Rig Set-Up?

First 31.7 Rig Tuning Guide.

This tuning guide is intended to get your First 31.7 rig set-up to a base set-up and is targetted at people new to racing the First 31.7. It is by no means definitive but provides a good start point.

The principles of rig tuning are straight forward, however, if you are at all unsure of what you are doing you should consult a professional rigger.

Knowing the pre-bend cut into you mainsail is key for the initial set-up of the rig. Here are some sailmaker target pre-bend numbers we are aware of but you should check with you sailmaker.

  • 30mm - Quantum
  • 50mm - Is a reasonable start point if you don't know the pre-bend cut into your mainsail
  • 65mm - Banks
  • 100mm - North, Sobstad

One other key fact you need to establsh is how your bottlescrews are threaded. On Electra The Caps and D1s have left handed threads - tensioned counter-clockwise (thread looking from above) and loosened Clockwise, while the D2s are right handed thread.

When tensioning or loosening the standing rigging, it is best to do a couple of turns at a time on one side and then perform the same adjustment on the opposite side of the boat. This will ensure that you don't over-stress or over-tighten the rig and keep the mast straight and in column.

The First 31.7 comes with two mast variants. The majority of boats are supplied with the LR rig (P=1080) and all the 31.7s I have ever seen have this rig. There is a larger rig HR or Lake rig with P=1120 of which I am aware there are a few in Finland. This guide is for the First 31.7 LR rig with some guestimates to help those with the HR.

1. Reset the mast tune

  • Completely let off the kicker, mainsheet
  • Take up the backstay tension to support the mast.
  • Get up the mast to the first set of spreaders and loosen the D2s to the limit of the threads.
  • Come down the mast
  • Completely let off the backstay
  • Slacken off the D1s to the limit of their threads.
  • Lower the boom on to the deck (don’t remove it just lower it.)
  • Loosen off the Caps shrouds until they are slack

 

  • For an initial set-up, the mast foot should be in the middle hole (aft hole for HR rig)
    • front of mast 65 cm from bulkhead (67 cm for HR rig)
    • IF YOU NEED TO MOVE THIS I SUGGEST YOU CONTACT A PROFESSIONAL

 

 

 

 

2. Set and Measure The Rake:

  • Attach the genoa halyard to the tack fitting and tension to keep the mast in place while you adjust the forestay length
  • The rake (set by the forestay length) together with the Cap, D1 and D2 tensions will determin the final pre-bend.
  • For the standard First 31.7 rig set the rake for your target mainsail pre-bend.
    • 30-50mm Prebend
      • 3rd chainplate hole from top
      • 222cm forestay measurement
      • 3 degrees rake
    • 60-70mm pre-bend
      • 2nd chainplate hole from top
      • 226cm forestay measurement
      • 3.5 degrees rake
    • 80-100mm pre-bend
      • 1st Chainplate hole from top
      • 230cm forestay measurement
      • 4 degrees rake
  • For the First 31.7 HR rig set the rake for your target mainsail pre-bend.
    • 30-50mm Prebend
      • 5th chainplate hole from top
      • 214cm forestay measurement
      • 2 degrees rake
    • 60-70mm pre-bend
      • 4th chainplate hole from top
      • 218cm forestay measurement
      • 2.5 degrees rake
    • 80-100mm pre-bend
      • 3rd Chainplate hole from top
      • 222cm forestay measurement
      • 3 degrees rake

     

       

  • Check the chainplate hole position gives the correct forestay measurement.
    • If you have a bottlescrew forestay, this is the easiest way check you have the correct rake.
    • Attach a tape measure (fibreglass or steel) to the genoa halyard
    • Adjust the halyard so that the tape measure reads zero at the top of the gooseneck black band.

 

 

 

 

 

    • Swing the tape measure forward and measure to where the stem head fitting meets the deck.

 

  • Adjust the forestay length of your First 31.7 until you have the required rake setting.

 

 

 

3. Centre the rig.

  • Tighten the cap shroud bottlescrews to hand-tight.
  • Tie a 1-2m length of shock cord into a loop.
  • Attach this loop to the main halyard.
  • Attach a spare shackle to the shockcord loop
  • Adjust the main halyard so that by tensioning the shock cord you can reach the toe rail adjacent to the 1st stanchion aft of the mast.
  • The main halyard of the First 31.7 is usually offset to port by the thickness of the sheave.

 

 

 

  • To allow for this offset, measure in the width of the sheave (approx 1 cm) from the inside of the foot of starboard cap-shroud with a chinagraph pencil.

 

 

 

 

 

  • Stretch the shock cord using the shackle and align to this starbard pencil mark.

 

 

 

 

 

 

  • Measure the starboard length of the shock cord.

 

 

 

 

 

 

 

 

 

  • Now stretch the shock cord tight to the foot of the port cap shroud.
  • Measure the port shock cord length.
  • When these port and starboard shock cord lengths are identical the mast is vertical in the boat.
  • If they are different, tighten the cap shroud of the side that measures the longest until they are the same.

 

 

 

 

 

 

4. Tension First 31.7 The Rig

  • Tighten the caps to 15% braking load (44 on the PT-2M Loose gauge
  • Tighten the D1s to 6% breaking load (32 on the PT-2M Loos gauge)
  • Tighten the D2s to hand tight

5. Check and adjust the Pre-Bend

  • Target Pre-Bend Settings for the First 31.7 by sailmaker:
    • 30 mm - Quantum
    • 65 mm - Banks
    • 100 mm - North, Sobstad
    • 50 mm - Is a reasonable start point if you don't know the pre-bend cut into your mainsail.
  • Now read my seperate article on how check and adjust the Pre-Bend.
  • If you cannot acheive the required pre-bend and D tension for the rake, you need to go back to step 2, alter the rake and try again. If the pre-bend is incorrect, it is most likely that you will need more pre-bend as sailmaker will err on the side of too much rather than too little pre-bend. Also older or stretched sails may require more pre-bend. If you need more pre-bend then lengthen the forestay to the next setting and try again.

6. This is enough to get you out on the water - tune the mast in the normal manner under sail.

Remember that this is just the observations and opinions of a keen amateur, and that if you are at all unsure of what you are doing you should consult a professional rigger.

Happy tweaking

AUTHOR: Andy Phelps – Electra GBR 8198T
DATE: 22 December 2005