Sail Loading on Rig, Rig Loading on Vessel

Boat with NO HULL

The 2009 version of the Mirabaud LX, Thomas Jundt’s foiler has a new hull that favours speed and stability by light wind. Its mast has also been reinforced in order to improve the upwind sailing angle, as well as the reactivity of the boat. Finally, the sensors used to trim the foiler’s flaps have been improved, allowing a better precision whilst sailing. Introduced in 2008 as “the boat with no hull”, the Mirabaud LX has recently proved that this wording could be translated into reality by sailing on its hydrofoils with no buoyancy at all. Thomas Jundt and his team have accomplished this challenge and validated a different and creative way to consider the sport of sailing.

...and check out this YouTube Presentation
http://www.youtube.com/watch?v=Lx6K1PzqnG0

 

Foilers have been around for decades of course and carbon fibre composites are allowing the concept to move into lighter air operation.



The times have moved on since this thread started and German.. Lloyds publish some reasonably well considered guidelines which I have attached here.

Any rig desin these days particulalry if a novel design, should be using FEA. All you need is beam elements and tension (cable) elements for the rig evaluation. Then a column buckling assesment when you find your compressions to refine the mast section.

The approach is to assess the sail forces for smooth water at the sail attachment points, these are applied to a non pre-tensioned beam and cable FEA model. A FOS accounts for pre-tension and dynamic loads. This approach seems to be working.

We use Strand7 for this and it is very easy to use.

 

Dyneema Testing Worldwide

DSM Dyneema, producer of Dyneema®, the world’s strongest fiber™, is recruiting the globe for 40 ‘Skippers’. They can test running-rigging made with Dyneema® fiber and share their experiences through social media.

If you are selected to join the 2011 Dyneema® Experience Team, we will re-rig your boat completely free of charge with ropes made with Dyneema®. All we ask of you is that you test and experience rigging with Dyneema® and share this with us, your friends, family and other sailors worldwide,

http://www.dyneemaexperience.com/?utm_source=scuttlebutt&utm_medium=mailing&utm_content=Join%2Bnow&utm_campaign=Dyneema%2BExperience%2BTeam

 

Dyneema

Hi Brian, Vectran is quite a bit stronger than Dyneema so I'm not sure where the claim of strongest fibre comes from? Published data is Dynema 2432MPa and Vectran 3000MPa ultimate tensile strength. But Dyneema (HM-PE) is a bit lighter. Density of Dynex is 980kg/m3 but Vectran is 1400kg/m3. But Vectran like PBO is a naturally highly oriented polymer and needs no heat treeatment or stretch processing to get to HM. But HM-PE is acheived by heating and stretching to orient the fibres. This process is not 100% efficient so there are non optimal fibres in the construction. Plus as the polymers have been stretched they like to return to their original condition. This is called relaxation. Commonly called creep but creep is different. VE/PBO being naturally oriented can be loaded at 50%+ UTS higher loads continuously with no relaxation. However HM-PE can only be loaded at 30% of its UTS continuously otherwise it can relax and loss its tension. So for standing rigging its a toss up. I like Vectran as I can tie knots in it, splice it and not worry about UV degradation of relaxation.
Regards Peter S

 

Just found this languishing in some old emails, and wanted to post it to this thread for future reference
Brian


Most modern cruising boats are equipped with 1x19 wire rigging, which I worked with extensively during my time as a rigger at Southbound Cruising Services in Annapolis, Maryland.

It is important to ensure that Dux is protected from any kind of chafe, such as where it contacts spreaders. Photo by Maria Karlsson
Breaking strength is the prime factor to consider in these situations. First, you must calculate the RM30, which is defined as the “righting moment,” or the amount of force in foot-pounds needed to heel the boat 30 degrees, using the boat’s beam and displacement.

However, while the RM30 serves as a good baseline for a rig’s normal working loads, few ocean-going boats remain within the realm of “normal working loads” under sail. Shock loads from falling off big waves, the added load of a knockdown or capsize, and other stresses all need to be accounted for, so a safety factor is added to create an RMmax. (Racers typically use a smaller factor to save weight, while cruisers use a larger factor for security.) These RM30 and RMmax numbers are then used to determine your wire diameter (and size all the other fittings in a boat’s rig, like mast section, spreaders, mast tangs and chainplates). Put simply, wire rigs are designed around breaking strength.

