Note: See Loos Gauge Readings section of Standing Rigging

Desired Result

Tensions

See Loos Gauge Readings section of Standing Rigging 
Shroud tensions 2017-04-25:
   247: Starboard:  12,   21,   04; port: 14,   22,   04
              Lbs: 270, >450, >240;      340, >450, >240
                %:  >5,   >5,   >5;       >5,   >5,   >5
   262: Starboard:  27,   37,   13; port: 30,   37,   12
              Lbs: 675, 1200, >250;      890, 1200, >250
                %:  11, 14.5,   >4;       14, 14.5,   >4

Procedure

  1. Get the mast straight athwartships
    1. Slack the lower shrouds
    2. Slack the upper shrouds
    3. Mark a point on both rails that is the same distance from the bow and approximately abeam the mast. The boat may not be symmetrical and the chainplates may not be installed symmetrically.
    4. Bring the main halyard to the marked point on one rail
    5. Tighten the halyard and cleat it off
    6. Bring the main halyard to the marked point on the opposite rail, the halyard should just reach the rail
    7. Adjust the upper shroud turnbuckles as necessary till the halyard just reaches the rail on each side
    8. Sight up the mast after each incremental change the in upper shroud turnbuckles to verify that the mast is standing straight, that the lower as sufficient slack
    9. Do NOT use a level in an attempt to determine if the mast is straight. Very few boats float without some list
    10. Make the upper shroud turnbuckles hand tight, as tight as you can get well-lubricated turnbuckles by hand
  2. Set the rake of the mast
  3. Introduce Fore and Aft Pre-bend
    1. Tighten the forward lower shrounds to pull the midsection of the mast forward 1/2" to 1"
    2. Use the main halyard pulled tight against the sail track as a reference
    3. Verify that the mast remains straight athwartships
    4. Tighten the backstay till the mast bends forward 1/2 to 1 times its fore-and-aft cross-section
  4. Tighten the aft lower shrouds by hand
  5. Adjust based upon load
    1. Go sailing on a day with 8 to 15 knots of breeze
    2. Put the boat hard and full on the wind
    3. Verify that the pre-bend should has changed. If the pre-bend has changed, adjust the forward lowers to re-establish the 1/2 to 1 times the fore-and-aft cross-section pre-bend
    4. Verify that the mast stands straight. Adjust the leeward shrouds, as needed.
    5. Tack and repeat the above procedure to adjust based upon load
    6. Once the mast is straight athwartships with the desired pre-bend, hand tighten the leeward shrouds

References