The cap shrouds attach to the mast about where the forestay attaches, and go to the floats. There is a tensioning adjustment rig that allows you to tune the rig as conditions change. The F-27, with its fixed rig, has a set of lower shrouds, and a baby stay in the front. The following is a link to the sail plan, and you can see the various bits of the standing rigging.

F-27 Formula Sail Plan

There is a modification that adds another set of cap shrouds (called upper cap shrouds) for the 27, that adds more stability to the mast up high. This seems to be a fairly common mod, although the double-spreader mod ultimately does the job better, and eliminates the front baby stay as well.