Rig Tuning

Introduction

It is important, but not necessary, to have a correctly Tuned Rig.
Boats which have badly tuned rigs are Slower, Point Lower, Heel more, make more Leeway and may be harder to Steer.

Rig Types

The Bermudan Style Rig can be divided into two main groups:-

Masthead Rig

 

  • Where the Backstay and Forestay are attached at the Masthead

 

Fractional Rig (Swift 18)

 

  • Backstay is attached at the Masthead
  • Forestay is attached some distance below the Masthead
  • More tuneable than Masthead rig
  • Large mainsail and smaller/fewer Headsails
  • More demanding to tune and to keep in tune

 

Rig Tuning

 

Three aspects of Rig Tuning are:

 

  • Trimming the Rig Sideways
  • Trimming the Rig Fore and Aft
  • Final tuning Under Sail

 

Trimming the Rig Sideways

 

  • Lightly tension the Cap Shrouds, Backstay and Forestay until mast is standing fairly upright
  • Remove the boom and loosen Lower Shrouds
  • Use main halyard to measure from one side of the boat to the other to set the mast upright.
  • Lightly adjust the Cap Shroud rigging screws to hold the mast upright

 

Trimming the Rig Fore and Aft

 

Adjusting the Mast Rake

 

    • Usually set with a slight aft tilt, but nil is OK
      • Improves the boats upwind performance
    • Usually between 2 & 3 degrees
      • 3.5 to 5.25 cm/m of Mast length
      • Swift 18 about 0 - 20 cm works OK, but instead of altering your rigging, or getting new rigging, the original setting of 0 degrees is OK, but never Mast Rake forward.
    • Adjust the Forestay length to set the Mast rake
    • Lightly tension Cap Shrouds again

 

Backstay Tension

 

    • Done after setting Mast rake
    • Set to Maximum of 20-30% of Backstay breaking load
    • Breaking load of 10% is a stretch in the stay of 2mm in each 2000mm of stay length
    • So 20% tension is 4mm per 2000mm of backstay length
    • I set mine at 20% Maximum and put coloured threads markers on the Backstay adjuster so I know when I'm at 10%, 15% and Maximum 20%.
      • Remember this is the Maximum, don't over do it and release Backstay tension after mooring.

 

Cap Shroud tension

 

    • Done after Straightening the Mast sideways and setting the Mast Rake
    • Lower Shrouds and Backstay must be loosened
    • Tighten Cap Shrouds to a Maximum of 20% of breaking Load
      • 4mm elongation over each 2000mm of Cap Shroud length
    • Again, check Mast is upright

 


Slack rigging can produce shock loads that can cause rig failure

 

Final tuning Under Sail

 

Cap Shrouds

 

    • Lower Shrouds to be only loose/handtight
    • Tighten Backstay to 2/3 of maximum tension
    • Take the boat out in winds that will heel to about 20 to 25 degrees
    • Check Leeward Cap Shroud, it should be handtight, not sloppy
      • If sloppy
        • Tighten rigging screw 1 or 2 turns, then Tack and adjust the 'now' Leeward cap Shroud the same amount
      • Leeward cap Shrouds should be tightened until it no longer curves to Leeward.
    • When happy, Pin and Tape the Cap Shrouds

 

 

 

Lower Shrouds

 

    • Adjust the Lower Shrouds so that the Mast is straight when the boat is heeling 20-25 degrees
    • Example
      • If the Windward Lower Shroud is too loose, the midsection of the Mast will fall off to Leeward, tighten the Windward lower Shroud to straighten the mast.

 

 

 

Rigging Summary

 

  • Handtighten Cap Shrouds until mast is vertical
  • Adjust Mast Rake with Forestay and Backstay
  • Tension Cap Shrouds to 20% of Breaking Load
  • 4mm elongation over each 2000mm of Cap Shroud length
  • Set Mast pre-bend
  • Check rig under sail