Winch Loads

[landroversforever]

How can I work out what my winch will be capable of pulling force wise?

I'm trying to do some stress analysis on the compression parts of the winch mount.

The winch in question is my Superwinch husky EW8, otherwise standard apart from the fact I'm fitting a BOW2 to it.

Is 10T a realistic force to use with a bit of a safety factor? I'm working on worst case, full load at one end (Taken by one of the blocks) and ignoring the structure below the winch. Currently getting 0.7mm as the worst deflection Which I don't think is too bad?

[elbekko]

I'm no engineer, but...

Torque of the motor * gearing + drum dia + added dia of rope wraps around the drum?

I think Filip did the calculations for Mike's Ibex a while back, so Mike should be able to chime in.

[deep]

I'm no expert but I did read around the topic about two years ago. I found a test of around ten winches, which basically looked at how far they went before something broke. Every one exceeded the stated rated load, some by only five or ten percent but others by nearer 20-30%. If you look at a 9,500 lb winch, on it's first coil at maximum pull, that rating is 4.3 metric tonnes, which means it could actually be capable of putting a five ton load on the mounts. Whether or not doubling that is sufficient allowance in your design depends entirely on how accurate your calculations are!

This is quite timely, because I am planning to put my 13,500 lb winch on my 110 (if VTNZ ever get realistic about accepting the import documentation, grr) and am having a real think around how best to mount it. I hadn't actually thought about calculating mount strength as my normal approach is "overkill in theory, then bodge". Not ideal, so why not do it properly this time?

[Bowie69]

Just a thought, snatch loading hasn't been discussed, only the pull of the winch. Load on the mount is not going to be proportionate to the pull of the winch, what load *could* go through it should you be in a situation where your 2.5T truck suddenly snatches on the line at 10mph as it disappears over a large drop and suddenly pulls the line taut.

Other thing, rear winch is often used for anchoring, so in reality if you are just looking at the pull figure, then you need to look at your front winch, which I suspect will pull harder!

Either way I suspect that 10T will not be quite enough if considering the worst case scenario. But then it depends on the allowable deflection in the mount.... lot of unknowns(!)

[miketomcat]

Filip did indeed do some calculations for me in my case he came up with a figure of 7.9t on my rear pin with a 135° wrap of winch rope and 3.3t on the pulley with a 45° wrap based on a ep9 so I did my pins at 14t breaking strain.

Mike

[elbekko]

In normal use I don't really see snatch loading happening, unless your brakes fail or you suddenly loose all traction without already hanging from the winch.

You'll want a factor of safety anyway, which should cover that eventuality.

[Bowie69]

That's the problem though, I agree normal use it should be OK, but abnormal use is just a slip-slide away, and rapidly becomes an oops.

I'd build mine to withstand an oops, especially given how much the fairleads must have cost!

[honitonhobbit]

Often wonder just how you can come up with an accurate calc. As Mr R proved, none of the quoted figures on any winch motors on the market are actually real. They are simply manufactured figures created by marketing guys sniffing fairy dust. So unless you specifically load cell your individual winch, then have your motor HP measured on the correct doo-hickey, all the figures are simply random numbers - like carbon footprint or VW emissions

[landroversforever]

Just a thought, snatch loading hasn't been discussed, only the pull of the winch. Load on the mount is not going to be proportionate to the pull of the winch, what load *could* go through it should you be in a situation where your 2.5T truck suddenly snatches on the line at 10mph as it disappears over a large drop and suddenly pulls the line taut.

Other thing, rear winch is often used for anchoring, so in reality if you are just looking at the pull figure, then you need to look at your front winch, which I suspect will pull harder!

Either way I suspect that 10T will not be quite enough if considering the worst case scenario. But then it depends on the allowable deflection in the mount.... lot of unknowns(!)

In that case, I'm more likely to be paying out as I approach the top to keep the winchline taught.

Anchoring loads is a good point, the front winch is a BOW2 powered Large drum TDS so in theory a 11500lb pull (5200Kg).

