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Over Hill Sailing Club
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Discussion Starter · #1 ·
Setting the tension on rigging, I have always used the method of changing tacks and adjusting tension until the lee shouds are equally taut, until they have tension but only a minimal amount. A couple of months ago I tried adjusting the tension on all the rigging using the "stretch" method, as described by Selden and other sources. This seemed to put WAY too much tension on the rigging. I was very concerned about having that much down-pressure on the mast, both from the aspect of bending the mast and deflecting the deck and beam that holds up my deck-stepped rig. It just seemed to be excessive to crank down that hard. Once the rig performs correctly with a straight mast, what's the point of additional wire tension? I took 4-6 full turns off my turnbuckles to get back to where they work perfectly well without all that pressure.
 

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Consider that most all sailboat designers intend that the set up of their rigs to be at 12-15% tension for normal sailing conditions ..... which means that sailmakers follow the exact same assumed tension when cutting jibs/genoas, etc., as the proper rig tension defines the amount of (catenary) SAG caused by a windloaded jib, etc. onto the forestay, etc.
If your rigging, especially the forestay/backstay, tension is much less than that value ... your boat will not point very well, it will be prone to 'skidding off to the lee' (and develop what 'feels like', but isnt, extreme weather helm), it will be 'cranky', and will quite possibly heel over aggressively, etc.

Rx: rig tension defines how much the leading edge of jib/genoas are 'cut'. Unless you specify differently from this 12-15% 'norm', the sailmaker will assume 12-15% wire tension and cut the leading edge of the sail to that expected wire sag.

;-)
 

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Chastened
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That's all correct, Rich but I don't seen an answer to his question in there.

He's inquiring what the purpose of the *extra* tension is, in the Selden tuning method.
That is to say, tension well beyond 12-15%.
 

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The Selden tuning method tells you how to achieve 15% of breaking tension using stretch measurements. They specifically tell you that 1mm stretch over 2m is 5% of breaking strength, and to tension to 3mm of stretch for 15% of breaking strength.
 

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I don't discuss my member
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SMURPH,
do you have a tension gauge?
What size is your wire?
Did you sail the boat with the stiffer rig settings?
 

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1982 Skye 51
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I have used both methods to tune the rig but i have gone back to the 1st method of taking the slack up in the lee shrouds. When I used the stretch method on my 10mm wire, i felt like i was trying to shove my mast through the keel. i didn't like that method, so i returned to the other way with no appreciable loss in performance and much less worry on my part.

i guess it is also pertinent that I have a straight mast, which is keel stepped and a tree trunk.
 

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Over Hill Sailing Club
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Discussion Starter · #7 ·
I don't have a tension gauge. That's why I thought to try the Selden method. Alex's assessment is correct, 3mm is the target over the 6'. In order to get that amount of stretch, you really have to put an uncomfortable amount of tension on the wire (1/4" on shrouds and lowers, 9/32" on headstay). Having dealt with materials all my life, I can sense this is simply too much stress on the materials involved. It may be fine for the wire but is no way ok for the deck, the long term health of swages, or compressive load on the mast. I can easily imagine the mast snapping under that much compression if any deflection were to occur. I have beefed up the girder and installed solid glass under the mast step but could still detect some deflection.

I understand how a lack of adequate tension can affect headsail performance but I believe there is a point of diminishing return.
 

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Heres the 'conundrum' ... stainless steel rigging wire (and with most structural boat design .... with an inbuilt 'factor of safety' of 1.5 for inshore designs, FS=2 for coastal designs, FS=3 or more for 'open ocean designs') has a 'yield' (permanent elongation) of great than ~30% UTS ... and includes all the boats supporting structure as well as the rigging. In spite of the loads that you surmise, those designers (probably) most assuredly have or should have built/engineered those designs to those accepted scantling/standards which include those 'scantling/historical' factors of safety. The factor of safety being applied 'and added' for 'unforseen and unknown' stresses that affect such designs. Simple 'strength of materials' from an engineering point of view.
If there are historical and repetitive FAILURES of your specific design, than by all means 'back off' from the standard induced stress; otherwise, I would suggest to simply accept what these quite knowledgeable designers have done.
 

