Re: Which is worse, a CAT that has some hull slap or Mono rolling on the hook?
If you're talking hull slap, I agree with "find a better anchorage". Our Gemini had an annoying rudder "knock" at anchor occasionally (rudders banging back and forth) that happened when we were cross to the current (or a current bouncing off the shore). This usually occurred when we had both a bow and stern line out (med mooring close to shore), and we could usually jury-rig a swim noodle against the rudder to minimize the thumps.
Never had hull slap at anchor, except in storms and powerboat wakes.