Dux, however, is fundamentally different, because the stuff is so strong you can ignore breaking strength. Instead, Dux is sized on creep. Creep, unlike stretch, which is an elastic deformation from which a material “rebounds,” is the permanent elongation of fibers over time under load. Like pulling taffy, Dux fibers that have crept will not rebound. If sized incorrectly, a Dux rig will eventually go slack under its pre-tensioned load.

To make sure this doesn’t happen, you need to look at a Dux creep chart. The key is to determine the typical pre-tension load carried by the rig, and the diameter of Dux that will not creep at that load. Again, strength is inherent—you’re inevitably going to end up with rigging that is far stronger than the wire it replaces. As a real-world example, Arcturus’s wire rig called for ¼in shrouds. Her Dux rig calls for 9mm shrouds— that’s a breaking strength of 7,300lb for wire versus 26,400lb for Dux.

Working & Sailing with a Dux Rig
Colligo Dux is marketed as “rigging reduced to its essentials,” and as such many riggers forego the use of turnbuckles in favor of old-timey (and cheaper) deadeyes and lanyards, like Colligo’s “Terminator” end fittings–solid aluminum thimbles, sized so that the radius of the eye-splice around them is large enough to avoid weakening the line.

A Dux end fitting on a lower shroud “Old-timey” lashings are an option, but they make it harder to get in the right rig tension

However, before leaving the Canadian Maritimes I made the switch back to turnbuckles. An aluminum mast expands and contracts with the changing temperature, and with lanyards it’s impossible to get enough pre-tension in the rig to prevent it from going slack in the cold. This is true even on a small boat like Arcturus, and owners of all but the smallest boats should consider this before switching to Dux.

People have asked how often we need to tune the rig. “Doesn’t the Dux stretch?” they say. No, it doesn’t. Less than wire, in fact. “Doesn’t it go slack when it’s cold?” Only if you don’t tune it correctly. “What about when it sits for the winter?” Nope.

In fact, Arcturus sailed 2,500 miles to Northern Ireland, spent the winter on the hard there (with the mast up), then sailed another 1,200 miles up the west coast of Scotland, across the North Sea, down and around the Swedish peninsula and into the Baltic Sea as far as 60 degrees north, without us so much as touching a turnbuckle. After the initial tune in Baddeck—when I bought some galvanized turnbuckles from a fishing supply store—the mast remained in column and the rigging was snug all the way to Scandinavia. It wasn’t until we downrigged Arcturus at the end of the 2012 season that I made any changes.

Some Science
Coincidentally, that’s about the time I became curious as to how the rig was really holding up. In practice, I felt it was bulletproof. I’d figured out most of the chafing issues and knew how to fine-tune it. But what was going on inside the rope’s braid that I couldn’t see? How much strength was the sun’s UV rays sapping from our shrouds? Were my splices done correctly to ensure maximum strength?

To find out the answers to these questions, I got in touch with John Franta at Colligo Marine, and arranged to bring him two of Arcturus’s shrouds, a port upper and a starboard lower, which were light enough to pack in my luggage for the trip home from Sweden. I dropped them off, and he promised to do some pull testing for me and report back on the data.
“This is one of my least favorite things to do,” he wrote me in an email when the results came back. “Trying to make sense of real world data, that is.”
John went on to explain that there are a lot of variables associated with this kind of study. “First, you have the line, and the way it is manufactured and the manufacturer’s variables. Then you have the post-processing of the shroud or stay, splicing, cutting, end-fitting design and so on. You also have how it is handled, has it been kinked, folded, what about load conditions and cycling? Then you have the exposure variables: UV, temperature, moisture...” A heck of a lot to swallow, indeed!

John then proceeded to tell me about Arcturus’s shrouds specifically: “One shroud broke at 20,765 lbs-ft and the other broke at 17,692 lbs-ft.”
In other words, one shroud lost a hair over 21 percent of its original breaking strength (26,400lb), while the other lost just over 32 percent.
“The other data that we have shows this on the low side of the fitted curve. Average [breaking strength for 9mm] after about two years exposure is around 22,000 lbs-ft,” or a loss of about 16 percent.

But therein lies the beauty of Dux—even a 32 percent loss in breaking strength in the three years since fitting the shroud (and the thousands of miles it sailed) leaves us with a shroud that is still 8,292lb stronger than a brand-new piece of 9/32in wire! Our built-in safety factor, thanks to designing around creep, allows that same shroud to lose 65 percent of its strength before it approaches the strength of the wire it replaced.

