GRCS vs Hobbs Drop tests to destruction| volvo dropped on it

Eric Frei

2004 Video courtesy of Frans sending it to me to make it available on the net.

Copy of approval to do so, has been listed on other forums over time and heavily linked to and viewed.

I have upgraded the WMV version, old one was quite poor but low file size, new one is 55mb and very clear.

Video is 11.06mins long, was edited by Berenek, very good quality, editing and viewing.

http://www.palmtreeservices.com.au/v...vshobbswmv.wmv

Attached Thumbnails

 

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wim

I learn somthing again , nice vid.

newguy18

cool video.I would hope no one would load any piece of equipment thatmuch where its critical but then again...nah.

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old schooler

Therrin

Wow they went through quite a bit of rope doing all that.

So.... is the Hobbs really more competent than the GRCS?
It appears that way in the drop test video. Seems that the GRCS had alot more problems. What's the deal?

newguy18

I think its one of those things were the grcs has more pieces than the hobbs so therefore is more likely to come apart,from what i understand the ratcheting bollard just slides off,but i could be wrong too.

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old schooler

treevet

Interesting video. I once had a bollard cave INTO a huge decayed beech trunk with a big piece. It still held it like a porta wrap.

They show 4 guys tightening the strap. We use a 3 foot steel bar that slides over the tightening tool to get leverage, works real good. Tightening and anchorage of unit and strap seem to be a big factor in capability not being wasted. Weakest link determines how strong the system is.

You wouldn't catch me hanging a huge piece with a GRCS after seeing that vid.

rbtree

Gerry sent many of us that DVD shortly after the test. While I commend Franz and all involved for that test, it basically showed what not to do. The various tests were designed to see what would happen to the ropes and devices. They all knew failures would occur. And they did.

As was noted in the video, none of the tests allowed the loads to run, and many introduced slack into the system. So, in real work, no one would ever do anything like what they did.

The damage that occurred to the GRCS was actually less bad than what happened to the Hobbs. The self tailer was sheared off, which may have broken the screw that holds the whole capstan assembly on to the gears, which suffered no damage.

The new visor plate that is available for the GRCS is designed to allow one man to mount it, and to help it stay in place...as the Hobbs design allows. A kerf cut is made into the tree to lock the unit to the trunk.

Also, 3/4 inch and larger lines were wrapped onto the GRCS capstan, and then locked off.....Also impossible in real world use, as even 3/4 inch line only can be wrapped 3 times, which does not allow enough friction to hold the heavy loads that would require that size line.

Based on that fact alone, for butt hitching, the Hobbs is the better device, as the capstan is longer and will fit plenty of wraps. The bollard can be used in place of the capstan on the GRCS, of course, which negates the ability to emply rapid slack removal, as the load is tipping over....a key factor in limiting loading forces when braking. If the load has little chance to develop momentum, it's easier to stop it if needed,

treevet

I think these unscientific tests had merit in that they tested the limits and displayed the weakest link. Then this weakest could be improved until the total system could be rated to a rational application because if you keep strengthening the weakest link you certainly will find the next weak link, and so on and so on. My inclination would be to always go with the Bollard except for extraordinary circumstances and be rid of the moving/weak links unless you absolutely need them. The little slack you rid the system of IMO is compensated by a stronger lowering device unit. Shock load will occur in both ratcheting and non ratcheting.

RC1

treevet

I think more than that was accomplished and would not have been accomplished any other way.

rbtree

If I only had a GRCS, I would agree. But the Hobbs is capable of handling 1500 pound butt hitched loads, the GRCS probably 1000, with 4 wraps of 5/8th line....However, it requires a top groundie to keep the shock loading as low as possible....that's where rapid slack removal is so key. The SWL of 5/8th line is about 1500 pounds, but the center of mass of a snubbed off load 4 feet long would probably fall at least 6 feet. That's a force on the line of 9000 lb. Rapid slack removal could reduce that loading by 1500 pounds, easily.

And, when there's room to properly brake the load over a good distance, those forces would be further minimized.

I noticed you commented inside qoutes of my post a bit above....essentially about incompetent ground hlep....yep that is a problem, and why training of paramount importance.

rbtree

Agree, it was a great test....Heck, I know most of the guys involved.....

newguy18

Well,i doubt i'm gonna rig a volvo in a tree at any point in my career,then again,could be fun.So as long as noone gets hurt.

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old schooler

OutofMytree

Hey, this is great. I can finally get that Volvo out of my Nanna's tree.

(WLL)

i have never been able to watch any vidds from ekka what can i do? please make instructions fer a comp dummy

Eric Frei

Two things.

1/ Try right click and "save file as" then watch it from your own file.

2/ Open Windows media player, click "file" > "Open URL" and in there you stick the whole URL.

Give it a go.

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Drouin Tree Service

Good on Frans for making the video!!

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Drouin Tree Services | Excavator Hire - Drouin and SE Gippsland | Landclearing Melbourne

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