Further to my previous reply, I have copied Oliviers instructions.
I will start with "How did AMEL install the masts and tune the rigging on Santorins, SMs and 54s?" It has now changed as the masts of the 64 and 55 are rigged with discontinuous side shrouds, and the tension is finally set thanks to an hydraulic mast jack tool system and wedges.
The mast steps are bolted through the deck in metal inserts glassed in.
They are installed horizontally, this means parallel to the saloon floor, or perpendicular to the main bulkhead (underneath).
"How did AMEL install the masts?":
First of all, the spreaders are attached to the top shrouds as follows:
-bring the shroud along the mast and mark it (with a permanent marker) at the bottom side of the spreader's hex nut. Mark both shrouds the same way at both speaders. At spreader's end, put the eye bolt at the mark.
The intermediate shrouds will be secured at spreader's ends only once the rigging is tuned.
As the main mast is hanging from the top (thanks to a crane), it is set on the mast step, centered thanks to both "hubs". The first shrouds to be secured are the 4 lower shrouds, which is enough to hold the mast in place. The crane is going away.
Then the forestay with genoa furler is installed on its chain-plate, then both top shrouds, then the backstay.
Once the forestay, backstay and top shrouds' turnbuckles are gently tightened by hand, the lower shrouds should be eased a bit, in order not to interfere with the operation of "setting the mast foot flat on its mast step":
-Concerning the top shrouds, this is made by measuring the distance between the top of the lower swage, and the bottom of the clevis pin which secures the shroud into the chain-plate. This distance must be the same on both sides.
-Concerning the forestay and backstay, they are adjusted (by hand) in order there is no gap between the rubber sole and the aluminum mast step (front and aft). If you see no gap from the beginning, and you want to check if it is close to a gap, ease the backstay (two turns) and tighten the forestay (two turns). If you start seeing a gap aft, then ease the forestay again (one turn) and tighten the backstay again (one turn). If there is no gap: GOOD, if there is still a gap aft, then come back to the original position (one turn less on the forestay, one more turn on the backstay).
Now, you can say the mast is "vertical" (in fact, the Santorins, SMs and 54s are never horizontal, back to front, but always with the bow up, which means the mast is leaning slightly aft).
It is vertical but it should also be straight as no strong tension has been put on the shrouds.
Once the mast is vertical, you will start tensioning the shrouds by pairs, checking that the mast is straight after each tensioning, like, for instance:
-two turns on front lower shrouds, two turns on aft lower shrouds, check
-two turns on top shrouds, check
-three turns on forestay, three turns on backstay, check
And so on until the shrouds feel very stiff. In the end, you will tension the front lower shrouds a bit more than the aft ones, in order to initiate a slight curve aft (the middle of the mast being in front of the foot and top) and then only the intermediate shrouds, not too tight.
To confirm the rigging is tight enough, go out sailing, close hauling with 18/20 knots. The mast should keep straight sideways, and not bend forward, the leeward shrouds should not be loose. If the mast bends forward, then tighten the backstay and the front lower shrouds.
If the mast is not "vertical" from the beginning, it will bend front if you a gap at the front or aft if there is a gap at the aft.
Once the main mast and rigging are set, you can start with the mizzen mast:
-first line it up with the main mast, looking at both from the far aft of the vessel
-then tension the shrouds in order to make a slight curve aft
This is a first description. I probably forgot some details, so... feel free to ask.