Technically, you can't increase the power (not unless you add extra energy). Due to friction in the pulleys you'll actually lose some power. But:
P = F * v (power = force * velocity)
By using a pulley you lower the speed of hoisting, and, as power must remain the same (excluding frictional losses in the pulley), F increases. That means you can lift heavier things. But slower. And power of the winch motor can stay the same.
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BTW, an easy way to calculate the new load rating of the hoist is by counting the number of steel cables from which the load hangs. When you use one pulley (near the load), it'll hang on 2 cables, hence load rating has doubled. Same principle applies when using n pulleys. Count the number of cables and multiply by the rated load of the original single cable. The above excludes friction but is a close enough approximation.
Don't ya love math & physics ?
Peter.
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