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Author Topic: Weight of a log  (Read 2036 times)

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Offline Daniel Parkka

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Weight of a log
« on: February 08, 2008, 04:44:32 pm »
I need to know how to determine the weight of a large log.  I am also interested in walking me through the math.

The tree is a white oak.  It is 16 feet long.  The narrow end is 14 inches in dia. and the wide end is 18 inches in dia.

I have used tree calculators on the web, but do not know how they are calculating thier results.  We had a trailer crash with 10 of these logs above.

Thank you,

Daniel James Parkka

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Re: Weight of a log
« Reply #1 on: February 08, 2008, 04:52:52 pm »
The math can only give you an estimate. If you look at our weight calculator in our tool box read the disclaimer on why that is so.

http://www.forestryforum.com/board/index.php?action=toolbox

Our calculators are written in javascript so the formula is shown if you view the page source.

   This calculator is useful in providing approximate weights for species, but the user should be careful in how the product is used. Wood varies considerably in weight per constant volume (density) on a regional level and at the local level. That is, the weight of a piece of wood from one area or tree will differ from the same species in the another area. The growth rate is the most significant factor in determining density, with slower growing trees having a higher density (therefore greater weight), than faster growing trees. This is due to the late wood cells (the dark ring seen when a tree is cut) having thicker walls and being closer together than the early wood (lighter wood between the rings).

     Where the board is cut from the tree is another factor, the heartwood portion of the tree (the center portion, often characterized by a change in colour) is composed of dead cells and will be lighter than the sap wood, where the cells are still living. Wood that is cut from the portion of the stem that still has live branches on it will be lighter due to hormones produced by the foliage.

     In different areas, genetics will play a factor in wood density, along with the growing site (moisture and nutrient characteristics of the soil). Where the tree grows on the hillside, eg south facing versus north facing slope, high elevation versus low elevation, areas of heavy snowpack versus light snowpack, constant winds versus sheltered locations all have an influence on the density of wood.

 
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Online Jeff

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Re: Weight of a log
« Reply #2 on: February 08, 2008, 04:57:05 pm »
Ya better have a stout trailer, as that load would be upwards of 14,000 lbs.
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Offline SwampDonkey

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Re: Weight of a log
« Reply #3 on: February 08, 2008, 05:39:05 pm »
There are seasonal difference in weight to. But, Jeff's disclaimer gives you an indication of the variability.

That's heavy stuff, hopefully someone has trailer brakes.  ;)

Pre-commercial thinning pays off. :)

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Re: Weight of a log
« Reply #4 on: February 08, 2008, 07:13:23 pm »
................
The tree is a white oak.  It is 16 feet long.  The narrow end is 14 inches in dia. and the wide end is 18 inches in dia.
................  We had a trailer crash with 10 of these logs above.
..........
Welcome to the forum. We like pics, and a trailer crash of 10 logs would be real interesting to see.

All 10 of the logs were 14" small end, 18" large end, and 16' long?  How is that?

Feed us a bit more information, Daniel.  We're all ears.  ;D
south central Wisconsin
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Offline rebocardo

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Re: Weight of a log
« Reply #5 on: February 08, 2008, 10:02:04 pm »
> but do not know how they are calculating thier results

I will give a simple version for you.

18 inches across is basically about 16 inches squared for surface area. 16 inches across by 16 inches tall.

(16 x 16 = 256 sq inches) x (16 feet length x 12 inches per foot = 192) =  49152 cubic inches

49152 inches / (1728 inches per cubic foot) = 28.44 cubic feet

White oak around here is about 70-75 pounds green so I always calculate on the high side

28.5 CF * 75 pounds = 2137.50 pounds per log

That is basically how it is done, there are other things to throw in such as the taper of the tree and such. But, if you do not take in account the taper from large to small end, you will most likely not overload your trailer, truck, or winch.

The simple way for loading and estimating a trailer is just to measure

((width x ht x length) = cf) x 70 # = load


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Re: Weight of a log
« Reply #6 on: February 08, 2008, 11:35:41 pm »
Simple to use the calculator in the FF tool box.  About 1400 lbs.  per log.   ;D

Fast grown white oak, or maybe the southern white oak might weigh more.

Not sure where this white oak being discussed is located.
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Offline Ron Wenrich

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Re: Weight of a log
« Reply #7 on: February 09, 2008, 06:45:57 am »
The formula for figuring up the cubic foot volume for a log is by using Huber's formula, which is pretty simple.  Cu ft volume= .005454 * (D^2) * L    D=diameter at midpoint of log and L=log length.  The midpoint diameter on these logs is 16", so the cu ft volume is 22.34.

Don't like that formula?  Smalian's formula is cu ft = .002727 * (SD^2+LD^2) * L     SD=small end diameter, LD=large end diameter and L=log length.  Volume now is 22.69.

When we developed the log weight formula, we used Huber's formula.  I figured it would be easier to put in one diameter easier than two, and then there's the problem of butt flare and rookie log scalers. 

The log weights are for green wood and come from the Forestry Handbook put out by the Society of American Foresters.  Weights were put into the calculator so you can see how heavy they are saying certain woods weigh. 

The disclaimer was put in there for 2 reasons.  One was that from our experience, log weights vary and you won't get two logs of the same species to weigh exactly the same with the exact same volume.  Too many variables.

The other reason was that we didn't want someone to come back on us with one of those "well, you said it weighed this much and it was heavier and you broke our equipment" type of arguement. 
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