Tow hook mounting

[85BJ73]

Ok, I have seen a couple of posts here, and been pointed in the direction of one when I asked a question about recovery hooks, all state rated hooks must be used. Fair enough, but the mounting of them is the part that seems to come un-stuck. ##EDIT: Please note I am refering to vehicles with a chassis or a lighter form of chassis, and no other form of body, nor am I referring to factory mount points, I am referring to the fitment of the recovery hooks available from Repco, Supercheap and other places and no other form of recovery point. This is a guide for those who wish to mount the hooks, and may not be aware that simply drilling a couple of holes and bolting on the hook may not be sufficient. end edit##
Please be aware that I am not trying to start arguements with this post, nor am I trying to preach to those whom have been doing this activity/sport for longer than me. Nor am I trying to tell inspectors what to do/how to do their jobs. What I am trying to achieve is to guide those who may be new, or don't have much mechanical/engineering knowledge.
I talked to the local LTSA certifying engineer, a heavy transport certifying engineer, and drew on my own experience from working on diggers and bulldozers.
Also I have seen many different mountings used on club trips and fundraising trips, where the mounting is unsuitable, but they were permitted to attend due to the hook being a rated one, regardless of the mount.
Now, for the technical part, most people seem to get the hook, and then search for somewhere to mount it. I have seen them mounted to the front of a Suzuki Vitara, direct to the chassis on the front. "So what?" I hear a few ask, well, the chassis is only 3mm thick, and, the worst part, the chassis is welded together along this surface, with a 3mm overlap, making it weaker. Then the holes are drilled and the whole lot is bolted up.
Now, according to my theory, and backed up by the two gentlemen I spoke to, most, if not all chassis are too thin, less than 5mm, hence too weak for the stresses we place on them during a recovery, and especially too weak to have the hook bolted directly to them, with no support.
It was pointed out a modified seat mount requires a 50x50mm x5mm thick steel plate, with m6 radiused corners and all edges to be chamfered before it will pass certification. Now, think about that, how much load is on a seat? Only a fraction of a recovery hook!!
Both of the people I consulted suggested a 5mm thick plate, the width of the total EXTERNAL width of the chassis be fitted between the hook and the chassis. That way the webs of the chassis will support the hook. The inside of the chassis should also be reinforced, with a similar plate that will fit inside the webs, or in lay mans terms, sit on the flat, preferably no less than 30mm longer at each end than the hook.
As I have a tendancy to "over engineer" I suggested a piece of angle iron be installed inside the chassis, as this will not bend, and allow the hook to tear out of the chassis. I was told it would be the best form of reinforcing, provided the square edge is ground off to prevent it "tearing" the chassis. Also a channel on the outside of the chassis, once again I was told it would be best, but may be hard to get one that fitted snuggly around the chassis, also there may be things on the chassis preventing the installation of said channel section. Another point too, was trying to keep the ingress of water out from between the plates, and preventing corrosion there.
I hope this may provoke some thought as to the reinforcing of your recovery hook position.
Once again, I am not trying to preach, or tell any one what the should or shouldn't do, nor how to do their job, I am only passing on the information that I got/was advised, by two people in the industry who were good enough to give me some of their time.
##EDIT:Basically, if you look at your mount point, and think it may not be up to the task, or it is thinner than 5mm, ask someone and or reinforce it. End Edit##
**Edit: Sorry for the length of this post**

[TJ]

Are you suggesting the manufacturer of the truck are wrong when for Jeeps they have a factory option to put rated tow hooks on the front and rear end of the chassis on a Wrangler? These holes are already there.

My concern here is that:

1) You are talking to certifiers about something that is not an issue at this stage and if more and more people start talking to them about non-issues, it becomes an issue. I agree precaution should be taken as to how you mount them and if in doubt consult an engineer (not necessarily a certifier). We have enough s*** to deal with the regulations currently, don't want anymore.

2) You are generalising about all makes and models, which is not true. Some are unibody construction, where mounting a recovery point is more difficult and needs thinking through.

3) Rated tow hooks are not the only form of recovery points on truck (e.g. D-mounts, Pintle hooks, etc..)

I am all for safety, over engineering and discussion. But please chose your avenues carefully. I know not all certifiers are the same, but at the end of the day they are in the business of certifying things. You give them a chance and they will want to certify that the foam in your seat is safe enough to handle your weight!!!!!

