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NotWal said..

^^^ Structural Mechanics 101. All that's missing are the diagrams.

With reference to what Bourke is explaining in terms of 'waterpressure', read the introduction of this doc including Fig. 5.1, then take a glance at the diagrams in Example 5.2

http://web.aeromech.usyd.edu.au/AMME2301/Documents/mos/Chapter05.pdf

For the purpose of discussion;

Profile = side view
Plan = top/bottom view, or outline.
A= Nose
C= Mast position
D= Water
E=Straps/Tail

The diagrams in Example 5.2 are a good representation of the 'bending' forces in landing a board on water.

Quite simply, in most boards and certainly Witchcraft the area on the deck(including rails) between the tail and to the front of the mast track is heavily compensated in tensile reinforcement. If the top of the beam/board is allowed to bend too much the bottom of the beam will buckle.

It should be understood that the bottom of the board is doing a comparatively small amount of work in compression as a result. With reference to Bourks mention of buckling requiring a force from the side - take a look at this link and find Euler's Law -

en.wikipedia.org/wiki/Structural_engineering_theory

It will help you to understand how carbon is relatively weak and fails readily in compression. A lateral impact/force such as in a flat landing scenario can exacerbate or initiate a catastrophic failure. I should also mention that torsional stability in a board is crucial for mitigating the occurrence of creasing of the bottom. The board twisting is tantamount to the board bending on on side, or compressing the bottom on one side - this is why a crease sometimes only presents on one side of the bottom. To combat this, fibres are aligned biaxially.diagonally on the deck - sometimes the bottom in some better constructions.

Things get mystical and magical when we start trying to optimise the fibres in the deck for strength and weight and in particular in the reinforcement of impact/local compression areas. In a wave board this is under and around/between the straps. On a slalom or race board with larger fin and related stresses this is in the bottom from the fin box forward about 700mm, effecting one of the crucial areas of rocker performance. The EPS foam core is the achilles heel, as mentioned before. Simply stiffening the skins is not enough. The lightweight foam toward the core of the board will gradually fatigue.

You may ask, 'Why not just tie the top an bottom skins together with a higher density foam between the top and bottom?'. Well in theory it sounds simple, but in practice, the forces exerted through the feet are so great and with repetition the high density 'blocks' will distort the bottom of the board. It actually accelerates the degradation of the board.

So, what is the magic formula for dissipating the repetitive shock(I know Bourke doesn't like that term) or compression to the areas under the heals? Thats a whole other mechanical principal and another set of numbers and scribbles.

I think the answer is to find a new core construction and therefore re-engineer the whole structure. In the mean time, I think it very wise of Witchcraft to keep their best practice methods under their pointed hats until they and others are able to fine a cost effective alternative.

The best thing anyone on here can do is to encourage the guys willing to put reputation and their livelihoods on the line to put their tweaks and innovations into practice.

Boardmaking is art & science, for some. Let it be so.

Peace, love & mungbeans

The structure of a sailboard is subject to a number of load conditions
1): Tension
2): Compression
3): Bending Moment (which is the combination of tension in the skin of one side of the board and compression on the other side
3): Shear (adjacent to point loads on the board - I.e. From the mast base, foot loads, impact loads)
4): Torsion (twisting of the board)
5): Fatigue from cyclical loads
The board can fail in any one or a combination of these load conditions.
Each material used in the construction of boards deflects as a response to these load conditions. Each material has an elastic limit and plastic limit when subject to this deflection. I.E. If the deflection is not beyond this elastic limit then the material will return to its original size once the load is removed. If the elastic limit is exceeded then a plastic deformation will occur, I.e. the material does not return to its original length. When the plastic limit is exceeded the material breaks. There are two types of failure that occurs. The first being serviceability failure, I.e. the permanent deflection is so large the board is no longer serviceable, or catastrophic failure, when the plastic limit is exceeded and the material breaks.
This whole process is further complicated by the composite nature of board construction, which relies of different materials performing different roles in the structure. Adhesion, which allows the transfer of loads from one material to another is critical to the integrity of the composite structure.
Different materials have different elastic and plastic limits in response to increasing loads. However if you were able to vary the thickness of each material so that each material responded in a similar way to the same load then we could compare the relative merits of each material in the construction of sail boards. I.e. To achieve the same elastic and plastic limit one material may weigh less per square mm than another material. There are standardised testing that can be carried out on each type of material to determine the most weight efficient material for each load condition. Significant work has been done in the use of these composite materials in the construction of racing sailing craft. I would be very surprised that mainstream sailboard companies do not avail themselves of this material analysis as well as computer finite element analysis techniques to calculate the different load conditions on boards and hence which particular material and where it is most effectively and efficiently used to withstand those loads. In addition they develop prototypes and test the boards under lab and real world conditions to see if they perform as predicted by the mathematics. The information they get from this testing then provides a necessary feedback loop to the designers.
Of course good design work can be undone by
- poor workmanship
- compromising good design for low weight, cost or fashion
Different manufactures, whether they be large, small or custom have varying degrees of access to the material strengths, analysis and design techniques. The smaller or custom manufactures rely more heavily on the feedback loop I.E. experience in many years of manufacture. As purchasers we rely mainly on reputation and experiences of other sailors we know.
I sail a 6 year old Futura with unfashionable Technora construction. It has some cosmetic damage to the paint as well as some small depressions in the top and bottom of the board. I sail at least weekly. I often sail it in large bay chop in 20+ kts. I recently hit a sand bank with my fin at at 25 kts with no damage to the board. There are no soft spots or cracks in the shell of the board. I would consider the design and construction of the board a success. The majority of sail boarders I know share the same experience. I have heard of some exceptions but they are few and far between.
There is no single answer to best practice board layup for strength. It relies on variables. The type of sailing, the importance of cost and weight, ease of manufacture. Each layup has its place. The trick is to find the one that best suits your requirements. Eg I don't sail on pebbly beaches with large shore breaks, so I don't need a board that performs so admirably when subject to Witchcrafts hammer test. But I do need a board that survives running into sand banks and impacts from mast and sailor as a consequence of catapults.

