More preparation...learning mechanical drawing

So, John Welsford's Navigator plans arrived in a nicely rolled tube.

A couple of things to note about the plans: There are 14 sheets in all, I think. Like many plans, some of the drawings are scaled, some are actual size, and some aren't to scale at all, but rather only for illustration purposes. Because Welsford is from New Zealand, his plans are drawn in metric, using millimeters as the base unit. Theoretically, this should make things easier, because I won't have to deal with all those squirrelly fractions that one wrestles with in Imperial measurement. It's much easier to know that 521mm minus 10mm is 511mm. Any schoolchild can do that in his head. Here in the States, we have to resort to calculators to figure out what 17/32 minus 5/8 is. The problem is that all my tools, rules, tape measures, etc are all Imperial, not metric. Just another small challenge to be overcome.

As an aside, it's still baffling to me why this country has never fully embraced the metric system. It's so much easier.

So after spending some time over the summer studying the plans and working up a 1/5 scale model to test out the basic construction techniques, my next challenge is figuring out how to accurately get a 1/5 scale drawing of various boat parts up to full-size, so that I can print them out and make templates so for all the cutting I will be doing shortly.

Test Model: Bulkheads 1-4 and Centerboard Trunkcase 1/5 scale

Test Model: Stem and construction detail for various bulkheads.
Cut-out notches on the bulkheads will be connected by stringers.

It seems simple at first – why not just scan the drawings, and then scale them up 500%? Well, I ran a test on this, and it turns out that scaling a pixel map up isn't exactly the most accurate process unless you really know what you're doing (and I don't!). There's something to do with the resolution of the screen vs the resolution of the scan vs the resolution of the printing device. If they're not all perfectly calibrated, the results are less than spectacular. The "full size" version of my first tests were something like 35% bigger than what they should have been and all fuzzy and pixelated, which would have made for not very accurate cuts in the shop.

Then I thought maybe I could draw them out full-size by using an opaque projector to put the image up onto a wall at full size, and then just trace the outlines onto paper. OK...yes, but where to find an opaque projector these days?? And what if your projector isn't perfectly square to the projected surface? This could cause distortions in the full-size image resulting in a seriously canted boat. Hmm. My options are narrowing.

Expert opinion seems to be that there's nothing for it except to "loft" the drawings. That is, take all the various measurements and offsets in the plans and transfer them to a full-size surface. It's called lofting because in the old days when they still made boats and ships out of wood, they would find a large, open (covered) space in a loft of a building someplace out of the way to lay all the various shapes and sizes out. As with many maritime words and phrases, tradition dies hard. Some people still loft by hand. But the modern equivalent of lofting by hand is to loft in a CAD software program, and then print the resulting images out to full size on a large-format plotter/printer.

So last week I downloaded some CAD software for my Mac, and began learning how to use it. For $20, I was able to get a copy of EazyDraw 6, which has all the features I could possibly need for a simple 2-D layout.

A few of the necessary tools needed to transfer the plan into a full-size computer drawing.

CAD drawn bulkhead. Note this is not just a half-breadth drawing but rather the full bulkhead.
Also note that the grayed out holes in the bulkhead represent two separate storage compartment entrances. This should be easier to access storage than the original drawing, where the mainmast would be in the way of anything going in or out of storage. 

Original Welsford hand-drawn bulkhead

By the time I'm done with this process I'll have perfectly accurate full-size version of each and every part of the Navigator hull. These will be arranged on a virtual sheet of 4' x 8' plywood, to economize on wood, and to minimize scrap. And then the cutting will begin.