Select to expand quoteGestalt said..Overner said..Gestalt said.
a H beam has a web. get rid of the web and you don't have a h beam. the web connecting the flanges gives the beam it's shear strength.
You are getting quite close to something big. Follow that thought to its natural conclusion and you will have found great wisdom.
Is it that h beams dont react well to twisting and therefore a h beam is not the optimal structiral shape for a windsurfer
Why all this talk of using a H beam for a windsurfer ? It would be too bloody heavy and sink , Don't get me started about the shape not being right ! Not to mention the rust 
Do these air inside boards have internal supports ? I would presume they would have to .
Select to expand quoteduzzi said..
Yes, exactly, a very different story than a student's attempt that brakes the third time out 
Hollow construction can of course be done without prepreg and honeycomb. And it can work in extreme conditions: Doyle built hollow B&J and wave boards (Aircore) in the Gorge the 90s.
Weight saving for an high tech solution is significant the only limiting factor is cost and technology ... nobody would ever think to build a sailboat that was not hollow!
(Actually, I take it back. There have been some examples of mini-transat boats with eps core.)
I know the original shaper of Airinside and he explained their patented technology to me when he was here on holiday many years ago (I think around 2004). So I know how they are made and it is quite clever but it is not cheap. And you need quite expensive molds which limit the amount of shapes you can offer or change a shape is costly. I have never actually seen one though, let alone sail it or have had to repair one. So I don?t know how it works in practice but where I think hollow boards can work fine for expensive slalom boards, it is simply not suitable for wave boards with lower volumes (compared to slalom boards), need to flex and are landed flat. That shaper also said there was not a hair on his head thinking of trying it for wave boards. Patrik isnt making any hollow wave boards is he?
What did those Doyle boards weigh? Gorge boards used to be pretty heavy. Are there still board makers in the Gorge? There used to be lots, like in Tarifa. At some point there were 13 custom brands in Tarifa.
i think things are getting off topic a little.
the web in a beam is the element connecting the flanges. whether it has holes in it or not it is still the web. (i wasn't referring to the fillet.)
in the case of a windsurfer the flange is the deck and bottom laminate and the web is the stringer. i think we can say the eps core is also acting as the web.
the original question was around how do we stop boards from breaking if there is no stringer. Bourke you mentioned some special sauce you use that you don;t want to share. i remain unconvinced because you don't seem fully across the science here.
lets look at the example of the H Beam, (UB as it is called in Australia) a H beam doesn't answer the question very well. adding carbon to the top and bottom laminates (Flanges) is the least efficient way of improving the strength of a board because carbon does not act well in compression. as per the test paper i linked adding more carbon does not improve sandwich construction compression strength.
with a H beam (UB) whilst one flange is in tension, the other is in compression. same with a board. wihen we put carbon into the system it's the compression side that breaks.
now if we stick with the H beam analogy then the way to strengthen the board is to use a stronger eps core (the web) or to make the board thicker. ie. increase the distance between the flanges or in this case the top and bottom laminates.
boards break for a couple of reasons though.
a. not enough tensile or compression strength in the laminate
b. the laminate delaminating from the core
c. torsional failure.
if we look at torsional failure. a h beam is not great in torsion. a windsurfer even worse because of the proportions of the board. ie width v thickness. to get around this we could introduce stringers or Beams to the rails. rail stringers resist torsion by turning the H beam into a box section of sorts.
another option is to wrap the laminate around the rail. no longer using a H beam or a box but becoming a cylinder. bean a long time since i studied structural mechanics but i do remember cylinders being very strong structural elements.
Select to expand quoteGestalt said..
i think things are getting off topic a little.
the web in a beam is the element connecting the flanges. whether it has holes in it or not it is still the web. (i wasn't referring to the fillet.)
in the case of a windsurfer the flange is the deck and bottom laminate and the web is the stringer. i think we can say the eps core is also acting as the web.
the original question was around how do we stop boards from breaking if there is no stringer. Bourke you mentioned some special source you use that you don;t want to share. i remain unconvinced because you don't seem fully across the science here.
lets look at the example of the H Beam, (UB as it is called in Australia) a H beam doesn't answer the question very well. adding carbon to the top and bottom laminates (Flanges) is the least efficient way of improving the strength of a board because carbon does not act well in compression. as per the test paper i linked adding more carbon does not improve sandwich construction compression strength.
with a H beam (UB) whilst one flange is in tension, the other is in compression. same with a board. wihen we put carbon into the system it's the compression side that breaks.
now if we stick with the H beam analogy then the way to strengthen the board is to use a stronger eps core (the web) or to make the board thicker. ie. increase the distance between the flanges or in this case the top and bottom laminates.
boards break for a couple of reasons though.
a. not enough tensile or compression strength in the laminate
b. the laminate delaminating from the core
c. torsional failure.
if we look at torsional failure. a h beam is not great in torsion. a windsurfer even worse because of the proportions of the board. ie width v thickness. to get around this we could introduce stringers or Beams to the rails. rail stringers resist torsion by turning the H beam into a box section of sorts.
another option is to wrap the laminate around the rail. no longer using a H beam or a box but becoming a cylinder. bean a long time since i studied structural mechanics but i do remember cylinders being very strong structural elements.
You have a few mistakes in your thinking. The important parts are the flanges. In a board they are connected through the rails all around the board and the EPS. This works quite well in handling torsion. You hardly see a board break in an angle which is what would happen.
boards break for a couple of reasons though.
a. not enough tensile or compression strength in the laminate
Tensile strength is quite easy to put enough. Compression by itself as well, the main problem with compression is creasing or buckling. And to stop that what is important is stiffness of the area under load. And carbon is stiff.
Making a board thicker reduces the loads in deck and bottom but (apart from any possible downsides for the sailing performance) also makes the whole board stiffer. And can absorb less energy when landing flat. Energy is force x distance. So if a board can flex twice as much, there is half the force. My way is to just make the local area stiffer that is under the highest compression or buckling load, not the whole board.
Select to expand quoteBouke-Witchcraft said..duzzi said..
Yes, exactly, a very different story than a student's attempt that brakes the third time out Hollow construction can of course be done without prepreg and honeycomb. And it can work in extreme conditions: Doyle built hollow B&J and wave boards (Aircore) in the Gorge the 90s.
Weight saving for an high tech solution is significant the only limiting factor is cost and technology ... nobody would ever think to build a sailboat that was not hollow!
(Actually, I take it back. There have been some examples of mini-transat boats with eps core.)
I know the original shaper of Airinside and he explained their patented technology to me when he was here on holiday many years ago (I think around 2004). So I know how they are made and it is quite clever but it is not cheap. And you need quite expensive molds which limit the amount of shapes you can offer or change a shape is costly. I have never actually seen one though, let alone sail it or have had to repair one. So I don?t know how it works in practice but where I think hollow boards can work fine for expensive slalom boards, it is simply not suitable for wave boards with lower volumes (compared to slalom boards), need to flex and are landed flat. That shaper also said there was not a hair on his head thinking of trying it for wave boards. Patrik isnt making any hollow wave boards is he?
What did those Doyle boards weigh? Gorge boards used to be pretty heavy. Are there still board makers in the Gorge? There used to be lots, like in Tarifa. At some point there were 13 custom brands in Tarifa.
RE Gorge boards: The Doyle gorge boards of the 90's were not super light compared to a Sandwich board though also not as heavy as some of the popular Glass polyester boards. They used a simple PVC foam construction with some internal Stringer but I don't think they had any other bulkheads. They were touted as fairly strong but expensive to build. Yes back in the heyday of the 80's & early 90's there were quite a few Custom builders - maybe like 10? There are still a couple of custom builders in the Gorge but now not solely devoted to Windsurfing but build surfboards SUPS & Foilboards...
Select to expand quoteGestalt said..
another "eco" cloth under development from hayden shapes. i think colan may be involved so fingers crossed sanded get some in the future.
This is greenwashing. Besides the apparent advertisement for the watch and the use of a light aircraft, if Hayden was concerned about land fills, he would be responsible for not only the 40% of construction waste that goes into landfill, but the eventual (I guess 90+%) of his products that go into landfill.
Select to expand quoteBouke-Witchcraft said..Gestalt said..
i think things are getting off topic a little.
the web in a beam is the element connecting the flanges. whether it has holes in it or not it is still the web. (i wasn't referring to the fillet.)
in the case of a windsurfer the flange is the deck and bottom laminate and the web is the stringer. i think we can say the eps core is also acting as the web.
the original question was around how do we stop boards from breaking if there is no stringer. Bourke you mentioned some special source you use that you don;t want to share. i remain unconvinced because you don't seem fully across the science here.
lets look at the example of the H Beam, (UB as it is called in Australia) a H beam doesn't answer the question very well. adding carbon to the top and bottom laminates (Flanges) is the least efficient way of improving the strength of a board because carbon does not act well in compression. as per the test paper i linked adding more carbon does not improve sandwich construction compression strength.
with a H beam (UB) whilst one flange is in tension, the other is in compression. same with a board. wihen we put carbon into the system it's the compression side that breaks.
now if we stick with the H beam analogy then the way to strengthen the board is to use a stronger eps core (the web) or to make the board thicker. ie. increase the distance between the flanges or in this case the top and bottom laminates.
boards break for a couple of reasons though.
a. not enough tensile or compression strength in the laminate
b. the laminate delaminating from the core
c. torsional failure.
if we look at torsional failure. a h beam is not great in torsion. a windsurfer even worse because of the proportions of the board. ie width v thickness. to get around this we could introduce stringers or Beams to the rails. rail stringers resist torsion by turning the H beam into a box section of sorts.
another option is to wrap the laminate around the rail. no longer using a H beam or a box but becoming a cylinder. bean a long time since i studied structural mechanics but i do remember cylinders being very strong structural elements.
You have a few mistakes in your thinking. The important parts are the flanges. In a board they are connected through the rails all around the board and the EPS. This works quite well in handling torsion. You hardly see a board break in an angle which is what would happen.
boards break for a couple of reasons though.
a. not enough tensile or compression strength in the laminate
Tensile strength is quite easy to put enough. Compression by itself as well, the main problem with compression is creasing or buckling. And to stop that what is important is stiffness of the area under load. And carbon is stiff.
Making a board thicker reduces the loads in deck and bottom but (apart from any possible downsides for the sailing performance) also makes the whole board stiffer. And can absorb less energy when landing flat. Energy is force x distance. So if a board can flex twice as much, there is half the force. My way is to just make the local area stiffer that is under the highest compression or buckling load, not the whole board.
Oh my ... nobody builds anything with composite materials using an uniform lay up. From a tennis racket to a 60 foot foil racing sailboat one of the great things about composites is that they can be easily adjusted to local load/strength/flex requirements.
And I think that the distinction between bottom and top is misleading. We talk that way because many laminate bottom and top in separate steps. And of course top and bottom require different lay ups. But as Gestalt points out the final product is (should be) like a cylinder ... ideally not much different than a windsurfing mast. A perfectly uniform layup (filament wounding helps!) with, again, local reinforcements.
H-beam? We do use a H-beam: the fin box. Experience apparently shows that you do not need or want any other top to bottom connection. Be it from fin box to mast box, or mast box to bottom.
Select to expand quote
I know the original shaper of Airinside and he explained their patented technology to me when he was here on holiday many years ago (I think around 2004).
If the technology is indeed 'Patented', then it is not by any means secret. 
I would hazzard a guess that is IS secret, and it is not patented. A patent search would confirm my guess. 
Edit: Well that was a rabbit hole! A search of Google patents was so far not successful in finding any patents for airinside, or hollow sealed hull construction. If it exists, it shouldn't be that hard to find, so I dont think it exists.
Select to expand quotesailquik said..
I know the original shaper of Airinside and he explained their patented technology to me when he was here on holiday many years ago (I think around 2004).
If the technology is indeed 'Patented', then it is not by any means secret.
I would hazzard a guess that is IS secret, and it is not patented. A patent search would confirm my guess.
Edit: Well that was a rabbit hole! A search of Google patents was so far not successful in finding any patents for airinside, or hollow sealed hull construction. If it exists, it shouldn't be that hard to find, so I dont think it exists.
If you want to see the construction look here: jinlicomposites.com/hollow%20monocoque%20sailboard%20construction.jpg
I cannot post an image yet as I am a noob, but it looks like a standard honeycomb sandwich with a thick core - Patrik said 7mm in one of his videos, but I have it on reasonable authority it is as much as 10mm in places. I also have on reasonable authority they use prepreg carbon, which will be part of the reason it requires expensive moulds and the boards cost a pretty penny.
