Rig tuning

Many variables and assumptions in there.  Don't know your class, but here is our process: remember that the reason for all of the tuning is to get the mast to match the luff curve of the sail....worth asking the sail maker what they expect the luff curve to be before you start.

Assuming here that hound positions (where the top of the shrouds hook into the mast) and spreader brackets are uniform in position on both masts - from experience you might want to confirm this.

Then 4 steps to measure mast rake:

1 - measure the mast foot distance from the back of the boat - if that is out from the advised position then move it..!..The rails that most classes use for the mast heel allow for movement, by moving the bolts fore and aft.  I believe that 1 hole = 15mm movement.

2 - check that the chain plates (or the U bolts underneath) are bolted to the gunwale in the right position....you'd think that was a constant, really wouldn''t you, but worth checking.

3 - hoist a tape up the halyard, and lock the halyard off in the sailing position Check that it is the right height....in a 505, we measure back down to the gooseneck bands (21ft 2ins from memory).  No point measuring rake with a tape that is hoisted to a position different to the normal sailing one - again this affects the measurements.

4 - measure the mast rake, and shroud (or luff wire) tensions, adjusting until you are close to the desired settings.

5 - ensure that the spreaders are square to the chainplates.  We do that by tying a line between each, flipping the boat on its side; aplying tension and lining up the 2 bits of string.  Adjust till square and deflected right.

6 - then check that you have the right mast curve (prebend).  This is usually done by touching the halyard to the back of the mast on the goosneck tape, and measuring the bend in the mast at spreader bracket height.