Mast and Rigging calculations

TANSL · Feb 17, 2016

Hi Jarmo,
Perhaps the self-protection of Windows or your antivirus have rated MyR as "malicious" or something similar and leave it unable to boot. The first time you try to start any new .exe file the system performs a check which can take some time. It seems that nothing happens but after some time he asks the user what he wants to do with that .exe file
Make sure the file MyR.exe remains in the installation folder, that has not been erased.
To exchange files and screenshots you can use, if you want, my email: 657677483@orange.es. The more information you give me on what happens, the better I can serve you.
Thank you for your interest and I'm really sorry on so much discomfort.
Cheers
Ignacio

brian eiland · Feb 18, 2016

Sail Loading on the Rig, ...Rig loading on the Vessel

TANSL said: ↑

LP, I think, with this discussion, I can also clarify a lot my ideas, so thanks for your answers.
In my opinion, if the force on the sail is reduced to a single force applied by the CE, we are considering the bending moment between the masthead and CE is zero, which does not reflect reality (imo). Therefore, it is better to decompose the total force in two, Ftp in the masthead and Fp in the pintle (no more contact points of sail with mast). The problem and, I think, that's one of my differences with E. Spomberg, is how this load is distributed.
I have more questions on how to make the model in the area between the deck and the base but I do not have an answer I can give as correct.
Click to expand...

I think you might find some very interesting postings and references in this subject thread I started a few years ago. Here is that first posting i began the subject thread with:

http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293.html

brian eiland said: ↑

Sail Loading on the Rig, Rig Loading on the Vessel

Several weeks ago as I was searching thru the internet for analysis of 'rigging loads', I ran across a couple of subject threads on this BoatDesign.net forum, that reinforced my observation as to what an inexact science this appears to be. One was entitled "mast loads" and another entitled "loads for swept spreader rig". I begin this posting with some excerpts from those threads.
shu:
"they (Larsson and Eliasson) don't provide a means of determining the shroud loads due to headstay tension"

terhohalme:
"Exact headstay tension is impossible to determine."
"Multiplier 15 includes all guestimated loads...."

shu:
'The tricky part in Larsson and Eliasson is that you calculate "real" athwartships static loads on the rig ..., then apply separate safety factors for the other components based on some multiplier. What was the assumed factor of safety for the forestay?' (Ed:not the exact quote)

terhohalme:
"Impossible to know exactly..." (Ed: about the Nordic Boat Std)
" Where do you really need exact numbers? Tightening sagging of foresail ...will mix the whole calculating process"

shu:
"However, this all assumes that you have a permanent backstay.... I see no accounting for the additional loads the shrouds must take to oppose the forward component of the load in the forestay."

"...changing the sag of the forestay can make large differences in the resulting shroud tension. I don't know if I can predict the sag as a function of the foresail loads."

tspeer:
"So it's not as simple as figuring the component of the righting moment that is borne by the forestay. I suspect the factor of 15 applied to the forestay tension was intended...."

shu:
"assuming half the propulsive force acts at the hounds"

SailDesign:
"I have seen sticks that were designed to death from a safety factor point of view, but were pretzels when you sight up them under load."

"you just need to apply the sailing loads to each length of rigging, calculate the stretch, and plot it…" (Ed: how does one determine these loads with any exactness)

gonzo:
" I have observed that many of the rigging formulas don't take bending into consideration"

shu:
" had started looking at getting uniform unit stretch in all the shrouds to keep the mast more or less straight, but kinda gave up when the 3 shrouds all came out at very different ultimate diameters for safety, when their working loads were much closer"
____________________________________________________

What really surprises me about these few quotes, and many other discussions on engineering a sailing rig, is the total dependency on the use of 'guesstimates' and a variety of 'multipliers', some of almost unknown origin and application.

I recently purchased a copy of Larsson & Eliasson's Principles of Yacht Design, specifically to investigate their analysis of these rigging loads. But what I found at the very opening paragraph of their chapter on Rig Construction, "in dealing with the dimensioning and construction of the rig, over the years different methods have evolved, ranging from old rules of thumb…to sophisticated computer models for exotic composite materials. We will take a middle line (approach) using accepted practices (old rules of thumb?).….." Page two (text 202) of their chapter, "It is common practice that the transverse and longitudinal stability are studied separately"
And this is supposed to be a modern analysis? Later in the chapter (text222), "another factor which improves performance is the rake of the mast. Although not numerically proven…"

In this modern computer age why have they chosen to ignore the "sophisticated computer models"? Are sailboat rigs such a complicated structural problem to analyze?? Even the more simplistic steady-state ones (minus some of the more complicated dynamic questions)?

