Whilst comparing my boat to others at the inlands it was soon apparent that the standard settings of rake and chain plates had quite a different result regarding shroud tension. On holes three with the mast at position four my shrouds are slack where others are quite tight. This is despite havinhg longer spreaders than most - 2&1/2 holes showing. Dropping down to hole four went some way to sorting this. So I'm not sure whether I've got long shrouds or a low D ring plate. My measurements are : shroud length measured from the outer ends - 4543mm and mast foot to the bttom of the mast bracket - 4961 mm. Does anyone know if these figures are near what they should be? 
Another anomaly is that despite the shrouds being of confirmed equal length one is always much slacker than the other. And this is before the main is hoisted. Would this suggest that the mast is out of column with a slight lean to one side? Will it make much or any difference to performance from one tack to the other?  
Does anyone else use longer spreaders? Again I seemed to be the odd one out as everyone else's were at the innermost setting.
Cheers guys! 

Thanks Al.�

I don't think it's really a great concern but I'm just interested to see if there is a difference. �Compensating by using lower holes will work just fine although I might treat myself to some plates with a finer adjustment. Just sons I can even things up from side to side. Assuming I'm not breaking any class rules that is. Lol.

Over the course of last summer I noticed that my shrouds got noticeably looser - may have been  the effect of sailing in the breeze or equally well the effect of digging the mast out of the mud a few times. I was wondering if enough tension over a season could lead to a bit of stretch - enough to move down a hole. Does that make sense to anyone ?

The bow shackle at the top of the shrouds deforms and and lengthens, this happened on the first sail I did in 20 knots of wind after I put new shrouds on.
With the slightly stretched shackle with mast rake on 4 my shrouds are just tight with the shroud pins in the third hole down, but I sail with them in the 4th hole down.
Mark 

I've just had a look at my shackle and it does look appreciably stretched compared with one in my spares bag. And I have indeed been out in some monster winds over the summer so that could probably have done the trick. 
Any reason that this type of shackle is used rather than a standard one? 

 On the subject of the deformed 'bow' shackle, my first thoughts were "how the hell has that happened when there is very little in the way of rig tension, certainly not in the league of 200s and 400s", but then I remembered having gone down the mine several times over the last couple of years! Indeed at our local championships in August I brought the boat to a virtual standstill in about 28 knots. That should do the trick!
 
 Furthermore, this may explain the slack(er) starboard shroud - I suspect that the U bolt fastener at deck level has also become slightly distorted from such wanton abuse. I've now evened this up by tightening the U bolt nuts slightly on the offending side. Curiously, there don't appear to be any stops built in to the 'U' so it was easy to screw this down to suit. 
 
Anyway, it may be of some help if anyone else encounters the same problem!