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Re: Mast Set Up/Rig Tension #501
05/09/07 05:40 AM
05/09/07 05:40 AM
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Different guides say different tensions.

From the Shore Sails Tuning Guide
Light Heavy
Uppers 1700 2000
Lowers 1300 1800

From UK Tuning Guide:
6. Tension the uppers and lowers gradually and evenly (counting turns as you go), until there are approximately 1800 lbs. On each, as measured with a Loos tension gauge. Start with the uppers, adding just enough tension on the lowers to keep the mast in column as the uppers get tight. Put final tension on the uppers with backstay fully on. Release backstay, and put final tension on the lowers. As you tension the lowers the pre-bend will be reduced (they pull back on the center of the mast). Tighten until pre-bend is no more than 2-3".

7. Upper and lower tension should now be close to even. This should leave you with about 2" of pre-bend (it probably looks like more, but you can measure it by putting the mainsail halyard against the back side of the mast, and subtracting 2" from what you see). Tighten the lowers to reduce pre-bend (make mainsail fuller), let off to increase, (flatten mainsail). Conditions and mainsail shape will dictate the correct amount of pre-bend.

Simply stated, the tighter the overall rig tension, the greater the headstay tension; as long as the tension is nearly equal on uppers and lowers. In lighter air, when more sag is desirable, ease both shrouds slightly, and ease the lower shrouds more than the uppers to allow for more pre-bend. In heavier air, use more tension (2000 lbs) on both; the lowers should be as tight or tighter than the uppers to reduce pre-bend.

From Banks Sails Tuning Guide
Uppers: 44 - 45 on the Loos Tension Gauge.
Lowers: 45 - 46
***Note: These are Loos Model B numbers. Using the chart at this link with conversion from Model B to PT-2 gauge (Numbers Extrapolated linearly at end of chart for PT-2 values on scale greater than 40): http://www.loosnaples.com/how-to-use-pt-series-tension-gauges
Uppers: 44 - 45 Model B
Uppers: 41 - 42 PT-2 (Off-Scale)
Lowers: 45 - 46 Model B
Lowers: 42 - 43 PT-2 (Off-Scale)

Echoing Bob Rutsch's comments - the Banks Sail tensions listed are too tight in my opinion, and if done this way tension the rig greater than 2000 psi. Bob's suggestion for 8-10 kts wind has readings of 40-42 on the Loos Model B that equate to 36-39 on Loos PT-2 which is 1100-1600 psi

[This message has been edited by whk (edited 05-09-2007).]

Re: Mast Set Up/Rig Tension #502
05/09/07 08:55 AM
05/09/07 08:55 AM
Joined: Mar 2006
Posts: 36
Ottawa, Ontario, CANADA
CAN106 Offline
Senior Member
CAN106  Offline
Senior Member
Joined: Mar 2006
Posts: 36
Ottawa, Ontario, CANADA
Thank you - this is the type of info that I have been after.

Do you have the rest of the UK guide online? If so, would really appreciate a copy.

-C.


Corey Glynn
Re: Mast Set Up/Rig Tension #503
05/09/07 10:02 AM
05/09/07 10:02 AM
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,668
Portsmouth, RI
UK Tuning Guide - http://www.ukhalsey.com/sails/onedesign/j30/J30Tuning.pdf

[This message has been edited by whk (edited 12-01-2008).]

Re: Mast Step Postion measuring [Re: Russ Atkinson] #12829
01/09/12 10:00 AM
01/09/12 10:00 AM
Joined: Apr 2004
Posts: 159
grand rapids, mi
311 Temptation Offline
Western Great Lakes District Governor
311 Temptation  Offline
Western Great Lakes District Governor
Joined: Apr 2004
Posts: 159
grand rapids, mi
Let me try to work it out.
*Mast has excessive prebend so headstay sag is excessive. Thats checks out.
*Top of main won't behave because the backstay is too tight, creating excessive prebend. The backstay is a fixed length, and it's tight because the maststep is too far aft, which places the masthead more forward than the backstay wants to allow. The mast never becomes straight. It's like you always have some backstay trim on, even when the purchase is fully eased. Consequently your top batten and the top of the main refuse to trim up. They spill. The top batten won't align.
*When you move the step aft to class position, you'll tighten headstay sag and you'll actually have a straighter mast at the mast head. Your main will look better upwind and your boat should perform better in light air upwind and downwind.

Last edited by 311 Temptation; 01/09/12 10:01 AM.

Dell Todd
#311 Temptation
Holland MI
Re: Mast Step Postion measuring [Re: 311 Temptation] #12830
01/09/12 12:03 PM
01/09/12 12:03 PM
Joined: May 2007
Posts: 1,234
Newport and Naples
Cap'n Vic Offline
Senior Member
Cap'n Vic  Offline
Senior Member
Joined: May 2007
Posts: 1,234
Newport and Naples
1. eliminate concept of backstay tension causing problem. that was really loose.
2. Mast at fractional is too far forward when set further back than 25mm at step ... I am thinking it is impossible to get Max headstay tension and length unless at min step set back.
3. continue to wonder why most of the comments in these two threads talk about the need to change factory positioning of the step {Production line error? or just not enough feedback in the manufacturing run}
4. remember that the original j24s were based on launching spin from bag ... what we are seeing, I'm thinking, is that engineering 30 years ago ... was winging it by today's sophistication. dito need to template keels.
5. is there any advantage to being set at 40 mm which seems to be the max set back over 25 mm which seems to be the min set back?
6. the races that killed me this week were talking VMG speeds of ~3 kts. real light wind races.

