# Expanding an outline...

Hey guys, i have a friend that is interested in having me shape him a 6’8 semi-gun. Now I have some dimensions from a template that I used a while back and made two previous boards out of. They are as follows: 6’8" 12 1/2"x18 3/8"x12 1/2" Now if he wants the mid point to be widened out to 19", what do i need to do to the nose and tail dimensions in order to maintain the same smooth curve of the outline? Thanks for any help at all! -Ron

I often see templates - plan shapes - that I like in a magazine. I divide the length of the board into 1/8ths and measure the width in millimeters (or some similarly small decimal, not fractional scale) at each 1/8 point. Then you scale your measurement up to the intended full width. The results can be applied to a board of any length, but note that as you go longer than the original board, the board becomes more slender and “gunny” so there is a limit to this. Only you will decide whether the scaled-up version represents the original. For instance, if the picture is 28 mm wide at the widest point and you want a board that is 19 inches wide at the corresponding point, the ratio to multiply all picture widths by is 19/28. Same for other widths.

When I taught cabinetmaking I would enlarge a pattern by simply placing a pencil into the hole of a washer that had a width of the same dimension that I wanted the pattern to be enlarged by. Now lets enlarge your templet as an example. You have 18 3/8’ and want 19". Thats a difference of 5/8". What you need to do is find (or make) a washer that has a difference of 5/16" between the hole in the washer and it’s outside edge. Next step is to put a pencil in the whole of the washer and trace around the templet with the edge of the washer running against the edge of your templet. You will increase the width of the templet by 5/16". When you trace the templet onto the blank you will have increased the total width by 5/8". You may have to adjust the length just a tad because that too will be 5/8" larger.

A washer or just use a pencil compass… Another thing you might try is taking your template measurements, multiplying by the appropriate fraction ( what, 19/18 was it? Round off the decimals to the nearest 0.125 and that’ll give you eighths of an inch ) and then lay that out. Connect the dots with a batten, as boatbuilders do. This will give you a nice and very fair curve, though you’ll find that some of your measured points are a bit too far in or out. Go with the line the batten gives you. If one is way, way off, check your calculations. http://www.digitalnorseman.com/bcvsp/loft.html http://ourworld.compuserve.com/homepages/jdory/images/loft1.jpg http://www.duckboats.net/lofting.htm for some illustrations of lofting with a batten. The latter also goes into some detail on how to select a batten, which is important. Hope that’s of use. doc…