Typically the clutch simply needs to be tightened. This is accomplished by either turning the wheel on your horizontal model or by using the capstan wrench to tighten the capstan cap. There are three styles of capstan wrench; a spanner wrench, a "Faspin" type rod or a large bronze socket into which a flat bar is inserted.  Place this wrench into the capstan cap (top of the windlass) and turn clockwise.

If your wildcat continues to slip you may need to replace the friction disc(s). 

See "Identifying your Windlass" and call the factory.  401-884-2550.