I think if I can get the deflection under 0.5mm I'll be happy. As the other side will actually share some of the load and the structure under the mount will help too.

That's the problem though, I agree normal use it should be OK, but abnormal use is just a slip-slide away, and rapidly becomes an oops.

I'd build mine to withstand an oops, especially given how much the fairleads must have cost!

Fairleads won't be under much of the load though really, although the rear fairlead bolts form part of the winch mount. Worst case the 'oops' is going to bend the blocks, I'll just remake them, its never going to let the winch come away from the car.

Often wonder just how you can come up with an accurate calc. As Mr R proved, none of the quoted figures on any winch motors on the market are actually real. They are simply manufactured figures created by marketing guys sniffing fairy dust. So unless you specifically load cell your individual winch, then have your motor HP measured on the correct doo-hickey, all the figures are simply random numbers - like carbon footprint or VW emissions

Its not so much wanting an accurate figure because as you say there are figures that are questionable. Its more that by putting some thought into the design it will be better overall than just saying sod it and building out of boiler plate ala Nige .

[Bowie69]

When talking about the fairleads, I meant if you ended up bending the bumper/crossmember/whatever, but take your point, you know your design better than us

Taking the anchor to the extreme, imagine anchoring yourself and then someone winching off your front bumper, with some monster hydro setup, anyways, think you have a good handle on things

[landroversforever]

When talking about the fairleads, I meant if you ended up bending the bumper/crossmember/whatever, but take your point, you know your design better than us

Taking the anchor to the extreme, imagine anchoring yourself and then someone winching off your front bumper, with some monster hydro setup, anyways, think you have a good handle on things

Ah I see. hadn't thought about bending the bumper or crossmember . Think that might be the least of my worries if I did

Valid point with the big hydro, however I guess I can never counteract everything like that without making it all from 50mm steel

[zim]

My honest answer would be with a load cell, as you use to test cranes etc. However for a home user i think you'll battle to find a cell

G

[Daan]

I'd say go twice the rated workload of the winch because of snatching. Towing point ideally in line with the chassis rail, so no bending. at the rear, my towing point is in the middle, with 2 diagonals to the chassis rails, so no bending load on the cross member.

[landroversforever]

The welded in recovery eyes are inline with the chassis rails Daan .

Just need to work out the line pull of the winch now!

[discomikey]

I have a very useful engineering reference book at work it features factors of safety for different applications I'll take a look in it tomorrow

[discomikey]

Often wonder just how you can come up with an accurate calc. As Mr R proved, none of the quoted figures on any winch motors on the market are actually real. They are simply manufactured figures created by marketing guys sniffing fairy dust. So unless you specifically load cell your individual winch, then have your motor HP measured on the correct doo-hickey, all the figures are simply random numbers - like carbon footprint or VW emissions

The only real way to tell is to anchor the winch to something solid and pull against something solid with a load cell in line till the motor stalls and record the highest load seen. Unfortunately not everyone has access to load cells big enough as they aren't Cheap!

Theoretical calculations (in this instance) are only really useful as a validation as there are many factors which they will not account for

[landroversforever]

I have a very useful engineering reference book at work it features factors of safety for different applications I'll take a look in it tomorrow

Not the machinery's handbook is it? Didn't think to have a look in my copy.

The only real way to tell is to anchor the winch to something solid and pull against something solid with a load cell in line till the motor stalls and record the highest load seen. Unfortunately not everyone has access to load cells big enough as they aren't Cheap!

Theoretical calculations (in this instance) are only really useful as a validation as there are many factors which they will not account for

Load cell is probably fairly easy to source from work. I know of at least two, I'm sure they'd go high enough. It's just the faff of mounting the winch to something.

Theoretical calculations are I think all I need, twice the line pull as Daan says is probably a valid figure to work on for the purposes of this as so much isn't included in the model. its literally just the ali block in compression.

