Rated recovery points.......are they really?
Submitted: Sunday, Aug 19, 2007 at 21:29
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Martyn (WA)
Forumites,
Really poops me to have to ask this question, I’ve searched in the archives and I’m searched a few other sites. Can anybody help with some factual advice. I’m
well aware that the recovery equipment you buy is rated to what ever the manufacturer specifies, in some cases fourby magazines test these devices. My query is more around the mounting point, bull bars will be rated, but what about when you attach rated hooks and plates to the chassis, you use rated parts the bolts the plate and you mount the plate or hook on a clean unpainted surface, torqueing the bolts to the specified torque. What says the chassis rail which in some cases is only maybe 3mm (or less) thick is rated to the same as the bit you are attaching. If the bolts go through the box section that’s better, providing you have something between the sides to prevent the chassis rail collapsing at the correct torque for the bolts.
If you weld the plate to the chassis the chassis could tear or bend when subjected to significant loads, the weld strength will be
well in excess of anything to can attach to it, within reason. So when your local fourby agent attaches a rated recovery point to your vehicle is the recovery point rated to the strength of anything you attach it to or just the chassis rail? What do fourby shops use as a guide or legislative document saying that what they have now built is a rated recovery point, to the same rating as the hook or plate they’ve attached.
Anybody shed any light on this one?
Thanks in anticipation to anyone who can assist
Reply By: Ingtar - Sunday, Aug 19, 2007 at 23:07
Sunday, Aug 19, 2007 at 23:07
If you were to go asking for 'rated recovery points' to be fitted to your vehicle, and a letter stating what they would be rated to, can be very expensive. I have heard of people being quoted thousands for this.
You raise a good point, and the rating of whatever hook or plate is only to say that that particular item will handle the load. How they are fixed and used is a different matter.
While 4wd shops may fit these I think if you went asking for the documentation they will become a little less helpful. Other than that I can only assume they work on experience as to what has worked.
As a personal opinion I like the idea of recovery hooks being mounted through both bullbar and chassis because obviously this provides a greater surface area, and most bullbars are thicker and with more than the typical 2 bolts. This spreads the load better.
However I know of other people who prefer to have the recovery points attached only to the chassis and not the bullbar, with the logic that if something goes wrong there won't be a bullbar sent flying through the air.
AnswerID:
258002
Follow Up By: traveller2 - Monday, Aug 20, 2007 at 15:18
Monday, Aug 20, 2007 at 15:18
Be wary of fitting too much to late model vehicles with crush zones built into bumpers and bullbars, looks funny when the bullbar is 60mm further forward on one side after a snatch.
At a club level we tend to go back to using a winch in preference to snatching to avoid high impact loads on what are much lighter/weaker vehicles these days.
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Reply By: Richard Kovac - Monday, Aug 20, 2007 at 00:07
Monday, Aug 20, 2007 at 00:07
Martyn Hi
As said it would cost a lot of money to get a documented / certerfied Recovery point / or mounting point..
I don't think anyone would know what to rate it too. a 6mm bolt will hold 3 tonne (but jerk it and it will brake).
The hooks, eyes etc. you can buy from 4WD or lifting gear shops are rated to maybe 3-4 times the load needed to be used for..
Why do you ask the question for?
Regards
Richard
AnswerID:
258007
Follow Up By: Martyn (WA) - Monday, Aug 20, 2007 at 08:51
Monday, Aug 20, 2007 at 08:51
Richard,
I "present" a bit of a technical tips session at the 4wd club I belong to, I was asked this question after a group had a bit of a discussion around a
camp fire on a recent trip. I like to present the best facts that I can find and this
forum in the past hasn't let me down.
I've got my own slant on this being in the engineering game so I was just seeing if there was any official document I could read up on.
I'm not sure about the 3 to 4 times comment, when a snatch strap gets loaded up and the vehicle doesn't move the loads on the strap and associated gear will be right up there.
I wouldn't like to suspend my Patrol on a 6 mm bolt either jerked or otherwise, are you sure about that?
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Follow Up By: Graeme - Monday, Aug 20, 2007 at 09:35
Monday, Aug 20, 2007 at 09:35
You might want to contact the "Cross Country Vehicle Club" in
Wellington New Zealand as they publish minimum standards for manufacture and mounting equipment including these items.
