The first thing you do is to unreeve the yardrope, keeping the end aloft at the crosstrees (perhaps the same rope will do), hook the block on under the cap, or if there is no eye-bolt there put a strap round the cap, hook the block on it, reeve the mast-rope through it, then through the heel of the mast, make it fast to the cap on the other side, and call out, "Haul taut the mast-rope;"
Source: wiktionary