Hinge Thickness For Falling Large Diameter Trees?

[SteveSr]

Hello,

Happy Thanksgiving everyone! Here is an interesting question to ponder over turkey and football.

The Forest Service guidelines specify a falling hinge thickness of 10% DBH as a maximum. The 10% number works out pretty good for trees under 20" or so. But what about a 48" tree? 10% is 5 inches which sounds like a near impossibility to wedge over, especially if the tree is dead and has no lean or weight. Think about trying to break a true to life 5" x 48" piece of wood. Think about a huge dead, dry piece of red oak.

Here is the situation: The tree in the photo is right next to a hiking trail and has been dropping widow maker limbs onto the trail. Due to this the trail section monitor has asked me to evaluate the safe removal of this tree. The tree was supposedly alive a couple of years ago until the town put a sewer line in the vicinity of the tree and damaged the root system.

As a disclaimer I have not laid eyes or hands on the tree as of yet. I do have it on good authority that the DBH was actually measured at a little over 48". The diameter tape was only 12 foot and that was the end of the tape!

For mitigating resources/measures we have access to rope rigging and a Tu-17 Griphoist so this could belay having to wedge the tree over.

Your thoughts?

 

[SteveSr]

Website won't take photos... Will try again later.

 

[Marley5]

48" is absolutely massive

 

[buzz sawyer]

I agree, 4.8" is a lot but 10% is maximum as stated, not minimum. I would take into consideration the quality of the wood and the amount of lean and how much weight is in the top.

 

[J D]

Well... I haven't cut oak (or any deadwood that big)... but for redwood & cypress around that size I would generally have a hinge around 3" thick... sometimes with the center bored out

 

[ZeroJunk]

And, here I was thinking it was 1/3 . Unless it was leaning too much. I dropped a 48 inch white oak a couple of years ago. Notched it about 1/3 and knocked it out with a sledge hammer. Went without incident.

 

[SteveSr]

I just added the photo... No Server Error this time!

 

[ZeroJunk]

I'm confused. Hinge thickness, notch depth ?

So, you are cutting to a certain hinge width and doing the rest of the work with a wedge.

That tree would scare me. I have several red oaks here in that shape that I won't touch.

Particularly not start banging on it.

 

[PV Hiker]

Could be a lot going on inside that tree. Limbs fall on their own and if chainsaw causing vibration could send another limb down. Risk factor of safety.

You'll have to visit the site to see and sound the tree to evaluate if there is holding wood or rotted out around the trunk base.

Looks like in the picture there is some weight to the side falling toward the open field. Is that fence in the drop zone?

Using a grip hoist might be better than banging on a wedge sending upper limbs down. Rig the grip hoist with redirect to not put the operator in the fall zone (dead tree and limbs shatter and fly many directions). If using pulling aid, consider using a bore cut behind the hinge just as you would felling a heavy leaner as the tension on the line is pulling the same.

There is more going on than just thinking about cutting face cut and setting hinge depth, a field trip is always best and evaluate from there. Good luck.
Patrick

 

[SteveSr]

I'm confused. Hinge thickness, notch depth ?

Hinge thickness is actually the fiber that gets bent over.

The notch depth sets the length of the hinge. USFS says >80% of DBH.

So, you are cutting to a certain hinge width and doing the rest of the work with a wedge.

Wedge(s) would be one possibility and if we get that far we might try that. However, we also have access to rigging (TU-17 griphoist) as a backup plan.

That tree would scare me. I have several red oaks here in that shape that I won't touch.

That is why I NEVER say that I am going to remove a tree and I am only there to evaluate if the tree can be removed safely.

I live in an older neighborhood and have seen several considerably smaller red oaks come down due to rot at the base. I will be checking this one carefully for this defect.

Particularly not start banging on it.

My plan is to use the attached rigging from a safe distance to shake the top of the tree to see if any more of the top is ready to fall. This should get rid of any widow makers.

 

[rwoods]

Only an armchair call from a firewood hack looking at a picture, so please don’t take offense. This tree is one you confront with plenty of experience. With all due respect, if you have no experience in felling large dead oaks, I seriously doubt you should be advising whether the tree can be safely felled, particularly, since what is safe depends heavily upon the felling method chosen and the skill, experience and judgment of the one behind the saw.

In my opinion, the one cutting this tree should be experienced and confident enough to size the situation. If not, he shouldn’t be cutting the tree without the direct supervision of someone who is. If the cutter is only seeking an opinion, ideally, it should come from one who has been there and done that many times.

Pulling on the tree to shake out widow-makers is not fail-safe as it can increase the risk of a widow-maker.

Ron

 

[J D]

@Kodiak Kid might have some valid input.
If dead oak has a tendency for the roots to rot & its looking compramised at the base I'd be putting a decent wire rope through that fork & pulling on it from a safe distance with the biggest machine I could get my hands on. What's the access to the area like?

 

[SteveSr]

Pulling on the tree to shake out widow-makers is not fail-safe as it can increase the risk of a widow-maker.

Can you elaborate on this? It seems counter-intuitive.

 

[SteveSr]

@Kodiak Kid might have some valid input.
If dead oak has a tendency for the roots to rot & its looking compromised at the base I'd be putting a decent wire rope through that fork & pulling on it from a safe distance with the biggest machine I could get my hands on. What's the access to the area like?

