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About Full Sized Patterns

We are often asked if our plans have full sized patterns. The ones that do will say so. For the most part they do not. Below is a letter from our friend John Kohnen explaining his views on the subject - it is a response to a question about the plans in the Rudder Magazine from the 1930's but we think it applies to all boat plans:

Rudder Boat Plans

Question: I'm researching boat plans that were included in the Rudder Mag in the 1930's. Can you tell me were full size layout patterns available to purchase at the time, or did the boat builder make their own - or simply use the measurements given in the "tables of offsets"and apply them to the actual plywood or timbers?

Answer: There were no full-size patterns to be had back in the '30s. Full-size paper patterns are a "snare and a delusion" anyway, as my boatbuilder friend John McCallum puts it. More trouble than they're worth, because the paper stretches, shrinks and changes shape. It's much more accurate to lay out pieces directly on the wood from measurements. I gave up the only time I tried full size patterns after I discovered that an important line on one paper pattern that I KNEW was supposed to be straight had a significant curve in it! <sigh>

Almost all of the plans in those old Rudders don't give any measurements for the pieces of the boat. The table of offsets is used to draw the lines of the boat full-size, "lofting," and then you can use the "laid down" lines to make patterns and parts, and to find bevels. The measurements in the table of offsets were taken by hand from a scale drawing, so can't be trusted to to scale up accurately. When you loft, or "lay down," the lines full size you correct any errors. You need to loft everything but the simplest boats in those old Rudders, but it's kinda fun anyway.

An excellent, and inexpensive, book on lofting is this one

Nowadays most designers use computer design programs that can check the fairness of a boat's lines using mathematical algorithms. Then they can get measurements for the individual parts from the drawings without lofting. Some folks use the table of offsets from old plans to get the lines into computer design programs, and then fair them up electronically. There's a program called FreeShip! that's pretty good, and free. It's got a steep learning curve that I haven't climbed yet:

You can practice lofting in any 2D CAD program. It's hard to tell a really fair line on a computer screen, but you'll figure out what's involved in the process. If your CAD program has a selection of curved line types (bezier, spline), and the boat you're drawing is small and simple, you might even end up with a useful electronic lofting that can be used to build the boat, but you might end up having to make adjustments as you build it.