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  #106  
Old 03-03-2017, 02:43 AM
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brian eiland brian eiland is offline
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When I think back to my very old teachings of how this would be solved I seem to remember that we might remove the mainsail itself, and replace it with little shear force, tensile forces, and moment forces at each of its connections with the rig(ing).

Or is that just too 'old school'??
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  #107  
Old 03-08-2017, 08:56 AM
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i am trying to figure out the chord and length of a straight daggerboard to reduce the leeway on 30-45ft displacement monohulls. i have already picked an asymmetrical foil based on Cl, Cd, Cm etc...

my question is how much of a horizontal lift force must a daggerboard generate to work against the leeway when going upwind? typical speeds of 6-8 knots.

100 lbs ?
200 lbs ?
300 lbs ?

thank you.
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  #108  
Old 03-10-2017, 04:51 AM
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brian eiland brian eiland is offline
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SMAR-azure, WOW

Quote:
Originally Posted by petereng View Post
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/n...ienceFinn.HTML

http://www.au.northsails.com/TECHNOL...S/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
I have to start out offering a big apology to you Peter.
I skipped over giving this posting of yours its due diligence,...and particularly as I read more about the SMAR-azure software. It really does appear to offer that 'plug into a big 3D model of all the rigging loads' I was looking for all these years.

I'm going to talk more about this very soon, and ask you some questions about SMAR-azure,...but first I thought I might briefly go back thru a couple of history marks that lead to this great new technology (I just want to confirm that I have some of this 'story' correct?)
SMAR-azure
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  #109  
Old 03-10-2017, 05:11 AM
petereng petereng is offline
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Hi Brian - Its not new its just become more accessible. The first aero-elastic job I contracted to Norths was over 15 years ago. It was a mission back then because I had to get North engineers who could do the work in between their Americas Cup stints! but it was being done regularly. Now there are packages that are much more integrated and friendly for sail-makers and boat designers. Plus computers have become so fast it is possible to do this in a short time. In my structural work 10 years ago it was common for me to leave a computer to run overnight to figure something out. I'd check it at about 3am to see if it was on track or needed restarting. Now the same problems are solved in 30 mins! Regards Peter S
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  #110  
Old 03-10-2017, 05:43 AM
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brian eiland brian eiland is offline
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History

I first became acquainted with a genuine desire to do a 'computer mapping of the rigging loads' in a document prepared by Chris Mitchell as he had worked on such a subject for his masters degree in engr in NZ. Very likely that is what also got him involved withe some major international sailing events.

I think the document was published somewhere around 1993 (but authored around 1986)
Quote:
http://www.aes.net.nz/about.html
AES (formerly called Advanced Engineering Services) started by Chris Mitchell in 1984 operating as a sole trader. In 1986 C Mitchell designed and was in charge of building the (alloy) twelve metre masts for KZ3, KZ5 and KZ7 in Fremantle. In 1988 he headed a team of engineers which designed the rig for KZ1 (used in the 1988 America’s Cup). Typical projects AES worked on at that time were an 80 foot Italian masthead sloop Wallygator 1989, Concorde yachts 40 metre sloops in Thailand

Chris Mitchell has Bachelor and Master of Engineering Degrees (Mechanical) from the University of Auckland (New Zealand), and wrote a thesis titled ‘The Computer Aided Analysis of Yacht Rigs’. Chris has had a paper published by the Royal Instituition of Naval Architects W8 (1993). Titled: Rigging Loads on the Yacht ‘New Zealand’ and Rig Design Formulae. Chris is a Professional member of the Naval Architectural Society of New Zealand, and is currently serving as a council member for the society
I find most of what he has written very interesting. So here is one of his early installments as a PDF document with some hi-lited portions that relate to the reasons I began this thread on the forum.

ChrisMitchell Structural Analysis of Yacht Rigs.pdf

Quote:
Originally Posted by paper
...some excerpts
The authors question whether any of the above simplifications are acceptable for application by professional naval architects.

The method is therefore risky for less common yachts such as catamarans, and 12-metre yachts for which these factors have not been established.