John I hit a mooring rope doing 30kn on my 7'10" Shalom entering a speed course and decelerated pretty quickly but did not crash..so stayed loaded as long as possible- damaged G10 fin and no apparent damage to the board. I'm not sure its much of a measure of the board overall, but its at the upper limit of what I need a light wind slalom board to handle in those circumstances.

There are some extremely well written posts in this ''Best Practice Board Layup for Strength'' forum, both about different product propertys and their advantages and disadvantages they all bring to board construction. Shows that there is a very good understanding of what is needed to build a board properly.
However Fact/ Data sheets,Compression formula are a great guide to start with , but that about where it ends, until you actually build the board and test it to see if it holds up. In our case I like to see at least 12 months of testing with our team guys when you change a layup or introduce a new materail before we start selling it to our customers. I only like to change one thing at a time on all our proto/ test boards so we can see if this one change improves or hinders the boards performance. If the board does very rarely fail we can then pinpoint the problem straight away. As I said before this trail and error testing approach takes time but guarantees that you are making real improvments to both board design and construction.

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Man0verBoard said..

Quite simply, in most boards and certainly Witchcraft the area on the deck(including rails) between the tail and to the front of the mast track is heavily compensated in tensile reinforcement. If the top of the beam/board is allowed to bend too much the bottom of the beam will buckle.

When the deck can flex/stretch within reason, this will dissipate the shock load. The force on the bottom will be reduced. When we talk about flex on windsurfboards, this is still far less compared to surfboards. Let alone kiteboards. The rigidity against flex is the 3rd exponent of the thickness. So allready if made in the same materials, a windsurfboard will be somewhere around 8 times as rigid against flexing compared to a surfboard. So letting the deck flex a bit, this does not compromise the structural integrity and helps dissipate peak loads.

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Man0verBoard said..


It should be understood that the bottom of the board is doing a comparatively small amount of work in compression as a result. With reference to Boukes mention of buckling requiring a force from the side - take a look at this link and find Euler's Law -

en.wikipedia.org/wiki/Structural_engineering_theory

It will help you to understand how carbon is relatively weak and fails readily in compression.

In this equation for buckling from your link: F=\frac{\pi^2 EI}{(Kl)^2}, it shows that the higher the modulus, the better the buckling strength.

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Man0verBoard said..
The board twisting is tantamount to the board bending on on side, or compressing the bottom on one side - this is why a crease sometimes only presents on one side of the bottom. To combat this, fibres are aligned biaxially.diagonally on the deck - sometimes the bottom in some better constructions.

Indeed the rail on the jumping side is usually the part that starts to fail first. Especially in concave shapes, V bottoms less so. But there is no need to put diagonally aligned fibres, the twisting force is not that big. On the previous board for the 110kg Pozo guywe did us biax and UD carbon and it creased diagonally, not stracht across like usual. No internal failure due to the Dyneema so then we replaced the biax with just UD and that worked.

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Man0verBoard said..
You may ask, 'Why not just tie the top an bottom skins together with a higher density foam between the top and bottom?'. Well in theory it sounds simple, but in practice, the forces exerted through the feet are so great and with repetition the high density 'blocks' will distort the bottom of the board. It actually accelerates the degradation of the board.

No, it does not. Maybe your idea is different to the way we do it but it certainly helps against breaking and fatigue and far less distortion of the bottom than without.

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Man0verBoard said..

