Beginner's guide to rig terminology...

that sounds about right. on my 49er, the ones that go to the top of the mast are the caps, then the lowers are the lowest ones (obviously) then the primary lines are in the middle. Its also a good idea to take the caps off when not sailing, as this allows the mast to be fully straight, we usually just wrap them round the trapeze lines.

And just to confuse you, caps are sometimes called capshrouds (obviously!) but also uppers, primaries are often just called shrouds or mainshrouds, and D1s are sometimes referred to as D2s (incorrect but common!) or checkstays.

 

Or a Laser, just as simple (prob not as fun though)

I think you're getting it.  Caps go to the top and control topmast bend.  Shrouds (or Main Shrouds) go over the ends of the Spreaders and finish at roughly the same hieght as the trapeze wires - these control mast rake.  Lowers (Lower Shrouds) generally go up to around the Gooseneck but sometimes as high as the root of the spreaders and they control (or limit) lower mast bend.

We haven't mentioned Diamonds.  Some boats have them, they generally go from the top over some spreaders and then back to the mast near the foot.  But since they go from the top they are often erroniously called Caps.  RS600s use them so that the mast can rotate.

 

Originally posted by redback I think you're getting it.  Caps go to the top and control topmast bend.  Shrouds (or Main Shrouds) go over the ends of the Spreaders and finish at roughly the same hieght as the trapeze wires - these control mast rake.  Lowers (Lower Shrouds) generally go up to around the Gooseneck but sometimes as high as the root of the spreaders and they control (or limit) lower mast bend.

K-kirk, to add to what redback has put, your shrouds adjust middle mast bend by means of spreader deflection as well as stiffness of the mast through the length of the spreader.  The more tension, the more the spreaders will force into the mast, adjusting the shape.
The length of the spreader on a twin wire rig can have other effects on the shape of the mast.  Longer set spreaders can have the effect of inverting the centre of the mast to windward, whilst shorter set spreaders can have the effect of pushing the centre of the mast to leeward. 
Also another note on lowers, by having tight lowers not only do you prevent the bottom section of the mast from bending but this straightening of the mast raises the overall height of the rig, again making a difference to your rake. 

At first it may seem like a lot to take into account but it all sets in fairly quickly. 

Doug.H

ps.  Would i be right in thinking that the 29er X has fixed spreaders??  That would certainly make life a lot easier. 

Edited by Doug.H