While docked alongside a floating finger pier, adjacent to at least one other empty slip, secure the docklines to the dockcleats with about 3 feet of slack.
With the spin halyard snapshackle in hand, cleat the spin sheet to the mast bottom, leaving plenty of line payed out. Now walk the halyard around the dock to your empty slipmate's finger . . . distance should be at least mast height, and pull the masthead down far enough to grab the main halyard shackle with a fully extended boathook.
True Blue . . .
sold the Nauticat