Five Years Later
Last summer, I finally got around to replacing our galvanized turnbuckles with classy polished bronze fittings from Hayn. Otherwise, what’s it like to live with a Colligo Dux rig, now that we’ve had some experience with it?
In practice, I’m not losing any sleep over the strength of the rope itself. Franta’s pull-testing results confirm that. Although there are simply too many variables in play to explain the difference in strength lost between the two shrouds he pulled for us, the rig is still much stronger than a wire one.
Still, we control what variables we can. For example, I’m meticulous about splicing the ends. One thing Franta noted after his tests was that both our shrouds actually broke at new splices he had to put in. “Your shrouds were too long for the tester we used,” he explained, “so we had to re-splice one end of them.” This suggests that in reality, the shrouds, when fitted on the boat, were likely stronger than the pull tests indicated.

Franta has seen this before, but doesn’t have enough data to reach firm conclusions. For now, it’s a guessing game, and he speculates that re-splicing old line might decrease its life expectancy. Colligo’s estimate, which is intentionally conservative due to the lack of data, is that new Dux has a working life of 5-8 years in the tropics.
To protect my rig I also prevent chafe wherever possible, using tried-and-true methods like parceling and serving, just like they did on square-riggers—laying down a layer of black self-amalgamating rigger’s tape (the “parceling,” minus all the messy oil and cotton) and then wrapping it with tarred nylon twine, using a serving mallet to get the turns super-tight (the “service”).

Now that Arcturus is hauled out for upwards of nine months in frigid Scandinavia, we take the spars down each winter and renew this chafing gear at the spreader tips before re-rigging each spring. We also keep a close eye on wherever the sheets and sails touch the rig. Furthermore, our spreader tips are lashed to the shrouds with sail twine rather than seizing wire. All of this takes time and effort and knowledge.

 

Synthetic Cabling for Boats

Hi Brian & Others
Seems what old is new again... Some info about synthetic cabling. Dux and other plastic cabling will increasingly replace steel rigging into the future. This has been the case in other industries such as heavy lifts, cranes & logging. So no news there. A few things to clarify the above:
1) Creep is the condition in which a material elongations over time due to a constant stress. Its unlikely that rigging actually "creeps" as the termination distance does not change so the strain cannot increase to maintain the constant stress. If you hung a weight on a tree limb so the load (hence stress) was the same and the line could elongate over time then you would have a creep condition.
2) "Relaxation" however is the decrease in stress due to an applied strain and this is a condition our rig can experience. We strain a line to a set level and the line relaxes (gets longer) reducing its stress.
3) Mechanical setting is the process of the fibers bedding in and slightly reorganising themselves into the best geometry. Whether its metal or synthetic cables this occurs. Once set there is no more play in the system, this is primarily what preload does, it provides a load that allows the rig to "set" and once set it remains like that forever (technically). Its like old fashioned re-tensioning of head bolts, we are removing all the mechanical compliance in the assembly. Buy the way for those out there that do FEA work you do not need to pretension FEA rig models because this mechanical looseness does not exist in a CAD model, I digress. This is one reason that new splices in old rope fail early. We have upset the "set" of the rope while the old splices have had time to bed in, the new splice hasn't settled and its fibres are not load sharing as well as a splice that has small loads and some time to settle into its job.
4) Synthetic cabling - There are two types; crystalline fibres and none crystalline fibres. Dux & Kevlar are non crystalline whereas PBO, carbon and vectran are crystalline. Lets start with crystalline. When these fibres are made their crystal structure is fixed or "aligned" so does not mechanically set like the non crystalline fibres. Just like our rope, individual fibres have structure and things called orientation and entanglment. Crystalline fibres are highly oriented and entangled at birth and stay that way. Non crystalline fibres like DUX are disorientated and poorly entangled at "birth". To create DUX fibres they are heated and stretched to highly orient the fibre bundle, then they are held at temp to set the bundle. This process is not 100% efficient so there is scope for some of the fibres to relax when in use. Vecran/PBO/carbon do not relax or creep due to stress related to this internal reorganisation as there is none, whereas DUX types do. Crystalline fibres can relax or creep due to other effects but these are not usually present in sailing conditions. There is lots of data available to design these things out there. But a rule of thumb is that if you load Dux under 30% of its BS then relaxation and creep is minimised and you only have to deal with the mechanical set.