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Over Hill Sailing Club
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Discussion Starter · #9 ·
Heres the 'conundrum' ... stainless steel rigging wire (and with most structural boat design .... with an inbuilt 'factor of safety' of 1.5 for inshore designs, FS=2 for coastal designs, FS=3 or more for 'open ocean designs') has a 'yield' (permanent elongation) of great than ~30% UTS ... and includes all the boats supporting structure as well as the rigging. In spite of the loads that you surmise, those designers (probably) most assuredly have or should have built/engineered those designs to those accepted scantling/standards which include those 'scantling/historical' factors of safety. The factor of safety being applied 'and added' for 'unforseen and unknown' stresses that affect such designs. Simple 'strength of materials' from an engineering point of view.
If there are historical and repetitive FAILURES of your specific design, than by all means 'back off' from the standard induced stress; otherwise, I would suggest to simply accept what these quite knowledgeable designers have done.
Yes, one would surmise that the system was designed for the strength of ALL the materials. In the case of these old Pearsons, they actually used balsa core under the mast step, believe it or not. This alone, makes me question the engineering. Many of them failed over time. As I indicated above, I removed the balsa over the header and laid in solid glass and laminated in two extra layers of 3/4" ply to the header under the deck but when this much pressure is placed on any span (the doorway underneath is maybe 20") there is going to be some deflection in a header maybe 5" in depth. Am wondering if the Selden specs. were meant for keel-stepped masts only.
 

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My remembrance of Alberg designs of this type indeed, require 'beefing up' that cross beam under the mast .... the Alberg 30 etc. Probably an inherent design fault .... 'creep' or 'plastic' deformation over time due to the loads.
In that case, Id websearch the A35 owners groups for the appropriate 'strengthening' of that cross beam, etc. to bring it up to consistent and equal to the structural design of that boat.

I know of several A30s (which were 'raced hard') which had to have this cross beam deck support modification, so the web literature should be available.
 

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Over Hill Sailing Club
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Discussion Starter · #11 ·
The A30s were notorious for this. The problem is with available depth. The only real fix I can imagine would be to replace the existing fg laminated beam with a stainless steel box beam or maybe even a solid piece of 6061 aluminum. Of course, the door height could be made lower so you'd have to duck down to get into the vberth:) Thanks for the input!
 

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Also take into account the idea that Selden's program was probably developed for boats designed well after the Alberg 30; boats perhaps better equipped to deal with the high loads created by newer materials. While the Selden program might work for your boat's rig, it may also turn your hull into a twisted pretzel.
 

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Over Hill Sailing Club
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Discussion Starter · #13 ·
Also take into account the idea that Selden's program was probably developed for boats designed well after the Alberg 30; boats perhaps better equipped to deal with the high loads created by newer materials. While the Selden program might work for your boat's rig, it may also turn your hull into a twisted pretzel.
Exactly. Selden's been around a long time though. I think Pearson got some of their masts from Selden: 1967. Thinking a bit further, it seems like wire size has actually decreased since then. A lot of the boats I look at have rigging that seems very thin. It could be that the larger, older sizing does not work using the stretch method because of larger size???
 

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Also take into account the idea that Selden's program was probably developed for boats designed well after the Alberg 30; boats perhaps better equipped to deal with the high loads created by newer materials. While the Selden program might work for your boat's rig, it may also turn your hull into a twisted pretzel.
That may be. However, if they designed the rig for lower tension, then they also intended to have sails cut with less 'catenary', as RichH said.
 

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....it seems like wire size has actually decreased since then. A lot of the boats I look at have rigging that seems very thin. It could be that the larger, older sizing does not work using the stretch method because of larger size???
No. All rigging wire (1 x 19) will stretch the same amount if loaded to the same percentage of its working load. Whether it is 1/8" or 1".
 

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It is important to take note that modern sails stretch much less than sails from 40 or 50 years ago and this can have a major impact on rig tension. Prebend for instance isn't as needed to day as it used to be, because the sails hold their shape much better.
 

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Over Hill Sailing Club
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Discussion Starter · #18 ·
No. All rigging wire (1 x 19) will stretch the same amount if loaded to the same percentage of its working load. Whether it is 1/8" or 1".
I should have been more clear in wording that. If the wire used nowadays is generally smaller (which may or may not be true), then its breaking strength would be less as well. 15% of the strength of smaller wire would be less.
 

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old albergs used 304 wire...as did some old pearsons...did yours come with 304 or was it already changed?

I much prefer slightly lose than slightly tight...thats all I can say

too many people love the all out tight here, maxstrength...backstay hauled in like crazy only to do damage on these older boats

if your mast compression beam is flexing too much fix that first before doing any "tuning" on the rig

I like 1-2 inches movement of cap shrouds no sails up
2 inches for lowers
3-4 for forestay
and around 4 no load on backstay and 2 when loaded

this is all no load...

ps Im not a fan of the tightening shrouds to leeward as too many people take TOO much slack out...they should not be banging around but definetly not be taught.

old boats losey goosey new modern high tech boats its just different...very different
 

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15% of the strength of smaller wire would be less.
Less what? Stretch? Not at all. 1mm of stretch per 2 meters of wire is equivalent to 5% of the breaking strength regardless of wire size. 1/8" wire will stretch 1mm at 5% or its breaking strength over 2 meters. 1" wire will stretch 1mm at 5% of its breaking strength over 2 meters. Obviously the larger the wire the larger the breaking strength and the larger the load at 5%.

From the Selden rigging guide, free online:
 

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