Making a half model

Half model making is the precursor to lofting. In a sense one is lofting in a different medium. Boat builders were obviously familiar with wood and the tools required to shape wood, and probably less familiar with working out a design starting with a blank sheet of paper and a pencil and some battens. They could carve a model and, working by eye, eventually arrive at a shape that, to their experience and aesthetics, would work. In 1995 I built a 21-foot sharpie yacht. I found just a few principal dimensions for a Lake Champlain racing sharpie in an 1880's issue of Forest and Stream magazine. I made a block that conformed to the dimensions for length, breadth and depth that I had, and then carved a model. Essentially I was fairing the lines between the known points, using my spokshave and block plane instead of a batten and pencil. When I was done and the model looked right, I drew station on the model, scaled the dimensions, and laid down the lines for my moulds.

The result was this boat: http://www.douglasbrooksboatbuilding.com/sharpie.html





I got my friend Tom first interested in the Dory Tender by having him build a half model of her. We made Xerox copies of the lines drawings and then, lining those up carefully on a block of pine laminations on a reference mark, he used a push pin to make marks along the lines, which he then connected using a pencil and batten later. You will notice on the block the layer of paper I glued between two lifts. I had once used veneer glued in the block to form the waterline of the boat, but even a very thin veneer is too thick, so now I use a sheet of paper in a contrasting color, and when the model is done (and the builder has correctly lined up the paper with the boats waterline) it makes for a perfect fine line in the model.







The block is then sawn out on the bandsaw, and this can take some contortions as the sawing proceeds. In a round hulled boat the waterline lifts are of various beams and basically automatically rough out the shape of the hull. With a hard chine hull you are forced to start with one large block of wood. One thing that I always do when sawing out a model is to SAVE all the offcuts. You can tape these offcuts back to the model and give yourself a larger, steadier base to rest on the table of the saw. If you do cut at an angle be careful when pushing a model through the blade on tilted table.





Using the sections on the plans I extended the line of the planking out to a point corresponding with the outer edges of the block, therefore letting us make marks corresponding to the plane of the planking. Connecting these marks at each station gave us a close approximation of where we had to saw. Also, when shaping the model, one can use templates made from these station sections to check the shape. We checked often by using a bevel gauge, taking angles from the section shapes and checking those same spots on the model.





Even the offcut from cutting the bow comes in handy later. Here I lay the offcut on the plans and transfer the end points of the plank laps, or chines. I can make some other reference marks to make sure I line it up correctly on the model...





...then I can use the offcut to mark these chine locations on the model blank. You can also use masking tape to fasten offcuts back to the model blank to provide a flat surface for resting the blank on the bandsaw for additional cutting. I never throw out any of my offcuts until the model is completely finished.









The tools needed to shape the model itself are basic: a small block plane, a spokeshave, sandpaper and perhaps a gouge for hollow sections. On a hard chine hull it can be tricky to keep the faces FLAT. You have to be careful to resist the tendency to work these facets into a curve. The same is true when sanding, but using a sanding block can save the situation.













Many people don't realize that half models were used to design boats. In fact, Nathaniel Herreshoff, America's most famous yacht designer, created all of his most famous designs from models. One trick used by designers was placing the model on a polished sheet of metal. Here I am using a mirror to give an idea of the shape of the actual boat. Metal was used because you can see the gap created by the thickness of the glass in the mirror, which creates a slight inaccuracy in viewing the design.

This model was a great success, as it convinced Tom that he wanted to build this boat, so we got to work on a very part-time basis last winter. By the way, these models can still be very useful to builders.

For instance, if they are made accurately, one could lay a piece of paper on the model's garboard plank, for instance, trace the shape, and then scale the actual size of the plywood needed for that plank. Given that the model is 1/10th scale the builder would want to allow for some inaccuracy but nevertheless this method can come in very handy.

Douglas Brooks
August 2009

Douglas Brooks (www.douglasbrooksboatbuilding.com) is a boatbuilder, writer and researcher specializing in the construction of traditional wooden boats for museums and private clients. He lives with his wife Catherine in Vergennes, Vermont.

© Copyright 2009 by Douglas Brooks

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