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  #41  
Old 01-23-2012
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Quote:
Originally Posted by DougSabbag View Post
Casey.... this was what I did not do after the main mast stepping 10 months prior to my rig "failure":
"Then you take the boat for a sail in a stiff wind and basically tune the rig so that the lee shrouds do not go slack..."

Assuming that the lee (downwind) shrouds / stays do go slack, and you adjust those to be, oh lets say 65 lbs of tension, then wouldn't the mast be bent toward that recently adjusted side when you come about?

Or how do you do this dynamic tuning, without pulling the mast to one side or the other, if you're adjusting it while she is heeled over?

Please pardon my ignorance, but what the hell, I am ignorant. :-)
Doug,
I also thought that tensioning the lee shroud would also drive the mast through the bilge of the boat as you kept tensioning each side as you tack. The key is, as someone previously posted, is do each side 1/2 at a time and do not exceed design tension. Here is part of the Loos gage owners manual, that describes loose vs tight rig.
http://68.171.211.157/how-to-use-pt-...tension-gauges

http://68.171.211.157/how-tos/tension-gauges

Last edited by casey1999; 01-23-2012 at 05:21 PM.
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  #42  
Old 01-23-2012
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Quote:
Originally Posted by tommays View Post


freedom of movement on two axis
Ohhhh, OK, yes, now that I see this, we did have those. Nevertheless, will these really absorb all the wrenching, for and aft, (pumping), if your mast is not tuned well enough?

According to the "rigging experts" who have listened to our story, that pumping action is what caused the metal fatigue which broke 2 chainplates at their tabs, just above the ribs, and just under the decking.

It is rather frustrating that some "experts" will provide a very reasonable explantion that fits with all the history and facts, and then some experts seem to be in denial of that, and point to pitting and corrosion as the culprit.

I feel more like I am in a room full of lawyers than reasonable men. :-)
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  #43  
Old 01-23-2012
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Quote:
Originally Posted by casey1999 View Post
Doug,
I also thought that tensioning the lee shroud would also drive the mast through the bilge of the boat as you kept tensioning each side as you tack. The key is, as someone previously posted, is do each side 1/2 at a time and do not exceed design tension. Here is part of the Loos gage owners manual, that describes loose vs tight rig.
How to use PT Series Tension Gauges

How to use Tension Gauges
Thank you very much!! I emailed this to myself to have on-hand!
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  #44  
Old 01-23-2012
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So if conventional tuning (and cable sizing) depends on the leeward side going slack, and that constnatly cycles the load causing cyclic stressing which in turn weakens the cables...

Does that mean it would be better for the working life of the shrouds, to spec shroud cables that could be tensioned down enough so that the leeward side never went slack? Keeping a uniform tension, or a more uniform tension, on the shrouds all the time?
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  #45  
Old 01-23-2012
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Quote:
Originally Posted by hellosailor View Post
So if conventional tuning (and cable sizing) depends on the leeward side going slack, and that constnatly cycles the load causing cyclic stressing which in turn weakens the cables...

Does that mean it would be better for the working life of the shrouds, to spec shroud cables that could be tensioned down enough so that the leeward side never went slack? Keeping a uniform tension, or a more uniform tension, on the shrouds all the time?
I would tend to agree with this statement. Even the Loos gage manual previously posted tends to contridict itself. On one hand it says if a lee shroud goes slack (0 lbs load) then the strength of mast and spreader is reduced by factor of 2, yet the tight tension diagram shows 0 lbs on the lee shroud, I would think you would want say 5% load.

I have in fact measured my lee shroud while sailing in a stiff wind and I do infact have 5% load on the lee shroud and 8% on windward.
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  #46  
Old 01-23-2012
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Quote:
Originally Posted by DougSabbag View Post
According to the "rigging experts" who have listened to our story, that pumping action is what caused the metal fatigue which broke 2 chain-plates at their tabs, just above the ribs, and just under the decking.
It is rather frustrating that some "experts" will provide a very reasonable explantion that fits with all the history and facts, and then some experts seem to be in denial of that, and point to pitting and corrosion as the culprit.

I feel more like I am in a room full of lawyers than reasonable men. :-)
Doug I feel your frustration. I hate it when experts disagree.