Re: Mast Step Postion measuring [Re: Cap'n Vic] #12831
01/09/12 12:17 PM
01/09/12 12:17 PM
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Originally Posted by Cap'n Vic
Vic - numbered comments map to your's....
2. Mast at fractional is too far forward when set further back than 25mm at step ... I am thinking it is impossible to get Max headstay tension and length unless at min step set back.
3. continue to wonder why most of the comments in these two threads talk about the need to change factory positioning of the step {Production line error? or just not enough feedback in the manufacturing run}
5. is there any advantage to being set at 40 mm which seems to be the max set back over 25 mm which seems to be the min set back?
6. the races that killed me this week were talking VMG speeds of ~3 kts. real light wind races.


#2 - correct. All the moving parts work together for optimal setup.
#3 - I think you answered your own question. You'll need to go through and check all the rig measurements. Note Dave Erwin's comment about his mast plate being off center when they rebuilt hull #87.
#5 - I guess if you had a main cut for that setup, it could work, but that is not what the sailmakers build the OD sails to.
#6 - every little bit helps to tune for light air. Your smaller jib doesn't help you either in those conditions.

Re: Mast Step Postion measuring [Re: Russ Atkinson] #12832
01/09/12 02:16 PM
01/09/12 02:16 PM
Joined: Sep 2000
Posts: 393
Rockwood, MI, USA
Russ Atkinson Offline
Senior Member
Russ Atkinson  Offline
Senior Member
Joined: Sep 2000
Posts: 393
Rockwood, MI, USA
I'm going to take a stab at answering Vic's question:
5. is there any advantage to being set at 40 mm which seems to be the max set back over 25 mm which seems to be the min set back?

First, while the position of the mast step, rake, and pre-bend are all tied together, they are also separate
Position of the mast step, by itself, should not affect the mast rake. In other words and for a moment think that you are starting with a mast that is straight and verticle (perpendicular to the waterline), then, moving the mast step aft, will not necessarily move the mast tip forward. Moving the mast step aft with the mast fixed at the deck will cause the mast tip to move forward but if the mast is free to move at the deck, then moving the step aft will move the whole rig aft thus moving center of effort aft which, in theory will induce wheather helm, which should help light air performance.
However, moving the step back will, in effect, reduce the amount of rake that can be induced (with the mast step further aft, the entire mast is moved back closer to the back of the hole at the deck level) therefore the mast will not angle aft as far as it would if the step were further forward.
Although I have not trigged this out, my guess is that moving the step back from 25mm to 40 mm will not induce as much affect on moving center of effort as setting the step at 25mm and raking the mast.
After mast step position is set, shroud tension, forestay length and backstay tension, as adjsuted, will then determine rake and mast pre-bend. Depending on where you want to induce mast prebend will affect when you block the mast at the partners.

Re: Mast Set Up/Rig Tension [Re: Rhapsody #348] #12853
01/10/12 06:20 PM
01/10/12 06:20 PM
Joined: Apr 2000
Posts: 678
Maryland, USA
Bob Rutsch Offline
Governor at Large
Bob Rutsch  Offline
Governor at Large
Joined: Apr 2000
Posts: 678
Maryland, USA
The One Design Class Rules topic Mast Step Position turned into a discussion on mast rake, headstay tension, etc. Searching using the word 'headstay' right here in Racing Tools and Techniques turns up a number of good discussions including weather helm, headstay sag, and prebend. There are also five sailmaker tuning guides accessible under Rig Tuning from the front page.

Re: Mast Set Up/Rig Tension [Re: Tom Olsen] #12854
01/10/12 07:12 PM
01/10/12 07:12 PM
Joined: Oct 2006
Posts: 83
Waukegan, IL
jhoskins Offline
Senior Member
jhoskins  Offline
Senior Member
Joined: Oct 2006
Posts: 83
Waukegan, IL
My experiences on these subjects:

Balanced rudder/weather helm- I replaced Madcap's rudder with a "balanced" rudder 2 years ago. It adds some power steering for my autopilot. I race solo and double handed races and use an autopilot often. I agree with other posts that a well set up boat in a windward/leeward race should not have much wether helm with the original rudder. Reaching is anouther story. My balanced rudder only helps a bit. The planform is shifted forward about 1.5''

Mast step- When I got the boat it was all the way forward and the RF headstay was 1'' longer the class max. This setup worked ok. I tried moving the mast step all the way back, and shortend the headstay. Much slower in light air and upwind.
Currently I have the mast step 1'' back from the molded step and the headstay length about class max. This seems to be the best set up to me.

Rig tune- I like the UK quide, and I do a light/medium/heavy tune. I have learned to tune to tighter settings, so to not get caught with headstay sag when the breeze comes up.


John
Madcap 358
Re: Mast Step Postion measuring [Re: 311 Temptation] #12864
01/12/12 10:00 PM
01/12/12 10:00 PM
Joined: Apr 2004
Posts: 159
grand rapids, mi
311 Temptation Offline
Western Great Lakes District Governor
311 Temptation  Offline
Western Great Lakes District Governor
Joined: Apr 2004
Posts: 159
grand rapids, mi
Originally Posted by 311 Temptation
Let me try to work it out.
...
*When you move the step aft to class position, you'll tighten headstay sag and you'll actually have a straighter mast at the mast head. Your main will look better upwind and your boat should perform better in light air upwind and downwind.


Let the record show my error. Suffice to say "when you move the step to the correct class position..."


Dell Todd
#311 Temptation
Holland MI
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