Bogged vehicle resistance

Submitted: Friday, Jul 08, 2005 at 23:45
ThreadID: 24566 Views:3729 Replies:7 FollowUps:2
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I am interested on opinions for the amount of force needed to remove a vehicle from a bog. I received some info on a winch course that for a vehicle bogged in deep mud on flat ground that the force would equal 1.25 multiplied by half the weight of the vehicle. eg. 1.25 X (2T/2) =1.25T. I want to be able to winch within SWL and decide whether to use my block/pulley. Obviously the amount of force will change due to type of surface and gradient. The reason why I doubt what I learnt is because by looking on some 4X4 sites the formulas a very different.

Looking forward to a response.

Allan
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Reply By: Alex H - Saturday, Jul 09, 2005 at 00:35

Saturday, Jul 09, 2005 at 00:35
G'day,
I can't vouch for the accuracy of the following, as its some years since I read it. In a 4wd magazine I read that the army have calculated that the resistance on a vehicle bogged in thick mud (really bogged - chassis deep) can be as much as ten times the vehicle weight. Never tested it, only once been bogged that deep, and with a handwinch and snatch block it took me four hours to winch 5 metres!!
Hope I haven't scared you too much - it was fun at the time :-)
Alex
AnswerID: 119517

Reply By: Patcher - Saturday, Jul 09, 2005 at 07:27

Saturday, Jul 09, 2005 at 07:27
G'day,

I've experienced the "ideal" situation you speak of. A vehicle bogged down to the chassis on a flat surface of sand & mud underneath.

I witnessed a 9000kg snatch strap snap like a rubber band and bend a TJM steel bar considerably. The vehicle had to be pulled out with a 7 tonne 4 WD tow vehicle with the cable pulled out about 100 metres. When the pressure was put on the bogged vehicle the suction created pulled the boom of the tow truck down so much that it lifted the front of the truck by about a metre !

No hand winch would have pulled the vehicle with the suction of the mud. I reckon a bull bag may have helped.

Cheers

Pat
AnswerID: 119523

Reply By: Mike Harding - Saturday, Jul 09, 2005 at 07:50

Saturday, Jul 09, 2005 at 07:50
Perhaps you could post details of the course which teaches this type of rubbish?

The above post (Patcher) sounds about the right numbers - ie. bloody big, due to the variables it's not really the kind of thing which can be calculated. However if we take the numbers you have been given and if a Landcruiser weighs 2 ton then half of that times 1.25 = 1.25 tons. So my little Black Rat $50 puller can extricate a bogged Landcruiser from mud. I have my doubts.

Mike Harding
AnswerID: 119525

Reply By: G-wizz - Saturday, Jul 09, 2005 at 10:07

Saturday, Jul 09, 2005 at 10:07
From
Billavista (an excellent 4x4 technical site btw)

Stuck (mire) resistance:

A pull of 100% of loaded weight will be required if the truck is stuck to a depth of the sidewall on the tires.

A pull of 200% of loaded weight will be required if the truck is stuck to the hubs.

A pull of 300% of loaded weight will be required if the truck is stuck to the frame..
AnswerID: 119535

Reply By: wilbur - Saturday, Jul 09, 2005 at 11:00

Saturday, Jul 09, 2005 at 11:00
Just a quick tip in heavy mud or peat try pulling on at lest a 45 deg angle you will be suprised how easy stuck vehicles come out as it breaks the suction plus pulls vehicles around on fresh ground using this method we have pull out vehicles that have broken the winch cable trying to get out.
AnswerID: 119537

Reply By: Shane (QLD) - Saturday, Jul 09, 2005 at 16:32

Saturday, Jul 09, 2005 at 16:32
Army Formula:

Mud : Weight /2
Sand : Weight / 7
Level Ground : Weight /25
Clay : Forgot
Turning resistance : Weight/2
Plus you add degrees of slope up to 45 degrees & then full weight, plus a 25% safety factor which takes in frictional losses etc. You then work out what tackle layout you require, whether it would be a simple , compound or compound compensating. Sounds like a lot of bullsh-t, but the above never fails .It's been a while, but that will give you a rough idea.
AnswerID: 119566

Reply By: Crackles - Saturday, Jul 09, 2005 at 20:00

Saturday, Jul 09, 2005 at 20:00
ALL those formulas & recovery charts are rubbish & written by training personel trying to quantify something that can't be done. Although some are closer than others it's impossible to take into account all the variables of vehicle types, assesories fitted, suspension height, tyre width, soil type, water content, slope, angle of pull, etc, etc....................Unless you have a mechanical PTO or hydraulic winch you wont have an issue with exceeding your SWL anyway as it will just stall.
Just buy recovery equipment stronger than the maximum double line pull. The rest is just experience that will tell you if you need to double block.
Cheers Craig..............
AnswerID: 119588

Follow Up By: Mike Harding - Saturday, Jul 09, 2005 at 20:19

Saturday, Jul 09, 2005 at 20:19
What he said.

Mike Harding
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FollowupID: 374672

Follow Up By: Allan-Pilbara - Sunday, Jul 10, 2005 at 03:55

Sunday, Jul 10, 2005 at 03:55
The details of the course are, it was designied to lift transformers up poles and recover vehicles from bogs. We bogged a vehicle in deep mud and calculated the pull required and measured it. It was quite close but we were in training conditions, where everything is perfect. The formulas were quoted from the Aust. army.

Allan
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