I guess my frustrations with understanding and defining the actual true loads on the rigging of a sailboat is best summed up at this Classic Marine website,

http://www.classicmarine.co.uk/Articles/rigging_loads.htm
"Rigging Loads- a study in guess work, or a tale of scientific progress?"

I will quote a few of the more notable passages from his very interesting summation:
a) He opens with a quotation from Douglas Phillips-Birt, "Masts are tricky things. It is not for nothing that Lloyd's, which is ready to specify the scantlings of nearly every other part of a yacht, washes its hands of them altogether and plants the responsibility for their size and shape squarely on the designer's shoulders.... suggesting that mast are perhaps a little beyond rational analysis."

b) For all its crudeness, this rule (a particular one) at least recognizes that the strength of the rigging relates more to the size of boat rather than the size of the rig.

c) You can see that these factors will bear on the issue, but the more you look at it, the less you can understand why they are combining in the way they are.

d) With a method so opaque in its assumptions, you never know what the range of validity is in terms of rig type, or arrangement of stays.

e) From Skene's book, the 'long method' is based on SAIL LOADING. Good Heavens! That is the first time it has been mentioned, which considering that it is the sails that load the rig, must be an improvement. Don't get too excited though. How much is the mast loaded and where? The answer is that nobody really (seems to) knows.

f) It provides not a real life start point for some rigorous analysis, but a common assumption that can be used to compare craft with each other, and/or with empirical data. To try to rationalize an assumption like this is at best pretentious—an attempt to ennoble guess-work, at worst dangerous—someone might believe it.

g) You may be getting the impression that this is not much advanced on earlier efforts.

h) Interestingly that the NBS method does not specifically relate mast loads to shroud tensions, but starts again with the righting moment.

i) Secondly, however numerate the rules appear, in practice they are all founded on empirical data.

j) So we are a long way from a complete picture of the loads in a rig, particularly tradition rigs. Why? For a start, the more sophisticated approaches have developed during the age of the BERMUDAN rig. The usual assumption that shrouds can be analyzed separately from fore/backstays probably holds better for Bermudan, than for gaffers, where there will be a complex interplay between peak halyard, runners, mainsheet, bowsprit, shrouds and so on.

k) And finally and MOST SIGNIFICANTLY, none of the methods derive loads from the force of the sails, which is after all what is loading the rig!!! Such an analysis could be fiendishly complex, but with ever more powerful tools and computers, I think it is not an unrealistic thing to attempt.

Brian notes, maybe I am being a little naive here, but I find it hard to believe in this computer era that we can't set up a three dimensional 'map' of a sailing rig and be able to analyze the forces in the individual components, and how they interact, and how changing one component's size, strength, geometry, etc, affects the other components, at least in a steady-state environment

I would imagine that we must first redefine the actual load paths that the forces of the sails use to transmit their power to the rigging. And then how and where do the rigging loads get transmitted to the vessel itself? I propose to start a new tread on this subject,"Sail Loading on the Rig, Rig Loading on the Vessel" . And I think it most appropriate to put it under the "Sailboat" subject heading as there may be a number of forum attendees that are only power boat oriented.

We have previously bunched all the sail loads together and assumed they acted thru the sail's CE. Granted this might yet prove to be a reasonable assumption, but I'm not convinced we have included all components of this summation of force (are there some vertical components we have ignored, etc?). Certainly this summation force is not necessarily acting at a perpendicular direction to the sail surface at this CE point, and it's not necessarily at a horizontal direction parallel to the water's surface. And remember the sail cloth itself can not exert a forward force on either the mast nor the forestay, at least not in an upwind situation. So how are these 'sail forces' getting physically transmitted to the vessel?

I'm sure there will arise considerable discussions about the magnitude of these sail loads, but at least this could be dealt with as a variable aside from the question of load path. If we have the load paths defined, then we can play around with a variety of different load magnitudes and look at those new consequences. And then consider how the load paths can deform in direction under different loads.

I don't pretend to be any kind of an expert in these engineering/computer structural analyses. I would just like to get a clearer picture of how the sails actually transmit their forces to the vessel; at what points, and in what path(s)??