[TJ]

It was pointed out a modified seat mount requires a 50x50mm x5mm thick steel plate, with m6 radiused corners and all edges to be chamfered before it will pass certification. Now, think about that, how much load is on a seat? Only a fraction of a recovery hook!!

A seat does more than just carry the load of the occupier, it actually keeps you restrained with the help of a proper seatbelt. If the seat becomes dislodged in an accident, your seatbelts are next to useless.

I am not trying to start an arguement with you, I just like discussing things through on their merit.

[85BJ73]

You are right in a couple of things, not all vehicles are the same, and I was only meaning the type of vehicle I mentioned, with a form of chassis, you will note I did not mention manufacturers mountings, nor did I mention unibody construction, as I had not looked into, nor dealt with them. I was merely trying to guide those with the sort of set up I was talking about. I was not trying to generalise at all, maybe in hindsight I should clarify my post, but, as I did not mention the types of vehicle and factory mounts, I took it most would understand I was referring to a specific type of vehicle. not all.

As for your points, let me clarify something, I know both of the people concerned, and I spoke to them in an informal situation, and you can rest assured, neither of them want to see ANY MORE regulations bought in, as it increases their work load. And hooks DO NOT count a s certifiable modification, nor do either of them see they ever will.
Also, I was discussing hooks, as most beginners are only looking at hooks, not pintles or d loops etc.

The plate on the set is fitted UNDER the floor, not on top, to stop the bolt pulling through the floor, which is the point I was trying to make, the bolt head and a washer is not enough.

Also, another thing, it is better to be involved at the start, if regulations are bought in, so you can have input, rather that have something thrust upon you that is un-workable. Why do you think the NZHRA got involved when the certification laws were being worked out? If they hadn't, then you wouldn't be able to modify anything, at all, period. That is what the LTSA wanted.

If my post is too objectional, or too many think it is incorrect, then I will happily delete it.

[Sadam_Husain]

You make good points 85bj73 coz theres no point having a nice 10000 lb hook with M12 8.8 bolts if its comming flying through the air at you or someone else coz whatever it was attached to wasnt structurely able to withstand the forces and loading

[TJ]

If my post is too objectional, or too many think it is incorrect, then I will happily delete it.

Not at all, I like technical discussions. We should have more of them here. I am late for a meeting, so will back to your other points later.

[85BJ73]

Cheers, that is the point I was trying to make, basically, look at your mounting, if it is less than 5mm, there abouts, reinforce it. All I was trying to do was suggest a way of reinforcing it too.

[KiwiBacon]

My concern here is that:

1) You are talking to certifiers about something that is not an issue at this stage and if more and more people start talking to them about non-issues, it becomes an issue. I agree precaution should be taken as to how you mount them and if in doubt consult an engineer (not necessarily a certifier). We have enough s*** to deal with the regulations currently, don't want anymore.

Fair enough concern.
But car certifiers aren't engineers, they're generally mechanics working to rule book written by others. Heavy transport certifiers are qualified engineers who are contracted by LTSA (or whatever they call it now) to do the work. There are only about 80 of these guys in NZ (http://www.rtce.org.nz) and they've already got plenty of work. 4wd's are not their market and they have no interest in submitting such things to the legislators.

I have a full Finite element analysis program (FEA) at my disposal, the results are certainly interesting.
For example, the square hitch receiver pins that people thread a strop thru are far weaker than the towballs that people know not to recover with.

[yorick]

I have a full Finite element analysis program (FEA) at my disposal, the results are certainly interesting.
For example, the square hitch receiver pins that people thread a strop thru are far weaker than the towballs that people know not to recover with.

Forgive my ignorance, WTF is a "square hitch receiver pin"

[85BJ73]

Another thing to consider too, if we take ownership, and prevent something going wrong, then there will be no need for regulations.....but I realise this is impractical/unworkable.

I have based my information on my past as a NZHRA member, being a close personal friend with a LTSA certifier, and having battles in the workplace with the heavy transport engineer, and seeing what both of them have had to put up with, and the type of people they have to deal with. Both of them said the same thing, the more things you regulate and that require certification, the more dickheads they have to deal with, the more work they have to do, and they are both of a similar opinion, a lot of the regulations and items that need certification need to be reduced, and they both get a list of things regularly that the government/LTSA are looking to see if they need certing, and most of the time they are saying no.
Also of interest, 4x4's seem to figure very low on the agenda, at least around here. I guess we have been off the radar a bit, luckily for us.

