For ease of construction, many boats are designed so that their plates can be cut out of sheet material (plywood, aluminum, steel, etc.) and wrapped onto the frames without introducing compound curvature or twist (at least, not too much twist!). Plate "development" implies that there is no (or very little) twist introduced into the plate. Plate "expansion" implies that the plate has quite a bit of compound curvature and must be subdivided into smaller pieces along butts and seams. This program currently performs plate development, but does not perform plate expansion. Plate expansion will be added in a later version of the programs. (This is more difficult, because the butts and seams have to be defined on the plates.)
To see how the development process works, follow these steps:
o Display the profile view of the boat.
o Select the "Develop-Select Plate" command
o Position the cursor in the middle of one of the vertical row/cols on the top-side plate.
o Click the left mouse button
The model is redrawn, but nothing else happens. This procedure tells the program that you want the top-side plate to be the current "develop" plate. Now you can use any of the other commands to display the layout for this plate or display the tabulated offset numbers for the plate.
o Select the "Develop-Layout View" command to see the development for this plate,. The program will display the plate marked with all of the frames, as shown below:
ProSurf and ProBasic will try to develop (layout) any surface consisting of only two rows or two columns. The limitation of two row/cols is a requirement, since the row/cols which are opposite to the primary two row/cols are the "ruling lines" and they must be straight. For this example boat, the sheer and the chine are the two primary row/cols, and all of the vertical row/cols (like stations) are the ruling lines. If you look at the power23 hull's top-side plate in section view, however, you will notice that this surface is not perfectly developable. This raises a very important point. Although a surface may not be perfectly developable, it may be buildable, depending on the material used, the size of the plate, and the thickness of the plate. ProSurf and ProBasic can give you some feedback on whether the plate is close to developable or far from developable (using the Gaussian curvature display - "Surf-K_Patch-Kpat All" command - developable plates are colored dark blue), but as the shape changes away from perfect developability, this program cannot tell you the exact point where it becomes un-buildable. In addition, as the surface of the hull becomes less developable, the accuracy of the plate layout shape is reduced. When you have to stretch and twist the material to get it to fit the frames, the material changes shape slightly. To accurately determine the pre-stretched shape of the plate would be very difficult. We usually tell builders that as the plate becomes more non-developable, add additional scrap material along a couple of the edges before cutting out the plate. This means that you may have to scribe and recut the plate, but this is preferable to finding out that the plate is 1/2 inch too short.
The best advice we can give for boats with not-quite-developable plates is to plot out the frames and plates at a small scale and try building a model out of stiff cardboard. This can also be important the first few times you use the program to build your confidence that the program works correctly. Keep in mind that if you cut out the frames and plates exactly, you must be very careful in setting up and aligning the frames. If something is slightly out of position, you will cause a chain-reaction of errors and find that the plates might not fit in the ends. This leads us to the following recommendations:
1. Use "enough" frames along the length of the boat, especially in high curvature areas. If you don't, then the plate will wrap onto the frames incorrectly and you may not get it all to fit.
2. Make very sure that the frames are positioned correctly and are not canted or twisted. If even one frame is slightly incorrect, you may cause a progression of errors.
3. Use the frame markings on the plate layout to align the plate to the frames. If something doesn't quite fit, stop and try to find out why. Many builders are used to cut-and-fit techniques, but the whole idea of plotting these templates is to avoid this extra work. If, however, you know that the plate is not quite developable, you may wish to add additional scrap material along a couple of the plate edges.
4. If in doubt, plot scale drawings of the frames and plates and build a model out of cardboard.
5. To develop a feel for how close to perfect developability you have to be, use the program to define a boat that you have already built out of sheet material. Then look at the colors displayed by the Gaussian curvature display. Dark blue indicates almost perfect developability. As the colors change to light blue, to green, all the way to red, it indicates more and more twist in the plate. If you know that this boat was buildable, you can see what curvatue colors are acceptable. Then when you design a new boat, you can use those colors as a guideline.
Plate development is not an exact process, since there is no well-defined point where a plate goes from being buildable to being non-buildable. Of course, you can use the program to create a perfectly developable boat, but you may not like that hull shape. We have found that many designers and builders prefer a little bit of twist in the plates. It allows for a much wider range of hull shapes.