Winching tips/math

[nismothunder]

Ok,let start off by saying that this isnt just powered winch owners,people that only have a hand winch(come-a-long).

Let start off with the basics.Let say we have a wd21 nissan pathfinder with a lot of mod,Sas,swampers,snorkle,lockers and the works.It ways 5800 hundred pounds with every thing in it,including three of your fat buddies.Man that thing could get through any thing,but some how you have gotten stuck.You have a 8,000 pound winch on front so that should be good,just hook up and go,BUT WAIT,theres somethings you should know before doing so.

 

1.The effort required to free a stuck rig depends on 4 things.

 

*Weiught of stuck rig

*Type of crap your stuck in(mud,sand,grass,pavement)

*Depth of which the rig is stuck(to the huds,fenders,frame)

*Slope of which(if any) you have to winch up.

 

The follow is an Approximent *mire* resistance values of diffrent terran when the rig is not grounded(up to the frame)

Hard surface=4 percent of total rig weight

Grass=15 percent

loose gravel=20 percent

dry sand=25 percent

Clay mud=50 percent of weight

 

The following depth resitance is encountered regardless of terrain.

 

Hubs=100 percent.total rig weight

Top of tires=200 percent of rig weight.

Hood=300 percent

 

Also,it is the stepness of a slope,not the leanth of which a rig must be winched that counts.

So add 10 percent of the rigs weight for every 5 degrees of incline up to 50 degrees,above 50 just add total rig weight.

 

In addtion,when ever a snatch block is used,add 10 percent of load for every block used to take into account of friction.

 

So if our pathfinder is sitting in 12 inchs of mud(or up to the hubs) on a 20 degree slope then it would require 5220 lbs of force to recover it.Or 50% X 5800(mire resistance) + 40% x 5800(grade resistence)=5220.

No problem since we have a 8000 pound rated winch right?

 

Nope,You have to take in the Available effort that the winch can give you.

 

Drum layer,100 %/8000

2nd layer 85 % or 6800 pounds

3rd layer 72 percent/5760 pound

4th layer 62 percent/4960 pounds

5th layer 53 percent/4240 pounds

 

The pathfinders winch would be indeed able to free it but only with it its final 3 layers of cable.

 

But what if the pathfinder was mire to the top of its tires,then the required pulling power is 13,920 pounds.Could its 8,000 rated winch still free it?Yes with a little help.

 

The simplest way is to run the winch rope/cable back and forth between the load and anchor one or more times.It is called a tackle system.

 

 

To be continued...

[ILoveMyPatty]

So what you're saying is, "Carry several snatch blocks and straps to attatch them to trees"..?

[nismothunder]

Yeah,pretty much,I have the formula to find out how many you need.

[younie91]

i heard that if you run your winch cable around a tree and back to a tow hook or another good anchoring place on your truck it doubles the rate that the winch can tow, making an 8000lb winch able to tow 16000lbs