[quote=benedict]I was hoping a wiser head would answer you first, but... Here goes:
Mast rake is more a matter of personal preference than something that's designed in for a particular boat. Rick White and Phil Berman both have good sections on mast rake in their books. I can't remember which one it is (Rick White comes to mind), but one of them also gives the history on mast rake experimentation by racers. It's a good read. And for twenty bucks, one of these books makes a really good addition to a sailor's library.
A really broad-stroke over-simplified statement would be if you're sailing a boat with asymmetric hulls, some aft rake can be useful. If you're sailing a boat with daggerboards, having it more vertical is useful. But this doesn't tell the whole story. Even on symmetric hulls with daggerboards, there are tradeoffs with raking a mast aft or not.
The more you rake your mast aft, the more the center of pressure on the sails moves aft. The more the CP moves aft, the more the center of resistance in the water moves aft. You can tune this to place the CR directly on, or aft of your daggerboards. (If you move it forward of your daggerboards, your boat tries to head downwind when you release the tiller. NOT a good idea. A little weather helm is far preferable to a boat that likes to run away as soon as you right it after a capsize.) But yeah, you can rake your mast so far aft that your tiller arm gets pulled out of its socket just trying to hold a steady course.
To some degree you can counter a heavy helm by raking rudders foreward. The problem here is if you have to hold your rudders several degrees to one side in order to make your boat sail in a straight line, raking them forward just reduces pressure on the tiller. It doesn't reduce the angle you have to put on the rudders. On a symmetric hull boat, having the rudders canted off to one side like that causes considerable drag in the water. Drag = slow. Better to start with neutral rudders and tune your mast for helm and speed.
As to how tight to rig your boat, I really don't know. By definition, I don't think it's possible to get a cat rig really tight. Your downwind side stay will always be loose to some degree, just because of stretch of the other stays under load. I aim to take as much loose action out of my stays as I can so the rig doesn't beat itself up when it's catching waves with its sails down. Once everything is set up, I'll take up luff tension on the jib to try to cinch things down. On a low wind day, I won't use as much jib luff tension. On a high wind day, I'll pull it pretty tight.
Sorry for the long spiel. This isn't really a simple subject. There's no one right answer. The best bet is to experiment with your boat and find out what works best for you. But before running that experiment, I highly recommend picking up Rick White's or Phil Berman's book.
Tom
P.S. I looked this up in Rick White & Mary Wells's "Catamaran Racing: for the 90's". Their chapter on mast rake is pretty good. Worth picking up a copy.[/quote]
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