Scientists (pertaining to wood structure) wanted...

[chris pearson]

Okay, I know I just set myself up for the wise cracks(you know who you are) to go off on tangents here. I'm helping a friend restore a yankee, 16 year old Pete. It was made in 1950 as you may have already read, but after all the times Ive run into this I gotta ask, cause I have no clue. Why do you find micro cracks perfectly across the grain on a rib? No apparent hit, and I didnt see any of them until Pete pointed them out, dont even ask me how he spotted some of them, and this is after sanding smooth, vacuuming, and blowing out with an air hose. Hell, we even found a few after the first coat of varnish. Now, this boat wasn't hit in these areas, no mismatch in the rib at all or splintering. They look like old cracks and I don't think they were caused by vibration from hammering tacks. Thoughts? I wonder how many I missed on my other canoes, I'm afraid to go out into the garage!!!!! Pete will inspect your restorations for a nominal fee, I think he could make a living doing it. I MADE him look at my OT Wolf Pond with a wet rag and he found a couple small ones that I missed!

 

[Dan Lindberg]

I don't know but, I have seen them also, usually on older canoes.

Dan

 

[Andre Cloutier]

Due to your disclaimer i wont say 'wheres the pictures' but i'm sure we've all seen what you are referring to, usually its attributed to the ribs being bent to quickly or with too much heat/too little water. I'll take a pic later, but lots of Chestnuts and Petes i've gone through have had them. Certainly nothing structural, but very visible. See, no wisecracks, just info - like remembering to take the plastic off cigars before you smoke them...

 

[chris pearson]

I'm impressed at the amount of restraint that must have had for you my friend. I wonder though, a compression type failure usually "creases", not just a barely noticable fracture. Almost like it occurs after its nailed in place? Perhaps the stress releases after some exposure to temp change, etc.?

 

[Craig Johnson]

I am glad my eyes aren't as good as Pete's. The worse my sight gets the easier the repairs. Early in my career we didn't finish up shingling a roof till about 9:00 pm. The owner said something I have used many times since. " looks pretty good in the dark."
Working on those tiny models must have sharpened your eyesight

 

[pete vourlitis]

Certainly sharpened my eyesight! "looks pretty good in the dark" , I really started to feel that way after the 10th cracked rib.

 

[Dan Lindberg]

Where are you guys seeing the cracks? ie, are they in the sharpest bend area or elsewhere?

What I remember is that they were anywhere on the rib, and not in the bend, ie, not compression cracks.
I attributed them to age, dryness, use, etc, and not initial bending.

Dan

 

[oldhaven]

I went through a few years fascinated by English longbows and self bows and made quite a few. The cracks you are seeing may be something bowyers call chrysalling. These are compression fractures that develop in the wood across the grain on the the belly or inside of the bow curve if the fibers in the wood are weaker or overstressed relative to those on the back of the bow. In a bow these may develop over time as the bow is flexed and surprisingly are not always fatal. They are usually found in the most stressed part of the bow stave if the wood from the handle area to the tip has not been tapered well so the stress is distributed over the whole curve. Chrysalling that is too deep or cracks on the stressed back of the of the bow are a reason to retire the bow. I don't have nearly as much experience in rib bending, but since the wood is not repeatedly over stressed once it is steamed and put in, and is backed by the planking, I would think these chrysals should not be a problem if they are not right through or do not go beyond the neutral axis of the rib. Maybe this is a good reason for tapered ribs, and I wonder if you can find them more in flat vs round bottomed canoes where the bending stress is concentrated at the turn of the bilge.

Ron