I think they are a one shot build too, similar to carbon bike frames. Tricky.
Edit: building a hollow board from a mould would be more environmentally friendly than pretty much anything previously discussed. As there would be less processing each time a board is build, less waste, and the end of life product is much easier to crush and compact.
Using a biodegradable core e.g. cork, balsa would also help. However, both are a lot heavier than PVC or Nomex honeycomb. The Corecork I have used is 200kgm3 and has poor compression strength and the balsa I have used (after it has soaked up most of the resin) is 350+ kgm3, compared to 80 kgm3 Corecell. Big weight difference and it showed - lightest corecork board I have built was 8.9kgs the lightest 100kgm3 with 10mm PVC core board was 6.5 kg both with 32kgm3 polystyrene blank.
The Airinside boards are supposed to be very repairable without any long term effects from taking on water. In guessing they will also take a jump well since the shell can flex without denting the core.
Really tempting for something like a foil or freestyle board.
Select to expand quotesailquik said..
I know the original shaper of Airinside and he explained their patented technology to me when he was here on holiday many years ago (I think around 2004).
If the technology is indeed 'Patented', then it is not by any means secret.
I would hazzard a guess that is IS secret, and it is not patented. A patent search would confirm my guess.
Edit: Well that was a rabbit hole! A search of Google patents was so far not successful in finding any patents for airinside, or hollow sealed hull construction. If it exists, it shouldn't be that hard to find, so I dont think it exists.
I do not remember it exactly and never checked his claims but I think to remember he said the patent was on the way how it was put together in one go, not the construction itself. IIRC he said that without a patent they would not have gone to Cobra in the first place. Before they were producing in Switzerland but they have about the highest wages of anywhere in the world.
Select to expand quoteImax1 said..
Filament wound windsurf board , mmmmmm ?
I discussed that with an expert in the field and it is not really suitable as most fibres should be placed longitudinal. The same problem as with masts.
Select to expand quoteduzzi said..
Oh my ... nobody builds anything with composite materials using an uniform lay up. From a tennis racket to a 60 foot foil racing sailboat one of the great things about composites is that they can be easily adjusted to local load/strength/flex requirements.
And I think that the distinction between bottom and top is misleading. We talk that way because many laminate bottom and top in separate steps. And of course top and bottom require different lay ups. But as Gestalt points out the final product is (should be) like a cylinder ... ideally not much different than a windsurfing mast. A perfectly uniform layup (filament wounding helps!) with, again, local reinforcements.
Oh my, a windsurfboard is hardly a cylinder is it? The bottom is far too flat to get any strength from its shape.
Select to expand quoteBouke-Witchcraft said..duzzi said..
Oh my ... nobody builds anything with composite materials using an uniform lay up. From a tennis racket to a 60 foot foil racing sailboat one of the great things about composites is that they can be easily adjusted to local load/strength/flex requirements.
And I think that the distinction between bottom and top is misleading. We talk that way because many laminate bottom and top in separate steps. And of course top and bottom require different lay ups. But as Gestalt points out the final product is (should be) like a cylinder ... ideally not much different than a windsurfing mast. A perfectly uniform layup (filament wounding helps!) with, again, local reinforcements.
Oh my, a windsurfboard is hardly a cylinder is it? The bottom is far too flat to get any strength from its shape.
I am so glad that after having learned that hollow boards last 3 times out, that they cannot be built lighter than eps cored ones, and that one should not build a board with a uniform composite, we can also learn about geometry!
Great also to learn that "the bottom is far too flat to get any strength from its shape". Not sure what that means but it sounds good!
Select to expand quoteBouke-Witchcraft said.. Oh my, a windsurfboard is hardly a cylinder is it? The bottom is far too flat to get any strength from its shape.
But its not flat. Its closer to a cylinder than a bit of flat sheet. So in engineering terms, the analogy is valid
Select to expand quoteBouke-Witchcraft said..
I do not remember it exactly and never checked his claims but I think to remember he said the patent was on the way how it was put together in one go, not the construction itself. IIRC he said that without a patent they would not have gone to Cobra in the first place. Before they were producing in Switzerland but they have about the highest wages of anywhere in the world.
