There was a saddle fixed to the centre of the pole. The topping lift and pole downhaul were a single line; shockcord above the snaphook, rope below, to a block at the base of the mast and then to a cleat somewhere. The snaphook attached to the saddle on the spinnaker pole.
The Castle is arranged quite differently.
- There is no fixing point fastened to the centre of the pole, since this introduces a bending moment into the pole. Instead there are two lines from one end of the pole to the other with a stainless steel ring tied in the middle of one (for the topping lift) and a snap hook tied in the midpoint of the other (for the downhaul). This looks like an odd way to do things, but it prevents the pole being bent by the downhaul.
- The topping lift still has shockcord, but instead of fastening to the mast several feet above the pole ring, it passes through an entry block into the mast and is anchored inside the mast near the base of the mast. This allows a heavier shockcord with more length so the topping lift force is remains relatively even over a larger range of vertical pole movement. The bottom (pole) end of the topping lift has snap hook which fastens to the spinnaker pole ring on the mast when not in use, and to the ring at the middle of the spinnaker pole when in use.
- The downhaul, which you're interested in, is quite different to a dinghy. There are two deadeyes on the foredeck. A line is tied off to one of the deadeyes, passes through a simple block, then through the second deadeye and off to a control cleat. The block gets clipped to the snap hook at the middle of the spinnaker pole when in use.
In this view, the same red downhaul line is visible running from the port side deadeye along the cabin roof to a cleat just out of sight on the right side of the photo, mounted next to the sliding hatch:
(Last two photos taken by Stephen, Castle 610, when he owned the boat)
Downhaul bridle block: