Monday, November 25, 2013

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.

But first things first...Building my workbench

I built the tandem wherry last year using a 2' x 8" sheet of plywood over a couple of sawhorses for a workbench in the garage. Seeing as I can't justify building a dedicated boat shop at this time, I think will have to make do with the garage for the time being. Maybe if there's a build #3 I'll find a dedicated workshop with lots of room.

However, I can definitely improve on last year's workbench. I shopped around online for woodworking benches, and found all kinds of options...most of them much more than what I wanted to pay for a solid work area. I figured that my woodworking skills would only improve if I could build my own bench. 

A little more online research turned up a design called the "Kirby" bench. This is a fairly simple, straight-forward kind of bench. Not too many doodads or specialized work areas. It also looked like something I could make with materials from my local Hope Depot. 

Overall it's 84" long, by 30" wide and I think 33" high (?). I put it on industrial strength locking casters, so I could move it around easily in my limited space. The top began as 3" rock maple planks laminated together with epoxy. I hand-planed it down to something like 2.75" inches. It's not perfectly flat (yet) but it will serve my purposes. The trestle is 3.5" cedar legs and cross-ties, hand mortised and tenoned, and bolted together with 3/8" lag bolts. I cut a wood stop into the top and bolted it to the leg, and I drilled 3/4" dog holes across the surface for any large-scale clamping I may have to do. I added a Jorgensen 10" front vise, and built a Veritas twin-screw end-vise (wow...that only took me a week to make!). It's finished with Tung oil to help seal the maple against spills, paint, glue, etc. 

The result is what you see below.
Laminating the maple top - lots of clamps needed!

The "raw" bench...basic shape, size, and layout.

The Jorgensen 10" front vise. Works very nicely!
Twin-screw end vise.
Screws can work in tandem for parallel clamping, or independently for skewed clamping.

Time for another build...

For those who don't know, last Christmas, Karla (my wife) bought me a Chesapeake Light Craft (CLC) tandem wherry rowing scull kit. I jumped right in during the holiday, and over a series of evenings and weekends, I managed to pull together a nice little boat. It was about 150 hours in the making, whereby I had my first experiences building anything out of wood, the use of marine 2-part epoxy, fiberglass, and marine polyurethanes. But the entire build was amazingly enjoyable and the end result is something we've been using frequently since the boat was finished last May. 

Well the bug has bitten, and now I find myself getting ready to embark on another project. 

I've always wanted a sailboat. So I shall build one. The question of which one has consumed many hours of research. In the end, I decided on the John Welsford "Navigator" design. Welsford is a New Zealand small craft designer and builder. He has a number of very successful boat designs, and is something of a legend in the small wooden boat universe. 

Why the Navigator? 

1) The construction process is one that I now have experience with.
2) She's small enough to be built in my garage, and to be able to be sailed single-handedly.
3) She's large enough where 3 or 4 people could enjoy an afternoon on the water, or 2 adults could camp-cruise her.
4) Welsford has done a great job in creating a small boat with really lovely lines and a sheer that could make you cry, while at the same time designing a boat that will offer plenty of fun and performance and stability on the water. 
5) It's a design that will allow me to make a very traditional-looking boat, with modern materials and technical enhancements. For example, I'm planning to put an electric inboard auxiliary motor in her, and use advanced composites like kevlar and carbon fiber.

From what I understand, Navigator is one of the most successful small boat designs ever, with more than 600 built around the world by amateurs like me. There are all kinds of photos of Navigators out there. Here are a few screen caps that will give you an idea of what I'm about to try to put together. This is Robert Ditterich's "Annie" Navigator at rest. 

Here's the same boat in a fresh breeze

And here is a line-drawing of the Welsford Navigator  in a racing sloop configuration. I'm planning on building the gaff-yawl rig, similar to the images shown above. 
If you're interested in more information about this boat, check out Welsford's website.

So the project begins. I will update this blog with pictures, and something of a narrative as I have time to do so between work, family, friends, travel, and yes...boat building. I hope you enjoy the journey!