OK. That bit about outsurcing the construction makes more sense for sure. I still have not found any Patents, but probably says more about my search abilities. Do companies have to provide patent # info on their products to protect themselves??
Select to expand quoteMark _australia said..Bouke-Witchcraft said.. Oh my, a windsurfboard is hardly a cylinder is it? The bottom is far too flat to get any strength from its shape.
But its not flat. Its closer to a cylinder than a bit of flat sheet. So in engineering terms, the analogy is valid
The deck is round enough to get a part of its strength from the roundness but the bottom not. This is the reason why you need thicker sandwich on the bottom than the deck.
Select to expand quoteduzzi said..
I am so glad that after having learned that hollow boards last 3 times out, that they cannot be built lighter than eps cored ones,
If you read back, you will find I did not say that. Select to expand quote.duzzi said..
and that one should not build a board with a uniform composite, we can also learn about geometry!
No, as different parts of a board gets different main forces, it is better to make each part biased towards that. If not you would end up with a too heavy board or a too weak board.Select to expand quote.duzzi said..
Great also to learn that "the bottom is far too flat to get any strength from its shape". Not sure what that means but it sounds good!
If you give something thin and flexible a certain round shape, it will become pretty stiff. But the bottom simply isnt round enough for that.
Select to expand quotesailquik said..
OK. That bit about outsurcing the construction makes more sense for sure. I still have not found any Patents, but probably says more about my search abilities. Do companies have to provide patent # info on their products to protect themselves??
I do not think so. Maybe the patent can be found under composite technologies. But I honestly do not care if there is a patent or not. And if there is it has probably run out. A patent can only be held for a max of 25 years IIRC. Patents arent cheap to register in the first place but after that the fees for patents get exponentially more expensive over time to keep upright and since this was already over 16 years ago and Airinside themselves do not exist anymore, maybe they stopped paying the fees. With a result that Patrik or anyone who knows the technology can now use the technology free. But that is all pure speculation on the little info I have.
Select to expand quotesailquik said..Bouke-Witchcraft said..
I do not remember it exactly and never checked his claims but I think to remember he said the patent was on the way how it was put together in one go, not the construction itself. IIRC he said that without a patent they would not have gone to Cobra in the first place. Before they were producing in Switzerland but they have about the highest wages of anywhere in the world.
OK. That bit about outsurcing the construction makes more sense for sure. I still have not found any Patents, but probably says more about my search abilities. Do companies have to provide patent # info on their products to protect themselves??
To be fair, it's difficult to protect yourself with a patent in this case. A patent usually is only obtained in a single country and at best can be transferred to a group of countries such as the EU. Hence, more than 1 pattent should be needed. For example a Chinese company can just copy the idea and export the product to the US without breaking the rules if the patent was only obtained in the EU. The best international callobaration is the PCT, which facilitates filing patents in multiple countries. Anyway, when obtaining a patent you need to publish your techniques/product so after the period of protection (usually 20 years sins the request) anyone can recreate it.
Edit: this is getting way of topic.
I'm looking forward to the actual build!
Select to expand quoteBouke-Witchcraft said..duzzi said..
Oh my ... nobody builds anything with composite materials using an uniform lay up. From a tennis racket to a 60 foot foil racing sailboat one of the great things about composites is that they can be easily adjusted to local load/strength/flex requirements.
And I think that the distinction between bottom and top is misleading. We talk that way because many laminate bottom and top in separate steps. And of course top and bottom require different lay ups. But as Gestalt points out the final product is (should be) like a cylinder ... ideally not much different than a windsurfing mast. A perfectly uniform layup (filament wounding helps!) with, again, local reinforcements.
Oh my, a windsurfboard is hardly a cylinder is it? The bottom is far too flat to get any strength from its shape.
i really just don't agree. a windsurfer may not be a right circle cylinder but it is definitely a non circular cylinder or a flat oval cylinder or whatever shape we want to call it. some boards look like RHS section. regardless of what we want to call it it is a tube and with that comes torsional strength that you don't get with other structural shapes.
if we really want to be nit picky the bottom is not really flat either.. there is V, concaves, convex surfaces which all add stiffness.
to quote a friend of mine..... it's time to dig up.
Select to expand quoteImax1 said..
Lucky son .
