Rig computations ?

[fcfc]

Hello,

How efforts in shrouds like that (one intermediate, and one top shroud, without spreaders) are computed ?

Is it possible without FEA ?

Thanks.

 

[Tomsboatshed]

fcfc:

There are a number of very good books which outline and provide an example of how such loads are calculated. I found “Principals of Yacht Design” (Larson, Eliasson, and Orych) to be useful; as is “The Complete Rigger’s Apprentice” by Brian Toss.

I find both books to be useful for this (and good reading too!)

I hope you find this useful.

Regards,

tom

 

[fcfc]

Unfortunately no.
Principles of yacht design does not deals with this kind of rig (rather recent AFAIK, way less than 10 years od).
Regards.

 

[fcfc]

Neither the ISO rule for rigs (12215-10)

 

[CarlosK2]

is a Pogo

Accueil - POGO STRUCTURES https://www.pogostructures.com/?lang=en

Pogo 30 or Pogo 36 with carbon mast

 

[fcfc]

It is not MY "D2".

The first drawing is Pogo 36, the second one is Sunfast 30OD.

I am pretty sure that if they put a "D2" there (without spreaders), it s because it is needed. And it has advantages over a conventional 1 ou 2 spreaders rig as ISO or principles yacht design drawings.

I am just wondering how did they compute forces in D2 and V2, since it looks like an hyperstatic problem.

 

[TANSL]

Sorry, I deleted my previous post because I thought CarlosK2's post made mine irrelevant.

I am just wondering how did they compute forces in D2 and V2, since it looks like an hyperstatic problem.

I think so, too. There are procedures to calculate hyperstatic structures but I don't know how they would apply to this case.

 

[CarlosK2]

Note how much it costs in money and technology to get a "20 square meter sailboat per ton" ... when the Displacement exceeds 1-1.5 Ton

The amount of sail, the staysail and the twist of the main have to fit

With 1 Ton you don't need a carbon mast, and you can enjoy a wonderful versatile fractional rig: MainSail = 2 x StaySail

Exaggerating according to my style, one could say that above 1 Ton most sailboats are actually motorsailers (because they hoist 10 square meters per ton) or should have a Schooner rig

 

[jehardiman]

I am pretty sure that if they put a "D2" there (without spreaders), it s because it is needed. And it has advantages over a conventional 1 ou 2 spreaders rig as ISO or principles yacht design drawings.

I don't think it has "advantages" over other rigs but is necessary given the sail and rig. Like the rig shown by CarlosK2, the only reason you would need D2 (and the associated baby stay) is to fix the mid-point of the fore and aft bend you are going to put into the stick with the boom tension. Yes it removes a spreader or jumper aloft, but I bet it has more to do with the sail fabric and construction, that being the only way to induce mast bend...there being no backstay (Pogo) or just runners (Sun Fast 30 OD). I would calculate it as if the mast ended at the D2 hounds, because everything above that is dependent only on the sail loading, much like jumpers on a fractional rig with a masthead kite.

 

[DCockey]

How efforts in shrouds like that (one intermediate, and one top shroud, without spreaders) are computed ?

Is it possible without FEA ?

Someone with an understanding of statics and very basic vector math should be able to create formulas for the shroud configuration in the first post equivalent to the formulas posted for other shroud configurations. The calculations can be done with paper and a pencil; a calculator, set of trig tables and/or a slide rule.

 

[TANSL]

This case is not so simple because, when considering the equilibrium of the node, when decomposing the forces, there are more unknowns than equations. Methods such as virtual work, for example, must be used to solve these so-called "hyperstatic" cases. (By the way, don't ask me how because I, at this moment, wouldn't know how to pose the corresponding equations.)
This is my opinion. Perhaps some expert can tell me where I am going wrong.

 

[CarlosK2]

Now on a more serious note

(the world on a large scale is such a horrible madness that I give my soul to comedy)

The problem is not the calculation of that cable, but that the mast is made of carbon, in fact the version with an aluminum mast is not like that, by the way: with an aluminum mast the Pogo hoist 17 square meters per ton

I'm sorry i can't be of help because i have no experience with these riggings with a carbon mast

 

[jehardiman]

How efforts in shrouds like that (one intermediate, and one top shroud, without spreaders) are computed ? Is it possible without FEA ?

This case is not so simple because, when considering the equilibrium of the node, when decomposing the forces, there are more unknowns than equations. Methods such as virtual work, for example, must be used to solve these so-called "hyperstatic" cases. (By the way, don't ask me how because I, at this moment, wouldn't know how to pose the corresponding equations.)
This is my opinion. Perhaps some expert can tell me where I am going wrong.

Actually it is fairly simple using moment distribution/Hardy Cross analysis as long as you keep checking Euler buckling (i.e. just like we did it in the 1970's). All the stays support no moments and assume columnarity. This method also allows for sectional taper to save weight aloft.

 

[TANSL]

We agree that this structure, and any other, can be studied by one procedure or another. The problem, from my point of view, is to give a real solution, that the OP can use, for this case. It is easy to say "use Cross' method", but how is it applied here? I think it would be more appropriate to apply the virtual work theorem.
I suppose you mention Euler thinking about the possible buckling of the spreaders or mast because in cables I do not think it is possible to make that consideration.

 

[jehardiman]

We agree that this structure, and any other, can be studied by one procedure or another. The problem, from my point of view, is to give a real solution, that the OP can use, for this case. It is easy to say "use Cross' method", but how is it applied here? I think it would be more appropriate to apply the virtual work theorem.

I think you and fcfc are overthinking this. While virtual work methods can give you deformation energy inside the system, a mast is a simple beam and can be treated as such by Hardy Cross/moment distribution as the shrouds are just tension members (i.e. point forces) only. Once converged, it is a simple matter to check sectional compression and buckling. Set it up in a recursive QUATTRO Pro spreadsheet, set the solver (much better that Excel's), and Bob's your uncle.

I suppose you mention Euler thinking about the possible buckling of the spreaders or mast because in cables I do not think it is possible to make that consideration.

Wellll...Duuhhh! Fcfc wants the load in shroud D2...it is a shroud so no moment. In order to find what that load should/can be, you need to determine the mast section you need assuming columnarity. Now you can do that based on an assumed sail area loading and then reduce that to a proportional loading of each shroud based on geometry, but I doubt a published set of generalized equations have been made for this indeterminate condition, especially WRT mast bend.