Discontinuous vs. Continuous Rigging & Spar Compression Loads

[Bluebeard]

Originally Posted by Elie

In my opinion, stretch and windage are less important on a discontinuous setup.But compression on the spreaders against the mast section is more important, and therefore speaders and spreader support in the mast must be significantly stronger. Charleston Spar provided me with a discontinued rigging setup, and :
1: spreders much bigger and rigid than expected;
2- in mast spreader support very strong;
3- Wire size diminishing with each pannel from to top to lower.
4- The lower stay size is much larger because it collect all the tension and bring it to chainplate.
5- All considered, the total weight is reduced significantly, stetch is noticibly reduced, and ajusting rigging tension on each shroud is a real complicated affair...

If you change the angle of the stays ( with a greater angle away from the vertical ) then the load in the spreaders will increase. But you have then changed the configuration so you are no longer comparing like with like and you cannot therefore reach a valid conclusion as pt 1.
Therefore pt 2 is irrelevant.
Pt 3 is plain wrong. All the lateral load on the rig is transmitted to the chain plates by the lower diagonal stay. The size of that stay in comparison depends on the rig geometry but it is unlikely to be smaller than any others.
Pt 4 if it is referring to the "vertical" stay from the lowest spreader to the chainplate is correct.
Pt 5, you refer to wire, in which case for two rigs of similar configuration, the loads will be the same and hence the wire sizes will be of similar cross sectional area, whether there is a single wire, as in a discontinuous rig or multiple wires as in a continuous rig.
Please explain where the weight saving comes from.

[Elie]

Besides the fact that I found your reply more then a bit stuffy, I believe that YOU are wrong. My setup had been made by Charleston Spar and I see as a fact that There is less weight and cable are smaller then what is found in a continuous therefore pt 3 is correct. Your comment about pt five is ridicule: The redundancy induced by multiple continuous wires that attach to the chain plate add unecessary weight to the system. In my discussions with the French mother compagny of Charleston Spar I was made well aware of the validity of all the points I mentionned in my remarks, and I stand by them. You may not agree, and believe whatever you want, but I will leave it at that : think what you want, since I don't wish to enter into a pointless exchange with what I consider a lack of savoir vivre and gross attitude.

[Don C L]

Originally Posted by Don C L

I sent an email to my naval architect/engineer buddy.. he got much better grades in elementary school than I did. I have never had rod rigging but I always wondered about the wisdom of forcing a bend in it at the spreaders. I do see the wisdom of locking in the spreaders though with the discontinuous... that would be worth the extra weight and complexity to me.. for cruising anyway. When I was quite young I wanted to get tapered rod rigging for my Columbia 24. Oh I am sure I would have gotten 2 or 3 more knots out of it if I had.

Well my friend is clearly too busy to do an analysis but he did say:

"Yes, this makes sense. The standing rigging and the mast are in static equilibrium with high tensile/compression loads respectively, even when the boat is sitting still in the marina. When you and I were having the conversation earlier I was referencing only the tension in the windward shrouds, as they have the highest loads. I have never done an analysis of this, but it's not at all implausible to me that the compression load on the mast can be many times the weight of the boat."

My response is, oh ****! I need to look again at my new mast support to see if I really overbuilt it!

[Bluebeard]

Originally Posted by Elie

Besides the fact that I found your reply more then a bit stuffy, I believe that YOU are wrong. My setup had been made by Charleston Spar and I see as a fact that There is less weight and cable are smaller then what is found in a continuous therefore pt 3 is correct. Your comment about pt five is ridicule: The redundancy induced by multiple continuous wires that attach to the chain plate add unecessary weight to the system. In my discussions with the French mother compagny of Charleston Spar I was made well aware of the validity of all the points I mentionned in my remarks, and I stand by them. You may not agree, and believe whatever you want, but I will leave it at that : think what you want, since I don't wish to enter into a pointless exchange with what I consider a lack of savoir vivre and gross attitude.

