Double Spreader Tuning



Quoted from the Sailpix archives:

Date: Tue, 13 Jun 2000

Hi everyone,

I’ve had a few requests for a summary of the tuning information I’ve received so here it is. Please remember I asked about a double spreader rig and not everyone stated if they had a single or double rig. I’ve gotten the impression that single spreader rigs are more common than doubles.

– There was a 50-50 split on whether the loos gauge was necessary.

– Everyone who had one indicated they couldn’t believe they ever got along without one. After reviewing the e-mails it seems people using the loos gauge have performance tuned their rigs under different conditions, and remembering the numbers they’ve recorded, can change their rigging according to the conditions they’re expecting.

– Everyone who didn’t have one pretty much used the same methods of tuning. I called Buzz Ballenger to get his thoughts on some of the tuning questions I’ve received (he doesn’t use a loos gauge, but he may not have to since he builds masts and spreaders). This is a summary of the methods used:

1. Using the main halyard and the upper (cap) shrouds, center the mast (measure to sheer on either side with the halyard). Note: there was one suggestion to center the mast with the lowers.

2. Straighten the mast with the lower and intermediaries. Use the main halyard and the groove to get the mast straight.

a.. Everyone says the intermediary shrouds should be the loosest.

b.. Buzz said the upper and lower shrouds should be at about the same tension. Some people (with loos gauges) had specific numbers (in the neighborhood of 20) but everyone without a gauge “performance tuned” – see below.

c.. I asked him if anyone used the relative tension to change the placement of the luff curve because of their sail’s design but he hadn’t hear of anyone who did this with an Olson. If anyone has experimented with this please let me know. I’d be interested to see what happened.

d.. As for pre-bend Buzz said you shouldn’t have any less that 1 inch – implying you’ll probably have a little more. He also implied that double spreader masts might need a little more pre-bend than single spreader masts. The pre-bend is affected by sail shape too so this will be individualized. The rule is: the greater the luff curve cut into the sail the greater the pre-bend needed.

3. Performance tune the rig. This is sailing with full crew and the #1 Genoa at around 12 knots. You should have:

a.. No bend in the mast.

b.. Leeward shrouds that are not tight but not all that loose too. If they can be deflected by hand but not “flopping around” they’re probably correct.

c.. I did receive a word of caution from more that one person with regard to over-tensioning the rig. If you don’t have a fabled bar-of-destiny (a strut running from chain plate to chain plate) you can deform the hull shape by over tightening the spreaders. Everyone has said the bar-of-destiny is a good thing. That’s about it. If I get any more info. I’ll post it to the list-server and if anyone has any more questions, send me an e-mail.

As a final note, Buzz Ballenger is a pretty cool guy and had no problem spending the time to go over my questions with me. He’s in Watsonville, CA and his # is 831.763.1196. Also if you have a favored tack, besides your rigging, you can check your hull/keel shape and your trimmer’s eyes.