Once again, my original post was meant as a guide/to make people think, not as a be all and end all, and not aimed at all vehicles, but only the type I mentioned, and to be used in context, the fitting of rated hooks that people can buy from Repco, Supercheap etc, etc.

[KiwiBacon]

I have a full Finite element analysis program (FEA) at my disposal, the results are certainly interesting.
For example, the square hitch receiver pins that people thread a strop thru are far weaker than the towballs that people know not to recover with.

Forgive my ignorance, WTF is a "square hitch receiver pin"

Sorry, been talking to too many yanks.

Square receiver aka Hayman Reece is the towbar type with a 2" square tube that is held in by a pin.

[pathfinder67]

I assume it is the same as a hayman reese set up.

[85BJ73]

At the risk of worrying some people, I spent lunch with the local certifier, and asked another couple of questions. I was told that as far as the LTSA side of things go, they are really only interested in modifications that affect a vehicle in it's normal every day operation on public formed roads, that affect normal operation in normal conditions. Hence tow or recovery hooks are not even considered, nor are they likely to be, as many factory points would then have to be looked into, and that would create a nightmare even the LTSA would not be interested in. Now, that is only the local guy's take on things, but as he was actively involved from the outset, and still is, I think it is safe to say that is how it looks for the moment. Also, just of interest, he is one of a few (that I am aware of) who is a certified automotive engineer.

I don't believe the heavy traffic side of things will worry us, as we do not require a COF, and as such fall well outside their spere of influence.

[TJ]

I do realise that your discussion was with a personal friend and may not mean much, but I was just suggesting that we should be a bit cautious in our discussions with people in the certifying industry. I have nothing against them, they have a job to do and they just do it. But its kind of like talking to politicians sometimes, you never know who picks up an issue and makes it their hobby horse.

As for your specific technical points, I fully agree - safety first. If you think it is safe enough is not good enough. Get somebody who knows what they are doing have a look (wihtin reason). If you happen to be the area expert, well just have a chat to yourself!

I have rear recovery points which are an overkill because they are attached to the rear cross member and the chasis with 18 grade 5 and 8 bolts!!! That thing is not going anywhere without doing some serious damage to the rest of my rig. And no, I did not have to drill any new holes in the frame, they were all there already for one reason or another. In fact, in the FSM it clearly warns about drilling holes in the top and bottom surfaces of the frame as well as the holes being a minimum of 1.3" from the edges on the side walls (and spread apart). Who thought Jeep could make such a logical statement!!

However, by doing that I have now shifted the weakest link to somewhere else. Most probably the attachment points and the thing being recovered. I can only control my own behaviour, so I want to be over cautious.

I know some clubs have a strict checking policy and guidelines to follow. It is up to the Trip Leader to refuse someone a ride along if the truck presented is deemed unsafe in any manner (as it puts others at risk of damage and injury). So if you were uncomfortable on a trip, raise the issue with the Trip Leader.

[85BJ73]

I know what you mean about a factory mount, my Toyota ones in the winch bar go through 5mm steel, I opted to add another 5mm plate braced and welded to the bottom of the bar, and then bolted to the chassis, giving a box like structure 10mm thick!!
I know some ceritfiers can be really anal, and I am lucky that the local one is not like that.
I am confident in my own mounts, but decided if I was going to post something here, I had better make sure it was not just my opinion, but I had some knowledge other than mine behind me.
I also admit I should have clarified that I was meaning vehicles with a chassis, or form of chassis, such as Landcruiser, Vitara, HiLux etc, lesson learned for next time, make sure I am more precise.
As for the mounts and trip leaders, it can be hard to raise a concern, when you have just seen some one do just that, and get a hard time, along the lines of "I know what I am doing, if ya doubt me don't come" and a few other comments using some lingo I won't put on here.
I have to travel a fair distance to some trips, as do others no doubt, and I am only trying to make a suggestion and help those who maybe thought drilling a hole in the chassis, body mount etc would be strong enough.

