Bogged vehicle resistance

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

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

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

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..

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.

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.

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..............