They are very helpful with this type of question.
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Follow Up By: Martyn (WA) - Monday, Aug 20, 2007 at 10:43
Monday, Aug 20, 2007 at 10:43
Thanks Graeme, I'll try that route
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Follow Up By: ross - Monday, Aug 20, 2007 at 11:24
Monday, Aug 20, 2007 at 11:24
Martyn ,all approved lifting gear sold in Australia has a safety factor of 3 or higher built into the SWL.
Hooks that can be attached to a crane have a safety factor of 4 ,or they did last time I checked.
Of course pulling horizontal loads from bog holes is almost impossible to judge without load testing equipment.
FollowupID:
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Follow Up By: Martyn (WA) - Monday, Aug 20, 2007 at 14:34
Monday, Aug 20, 2007 at 14:34
Ross,
Thanks for the comments, I have no problem with the gear being rated it's what the "gear' is attached to that I'm chasing a rating for, like the chassis rail. Having the hook rated three times the safe working load is all
well and good but if the bearing in the head sheave is rated less that's what the SWL is if you know what I mean.
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Follow Up By: Richard Kovac - Monday, Aug 20, 2007 at 21:36
Monday, Aug 20, 2007 at 21:36
Martin Hi
that's why I asked, you wont to no the answer that's good.. :-)
I would try someone like TL engineering or sling rig
grade 5 bolt = 120000 lb/in2
grade 8 bolt = 150000 lb/in2
.250" x .025" x.7854 = 0.0490875 in2
G5 0.0490875 in2 x 120000 lb/in2 = 5890.5 / 2240 = 2.629 ton
G8 0.0490875 in2 x 150000 lb/in2 = 7363.125 / 2240 = 3.28 ton
and no I wouldn't hang my 3.2 tonne off a 1/4" bolt ever .. LOL
Cheers
Richard
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Reply By: AndrewX - Monday, Aug 20, 2007 at 09:27
Monday, Aug 20, 2007 at 09:27
Use only the following:
The hooks fitted to your 4wd.
Your hitch receiver.
NEVER use the "tie down" plates. They are only for transport security.
If your vehicle doesn't have recovery points NEVER use a snatch strap.
I also have a feeling that your vehicle might sink right into the mud and disappear before you finish weighing up the pros and cons and come up with a decision lolol.
AnswerID:
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Follow Up By: Martyn (WA) - Monday, Aug 20, 2007 at 14:41
Monday, Aug 20, 2007 at 14:41
Andrew,
By your response I don't think you have grasped what I was asking. I'm
well aware of tie down points etc I was chasing some factual data about the rating of what you attach rated tow point too, aka the chassis rail. From what I understand we as in the general public accept that when a 4wd accessory fitter fits recovery points these are then rated to swl of the stuff we attach to it, I'm after how the 4wd accessory fitter comes to this conclusion if he doen't have any manufacturer specs to work with.
Trust me, I wouldn't loose my vehicle making a decision about what to attach my recovery equipment to and if it was strong enough.
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Follow Up By: AndrewX - Tuesday, Aug 21, 2007 at 09:36
Tuesday, Aug 21, 2007 at 09:36
Au contraire Martyn it is you who hasn't grasped it.
Use only the following:
The hooks fitted to your 4wd as original equipment by the manufacturer.
Your hitch receiver if you have one.
DO NOT USE anything other than above!!!
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519501
Reply By: Member - Brian H (QLD) - Monday, Aug 20, 2007 at 15:42
Monday, Aug 20, 2007 at 15:42
I guess you have gone down the avenue of asking the makers IE Toyota, Nissen, Holden etc.
Or for that matter bullbar makers and see what they say about the ratings where you mount. As they say they do research and development on these (that why they are so expensive :) ) so I would assume they MUST know.
Brian
AnswerID:
258095
Reply By: Mike Harding - Monday, Aug 20, 2007 at 16:30
Monday, Aug 20, 2007 at 16:30
Hi Martyn
I suspect most of the 4WD
places use that old tried and [not always] trusted engineering maxim of "she'll be right mate".
Mike Harding
AnswerID:
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