Monday, November 29, 2010

Dockyard mystery, or, Gloating over small success

Tonight I've been going over the stem we removed from the No. 2 Monomoy. What seemed like a reasonably open and shut case of some parts needing replacement is rapidly turning into a whodunit murder mystery of boat restoration. This is going to get technical, so if you're only here for my wit and interminable charm, now is the time to chime out.

The stem is in two pieces that were scarfed together with one of those pesky curved scarfs I'm dreading reproducing and nobody seems to know how to cut. But that was the least of my concerns as I started my work for tonight - tracing the outline of the removed pieces to make patterns to make the replacements. The scarf didn't fit very well and there was some nasty checking of the timber in the vicinity of the joint. But this I just wrote off in my mind as the product of the fasteners working loose. Obvious!

This is where, as you have probably anticipated, the plot thickens. I hadn't given it much thought but the gap in the scarf was in the middle of the joint, not the ends as you might expect if you were to force the pieces back and forth. Photo 1:

See what I mean? Look at the stopwater hole (the big one right through the center of the scarf) - its not even aligned properly. What could cause this? I thought it highly unlikely that the wood should back off from the center of the scarf and leave the ends relatively tight. And it turns out, I don't believe that it did.

If you look at the lower part of the scarf in the photo above, you'll notice a considerable amount of checking, where the wood grain has opened and expanded. And even in the small section of curve you can see, the outer curve (bottom) is not even close to fair. Clues. There is clearly distortion here, but what was the shape originally? I need to know this if I'm going to have any serious accuracy in the replacement parts. I need to play with this shape.

First, I started by finding an index - some point on both pieces that I know was lined up originally. The stopwater is the perfect index point. When the pieces were joined and bolted together, that hole was drilled where the joint passes through the back rabbet line (deepest part of the rabbet). I started by lining that up. But when I did, the rabbet was thrown dramatically off. Photo 2:

Yes, the stopwater hole is aligned. Unfortunately that's about the only thing. Well no - the bearding line (where the inside of the planking meets the stem, above in illustration 2). The rabbet is completely off - like nearly 3/8" off. I should also note that I had to cut off a chunk of the piece on the left - go back and see photo 1, you can see my saw cut (I put the piece back for the photo). On photo 2, the gap is clear - that big black wedge shaped void. And as my mind wandered, suddenly I saw it. The rabbet is not off. Somebody MADE it that way. Look again. Photo 3, a little closer view. A red arrow points to the smoking gun.

SOMEONE and I'm not pointing fingers (at the idiots and assholes who may have repaired - or thought they were repairing this boat before me) but the rabbet was cut back to match the misaligned pieces! The photo doesn't do it justice - its more than apparent in the flesh. Wood flesh. Real life. Whatever. Bastards.

Okay. I'm onto something here. Clearly I've found the original orientation, and I'm getting farther afield from my index point - remember that's the stopwater hole - but the inner and outer curvature still eluded me. Look again at the parts aligned on the stopwater, from a distance. Photo 4:

Okay. Stepping back and looking at it, I realized that the answer was remarkably simple. Go back to Photo 1, and look at that checking in the wood of the lower part of the scarf. I'll wait.

The checking forced the wood to expand, forcing the lower right portion of the scarf to push to the right and throw the scarf out of alignment. The maintainers unknowingly just kept shovelling putty into the gap. When somebody got around to repairing the resulting sprung garboards (which explains the condition of those parts quite well) they had to chisel back the rabbet to make it fit. If I were to just carry the curve from the right piece onto the part of the left piece that isn't checked. And surprise surprise - its a fair curve. Look at Photo 4 again. It seems so obvious to me now. Elementary, my dear readers. Yeah right! Took me about three hours of heaving and hawing, adjusting, readjusting and playing with the batten.

Now I can proceed tomorrow with finishing up the pattern. Why didn't I do it tonight? I dunno - because I've been too busy BLOGGING about it. Oh well. Small victories.


No comments: