ship's deck planking.
So, the
sides of the frames were given a design offset of 3/16 inch (1/8 inch for balsa skin + 1/16 inch for fiberglass covering). The
top of the frames where the frames meet the main deck was given a design offset of 1/8 inch. The frames were cut with a jigsaw so there is some variation and error but this is corrected either by filling or sanding later.
English units were used because that is how the thickness of the plywood and balsa was measured, cut and sold.
The model is huge. Shown below is a photo of it dwarfing a 1/350 scale Tamiya
Missouri in front of it.
Hope this helps.