A sliding loop of rope or chain by which a running yard or gaff is connected to, while still being able to move vertically along, the mast.

装于帆桁中央两侧的索具：能滑动的绳圈或链子，用来把帆桁或缆索拴在船桅上，使之仍可以随意升降。

youdao

She has no mast, no sails, no complicated bits of rope that you have to pull to make her move or turn.

CNN: Al Salamah: The ultimate yacht