Many a yacht crew has to struggle with heaving in a purchase because the lead off the final block is bad. The purchase will have been calculated assuming it works properly, yet if the fall is graunching around the cheek of the lower block as in picture 1, the friction is gruesome when the load builds. In this case, as in so many, the rope is also too big for the blocks, so some degree of interference is inevitable. If you don’t fancy coming down a size, you’re stuck with that, but by reversing the blocks, the other problem goes away. And there’s more… The purchase has been powered up as well. A purchase delivers power ratios according to the number of parts of the rope at the moving block – in this case the top one. By reversing them, we get 5 : 1 instead of 4 : 1. The purchase is said to be ‘rove to advantage’ and no friction comes along as a bonus. Joy!
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