Its good that you used recycled foam , but because its beautifully CNCd from a block and not wire cut , what happens to the two cubic metres of foam dust ?
Id love to know what happens to the cubic km of dust that a board factory produces , how they must process it . It can't just get dumped at the tip. Do they melt it into a small block as there making it , then dump it . Does it get recycled ? Recycling is usually more expensive than virgin materials and if that is the case with foam I doubt a third world country would do it . I think we would be horrified if we knew what that secretive Cobra factory do.
I did read somewhere that Starboard make pavers out of waste . Do they chop up all waste and melt it together ?
Ironically the bags of foam dust we suck up throughout our dust extraction system is readily and easy off loaded for recycling, but the block corners, lumps edges of sheets are harder to shift as the recyclers expect them to be contaminated (resin, paint, metal swarf or what ever), given we mill EPS blocks into very weird and wonderfull forms for the film industry there is an embarrassing level of waste.
Select to expand quoteGestalt said..
another "eco" cloth under development from hayden shapes. i think colan may be involved so fingers crossed sanded get some in the future.
Their Idea may be sound but this green wash video does them no favours. So they shape in an open shed with no extraction booth, they let excess resin run straight off on to the floor, don't use respirators, they travel to the "bubble" by sea plane, and they think they are heroes of the environment.....humm I think not. I can only imagine the slick around their "bubble" being a bit like a mini North Atlantic garbage patch full of foam dust and a slick of un cured emulsafied resin! 
en.wikipedia.org/wiki/North_Atlantic_garbage_patch
Select to expand quoteGestalt said..
if we really want to be nit picky the bottom is not really flat either.. there is V, concaves, convex surfaces which all add stiffness.
But only a very minor bit. Bottom shapes are usually just a few millimeters deep/high. Unless with a very extreme bottom shape, (which there is none, maybe that Starboard (forgot the name) from over 10 years ago with an extreme double concave), strength wise it hardly makes a difference for the stiffness against a locally applied perpendicular force. There is the slight bend of the rocker as well off course but this hardly makes a difference either. Why do you see boards getting a negative rocker in the creasing zone or do you see a deeper concave on the jumping side of say "less strong" made boards? Many people only jump on one side so this is easy to check. Also many slalom boards get a negative concave/rocker in front of the fin box.
It doesn't matter that the bottom is nearly flat Bourke!! the board in cross section is much closer to a cylinder than a piece of flat wood or foam is
that gives it rigidity, and it IS a cylinder in engineering terms. Not a perfect cylinder, but structurally it is more like a cylinder than a flat foam blank is - due to the sandwich layer.
bit like how corrugated steel works - and it matters not that it is almost flat. It still stronger and stiffer. so not it is not perfectly round but it does have qualities closer to a cylinder than a bit if flat foam. That's the point
Select to expand quoteBouke-Witchcraft said..
I do not think so. Maybe the patent can be found under composite technologies. But I honestly do not care if there is a patent or not. And if there is it has probably run out. A patent can only be held for a max of 25 years IIRC. Patents arent cheap to register in the first place but after that the fees for patents get exponentially more expensive over time to keep upright and since this was already over 16 years ago and Airinside themselves do not exist anymore, maybe they stopped paying the fees. With a result that Patrik or anyone who knows the technology can now use the technology free. But that is all pure speculation on the little info I have.
I actually find this most interesting and it could be of great practical fun value to me. For a start, if I was to make a board, purely for myself (not for sale for profit) I can use any 'Patented' technology I wish to. 
And indeed, if the patent has expired, I can even make it commercially as you point out, but this is of far less interest to me.
I have made hollow sandwich boards before years ago bit the weakness of the constrction is always the perimiter (rails) seam join, or if that was made strong enough, the penalty is weight. For Kayaks, it was easy to make a strong light inside join as one has access to the inside of the craft through the cockpit opening. For sealed hollow craft it is a very different matter. I have some moulds with which I would like to experiment again so it would be great to know a bit more.
One mould I made has a separate 3rd deck insert piece which enabled the perimeter rails to be acessed and laminated from the inside to make it seamless and very strong. The deck insert join was under far less load and simply glueing it in with a flush overlap was plenty strong enough.
Making hollow boards could be VERY eco friendly, as one totally eliminates the plastic foam core and all the waste from 'shaping'. So this is totally 'on topic'.