UV is high energy radiation and it attacks the bonds of plastics and breaks them down. PBO is particular UV vulnerable. DUX and Vectran take an initial degrade then stabilise. Only the outer fibres degrade so most of the fibres are fine.

A note about the loss of strength of your fibres in test. Its nearly impossible to estimate this accurately (as Franta says) the best way is to have keep a piece of pristine rope from the same roll and put it in the cupboard. Then when you test the old one you know the control rope and the test rope are identical as it can be. The 30% drop could be that that particular piece started life 30% below average.

Hope this helps and no one should be concerned using synthetic cabling on their boats, just read up on how to look after hemp ropes and its about the same. Regards Peter S

 

Applied Engineering Services,...updated link

I have come to find out that some of the links in this posting have gone bad, so here is an updated one for AES
http://www.aes.net.nz/

 

Vectran vs Dyneema

Just wanted to repost your astute observations in one thread for future reference.

 

Looking back over this subject thread I started a number of years ago, and still asking myself some questions.

For instance, what if we were to remove the headsail (maybe a genoa) on a std sloop rig, and replace it with the loads that it is exerting on the rigging of the vessel (somewhat std operating format when analyzing mechanical loading,...remove the element and replace it with the loads at its connection points).

For simplicity in this case just assume a non-heeling vessel (say a catamaran straight up)

So we remove the headsail and replace it with the forces at its connecting portions.
1) We have a whole lot of forces distributed along the forestay all pulling backwards in the plane of the sailcloth at its leading edge.
2) We have the head of the sail force pulling down and forward.
3) We have the tack force pulling up and rearward.
4) We have the clew (sheet attachment) force pulling forward and upward

The head and tack forces are offsetting loads as they are both act along the same forestay.

So what other forces of the headsail are pulling the vessel forward?.... I only see the sheet force:!:
It appears to me that there is an upward component to this force that we often ignore when we just utilize the old 'sail loads bunched together acting thru the CE of the sail' :?:

 

Hello Brian -Indeed they are many software packages that can directly analyse the aero sail loads imposed upon a rig and consequently calculate the component loads. This is called an aero-elastic analysis. There are simplified methods allowing manual calculations of these things based upon the assumption that the heeling loads (aero loads) equal the righting moment loads (static or dynamic equilibrium). Due to the large SF used in most of these things and the requirement for adequate stiffness to perform properly these approx approaches work OK. But companies like North Sails can do as you suggest. The issue is do we do a huge amount of CFD to get what you want or again do we simplify the aero side to get the structures result? If we want the structures (elastic) side we simplify the aero side so the answer is easy to get at. eg we neglect trying to find the eddies at the corner of the sails or the trailing vortex etc. then use this info to generate the edge loads of the sails, then these loads can be transferred to the structure. Computationally this is not a linear solution so takes quite a bit of computer power/time and its done in many cycles to find the sail eqilibrium shape (or flying shape). There are alot of "internal'" forces in a boat rig that just keep it in shape (preload, catenary loads etc) and do not contribute to forward boat movement. Hope this helps. See below links - Peter S

http://cdn2.hubspot.net/hub/209338/news/ScienceFinn/ScienceFinn.HTML

http://www.au.northsails.com/TECHNO...ether/tabid/17825/language/en-US/Default.aspx

www.smar-azure.com

I do a lot of rig analysis but make assumptions about how the sails load the rig. eg is it linear? is it non linear? what is the forestay load? etc etc. Since my job is to size the components we are generally working with the upper loads imposed and even more due to applied SF's for say fatigue of wires. There are industry guides on these things. So once I size the rigging we step back an say is this reasonable? yey or nay. To calculate the "instantaneous" service loads in various conditions is a whole different ballgame and requires sophisticated aero-elastic approaches. Cheers

 

Hi Brian - I had a quick look back at this thread and you discuss "Creep" I'd like to comment on this. Creep is the permanent extension or elongation of a material under an imposed load. On a boat rig this technically can't happen and the industry needs to look up "Relaxation". Polymers are long chain structures quite different to metals. Dynice is a non crystalline material and has been heat treated and stretched to "orient" its long polymers in the rope direction to strengthen and stiffen the fibre bundles. But this orientation process is not complete. Vectran and PBO are crystalline fibres and are naturally oriented when made. Another factor is "entanglement". Polymers are twisted and chained and wind around each other enabling then to stay together. Weak hydrogen bonds help to keep them to together as well.

