14 February 2010

A Garboard Tragedy - Act 1

Last week I woke up and decided I wanted to learn to play my favorite piano piece, William Bolcom's "Graceful Ghost Rag".

It is true that I don't actually know how to play the piano, but I figured if I just practiced this one piece for a bit, I could figure it out in a reasonably short time.

After all, learning anything is just a matter of time and practice, right?

Well, as my favorite piano teacher (Helena) will tell you, time and practice are not the only requirements. You need to practice what you are ready for.

I could practice the "Graceful Ghost Rag" from now until doomsday, and never get it right. The reason: I don't have the necessary foundation for it.

However, if I started off with Book 1 of any piano method (complete with cute animal pictures and the obligatory rendition of "Merrily We Roll Along"), and work my way up the scales (at least the 45 basic ones), and practice an hour or two a day, then I just might be ready to start working on the "Graceful Ghost Rag" in 5 years or so. At that point, I'd know enough to understand what I was practicing.

No doubt a good book and/or good teacher can help flatten the learning curve, but there's no short cut for practicing, or getting around the rule that you can only learn what you are ready to learn.

I ran into this seemingly universal law this week when I tried (and failed) to 'get out' a pattern for Cabin Boy's garboard plank. As I sat in my moaning chair, thinking back on my dismal failure, I realized that my mistake had been in the very first step, and that everything I'd done in subsequent steps had been doomed to failure.

And this put a smile back on my face. I will try to explain...

The first step in getting out any plank is to spile it. Determined, this time, to follow the advice of the Boat Building Books as closely as possible, I read and re-read the pertinent sections of Greg Rossel's Building Small Boats until I believed I understood exactly what I was supposed to do.

One important point was to not try to use one, long, single piece spiling batten. Such a batten cannot be curved around the forms in the right place without being edge set. And edge setting a spiling batten is a sure path to depression, suicide, and worse, I was assured.

What does 'edge setting' mean? To see it for yourself, cut a one inch strip off a piece of copy paper. This long, thin rectangle is your 'plank'.

Then draw a straight line on another piece of paper. Lay your paper strip so it's upper edge aligns with this straight line. See how your 'plank' lies nice and flat?

Now draw a line with a slight curve and try to lay the upper edge of your paper strip along this curve. You can bend the paper so it follows the curve, but the inside edge of the strip will curl up. Try as you might, it is not possible to have your straight 'plank' both follow the curve and lie flat. It must stand up on its edge to follow the curve. Your 'plank' is thus 'edge set'.

To avoid these horrors, I dutifully built the recommended two-part spiling batten, made from two straight pieces of 1/4" plywood, spliced together with my first gusset.

My first gusset... clamped while the glue dries. Also fastened with screws.
photo jalmberg

Here's the spiling batten tacked into place in between the bottom of the chine log and the 'lining off' lines that mark the top of the garboard plank.

My first spiling batten
photo jalmberg

When I sat down to write this blog, this was the first photo I looked at. As usual, this photo meant nothing to me when taken, but was like a thunderclap of Revelation after the fact. Experienced boat builders can already see the problem, I'm sure.

"In religion and theology, revelation is the revealing or disclosing, or making something obvious through active or passive communication with supernaturaldivine, ...). It is believed that revelation can originate directly from a deity, or through an agent, such as an angel. One who has experienced such contact with or communication from the divine is often called a prophet." 

- Wikipedia 

However, not being a prophet, I didn't receive the message, and was thus doomed to play out this tragedy, until it's bitter end.

Once the spiling batten is tacked into place on the forms, it is time get out your dividers. I used the ones I use for navigation.

The purpose of spiling is to capture the perimeter of the complex space that a plank needs to fill. More specifically, you want to capture just enough points on the perimeter to allow you to connect the dots and draw the complete shape.

One way to spile is to use a simple geometrical fact: if you draw an arc around a point "A", you can rediscover the point from the arc by drawing two arcs of equal radii from any two points on the arc. The two arcs intercept at the original point.

Geometrical basis of spiling
photo jalmberg

In spiling the garboard, you choose various strategic points on perimeter of the proposed plank: points on the stem rabbet, chine log, transom, and the lap points on the station forms.

From each of these points, you draw an arc onto the spiling batten. Ideally, the spiling batten is big enough so that all the arcs are of equal radii. That minimizes the chances of error. Unfortunately, my spiling batten was NOT big enough for that, but I thought I had a way around that problem.

Naturally, this hubris generated at least one big error, which I'll describe tomorrow.

>>> Next Episode: A Garboard Tragedy - Act 2

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  1. I practiced the Moonlight Sonata one week and got as good with it as you probably did with the Rag.

    Actually, your spiling batten is plenty wide enough if you know the various ways of using it. BTW, it is absolutely critical to use the same size arc for evrey measurement. Lock those dividers down tight.

    You've probably solved the problem by now and learned a valuable lesson. The best learned lessons in boat building are those stemming from these little puzzles (we don't call them errors).

  2. Well, I *hope* I've learned enough to do it right the second time. Only time will tell.

    BTW, I believe you can use different divider widths as long as you record the size of the divider used somewhere, so you can reset the divider to the proper size when necessary.

    As you'll see tomorrow, I forgot to reset the dividers for one set of points, but it turned out I didn't need that particular set of points.

  3. However, now that you've made me think about it, I've suddenly realized a way to use the same divider settings for all the points... Duh... so simnple!


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