Your response doesn't surprise me.
It's not savoir vivre or attitude, it's engineering!
Is your opinion or the sales pitch you have been given based on engineering logic?
If it is please send it to me and if I'm wrong I'll publically eat my words and apologise.
But I'm quite safe.

[Bluebeard]

Originally Posted by Elie

Besides the fact that I found your reply more then a bit stuffy, I believe that YOU are wrong. My setup had been made by Charleston Spar and I see as a fact that There is less weight and cable are smaller then what is found in a continuous therefore pt 3 is correct. Your comment about pt five is ridicule: The redundancy induced by multiple continuous wires that attach to the chain plate add unecessary weight to the system. In my discussions with the French mother compagny of Charleston Spar I was made well aware of the validity of all the points I mentionned in my remarks, and I stand by them. You may not agree, and believe whatever you want, but I will leave it at that : think what you want, since I don't wish to enter into a pointless exchange with what I consider a lack of savoir vivre and gross attitude.

Sorry, one further point.
It is only a pointless exchange if you regard this forum as an suitable place to express prejudices and unsubstantiated opinions.
It is quite clear that there are people here ( myself included ) who are looking for valid information and that if they accept information that is wrong it could be expensive or even dangerous.
Therefore I cannot leave your statements unchallenged.
Please produce the engineering to prove your claims.

[Elie]

Originally Posted by Bluebeard

Sorry, one further point.
It is only a pointless exchange if you regard this forum as an suitable place to express prejudices and unsubstantiated opinions.
It is quite clear that there are people here ( myself included ) who are looking for valid information and that if they accept information that is wrong it could be expensive or even dangerous.
Therefore I cannot leave your statements unchallenged.
Please produce the engineering to prove your claims.

I will certainly not 'produce proof' of my own rigging engeniering, (suffice to say the proof is in the pudding), no more than you would substantiate you own categoric and baseless pretention. Take it or leave it, and please spare me this specious quasi legal argumentations, its almost comical. Anyway like in other forums, member decide for themself about the quality of info.
For the other that may be interested, have a look at this site where Navtec talk about the subject... http://cableloft.com/pdf_for_web/1-m...troduction.pdf

[Bluebeard]

Originally Posted by Elie

I will certainly not 'produce proof' of my own rigging engeniering, (suffice to say the proof is in the pudding), no more than you would substantiate you own categoric and baseless pretention. Take it or leave it, and please spare me this specious quasi legal argumentations, its almost comical. Anyway like in other forums, member decide for themself about the quality of info.
For the other that may be interested, have a look at this site where Navtec talk about the subject... http://cableloft.com/pdf_for_web/1-m...troduction.pdf

My position is based on engineering.
If you believe it to be specious quasi legal, then you have a problem.

I can produce calculations to back up my points.
There is clearly no value in giving proof to you, but if anyone else in the forum is interested please let me know and I will draw up the engineering. Somebody will have to explain to me how to load scanned document on to here though. ;-))

[Don C L]

OK you guys, here is something to chew on.

The article is by Gunter Grabe and it appeared in: High Performance Yacht Design Conference, Auckland, 4-6 December, 2002

I cannot republish the entire article but here is the abstract:

Abstract. The “DYNA” is a research sailing yacht of the TU-Berlin, also called the “Sail-Force-Dynamometer”. She is an entire measuring device for aerodynamic and hydrodynamic forces. The focus in the paper is on measured and computed forces in the standing rigging and in the mastfoot. The aim of the work is to better predict loads and deformations of rigs from high performance yachts for design purposes. The forces in the rig are measured with 20 separate force transducers for mast compression, all shrouds, stays and sheets. A global FEA model of the rig is built up. Geometrical non linear computations for the load cases dock pretensions and sailing upwind with 30° heel are performed. Results are internal forces and deformations of the rig. The loads from the sails are calculated by a load model based on the righting moment of the “DYNA” and the sag angles of the sails. The results of the measurements and the computations are compared with each other.