Creep - if you hang a weight from a tree with dynex (or kevalr) at a suitable load the unoriented bits will start to orient and the rope will extend. The fibre bundles will also start to disentangle and allow the rope to extend, plus some of the hydrogen bonds will slip allowing the bundles to slip past each other. All of these mechanisms contribute to creep. As the rope is strained but is free to keep extending at the end allows these mechanisms to work.

In a yacht rig we have fixed termination lengths so we can't keep extending the cable, so "creep" can't happen. What we do experience is "construction stretch" and "relaxation" . Once the construction stretch and all the fittings bed down and the rig is correctly preloaded it should not stretch. Relaxation in oriented product (non crystalline eg dynice) is the remaining non oriented polymers orienting (mainly) In crystalline polymers its the hydrogen bonds slipping. In Vectran this load to BS is over 50% of BS> In dynex I think they quote 30% BS for "creep". But I think we are over sizing polymer cabling too much at the moment but once we get more long term experience with it we will see much smaller lines being used. (by the way a polymer chemist would say I have oversimplified this a bit but its close enough for sailors) Peter

https://www.youtube.com/watch?v=x4pShcrpUbw&feature=youtu.be

I did a talk on Yachting materials you maybe interested in, ignore the first 13 mins, the editor put some stuff in front of my talk.

 

Lifting Force?

Thanks Petereng for your references to more sophisticated analysis tools, but I have a very basic question for you.

Do your tools indicated a lifting force by the headsail?

 

Headsail Lifting Force

Perhaps I need to clarify this 'lift force' I am asking about.

I am NOT talking of the tradition 'aerodynamic lift force' we think of when speak of flow over an airfoil, ....but rather the upward lifting force provided by the headsail thru its sheet restraining line as I posted just above.

I've mentioned this before, and more than a few have poo-pooed the idea,...but there are some believers:

 

Hi Brian, I wrote a reply yesterday but it seems It didn't post. In short yes jibs and spinnakers provide a vertical force called heave. The forward force is called surge and sideways is sway. There are two force systems to consider the "Body" forces which are the aerodynamic forces and the "internal" forces which are the membrane loads in the sail and consequent forces at the head, clew and tack. The aero body forces are quite small compared to the membrane forces. The body forces propel the boat the membrane loads are sometimes called secondary loads and just keep the shape of the sail in place (called the flying shape) These loads are also called edge loads and are the catenary loads created by the body forces on the sails. The aerodynamic lift of any sail is rarely horizontal so there will be off horizontal vectored loads as the boat heels and pitches etc. The jib and spinnaker are set on an angled forestay which means the angle of the sail is slightly up which means there is a slight upward lift vector always.

I use Strand7 FEA software and to calculate these loads I need a pressure map of the sail as it does not do CFD. I looked at my prior projects but the ones in which I have had contract aero-elastic work done don't have jibs. They have been freestanding cat rigs.

So to answer your question. 1) all sails produce a slight heave load upwards especially spinnakers 2) The sheet load is mainly the reaction to the membrane loads and a small part of it is the surge load (producing motion) Hope this helps.... Peter

If you made the sail out of a stiff material say aluminium or carbon fibre in the same shape as the flying shape this would remove the membrane loads and the resultant load would only be the body load or aero lift. This is done in wind tunnel testing of sail shape for this reason and its difficult to set a soft sail in a a wind tunnel. eg a rigid wing sail like on the AC and C class boats do not have sailing membrane loads to consider. But they do have to consider the membrane loads of the shrink wrap shrinking onto the wing during construction as this creates forces that can distort it. But these forces are again internal and cannot help in providing motion to the boat. Its like the preload of the rig, you can preload it as high as you like but these forces remain in equilibrium internal to the baot and therefore cannot provide motion. So the sail membrane loads are like a preload that remains in static equilibrium while the body loads are not in equilibrium and provide the net force in surge to move the boat.

 

On another subject thread I had posed this question of Saildesign, but it appears as thought he has nor participated in the forums since 2014.

Since the question is very much directly related to this subject thread I thought I would post it here,.... for anyone else to come answer it.

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 analysis of my rig.

I repeat the question,
....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? (just the mainsail alone for first example)