The analysis uses a three dimensional space frame modeling the rig by a series of one dimensional ‘beam’ elements

The first step towards a load model is therefore a membrane model of the sail itself. Rather oddly this basic step is ignored by most recognized works (e.g. Kinney 1973). The most common approach is to apply an assumed aerodynamic force distribution directly to the mast….this is normally approximately triangular in shape as shown in Figure 3 and implies a rigid sail able to support bending moments. Some analysts have tried to overcome the grossly inaccurate results that this produces by inventing unlikely pressure distributions on the sails.

The membrane stress model used by the authors essentially consists of a strip of high stress running from the top of the sail to the end of the boom (along the leech). In most respects it corresponds quite well with the reinforcing and structural design sailmakers have been using in sail design for a number of years. It is not based on a detailed structural analysis of the sail, but rather on a simple model which at least shows understanding of the way in which loads are carried and transferred by the sails. The stress magnitudes are determined by estimates of the mainsheet loads, and by consideration of the righting moments, center of pressure and sail shapes.

The authors have also found that the ability of the programs to quantify the displacements of a rig under different loads and supporting rigging of great assistance in focusing on the critical components of the structure. While there is still scope to improve the model described here, it does at least provide an accurate base from which rigs can be tuned, compared and improved, in an objective procedure, more suited to the engineering community.
Quite good for its time, but could be improved upon, but still it was pointed in the direction I was seeking...a force mapping of a sailing rig.
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  #111  
Old 03-10-2017, 05:55 AM
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brian eiland brian eiland is offline
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History

Then I ran across this FEA analysis paper...

Grabe_HP-Yacht_02(1).pdf

Quote:
High Performance Yacht Design Conference
Auckland, 4-6 December, 2002

THE RIG OF THE RESEARCH SAILING YACHT “DYNA”
MEASUREMENTS OF FORCES AND FEA

….excerpts from PDF by Brian Eiland.....

To dimension rigs of sailing yachts there are traditional and simple procedures like that of Skene and S&S....All these dimensioning procedures work with the righting moment at 30° heel of the hull to predict compression forces in the mast. Pretensions in the standing rigging are neglected assuming the shrouds on the leeward side fall slack. To define the moments of inertia for the mast cross sections the Euler buckling formula for columns is applied. Reserve factors found by experience take into account the different clamping of the masts in different rig types. This procedure makes it difficult to design rigs with new geometries of spreader arrangements and standing rigging (for example rigs with no runners and no backstay or rotating rigs).

FEA has been used for the simulation of rigs for the last 10-15 years. With the FEA it is possible to design new rig types, geometries and also big rig sizes.

The sail loads predominate in the total loading of the rig. The pressure distribution on the sail surfaces caused by the stream of the air is transmitted through the sailcloth acting as a membrane to the rig. The sail membrane acts with pressure loads along the luffs on the mast tube and the headstay and single forces are acting at the corners of the sails in halyards, outhaul and cunningham. The halyard forces act twice on the sheave axles in top of the mast. The corner forces and the pressure loads are effective in three dimensions. They depend on the apparent wind angle, the wind speed, the shape and trim of the sails and the bending of the mast.

But when the sails and the rig are both loaded both will be deformed. That changes the shape of the sails and the procedure starts again with a CFD computation. With a costly (and hopefully converging) iteration procedure the problem can be solved like big sail making companies show (unfortunately the programs are not for sale). But in spite of the expenditure there are limitations in accuracy and in the size of the apparent wind angles.

CONCLUSIONS
Force measurements and FEA computations of the rig ofb the “DYNA“ are performed. There are differences in the measured and computed values of up to only 7.4 % withreference to the maximal measured force in the mastfoot. That sounds good. But the absolute differences are up to 4,120 N. On one hand that is a lot. On the other hand the 30° heel load case is much more diffcult to simulate than a load case with less heel such as 20°. That is caused by the much bigger sail loads in the 30° heel condition in relation to the pretensions. The leeward shrouds fall loose and the pretensions in the rigging are changed dramatically. To aggravate the situation the shifting of the pretensions in the “DYNA“ rig are not only in athwartship direction but also in the fore-aft direction since the spreaders are swept aft. An inline spreader rig is
easier to compute.