My friend's added note:
It was a 33' boat with a displacement of 9,171* pounds. The compression load at the base of the mast with 30 degrees of heel was about 12,600* lbs. (1.4 x displacement). I could imagine it going well beyond that with greater heel angle and with dynamic loading.

[Adelie]

Originally Posted by Elie

In my opinion, stretch and windage are less important on a discontinuous setup.But compression on the spreaders against the mast section is more important, and therefore speaders and spreader support in the mast must be significantly stronger. Charleston Spar provided me with a discontinued rigging setup, and :
1: spreders much bigger and rigid than expected;
2- in mast spreader support very strong;
3- Wire size diminishing with each pannel from to top to lower.
4- The lower stay size is much larger because it collect all the tension and bring it to chainplate.
5- All considered, the total weight is reduced significantly, stetch is noticibly reduced, and ajusting rigging tension on each shroud is a real complicated affair...

You have item 3] backwards, vertical wire size will decrease from bottom to top. I expect the diagonal sizes will also decrease bottom to top but not as much. You got this right in 4].


1] Spreader size and rigidity will be dependent on angle of diagonals to verticals and on pre-loading.

Since racing boats prefer heavily pre-loading their rigs in order to get the least sag in shrouds and stay and they are also more likely to have discontinuous rigs there is a really strong argument that spreader size and discontinuous rigging are correlated rather than being causally linked.

[Don C L]

Originally Posted by Don C L

OK you guys, here is something to chew on.

The article is by Gunter Grabe and it appeared in: High Performance Yacht Design Conference, Auckland, 4-6 December, 2002

I cannot republish the entire article but here is the abstract:

Abstract. The “DYNA” is a research sailing yacht of the TU-Berlin, also called the “Sail-Force-Dynamometer”. She is an entire measuring device for aerodynamic and hydrodynamic forces. The focus in the paper is on measured and computed forces in the standing rigging and in the mastfoot. The aim of the work is to better predict loads and deformations of rigs from high performance yachts for design purposes. The forces in the rig are measured with 20 separate force transducers for mast compression, all shrouds, stays and sheets. A global FEA model of the rig is built up. Geometrical non linear computations for the load cases dock pretensions and sailing upwind with 30° heel are performed. Results are internal forces and deformations of the rig. The loads from the sails are calculated by a load model based on the righting moment of the “DYNA” and the sag angles of the sails. The results of the measurements and the computations are compared with each other.

My friend's added note:
It was a 33' boat with a displacement of 9,171* pounds. The compression load at the base of the mast with 30 degrees of heel was about 12,600* lbs. (1.4 x displacement). I could imagine it going well beyond that with greater heel angle and with dynamic loading.

OK, here is the link:

http://www.fhkiel.de/fileadmin/Data/...P-Yacht_02.pdf

[TheThunderbird]

In static terms, there is no difference between continuous/discontinuous rigging,

However, joints of verticals and diagonals work differently . It is important that the spreader is charged orthogonally, with the least bending or torque ... and here discontinuous comes at an advantage.
Also, the close alignment of the diagonal is easier in a discontinuous rigging, in principle at least (generalizations can't be avoided here...)

Discontinuef rods were introduced to play with diminishing diameters upwards, for weight and Windage benefits on racing designs,

Dynamic stress is way all more important in design, hereby continuous is better and more elastic , less parts, easier trimming (on deck!), lower concern for faulty joints...

The proper design and positioning of running back-stays vis-a-vis staysail, inner forestay, and the reefed main, all add to mast stability more effectively than the continuous/discontinuous rigging dispute)

In that, the Solent and the cutter rigging with masthead look superior to me:-)

In terms of ultrasonic checking, for extraordinary maintenance, a full rod rigging is better than 1x19wire, and if discontinuous easier to change

[barnakiel]

Imho the differences will be marginal. Imagine the shrouds can work somewhat at the spreader tip. But such an assumption assumes a poorly set up rig in the first place.

I think the reasons for choosing the discontinuous system are elsewhere.

b.