Wood Science 101 (16) - Wood Weight Estimation Finally Pays Off

A couple of weeks ago, I was passed on an email with pictures from a Penn State student asking about the species of a log on display at a local bike shop. He wanted to know, because the log was the object of interest in a contest - guess the weight of the log and win a mountain bike. It looked like an oak, but I decided to stop by the shop since I go by it every day on the way home, just to confirm.

Measurement of the rays, which were very visible through the gashes in the bark from the grapple that skidded the log from the woods, confirmed that it was indeed a red oak, and probably a northern red oak (Quercus rubra) or a scarlet oak (Quercus coccinea).

Information conveyed back through channels to the student, I got to thinking about the poor, undernourished nine-year-old waif living under my own roof. Being the sixth of seven in the Ray clan, he had become quite used to hand-me-downs, and had never had his own new bike. Wouldn't it be fun, I thought, if we made an adventure of measuring the log together and entering the contest?

This undertaking, however, was fraught with potential downside...the biggest being, of course, that he wouldn't win, and I would fall forever from his eyes as the king of everything in the Kingdom of Wood. But, since I've discovered that Dad is pretty much completely discredited by the time each offspring reaches about the age of thirteen, I was only risking about four years. And, I figured since timber estimation has always been one of my strengths, we might actually have a pretty good chance. And if he won, the upside would be priceless.

So, on the last day of the contest, off we went to measure the log. It measured 8'4", with a 30-inch diameter at the top end and 38-inches at the butt. Since the butt had some pretty good swell, I figured a 33-inch average diameter, and a couple of eyeball measurements along the length made me feel pretty good about that estimate.

Now, at this point, I could have used any of a number of timber-estimation formulae that have been published over the last century. But, in a case like this, I always tend to follow the principle, Keep it Simple. And nothing is simpler than using a volume table built on empirical data.

So, once again, I conferred with Doctor Google...and found a Log Weight Chart at SherrillTree.com. The folks at Sherrill Tree, a company that sells gear for professional tree climbers, had posted a chart from the US Department of the Interior, which probably originally came from the US Forest Service. I knew this would be a pretty accurate reference since some government research team seventy-five years ago had probably spent years cutting and weighing green one-foot sections of different species of trees found in our forests.

Ah, the green thing. I knew that many of the contestants would look up the weight of wood and use a number from a dry-weight (12% moisture content) table. Sorry folks, not the right thing to do. I made sure to ask the owner when the log was harvested and weighed...did they weigh it right on the landing immediately after cutting, or did it sit around for a few weeks before they figured out which log was going to be used.

He confirmed for me that the log had been harvested the last week of August, and had been weighed immediately upon harvesting. Since we had a fairly normal, slightly cool and wet, summer, I figured the green weight data in the table would probably be about right, once I performed a little of my magic on it.

Part of that magic included figuring out the weight of that bottom foot of the log, which had a pretty good notch out of it. From the table I decided to apply 375 pounds to each foot of the log, 375 being my interpolation of the weights listed for red and white oak averaging between 32 and 34 inches average diameter. 375 times 8 gave me 3000 pounds. Now for that extra 4 inches and the notch.

Since I knew the butt was 38 inches in diameter, a further extrapolation from the table told me that a one foot section would weigh about 500 pounds. So, one third of that would get me an additional 167 pounds. Then I thought about all the notches I've ever hefted, and seventy-five pounds for a large one seemed about right. I closed my eyes, focused on the numbers in my head, and one visualized...3093.

So, we wrote down 3093 on Wesley's slip, and left the rest up to the timber gods.

Two days later, The Wife's phone rang, and the voice on the other end asked for Wesley Walker Ray. She mentioned that she was Wesley Walker Ray's mother, and what did they want with him?

She was astounded to hear, that Mr. Wesley had guessed the closest to the weight of the log...his guess of 3093 was only three pounds from the actual weight of 3090. He was the winner of a new $1,599 mountain bike.

A future great mountain-biker.

We picked up his bike yesterday, and after being trained on all the high-tech functions of the bike by the good experts at The Bicycle Shop, Wesley mounted it and rode it home, climbing a darn steep hill in State College "using only half-effort" he yelled at us as we coasted along side him in the car. The smile on his face was bigger than those 29" tires on the bike.

So, Going Wood all these years has finally paid off for me. Guessing the weight of an oak log...$1,599. Seeing that smile...priceless.

Tip Amount


James C said…
YES! Awesome story.
Anonymous said…
Art Lee said…
Yeah, Science! and dad with a PhD!
-Art Lee
Keith A. said…
Great experience. Perhaps a future in our industry, having reaped a success at such an early age!
Fireball Doowah said…
Great story. Looks like you learned something in College Station.
Anonymous said…
I pass by this bike every couple days on my way home and I can't tell you how happy it make me to know that you and your son won it. Go Wood!
Anonymous said…
Chuck, another big smile on this reader. Congrats to your son and I hope that you are able to enjoy his bike together for those four years you risked by taking on this project.

Susan S.
Chuck Ray said…
thanks,everyone. By the way, Fireball, I learned everything I know about timber estimation in Forestry School at SFASU in Nacogdoches. Hands-on forestry at its finest.
Anonymous said…
It would have been simpler to just look at the end of the log. It clearly says "3090."

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