I've made some Rule of Thumb statements about bars representing entire sheets of material and tried to prove that with illustrations of a 'take off strip' or bar being used to pattern a rectangle. In the examples of the previous post the same bar could be used in different references to the sheet being patterned and if the take off (taking up) method was observed and reversed as faithfully; putting down the reference points and connecting with lines (our original in those examples were all rectangular shapes composed of straight lines) - the result was a fair version of the original shape.
This method will work for any shape that sheet of aluminum can be cold formed to assume. For example, the developed surfaces of a boat's bottom or sides. We have skipped the determination of developed surfaces and are relying on the designer to have drawn a set of Hull Lines, in three views Body Plan & Profile that described a hull which can be formed of cold wrapped or un-stretched sheets of aluminum.
The un-stretched sheet of paper, plywood, steel or aluminum can form any of three geometric shapes; #1 flats, the native plane of the milled sheet material. #2 a cylinder or section of a cylinder- where the entire sheet or some portion is aligned to a line that is the center axis of the cylinder; and #3 a cone or conic section like the bow of planing boats both above and below the chines most often derives from some conic section.
Therefore: a strip of the same material can represent the shape of the entire sheet of the hull panel's outline if that strip is held to the frames (Body Section Plan; Station Cards of a plate model) and marked to take off the Station's Lines of intersection the distances.
To illustrate this idea, by why of introduction before we do the steps with the plate model, here are a series of images to bridge what has been shown with those methods of work applied to the plate model or Station Card model.
This image of a rectangular sheet of material shows the take-off strip aligned across the middle and reminds that the grid would be shown on top of the strip as well as distances above and below, ends noted and any other details that were needed to help recreated the original shape.
This sketch,above, shows the same panel and take off strip as the previous image but viewed from the right end where the cylindrical shape can be more easily confirmed.
Note: the arc distance along the sheet face would be longer than the chord or flat distance from the strip to the edges of the cylindrical section BUTT they'd be recorded or 'taken-off' from a distance along the grid line- so the final shape would measure enough wider (offset over the chord's length PLUS the arc's added fraction) so a 'true length' along the frame or grid's intersection with the final sheet will be taken off by the pattern strip.
Taking the next logical step, above, this sketch shows an irregular and curved outline to a cylindrically cupped sheet. This instance, with the original item to copied or taken-off (take up) has curved edges and therefore when the points are laid down, they will require a batten to connect the points in fair curves.
However the same method of work will apply, step by step, the exact techniques shown for the first example in the previous post, or any example leading to this one, will apply here too. Record the grid, the distances along those grid lines to an intersection point and reverse the all those steps on the new material; however in this case instead of using straight edges to connect the various points battening curves will be used.
This last of four images that bridge to the plate model images (following) moves the view point to the end of the previous image's panel and confirms the shape in cross section of the panel. Again, by taking off distances along the face of the grid lines, the trued outline of the final shape will be recreated by the modeling or pattern taking technique in these sketches.
Here is a review of the builder's plate model so far, also called a Station Card model which is like the framed up boat (shown keel down)
Another review sketch- this set of topsides intersections with the Card's edges (Station Cards not shown for clarity) is the shape we want to outline.
This image of a take off strip on the model shows how the method of work applies to the builder's plate model. By laying the strip flat to all the frames' edges, marking the stations as a grid on the strip then measuring along each StationCard's edge to the chine or sheer the entire sheet's outer edge curves can easily be taken off; to be accurately laid down on a blank sheet out of which the full hull panel will be battened fair and cut.
Above, the builder's plate model inverted, again, so the strip's orientation can be see from another point of view.
The gridlines drawn on the pattern or take off strip are the frames/stations/sections' edges as they touch the strip and the distances are above and below the strip's edges to the chine or sheer.
What will the points look like when they're put down? Above is the strip (left) and to the right is the use of the strip's pattern information. Notice the grid lines of the points on the outline of the hull panel are not all vertical to the sheet, but the are lined up with the strip's orientation to the original Station Card model .... and we know from the first post on this method that the orientation doesn't matter as long as we keel the grid (Station Cards') edges marked for redrawing on the final material. We also know that the distances, even if curved on a cylinder or cone can be relied upon since the bar/pattern distances were taken along the egdes of the grid lines -an in our case shown above, the grid lines are the edges of the Station Cards of the model.