So, what is the magic formula for dissipating the repetitive shock(I know Bouke doesn't like that term) or compression to the areas under the heals? Thats a whole other mechanical principal and another set of numbers and scribbles.

I think the answer is to find a new core construction and therefore re-engineer the whole structure. In the mean time, I think it very wise of Witchcraft to keep their best practice methods under their pointed hats until they and others are able to fine a cost effective alternative.

The best thing anyone on here can do is to encourage the guys willing to put reputation and their livelihoods on the line to put their tweaks and innovations into practice.

Boardmaking is art & science, for some. Let it be so.

Peace, love & mungbeans

Why should I not like the term repetitive shock? Shock is something different than impact.

I think the way things stand at the moment, it will be hard to find a cost effective alternative. For hard use, forces are simply high so the solution is not going to be simple or cheap.

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OESaustralia said..

There are some extremely well written posts in this ''Best Practice Board Layup for Strength'' forum, both about different product propertys and their advantages and disadvantages they all bring to board construction. Shows that there is a very good understanding of what is needed to build a board properly.
However Fact/ Data sheets,Compression formula are a great guide to start with , but that about where it ends, until you actually build the board and test it to see if it holds up. In our case I like to see at least 12 months of testing with our team guys when you change a layup or introduce a new materail before we start selling it to our customers. I only like to change one thing at a time on all our proto/ test boards so we can see if this one change improves or hinders the boards performance. If the board does very rarely fail we can then pinpoint the problem straight away. As I said before this trail and error testing approach takes time but guarantees that you are making real improvments to both board design and construction.

Well, whenever something fails or looking to improve the shape, it can be a real help to use science. Science is helping us everywhere to speed up evolution/trial&error big time. We?d still be hunters and gatherers if it wasnt for science. Sometimes the solution is somewhere else than the part that failed. Sometimes we keep on doing things simply because weve always done them like this. So we have to constantly question the things we do. Making boards is nothing but physics. Nothing magical about it. It is about finding the right physics. When I hear a shaper say: "I had to change the flow of the rail", I think OK lets hear it what and why, that would be interesting. But they want (cant?) and where others goo whoooo, what a master, I think, what a load of bull.

Bourke,

'magic' is a pun on semantic of your brand name. I was taking the pith, if you like.

Life is short, art long, opportunity fleeting, experience deceptive, judgment difficult.

Yours sincerely,

Fixer of The Dings

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Witchcraft said..

Making boards is nothing but physics. Nothing magical about it.

Well that's all a bit depressing isn't it. Science is great but it doesn't hold all the answers, the world was once flat after all. Something that is good on paper doesn't always work, just as mucking around often doesn't work - a combination of science and hands on testing 'magic' is worth far more than either one on it's own.

I'm guessing it must not be windy over there at the moment? Luckily it's mast high and windy here so we'll catch a few magic carpet rides for ya bro ;)

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McSmurfin said..

Witchcraft said..

Making boards is nothing but physics. Nothing magical about it.

Well that's all a bit depressing isn't it. Science is great but it doesn't hold all the answers, the world was once flat after all. Something that is good on paper doesn't always work, just as mucking around often doesn't work - a combination of science and hands on testing 'magic' is worth far more than either one on it's own.

I'm guessing it must not be windy over there at the moment? Luckily it's mast high and windy here so we'll catch a few magic carpet rides for ya bro ;)

Aaaah, but that is why I said that we need to find the right theory.....If the theory does not work, the theory is wrong and we need to rethink the theory. Still just using some basic laws can be a great help at times to speed things up. Another well respected local shaper (former world champ now semi retired) used to put 10+ layers of carbon at the heel area for one of his teamriders and it still broke. So I told him my method which saved a lot of weight and no more problems. Like I said, if something breaks, in some cases just puttin more of that what broke may not be the best solution. He also told me some of his tricks. There are 7 shapers in our village of which 5 also make windsurf boards which is good for competition.

good thing making boards has nothing to do with humility

Bump

Im enjoying this one.
I see the Gman is back as predicted

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ikw777 said..

Following on from the board strength thread, I'm looking for opinions on what would be current best practice layup for an open ocean freeride board. It has to be strong and durable and flexible enough to soak up the bumps. Ultra light weight is not a driving factor so for a 100 litre board we might aim for the mid 7kg mark?

Im curious after all this dicussion what have you decided would be the best layup for you to use?

Well, the thread was very educational, but I really turned off when the dumbarse fighting started.

I've decided board building is too damn hard. I'll keep growing my board repair skills, but I'll let the pros build the boards. God knows I'll probably wreck those too.

had a gust of wind blow my board off the roof onto the bitumen on sunday. it hit the pavement very very hard and made a very loud noise.

lucky the rails are more than say, 3 layers of glass....

result was a small 3-4cm crack. gotta love carbon Kevlar.

still, not keen to hit it with a hammer.