Noted rigger Brion Toss relates to the "Flow of Forces. This is perhaps the most critical component of thorough rig appreciation. The pull of the jib on its stay, for instance, stresses the stay and its attachment points. But it also stresses the backstay, and thus the stern. Depending on hull structure and load level, the stress on the stern can also affect the alignment of the prop shaft. But wait, there's more. Some of the jibstay load is lateral, so that the upper shrouds are also stressed, siphoning so much of the load away that one can almost always make the backstay smaller than the jibstay, which reduces windage and weight aloft, as well as reducing rig cost. The upper shrouds, in turn, compress the spreaders, and all the wires at the masthead compress the mast. And so it goes, with the force from that one sail flowing around corners, in tension and compression, and intermingling and interacting with the forces from other sails as it makes its way to the water. If you can see this flow, really see the rig as a system, you will automatically be in good shape….to avoid missing significant relationships as well as significant details"
Click to expand...

brian eiland · Feb 18, 2016

One of those very interesting postings, with great links occurred here, posting #41 :
http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-3.html#post35427

TANSL · Feb 18, 2016

brian eiland, the paragraph that you are referring to, post #16, is concerning the case of free-standing mast that has nothing to do with the method proposed by the NBS. Therefore, his comments do not come.
With regard to abstract you make from other threads you started, I find so interesting that I promise you to read it carefully. Btw some comments are somewhat curious, if not humorous.
At the moment what I can say is that the NBS is a method that greatly simplifies things and, a few years ago to normal vessels, was very simple and very effective. Of course, it produces masts and rigging oversized, but that, when it is not about racing boats may not be very important. A good designer should always know the tools on his hands and should not use then when they are not adequate. Today, with programs behavior of fluids and existing programs of calculation a rig can be optimized to extremes that were unthinkable only 15 or 20 years ago.
If you want to demonstrate that the method of the NBS is obsolete, I would advise you not to waste your time on it. We all know that is outdated but it should not be discarded. Do you know the Cross method for calculating structures ?. It is obsolete but nobody would say is wrong.
The method of the NBS will be incorrect not by itself but because the designer uses it improperly.

TANSL · Feb 29, 2016

I am pleased to announce that is now available on my website the latest version of MyR, software for calculating mast and rigging. Thanks to the collaboration of some users it has been possible to fix several bugs and to add some accessories:
- Calculating the upper panel of fractional mast.
- Calculation of the pillar under deck for deck stepped masts.
- Catalog of profiles of masts and booms with automatic selection of possible profiles.
- Calculation of self standing mast.
Thank you all for the good reception given to this software.

brian eiland · Mar 7, 2017

I'm going to ask this question again.....

brian eiland said: ↑

Isn't the 'parametric', or 'distributed' loading of the mainsail on the mast one of the factors that affects the mast staying in column, and thus is a real concern when figuring the strength of the mast to resist bending (getting out of column) in order to be able to accept even higher compression loads??

Or put another way, isn't the distributed loading of the traditional mainsail helpful in allowing the mast to stand up to the loading??

If this is the case, then shouldn't the distributed loading by the mainsail be included as a factor in determining the proper mast size rather than totally subrogated to 'the max force it is likely to see as a result of the righting moment'??

SailDesign had written,
"First of all, for practical use in calculating mast strengths, ignore the "lift" forces on the sail,and concentrate on the max force it is likely to see. In our case, it will be max righting moment."

I've been concerned with the lack of 'distributed loading' on my mast-aft design as I do not have a sail attached to the mast extrusion, but rather 'point loading' by the rigging strands that are transmitting my sail forces to the vessel...

....and that brings up another question of how exactly do the sail forces (the forward driving portions in particular) get transmitted to the vessel...primarily thru the mast or what piece(s) of rigging? and what share each assumes?

SailDesign had written:
At last count, I have a collection of about 15 spreadsheets for rig
calculations.

Brian ask:
Steve, would you mind sharing a few of these with me. Then I may have a few more questions of you. I am looking for a preferred format, or possibly a modified format I might use in a full structural anaysis of my rig that is to begin very soon.
Click to expand...

valber · Mar 22, 2017

Alik said: ↑

TANSL, thanks for great efforts. It would be great to see something about catamaran masts, those are note covered...
Click to expand...

TANSL said: ↑

Alik, thank you for your words. I'll study the case of catamarans...
Click to expand...

Thanks for the useful tool, Ignacio!
Are there any news about the calculation of catamaran masts and rigging?
For current design I will go to FEM analysis. But may be are there some calculation methods for initial stages of cat design?

TANSL · Mar 22, 2017

Sorry but the application has not been very successful and I have stopped working on it. I have fixed bugs only, if there were, but I have not continued to develop it.

valber · Mar 22, 2017

TANSL said: ↑

Sorry but the application has not been very successful and I have stopped working on it. I have fixed bugs only, if there were, but I have not continued to develop it.
Click to expand...

That's a pity!

TANSL · Mar 22, 2017

Thanks Valeriy.
Best Regards.

mikeny · Mar 24, 2017

I rarely see the use of Steel Mast and in BS book he used a 5 inch steel tubing 1/8 inch wall thickness. Anybody else to use the steel mast

Mermaid Co · Mar 27, 2017

Online Ship Design,Towing,Lifting,Transportation Offshore Installation Calculators

http://www.mermaid-consultants.com/

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Mast and Rigging calculations

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Mast design software

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