Prior to my life as a database administrator I was a hi lead logger in coastal British Columbia, which involves harvesting logs with machines capable of putting huge strain on cable and hydraulic systems. What got me to thinking this was a friend just let me know someone we know was recently killed in an accident where the machine was operating outside its intended purpose while doing a very hard pull with a cable drum and we were discussing how it may have happened. In the discussion we were discussing how different strains were put on certain parts of a cable yarder, depending on angle of pull, lean of the spar, etc. In the discussion I was recollecting how a drum that is capable of holding 1000' of 1 3/8" cable has a lot more pulling power the less line is on it, as it drops the gear ratio. I used to run these machines and extra care had to be taken with the throttle if you were pulling with the drum on the bottom tiers of cable as things could break easier. The drums are powered by a torque converter, so it's more like an automatic transmission, if you will. One thing I always wondered about was how would one figure out or what formula would you use trying to figure out the torque difference for the drum as each tier of cable was added (or removed) The drums are about 2' deep, (I'm just going from memory here) so the diameter of it would range from around 18" to 48" through the full capacity. I'm sure there'd be a mathematical formula that would calculate the difference in pulling power decreasing as the drum got fuller from the bottom tier to the top tier, but I have no idea what it would be.