2:1 Purchase
2:1 Blocks are almost exclusively designed to attach to furler top swivels for 2:1 halyard system. 2:1 Shackles can be used for 2:1 halyards on smaller code zero and asymmetric furlers but are mainly used for a 2:1 purchase under the furling drum. Size the 2:1 block/shackle to be equivalent to the SWL of the furler. OR if it is a pin connection - to match the pin diameter on the furler / swivel. Read more...
Note: be careful to double check shackle jaw width related to drum/swivel spindle. For a halyard, it is deadended on the mast and then runs around the bearing surface of the 2:1 shackle/block and then into the halyard sheave and down to deck level. For a 2:1 Tackline, the line is deadended at deck level and then up around the Frictions sheave and then down to a block on the deck and back to a jammer cleat / winch for tensioning.
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