I split this out before it got lost in the referb topic. Best to start new topics when the subject changes, people stop looking at a topic if they think they already know what is in there.
The best arrangement I've found is a line tied into a bridle, secured to the main beam just inside the hulls( wrap the line around the beam a couple of times before tying it off so it doesn't slide towards the center and put strain on the tramp), so that it extends a foot or so in front of the bows, with a loop tied into it dead center. You can adjust the distance of the loop ahead of the beam to see what works best with your particular boat. This gives you some ability to limit the boats strong desire to wander back and forth, either being towed or at anchor, and transfer the load to a solid part of the boat. But cats really don't like either. If towing I've found it easiest on the boat to have someone aboard steering. I'll only leave a cat at anchor for a short time when I'm nearby should the breeze pick up. They're easily damaged being jerked around in a chop.
Don't tie off to the crossbeam, the others are right -it'll wander back and forth all day and sit parallel to the waves resulting in some violent side to side bobbing. You HAVE to tie off at the bows to avoid this. I added a small shackle to each hull's forestay bridle attachment. Then i tied a length of rope between them, and tied a loop into the center with a hook. The resulting bridle is just long enough that I can hook it to the front crossbeam when not in use and not drag in the water. With this setup my crew can lay on the tramp up front, hold the hook on the bridle and clip it to our mooring buoy as I sail up to it. The bows will always point into the wind/waves. As Dave says though, it's not a good idea to leave a cat tied up unattended. I just do this between outings on sailing days.
-- Jason Kasper
2000 Mystère 5.0XL
Lake St Francis (St Lawrence River)
Lancaster, Ontario, Canada --
I second the shackle to each hull forestay bridle attachment. But I'm too lazy so I just use the shackle that connects forestay and bridle. In any case, make sure to attach the line to something free of edges and moving parts that could cut it. It happened to me, I attached it to the mentioned shackle and the thimbles of the bridles did cut the rope. That was on a N5.0, what I did after that incident was adding another shackle at the same point. And instead of attaching the line directly to that shackle, I start from the center of the front beam, pass it through that shackle and then back to the tramp pocket. (So it's also my righting line, I just pull it back when needed). Now on my N5.5 the bridal foil has a hole where I can pass the line, no need for an additional shackle.
If you will be leaving the cat on the water, anchored or attached to a buoy, make sure to limit mast rotation. Constant movement, especially on short waves of lakes, not so much on the beach, may damage your stays. (been there too..).
On my old N5.0 I didn't have a mast rotator and never could limit mast rotation..
My N5.5 had a mast rotator but no cam cleats on the boom, I added them and almost never use them, except in this specific situation... https://www.youtube.com/watch?v=ubuLmnrZAt4
Go to 4:48
Another vote for the anchor bridle! I use it a lot and it works flawlessly. Less experience towing but as an anchor bridle it can't be beat.
With one addition. You may need a retrieval line to the center of the bridle to make it easy to get at once deployed. It needs to be just long enough so that it never takes any strain, whatever the direction the anchor is pulling in (Except backwards). Tie the other end off to somewhere you can get at. I found out the hard way and my Nacra 5.2 forward decks are round, thin and slippery when wet... So it wasn't easy getting the anchor back in!