[Lewis]

I'm probably missing something here as this seems too simple, but surely your mounting point only needs to be stronger than the four fixings which will be in shear on a normal lowline winch (I appreciate your query relates to a husky which is not a conventional lowline)

[landroversforever]

That's where it gets a bit more complicated Lewis

As you said, the husky isn't like a conventional winch and reliant only on the 4 bolts, it normally has the fairlead attached through the mount to a set of holes in the winch. In my endeavour to save weight I didn't just want to make the mount out of 6+mm steel for the strength to counteract the leverage of being built up from the southdown.

So by having some blocks machined to sit between the fairlead bolts on the crossmember (they will actually bolt into helicoiled threads in the block), and the winch then bolted to the back of them. All the winch loads are trying to compress these blocks. I'll of course be having a mount under the winch as well, but it means that it can be of much smaller steel, probably around 3mm, with bracing/returns etc to make it more rigid.

Does any of that make sense Lewis?

[Lewis]

If the winch is effectively trying to compress the crossmember then all you have to do is hold it in place? My winch is bolted feet forwards so the bolts are only holding it upright

Anyway, my point was, look at the shear strength of four m10's, and make sure your mounting point exceeds this load when applied in the correct plane. That would be sufficient surely?

[landroversforever]

Well sort of.

The front face of the winch is actually 150mm back from the face of the crossmember, so the aluminium lumps need to be able to take the compressive load.

Ah I see what you mean now. Looks like an M10 will take about 3000Kg in shear, so the bolts are about 12000KG.

Done a bit more thinking about the line pull of the winch:

Standard Husky EW8 is 8500lb pull with a 2.8HP motor. Same winch with the BOW2 has 6.8HP so about 1.6x more power (assuming the torque is linear). Assuming all things linear that ends up with about 13,600lb pull or 6.2T. So for the purposes of my model I think working on about 12-12.4T is sensible?

Front winch according to goodwinch will pull 11,500lb, so doubled is 23,000lb and that is just under 10.5T.

Basically playing with the shape of the cutouts and weight removal to reduce the amount of deflection .

[elbekko]

Ah I see what you mean now. Looks like an M10 will take about 3000Kg in shear, so the bolts are about 12000KG.

But you're not actually loading the bolts in shear though, are you? There's also (mainly) the friction of the winch against the mounting plate, clamped by those bolts.

[landroversforever]

That's more for calculating the rough force Ben.... Mine won't see anything like that in any direction as I've got the blocks in compression between winch and crossmember.

[elbekko]

Yeah, just saying, if you want to see how much a regular winch mount can handle by looking at the bolts, the pure shear strength of the bolts isn't all you have to look at.

Honestly though, I think some common sense engineering should be plenty. I don't think compressing those blocks will happen that easily, but that bit you should be able to look up? Maybe make sure your bolts don't come loose if they do compress. The actual winch mount, make sure there are some lips on it to prevent deformation. We made Filip's hydro winch mount on the P38 out of 4mm plate, with some strategically placed angle iron welded under the winch bolt holes. This was mounted feet down though.

[sean f]

Not quite what is being asked in this case but for general calculations.

Remember you are dealing with line pull effectively a point load, with a standard low line winch there is also an element of rotational forces on the mount (why the line should come out the bottom of the winch!), mounting feet forward mostly negates that as I believe is being done in this case on the mount but it will still be there on the bumper mountings to the chassis.

Also think about where the recovery eyes are, if you do a double line pull then 5 tonnes is applied on each line hence 10 tonnes total, if the recovery eye is part of the winch bumper, make sure the entire bumper doesn't come off!, what is it actually attached to and how?.

Multiple pulleys and it can get confusing, had to give a talk to a senior engineer early this year to explain why when pulling a 250klbs load up it showed 240klbs on the weight indicator but when lowering it it showed 260klbs, all to do with the number of sheaves in use and where the load was actually measured from. It was a very big winch, think the system was rated at 1,200klbs!.