[mudlva]

Just to add my two cents worth and in the dealings with the chap thats does my lvvc's

to be fear he realy doesnt give a crap about my recovery hooks or mounts etc as long as when you install the said hook etc you arnt structually weakening the chasis by drilling to larger a hole or in the situation of having a bolt pass throu the chasis then it would require a spacer pipe or simmilar so not to crush the chasis.

his main concern was that the brakes worked good that the new seats and belts worked good and basicly that the motor trans etc was mounted soundly.

of couse he did look at the hooks and all the bar work but its not up to him to decide if they were strong enough to do the job that we wanted the gear to do but that they were mounted so that i event of a crash that the bars etc wouldnt become a hazzard to either our vechiles or to other vechiles etc.

the mentioning of reinforcing the chassis is sound information but in the years that i have been involved in this sport the main chassis failure seams to be the parting of vechiles chasis members that have been welded by the manufacture to other sections eg pajero rear hook mounts .

as a general rule of thumb the chasis side will distrort before ripping, this hopefully will be pick up before the next big snatch and the rope reposistioned or changing to a second method of recovery. with the repair being a completely differant subject

cheers and keep four wheeling

[85BJ73]

Original post edited, maybe it will remove some confusion? Thanks TJ for your feedback too, I have a lot to learn about posting on some forums, and I see I need to be more precise too.

[TJ]

Original post edited, maybe it will remove some confusion? Thanks TJ for your feedback too, I have a lot to learn about posting on some forums, and I see I need to be more precise too.

You are welcome mate. I read some of the stuff I wrote a while back and say to myself what was I thinking (more like not thinking)

May be we should put together a leading practice guideline for mounting recovery points on a vehicle? And then that becomes part of the sticky or FAQ in the technical section. I am sure all of us can learn from each other.

[85BJ73]

Yeah, that sounds like a good idea to me. maybe we can get a couple more people to give some ideas, then do like you say, and put it where it can be acceessed easily for reference/guide to help those out who may benefit from the knowledge of others.
Any more suggestions?

[PeterVahry]

There are many issues and opinions about tow hooks and as TJ suggested, although your own one may be over-engineered the other end can be a mystery.

One writer mentioned the use of crush tubes through the chassis which is an aspect often ignored. The use of suitable bolts and maintaining their tightness is paramount. If a chassis crushes slightly, the strength value of the fastener changes dramatically.

Tow balls may be stronger than a pin through a receiver hitch but that pin does not have the weight of a tow ball and the pin failure would possibly be less dramatic since it is located at both ends and prone to bending. Of course if a hook is fixed to a tube that is restrained by a pin, then the weight if the pin failed is frightening.

Which component should be the one to provide the failure point anyway? Maybe it should be the rope/strop?
Should the rope always have a second tether at each end to restrain any connection failure? That would reduce the fear of projectiles perhaps. Then we could feel slightly safer maybe pulling an unknown engineering value under high load.

This is one of those debates with almost infinite variables but some good options for reducing risks.

[KiwiBacon]

Tow balls may be stronger than a pin through a receiver hitch but that pin does not have the weight of a tow ball and the pin failure would possibly be less dramatic since it is located at both ends and prone to bending. Of course if a hook is fixed to a tube that is restrained by a pin, then the weight if the pin failed is frightening.

My point with the receiver pin was this:
Everyone knows it's bad form (dangerous) to recover using a towball. But many people are instead using points which are actually weaker.

Many towbars (the frame, not the ball) are also not strong enough to snatch from, but others certainly are. If your square receiver towbar is strong enough to snatch from, then use a tube with a shackle attachment, do not put the strop around the pin.

[85BJ73]

Good points are coming through here. Peter raises another couple of good points about restraining the rope/strop, something I had not thought of. The most frightning recovery I saw was in the field, when I saw a 25mm hawser part company, one end taking out the "A" pillar of the truck being recoverd and on through the back cab panel, and the other end seriously damaging the rear armour plating on an M113.
I know my truck's points are more than strong enough, and when I go to do a recovery on another vehicle I don't know, I tell the driver I reserve the right to check the recovery point, if possible, and if I am not happy with it, then I will tell the driver I choose a to hitch up to, or I don't do the recovery, simple really. That said, if there is no choice, or in the case of it has to be done now, or the situation will deteriorate further, then the recovery is done.
I also share the concern over people using the socket and pin type towbar point, with a rated hook on the towbar tongue, while the hook is rated, the pin is not. One person who was questioned about it was heard to say "mate, I towed a bayler with that, it'll never let go" I guess he has never thought about how much weight his vehicle will be when it is stuck, and the stresses involved when the recovering vehicle, say my 2.2 ton 'cruiser pulling on it, will generate!!
I know through my work with heavy machinery, the weight/loading increase dramatically when stuck, pulling lifting etc.
The way I see it, and what I am trying to do is excatly what is happening, lets talk about it, get some good ideas that all agree on, then educate/help/guide people in this subject so we all can be safer!!
Maybe, as already suggested, once the good ideas have come through, someone could post it in the tech section, as a guide only??
Cheers all, and the more feedback/suggestions we get, the better, keep 'em coming guys, this can only benefit us all.
Shane

[KiwiBacon]

Good points are coming through here. Peter raises another couple of good points about restraining the rope/strop, something I had not thought of.

