How much more does a crotch weigh??

treehumper

Well-Known Member
#1
I know there was a discussion about this back in '08 but it seemed to never get to the crux of the matter.
Doing log weight calculations presumes a tapered shape of uniform weight/cu.ft. i.e., inputs are small diameter, large diameter, length and cu.ft weight by species. While that's fine if the crotch is relatively small in comparison to the overall piece an allowance can be made that gives you the wiggle room.

However, dealing with large unions where the overall volume could account for 1/3 to 1/2 of the piece in question then the difference is significant. When it's applied to a load chart and specifying a crane the difference translates into some significant dollars and potential for disaster.

Has anyone found any information that quantifies the increase in weight in any manner?

Oh and cutting it smaller isn't really an option.
 

NE Tree

Well-Known Member
#3
I hope someone comes up with a good answer to your great question. This very thing got me into some trouble and gave me a pucker factor 10 on a crane job a couple months ago. 20 foot spar with major crotch on top. I rigged it up as far as possible and we calculated what we could take. Everything looked good, I cut the piece and it flipped and went into a swing, spinning around the spar...not cool. Long story short, the crotch was far heavier that the 3 of us thought it would be. (Very thankful I like to have about 50% margin on crane picks) I think it'll be hard to get a good answer on this one though. Maybe a pound per cubic foot from a crotch and one from a strait log comparison would give a good idea
 

flyingsquirrel25

Well-Known Member
#5
Any serious crotches, as in girthy, have a significant weight increase. Not only is the grain denser, it's also twisty and retains more water. A smaller pick might be a wise decision. Be safe.
I would agree. Crotch wood is denser and I believe weighs more per foot cubed than the GWLC implies for normal wood. Time and time again you see it on the scale. We account for the possibility that it will be much heavier than the calculations and over time you can get a knack for estimating their weight. I like to put a number in my head (even if I'm not climbing) and check with the operator as to my accuracy... As long as I'm not jammed up chipping brush :).
 

treehumper

Well-Known Member
#6
Typically, I'd cut a a piece to include the crotch below the chokers to avoid inversion. I've taken it such that the choker was around the crotch wood to achieve the same end.
Any serious crotches, as in girthy, have a significant weight increase. Not only is the grain denser, it's also twisty and retains more water. A smaller pick might be a wise decision. Be safe.
Absolutely, but not an option. This is the challenge:rico:

Strategies aside it's the need to calculate the load that is the issue at hand. While I can guess, I'm hoping someone has done some research or can steer me to any papers on the subject (@KTSmith, @mrtree ??).

Google has not been good to me. I've come up with stuff that discusses density -no specific numbers- and strength but not weight.
 

ROYCE

Well-Known Member
#7
Typically, I'd cut a a piece to include the crotch below the chokers to avoid inversion. I've taken it such that the choker was around the crotch wood to achieve the same end.

Absolutely, but not an option. This is the challenge:rico:

Strategies aside it's the need to calculate the load that is the issue at hand. While I can guess, I'm hoping someone has done some research or can steer me to any papers on the subject (@KTSmith, @mrtree ??).

Google has not been good to me. I've come up with stuff that discusses density -no specific numbers- and strength but not weight.
I think coming up with an answer for that could be very difficult. I am thinking your wanting an equation, or rule of thumb maybe? I don't have one to share, sorry. I just have experience and am very cautious when I get to the large unions. I also make sure to cut all the large limbs off flush, to remove as much weight as possible. I would be interested to see if anyone has any solid info on this. But it's kinda like asking "how much does a red car cost?"
 

monkeylove

Well-Known Member
#8
I think that answer is probably about as hard to figure as those Burl guys have answering their weight. Didn't someoneon here a fes months bsck hsve a burl that weighed almost 10,000 lbs?
 

treehumper

Well-Known Member
#9
Yeah, I may be asking for the angels on a pin number but I gotta ask.
am very cautious when I get to the large unions.
I'm the same when it comes to it.
It's surprising that nobody has come up with some sort of equation or factor for the increased density (or weight) of crotch wood.
 

ROYCE

Well-Known Member
#10
Yeah, I may be asking for the angels on a pin number but I gotta ask.

I'm the same when it comes to it.
It's surprising that nobody has come up with some sort of equation or factor for the increased density (or weight) of crotch wood.
I know of many crews that think the last cut, closest to the ground is the heaviest. They haves gotten into trouble picking those large union sections and are surprised when they realize just what they weigh.
 

96coal449

Well-Known Member
#11
You also have to factor in type of wood and the season. Softwoods gain more weight than hardwoods during the rainy season. The exact opposite can occur during a drought. What I'm saying is, I believe softwood with its less dense grain absorbs more H2O.
 

treehumper

Well-Known Member
#12
It's a real quandary. It's a convergence of factors that are creating this dilemma. Imagine, you can't limit your pick size but must determine your crane capacity based on the estimated weight of the tree.
 
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flyingsquirrel25

Well-Known Member
#13
It does sound like a quandary. Is there a specific reason why you can't make a smaller pick? Or are we even talking about a specific tree? One other option is to go grossly over board on crane size. For safety factor... And it's always fun playing with big toys!!!!
 

KTSmith

Well-Known Member
#16
I don't think I can point you to a published formula that would adjust weight estimates for major forks in tree stems. There is research from wood tech and utilization folks on changes in wood density associated with forks. But that would be for the volumes of wood sampled, not a "correction factor" for the log or piece as a whole. I'll poke around and see if the carbon storage folks make a correction for that, but I bet they don't. Most modelers (which I am not) assume homogeneous composition of uniform geometry. That is definitely not what most of us deal with! I know this is critical information, but I don't know of any empirical studies of cutting the pieces and weighing them!
 

mrtree

Well-Known Member
#17
I also have no literature to point to. I was wondering if somebody such as George Nakashima ever wrote anything?

I remember in the early 1990s (?) there was quite a few articles on rigging and forces but I cannot remember if there was anything about crotches and "wet" wood. There has been at least one article somewhere pointing out the perils of not accounting for "excess" water in the wood (after a crane tipped!).
 
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cerviarborist

Well-Known Member
#18
Can the diameter be measured below the crotch, as well as measuring the diameters of the stems above the union? Seems you could then calculate weight as separate green logs and add them together to start easing into the ball park. If the trunk is full of concrete and steel, you're still going to have to add a fair amount of "Tennessee windage"

If the concrete and steel in the tree is the reason for taking a big pick, what about using a diamond chainsaw on those portions of the tree?
 

KTSmith

Well-Known Member
#19
Thanks Cerviar, you suggest a reasonable way to estimate volume in pieces that are not a tapered cylinder. I was thinking more about differences in density and maybe moisture content associated with forks as well as changes in volume. But so far, I've been no help with that.
 

treehumper

Well-Known Member
#20
Thanks guys. It's a puzzler. There is no specifics on density variations in unions and associated weight. Most papers I've looked into deal with timber wood and thus crotches are a not a factor. We've looked into the Stihl concrete chainsaw but the standard bar is way too small and if we were to go with something bigger it would require retensioning almost as it cuts!

Nakashima may have but it doesn't come up in a google search. I'll try it with his name in the search. @macswan it is in anticipation of this but we'll know if we got the contract Monday or Tuesday.
 
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