Rig Setup & Tuning

Mast/Rig tuning is one of the important speed/point factors, for two reasons:
  1. The prebend in the mast has to be synchronized with the luff curve cut into the main, nothing is slower than getting this wrong
  2. You want as much sag in the headstay as is reasonable for the wind conditions you normally sail in, plus some flexibility thereafter

Initial Setup and Tuning

JBoats provides a good initial rig setup and tuning guide.

Don't under estimate the effects of rig tune. When we first got the boat we used the tuning advice from the jboats website and also from ullman sails. We later found out from some experienced J/27 racers that those rig tensions were too tight, especially for light air. Loosening the uppers and lowers to 900 lbs in light air transformed the boat and made the difference between winning and losing. The tuning style we use is from Doyle sails. Its also an easy way to tune as you set to a base setting, then from their you only adjust forestay length for different conditions. Here it is if anyone is interested:

This is your base setting from 0 to 10 knots:
  • Base Forestay length: 31' 6"
  • Base Rig Tensions: uppers 900 lbs, lowers 900 lbs, int. hand tight

From here, we adjust the forestay from base as follows:
  • 11-14 knots: Tighten 1/2" (approx. 6 to 8 full turns)
  • 15 knots +: Tighten 1 1/2" (approx 18 full turns)
The J/27 is one of the most sensitive upwind boats I've ever sailed. Your forestay sag and rake have to be spot on for different wind conditions or you are toast.

The even (upper and lower with intermediates hand tight) shroud tensions originated with Chris Princing back in 1997 or so, when he was using Doyle sails from Newport RI. He also originated the zero prebend main tune for J/27's, which works very well with the even shroud tensions. This Banks/Doyle tuning guide can be found here Banks Tuning Guide (requires access to the J27 Yahoo! group website)

Additional Suggestions

The objective is to use the headstay sag in light air and to start using the backstay above 10-12 knots (depending on crew weight, sea state, etc.) to reduce the sag and flatten the main and the Cunningham to bring the draft forward.


  1. Drill sufficient holes in the beam that the mast butt sits on so that the luff curve can be adjusted from 4” to zero inches – a range of 6” adjustments in 1” steps
  2. A reasonably long headstay, 31’ 5” – 31’ 7” pin-to-pin is necessary to get sufficient headstay sag with reasonable shroud tension


  1. Undo all of the turnbuckles so that they are loose
  2. Use a car jack with a piece of 2x4 as a load spreader to support the mast against the front bulkhead, since even with the shrouds loose the mast will want to move forward.
  3. Undo the mast butt screws and ease the mast forward or aft depending on the amount of prebend required
    1. Assuming approximately even final tension on upper and lower shrouds between 800 and 1000lbs for a deep luff curve main (3.5 – 4.0”) try about 6.5” from the rear bulkhead
    2. For a zero luff main try about 9” from the rear bulkhead.
    3. This will depend, in part on the stiffness of the mast
  4. Ease the mast forward or jack backwards to the desired position. Make sure the butt plate is even on the mast seat from side to side, then tighten the bolts, let mast run as far forward as possible against the bolts before final tighten.
  5. Leaving the intermediates loose, tighten the uppers and lowers until taut then put in even tension, approximately 600 lbs on both uppers and lowers.
  6. Next, determine if the mast is straight by using a heavy weight (full 3 gallon gas can or heavy tool box is fine) or calibrated spring at the end of the genoa halyard (the mast halyard would be better but since there are no supports above the uppers the tip always wants to move around a lot)
  7. Starting at the toe rail on the port side, pull down on the halyard and let the weight rise back to a static position to take the slack out of the system
    1. Repeat 3-4 times
    2. Mark the halyard where it intersects the toe rail, you can use a small straight edge set on top of the toe rail and butted against the shrouds as a marker point
    3. Move the halyard/weight over to the starboard side, making sure you keep a little tension as you move it across the boat and that you do not get it snagged on a spreader, halyard, headstay, etc. and repeat
    4. If the mark from the port side is above the starboard toe rail then the mast is canted to port and you follow the procedure below, if it is below then it is canted to starboard in reverse the procedure
    5. Adjust the starboard turnbuckle until the mark is about half way between the initial measurement and the port side mark
    6. Mark the halyard at the toe rail and move it back to port
    7. Repeat on both sides until you have a mark on both sides that is even – your mast is now centered!
  9. Put the wedges in to secure the mast collar making sure that the back of the mast is hard against the back of the collar
  10. As you adjust the turnbuckles make sure to do even amounts on both port and starboard
    1. On the uppers do no more than 2 turns at a time each side
    2. On the lowers do no more than 1 turn at a time each side since they are so short
  11. Adjust the uppers to about 850 lbs
  12. Tension the lowers, keeping the mast in column, to about 850 lbs – at this point each half turn will add about 100 lbs
  13. Check and record all tensions
  14. Sight up the luff track in the mast to make sure it is in column, if not straight adjust the lowers as necessary
  15. Hand tension the intermediates, constantly checking for straightness
  16. Measure prebend using a piece of card on the main halyard stretched tight making sure to deduct the distance the masthead sheave sticks out
  17. If it looks right put up main and go sailing
  18. If it looks wrong start again

The whole process should take about 2 hours

  • Slo-Poke
  • Blackadder
  • Balance Act