I'm generally against additional restraints of the rope. These are my reasons why:
Assume it's the tow vehicle that has lost it's mounting hook, it makes the explanation easier.

Firstly the weak point should always bee the rope/strap. This is the softest part which will do the least damage when it lets go. I have been in situations where straps broke, but I'm sure others experience will eclipse mine here.
If you have a mounting point let go, the strap is suddenly in full recoil and the tow vehicle is probably still moving forwards. The secondary strap then has to take the momentum of the strap heading backwards in full recoil with attached hook and the tow vehicle still heading forwards.
The forces involved here can easily be as great as those which just removed a tow hook from the tow vehicle. In addition, the mounting point of the secondary strap is probably the second choice and weaker than the mount that just let go.

The result would be a few extra projectiles (snatch strap with rope, second mount etc) heading for the stuck vehicle along a modified path.
If one hook lets go, then you know the path it'll take. If the second strap and hook join the party then you don't know where it's headed.

These "rated" hooks intrigue me. I have a new one here which I plan to model up and run through COSMOS FEA to see what the rating actually means. There's no indication whether their numbers are for a one off failure (overload) or multiple use (fatigue) or even what standard (if any) they have been designed and manufactured to.

[tgaguy1]

[quote="KiwiBaconThese "rated" hooks intrigue me. I have a new one here which I plan to model up and run through COSMOS FEA to see what the rating actually means. There's no indication whether their numbers are for a one off failure (overload) or multiple use (fatigue) or even what standard (if any) they have been designed and manufactured to.[/quote]

I was always told that the 10000lb rating is the force at which the hook will straighten and let the strap go. It will be of interest to see what conclusions you get with the COSMOS FEA results.

[85BJ73]

Hmmm, very valid point about retraining a strop, maybe a winch blanket draped over one as per a winch cable?? But we are getting off subject a little, but none the less valuable discussions.

I too would be interested in the findings you come up with in regards to the hook. One question though, does your program account for the type of material and the method used to manufacture/form them?

[KiwiBacon]

Hmmm, very valid point about retraining a strop, maybe a winch blanket draped over one as per a winch cable?? But we are getting off subject a little, but none the less valuable discussions.

I too would be interested in the findings you come up with in regards to the hook. One question though, does your program account for the type of material and the method used to manufacture/form them?

Yes I like the winch blanket idea. Anything that can work like a parachute.

The program I use will display material stress and elastic deformation (i.e. will show flex, but not permanent bends). To relate that back to the material used you've either got to know what it is or use some basic tests to find out.
It can't account for things like casting flaws which make extremely weak spots in the material.
For steel there's a very good hardness/strength relationship. So simply filing a corner of an unknown piece of steel and filing a piece of known strength steel gives a result that is good enough for many applications.
I'd expect recovery hooks to be of a softer material like mild steel. High strength steels aren't much use in such a piece as to use the higher strength the hook has to flex a long way.

I'll get started on it once I've done the banking. Which I should have done this morning.

[Sadam_Husain]

I was always told that the 10000lb rating is the force at which the hook will straighten and let the strap go. It will be of interest to see what conclusions you get with the COSMOS FEA results.

And never under-estimate what happens when a strop lets go, theres some posts on here from another forum member that had a strop that let go come in through his rear window out the windscreen and back in showering him with glass and crap
You wouldnt want to be in the fireing line with that, I always try and use my passenger side hooks to try and minimise my chance of being in the fireing line if something does go wrong

[Sadam_Husain]

Yes I like the winch blanket idea. Anything that can work like a parachute.

at upto 500-600kph it would need to be a pretty big blanket

[85BJ73]

Yup, true, but something has got to be better than nothing, and I agree about hook choice too, you gotta be aware of where object may go if they let go.

[PeterVahry]

Think about the dynamics of a secondary retaining rope, which is probably going to be lighter than the main rope.
The first rope breaks free under load, maybe also with some steel attached, and the stretched rope shrinks and heads for its other end. The restraining rope absorbs much of that acceleration, although not all probably. The lighter rope then fails but with a lower level of energy stored. The combined absorbing of energy should be enough to reduce impacts and any directional change would be influenced by where the restraint was attached.