Shown here all the points are battened to connect in curves, but the bow stem and the transom lines are just projections of set of intersections of them model onto the strip. These two lines may be curved, cambered, bowed but the line on the strip will record that section of the pattern, other techniques may have to be used to determine how to recreate a curve if one is shown on the plans?
how do you 'record' the curves of the outline pattern so they can be reused? How do you work to repeat the panel in the future or keep the same curves for reference? Here is an simple method of laying a grid that is 90deg to a blank sheet onto the curves of the topsides hull panel. Notice the original pattern lines or Station Cards /Formers/Body Sections grid lines are shown to confirm the modeling process will not return a 90 deg grid to the new sheet. However the patterning process will take off an accurate shape of the sheet required to meet edge to edge with a hull design of the model.
The builder's plate model in a 3"=1'-0" scale can be used to sheet hulls at least to 40'-0" LOA, as I have personally used a model of paper and wood, shown above, to take off the hull panels of that size boat. I ended up accurate to one sheet thickness in length and less than a 1/16" in beam and the boat was build skin first followed by main bulkheads, fit to the shape not lofted. I have made skiff this way for a long time, to avoid the labor of framing first, but even if you use a frame first building method(?) this method can be applied to both a plate model or the full sized frames to find the shape of the outline of the main hull panes.
If you have a set of frames already for sheet, this method of 'taking off' the full sized hull panel outline will work very accurately if the steps are accurately repeated and the strip is well and firmly clamped to your frames.
This method can be used (as noted in a previous post several above) to fair the frames as well. Notice that a hull thickness flat bar laid as shown in these images will represent the hull sheeting? This will reveal several aspects of your hull frames' outer edges- higher than neighboring frames and lower than neighboring frames.
Last, relating to this aspect of a plate model; is a review of the discussion of chines or longitudinal hull seams. Mr Hankinson has an article on the site about aluminum boat building and he reviews some of the various chine joints possible. I recommend you find and read that article to explore some of the implications for the chines' fit in respect to chine flats' outer edges OR in the case of a single chine the topsides to bottom seam's design in section. Some of these joints would require an overhang at the chine, others may require other allowances.
In some of Mr Hankinson's designs, he shows a large diameter round bar to weld both the topsides lower edges, and the bottom's outside hull panels' edges. This chine bar is only needed if your work is not refined enough to fit the two sheets to other joint designs. The round bar has an upside- wide target, huge weld sink for low skilled builders, but... the down side is the large heat sink makes good welding harder and putting the bar on 'fair' is a big job because once in tension along the chine point of frames; heat distortion from tacking is hard to avoid. (Catch22 of chine bar; to get weld hot enough to hold huge bar- heat is enough to allow bar to bend unfair but... an if the welds are cool enough to keep bar fair, it may not be held to the frames adequately to stay put while patterning hull panels.
LAst about chine bars, I think they were shown to reduce error by inexperienced or low skill builders, now you have clearly shown, adequately illustrated methods to allow fitting to at least 1/4 of any sheet thickness (this thread) the better joints would be those explored in Mr. Hankinson's article about welded aluminum boat building. The most simple of which is an inside edge to inside edge seam I've shown here and on the adjacent threads about working and planning in welded aluminum.
I'm pretty confident that if Mr Hankinson knew his plans buyers and future builders would all read these posts, practice the work methods shown, and apply the trade craft reviewed here; he's say you could skip the chine bars and go with sheet edge to edge joints without any hull compromises?
As usual, I welcome questions, please note where and what text I've goofed up? What image makes the information here confusing and I'll try to help make sense of what I confused!
This method, shown above is not very agile for chine flats and so we'll start to explore a method that lends itself to that surface. The same method will be a basis for outlining and cutting forward hull longs that may be so tight in curvature they have to be rolled, formed or cutouts?