How much force can a person pull on a rope?

[kevinz]

Can anyone quote me an authoritative source for the amount of force an average person can exert pulling on a horizontal rope? I found this source: http://www.lewmar.com/webcat/technic..._tech_ref.html which says 75lbs. Is this accurate? Any authoritative sources? How about peak force when heaving together?

I ask because I just broke a 5/8" piece of nylon webbing by five guys pulling on a 4:1 tackle. The nylon sling was tied in a cow htich, and oddly enough broke in two places, about where the two legs went under the loop of the cow hitch. All five guys hit the deck, which was probably lucky, because the 10-15 lb double block ended up behind them all; it must have flown over their heads.

75lb x 5 men x 4 mechanical advantage = 1500 lb
Breaking strength of 5/8 inch tubular nylon webbing = 1500-1850 lb (from various sources).
Haven't been able to find a source for how much a basket hitch (essentially a cow hitch) reduces breaking strength.

Thanks for your suggestions.

-Kevin