I have a mental picture of what happened, let me know how accurate it is.
The shrouds were a little loose. The wind picks up and the top of the mast is whipping around more than it should. Maybe the top of the mast moving a foot out of column from where it should be. The mast is lets say about 60 feet tall. The top is a foot or two out of column. How much does that affect the angle of the shroud between the deck and the shroud. Maybe one degree.

So the theory that the chain plates were damaged by loading in one storm does not make any sense to me at all.

The place that they broke is exactly where they would be expected to break if they had oxygen depletion corrosion.

Now the mast whipping around certainly didn't help but there was another thread where someone gave his old chain plates to a friend with a machine shop to use for scrap metal because they looked perfect. A few months later the machine shop guy tried to cut one in a shear. It shattered and crumbled.

My son is a rigger in Annapolis and I asked him about this a long time ago. His response was that if you are going to go to the trouble and labor to remove and re-bed then he would never even consider not replacing them.
Of course at rigging shop rates it is a no-brainer but even for do-it yourselfers chain plates are not forever.

I would submit that if there is anyway you can damage a chain-plate by pulling in any direction that is generally up with the wire shroud meant to be attached to it, the chain plate is not properly designed or is damaged.
The chain plate should be able to handle much more than the wire.

Last edited by davidpm; 01-23-2012 at 06:40 PM.
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  #47  
Old 01-23-2012
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My exposure to conditions like these are limited to one week in a Farr 395 with a full crew.
The wear and tear on the boat is impossible to explain. It sounded like someone was beating the hull with a sledge hammer. You could hear the fiberglass crack like it was being destroyed in a giant grinding machine.
The idea that any part could sustain loads that would damage it is very understandable.
The chain-plate however is the last part that should fail. The tangs, swages or wire, turnbuckles, pins even cotter rings I could see failing first by design.
The chain plates should be strong enough that they do not flex under any normal condition to suffer any fatigue.
I have had a few off forum communications with Doug and consider him a friend.
If he is going to do this again, which is is planning I think this is an important enough subject look at carefully.
If the failure of the Gulfstar rig was 99 percent warn out chain-plates and 1 percent rig tuning that will affect his and many others decision making.

As usual I'm open to learning new stuff.
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  #48  
Old 01-23-2012
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Quote:
Originally Posted by davidpm View Post
The chain plate should be able to handle much more than the wire.
Not necessarily, ..... even with apparent 'beefed up' thickness, etc. Many chainplates have kinks and bends that cause undue 'flex', etc. that are considered 'stress risers' by structural folks. Such 'geometrical anomalies' cause the 'lines of stress' to become 'concentrated' and act upon such 'localized' zones with much more than the 'average' stress applied to the part ... sometimes many 'times' more than average at or through the 'anomaly' ... makes a good or well experienced engineering designer to 'wince' when they see such.

Material strength and 'longevity' depends a LOT on 'geometry' and not simply 'cross section'; Fatigue endurance depends a LOT on the simple lack of 'surface roughness', and lack of 'flexure', etc. Fatigue cracking is the first progression in 'crevice, etc. corrosion issues, etc. and fatigue is additive and can begin during the manufacturing process of the metal.
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Old 01-23-2012
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I am not capable of tuning under sail simply because I need to keep my hands on the wheel and would probably lose the tensioner over the side, but I do try and balance the rib dockside. My problem is trying to tension the forestay as it has the self furling covering the stay and therefore I cannot connect the tensioner directly. Is there a solution to this?
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Old 01-23-2012
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Originally Posted by ron_hudson View Post
I am not capable of tuning under sail simply because I need to keep my hands on the wheel and would probably lose the tensioner over the side, but I do try and balance the rib dockside. My problem is trying to tension the forestay as it has the self furling covering the stay and therefore I cannot connect the tensioner directly. Is there a solution to this?
I put boat on auto helm and measure tension. Have a line around my wrist and attached to the Loos gage- cannot loser overboard. As the Loos instructions say, you cannot measure forestay tension if you have a roll furler- you need to measure backstay tension and then you can use trig to calculate forestay tension based on the angle of the forestay and back stay.
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