This is close to a sewer line easement and we will have rigging that can pull 4000 lbs. Unless the base is severely compromised I doubt that we could pull it over. However, we might be able to pull part of the top out of it.

 

[firekindler]

Hello,

Happy Thanksgiving everyone! Here is an interesting question to ponder over turkey and football.

The Forest Service guidelines specify a falling hinge thickness of 10% DBH as a maximum. The 10% number works out pretty good for trees under 20" or so. But what about a 48" tree? 10% is 5 inches which sounds like a near impossibility to wedge over, especially if the tree is dead and has no lean or weight. Think about trying to break a true to life 5" x 48" piece of wood. Think about a huge dead, dry piece of red oak.

Here is the situation: The tree in the photo is right next to a hiking trail and has been dropping widow maker limbs onto the trail. Due to this the trail section monitor has asked me to evaluate the safe removal of this tree. The tree was supposedly alive a couple of years ago until the town put a sewer line in the vicinity of the tree and damaged the root system.

As a disclaimer I have not laid eyes or hands on the tree as of yet. I do have it on good authority that the DBH was actually measured at a little over 48". The diameter tape was only 12 foot and that was the end of the tape!

For mitigating resources/measures we have access to rope rigging and a Tu-17 Griphoist so this could belay having to wedge the tree over.

Your thoughts?

View attachment 1222720

Yeah, with no lean or limb weight 5" seems like a lot. But with that diameter trunk you've got options, as long as the wood is solid. One is to begin the back cut before the face cut. Cut in enough to set snugly a fast tapering short wedge with enough room for the bar to fit in the kerf in front of it. That should keep it from sitting back. Then put in the face cut, but deep enough to really undermine the center of gravity. With some snags with hardly any top weight I've faced over 50%. Just be sure to not get pinched on the face cut from the wedge in the back. Then finish the back cut, with a good complement of other wedges. Some I really like are the 7" and 10" double tapers, that start off fine to get started and then get much thicker in the rear to finish it off. Also the rifled wedges for doubling up. And my secret weapon is the 15" with rounded leading corners. If I don't want to cut the back any deeper, I'll set it right behind and parallel to the holding wood and side wedge from there. The rounded corners keep it from digging in to the holding wood and getting stalled. And especially with a narrow hinge the standard wedges could actually poke through the hinge if it doesn't drive straight. But if it's not too far from the road, that griphoist is your ace in the hole. But I wouldn't want to carry it (or the rest of the rigging) very far at all. Good luck!

 

[firekindler]

Yeah, with no lean or limb weight 5" seems like a lot. But with that diameter trunk you've got options, as long as the wood is solid. One is to begin the back cut before the face cut. Cut in enough to set snugly a fast tapering short wedge with enough room for the bar to fit in the kerf in front of it. That should keep it from sitting back. Then put in the face cut, but deep enough to really undermine the center of gravity. With some snags with hardly any top weight I've faced over 50%. Just be sure to not get pinched on the face cut from the wedge in the back. Then finish the back cut, with a good complement of other wedges. Some I really like are the 7" and 10" double tapers, that start off fine to get started and then get much thicker in the rear to finish it off. Also the rifled wedges for doubling up. And my secret weapon is the 15" with rounded leading corners. If I don't want to cut the back any deeper, I'll set it right behind and parallel to the holding wood and side wedge from there. The rounded corners keep it from digging in to the holding wood and getting stalled. And especially with a narrow hinge the standard wedges could actually poke through the hinge if it doesn't drive straight. But if it's not too far from the road, that griphoist is your ace in the hole. But I wouldn't want to carry it (or the rest of the rigging) very far at all. Good luck!

@HumBurner

 

[PV Hiker]

Sure you can try throw line on the upper limbs and pull and see if they snap off. The more the top is removed the better when cutting at the base. By pulling on the top it can give you information as to how the reaction is down near the base for movement and for rotted roots or trunk. Might get lucky. If anything you'll know more about the tree.

Like you say, the target zone includes the use trail, then what ever you do when you touch it, it is best to finish it for creating a hazard to the public users of the trail.

 

[Gologit]

Only an armchair call from a firewood hack looking at a picture, so please don’t take offense. This tree is one you confront with plenty of experience. With all due respect, if you have no experience in felling large dead oaks, I seriously doubt you should be advising whether the tree can be safely felled, particularly, since what is safe depends heavily upon the felling method chosen and the skill, experience and judgment of the one behind the saw.

In my opinion, the one cutting this tree should be experienced and confident enough to size the situation. If not, he shouldn’t be cutting the tree without the direct supervision of someone who is. If the cutter is only seeking an opinion, ideally, it should come from one who has been there and done that many times.

Pulling on the tree to shake out widow-makers is not fail-safe as it can increase the risk of a widow-maker.

Ron

Well said.

 

[rwoods]

Can you elaborate on this? It seems counter-intuitive.

A shock load can weaken a dead limb without causing it to fall. The test pull(s) could lead one to conclude that the remaining limbs are strong enough to remain attached and intact during the fall when in fact one or more limbs might now be weaken enough to break during the stresses of the falling Thus, standing alone, trying to shake widow-makers should not be considered a fail-safe test.

Ron