Sketchbook: Cutting Patterns Accurately
A. Because the interior dimensions on a boat are rarely straight, whenever you are thinking about adding a small locker or bulkhead you must measure, cut and trim the panels very carefully.Make sure the boat is horizontal so you can use a spirit level, along with an integrated laser, to project datums across the boat. Once you establish a fixed datum point, transfer as many measurements as possible to a pattern made of cardboard or hardboard. After cutting the pattern, put it in place and make sure it fits correctly before you start to cut the actual pieces of wood or plywood.
B. It’s easier to take internal measurements with two sticks held in your hand, or take a piece of plastic conduit with a snap-on top that slides with a stiff action that holds it in place.
C. Transfer awkward shapes either with a profile gauge (which is like a comb with movable teeth) or by scribing around the shape with a compass held at a fixed angle.
D. A spiling block can do a similar job. After you have clamped a board in position, run the block over the relevant lumps and bumps and mark the corner positions as you go. Remove the board and use the spiling block to transfer the marks to a pattern. Having a long and short edge on the block makes life easier—but number the corners so you don’t forget which edge is which! E. When cutting a panel, measure the widest point to allow for any tapering; make a vertical cutout shape if you are going to have to slide the panel in vertically. E. When cutting a panel, measure the widest point to allow for any tapering; make a vertical cutout shape if you are going to have to slide the panel in vertically.
F. A spokeshave is ideal for inside curves and shaping bumps and tapers, but it must be razor sharp to deal with all the end grain in plywood.G. For measuring bigger areas use a pointed stick with notches in it. Mark the notched positions on a board and use the stick again to transfer the shape on to a pattern board. A pattern board will also show whether you can get the full-sized panel in through the hatch!
Dick Everitt has been an illustrator, journalist and engineer for over 40 years. He has sailed many thousands of miles on all sorts of craft in various parts of the world
