Technical brochures
Sparcraft-us recommendations
Masts
© Charleston-Spar
  
 Summary

TENSIONING THE MASTHEAD RIG

The top of the mast must be vertical in the yacht, so use the main halyard and measure carefully to a fixed point on each side of the yatch. Hand tighten the cap shrouds to centre the mast.

The shrouds can now be tensioned by adjusting each turnbuckle in turn by approximately 3 turns at a time per side. The mast stays in aligment as the tension is increased. The forestay and backstay should be tightened to about the same tension as the upper shrouds, allowing for approximately 1° to 1.5° of aft rake. This rake will improve upwind performance and allow the rig to set in the correct position when the sails are set. For a 10 metre mast, the top needs to be set aft by approximately 200 mm. Mast rake will also contribute to the weather or lee helm affect on your yatch. Increasing the rake aft will increase helm and vice versa.

Some weather helm, when sailing is desirable for best performance and control. If you have a double spreader rig then tension the intermediates next. These should be tensioned slighty looser that the cap shrouds to allow for natural mast bend and stretch from the shroud. Check the alignment of the mast by regulary sighting up the rear sail track. When you are confident that the mast looks correct so far, proceed with the tensioning of fore and aft lower shrouds, or lower shrouds and inner forestay. Certain classes may have specific measurement and tuning information which can be used as a supplement to these guidance notes.

 

TENSIONING THE MASTHEAD RIG

with spreaders raked aft

Aft raked spreaders support the mast sideways and additionally fore and aft. When the tension is increased the spreaders drive the mast forward creating pre-bend. It is essential to work carefully stage by stage to achieve the correct rake, pre-bend and tension.
Start with the cap shrouds, centring the mast in the yatch (see how to centre the mast in the "Tensioning the Masthead Rig" section). Adjust rake with the forestay and then tension the backstay to induce mast bend. Work from the top tensioning each cap shroud about two turns at a time, followed by the lower shrouds and intermediates. Return to the caps and repeat the exercise until the mast is under the required tension. The required tension won't be known exactly until you go out sailing, but each shroud should be fairly snug (see Masthead Rig Tuning for Safety & Performance).
Check regulary for vertical alignment along the sail track.

 

TENSIONING THE FRACTIONAL RIG

with spreaders raked aft

Adjust the forestay to get the required amount of rake. Then each cap shroud should be tightened by two or three turns to increase tension, checking that the mast stays vertical. As tension is increased this will drive the mast forward, creating pre-bend.
If fitted, tighten the intermediates and lower shrouds which will reduce pre-bend. Some pre-bend is however desirable, so leave about 6-7 cms set. At this point the caps, lower shrouds and intermediates should be tight. Backstays are the last adjustment to make, as they tension against the other rigging. When the spreader angle is about 15° or less then more tension is required in the backstay to support the mast correctly aft. When large angle spreaders are fitted (more than 15°), they will also support the mast, so the backstay do not have to be tightened so much.