The upwind load case leads without doubt to high loads in the rig. But there may be other load cases like sailing downwind (reaching/running) with a gennaker or spinnaker that yields still bigger loads. These loads are no longer limited by the righting moment of the sailing yacht.

Only the apparent wind speed and the set sails define the loading of the rig by the sails. For downwind courses new load models have to be developed. The comparison of the measured and the computed forces shows how well the forces in a rig of a sailing yacht sailing upwind can be computed and predicted by applying the FEA for rigs. To design a rig also other loadings than the sail loads alone have to be considered like the self weight for big rigs and the accelerations in a sea way.
So by year 2002, marginally better, but still could see improvements.
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  #112  
Old 03-10-2017, 06:31 AM
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When I look back I now remember that I only became computer literate in the year 2000 when I was trying to follow "THE RACE" around the world. And I only started this subject thread in 2003.

I was (and I think a lot of the sailing public) was totally unaware of these new computer methods of rigging analysis. Many of us were still (and still am) utilizing the old text books. All this America's Cup stuff was a big secret from us ordinary guys.



I wanted to know more about a big 3D model I could just plug different designs into, and be able to make changes too a few individual components, and see the effects on the rig as a whole. One of those items I wanted to look at was the 'aft jumper strut' on my aftmast rig and its interaction with the forward pair.



Quote:
Originally Posted by brian eiland View Post
Dear Phil (pbmaise),
I would ask you to go back to my posting #345, and review just the first portion of my vector analysis.
Rigging Force Review for Aft-Mast or Mast-Aft



If you were to do the same thing with your configuration: say take a one inch long vector down the direction of the forestay, ...then break this vector down into its two component parts, one down the mast, and one perpendicular to it, pulling the masthead forward. That component that is perpendicular must be offset by an equal force pulling back on the masthead. Draw that somewhat horizontal vector in. Now look how your backstay might produce that backward force (that horizontal vector is one of the two component parts that make up your total backstay vector (load).

I think you will find it is a VERY LARGE load because of your 'shallow angled' backstay(s). That is the reason I incorporated the aft-jumper strut to get a better angle for my masthead backstay to resist the forestay loads. Its a game of angles.

And unlike your quest, I was looking to get the same overall sail area as the sloop rigged boats on a substantially shorter mast.

Please do that little vector analysis I suggested above and tell us what you think then.
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  #113  
Old 03-10-2017, 10:37 PM
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Stephen Ditmore Stephen Ditmore is offline
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Quote:
Originally Posted by frers33 View Post
i am trying to figure out the chord and length of a straight daggerboard to reduce the leeway on 30-45ft displacement monohulls. i have already picked an asymmetrical foil based on Cl, Cd, Cm etc...

my question is how much of a horizontal lift force must a daggerboard generate to work against the leeway when going upwind? typical speeds of 6-8 knots.

100 lbs ?
200 lbs ?
300 lbs ?

thank you.
You should be able to get the righting moment of your boat for each 1 degree heel, RM1, from its rating certificate, or that of a sistership. You'll also need to know the heeling lever: VCE - VCLR (vertical center of effort minus vertical center of lateral resistance. You're looking for the height between the two, so if measuring from the waterline, express the second value as negative so you add them together.) You'll want to know (for wind speed x) the heel angle and the speed of the boat through the water. Transverse force = RM1 * angle of heel / heeling lever. This will be both the transverse force on the sail / rig, and the equal opposing force on the hull and appendages, including your daggerboard. If said daggerboard is vertical when the boat is upright (not canted), then no need to separate out the horizontal and vertical components, since they will be same for the board as for the rig. Where lifting line theory wants V^2, input and square the speed of the boat, and solve for area. For your foil, look for the angle of incidence where L/D is best, and use that lift coefficient.
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