MarkM,
You must first determine what your line speed will be. (adjust numbers where necessary and anyone please correct me where I am wrong) example: engine rpm=3600 divide by 6 for output shaft speed(6:1 gear box)=600rpm X first (drive) pully size (2in) divide by next (driven) pully (6in) X sprocket teeth (10) divide by next sproket (30 teeth)=67rpm X circumference of cable drum (8in) = 533 feet per minute.
Since 1hp=550fps, you could pull 60lbs 550 feet in 1minute, or 60 X 550/533(your speed)= 62lbs pull X 8hp(your engine)= 495 lbs pull.
Sounds way too fast, and each winding of cable will be faster with less pull.
Back to the drawing board!
If you use different pullys and gears and drum size to reduce your speed by 1/4, you will 4 times your pull. ie 1980lbs at 133 feet per minute or 2 feet/second.
Think about a farm tractor winch: 40hp will pull about 8,000lbs. You have 8hp (1/5), therefore, at the same line speed you will also pull 1/5 of the load, or 1600lbs. How fast is a tractor winch at 540rpm? (2 feet/second?) Anyone know?
Keep me posted about this winch, I have had plans for one for about 10 years but been scared to try it out.
Stephen