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geoITA said..
in fact, we are not talking about elastic deformation, not at all.
I know that shape changes with time, quite quickly. Few years ago I had one of my boards re-shaped because of this reason. I asked a well known Italian shaper to take care of that and we talked about the problem. He told me that even his better built custom boards were prone to bottom deformation after just a few sessions. So I lean toward giving credit to his words.

I'll repeat for clarity - if the shape changes markedly within a few uses, then it implies one of..... a/ it will continue to change markedly b/ it will 'bed in" to stop changing.

If it is (a) then we would see banana-rocker or concaved-rocker everywhere... which we dont
If it is (b) then the board shaper didn't take into account the changes that do occur on first uses... in which case, why would you purchase from them.

What we actually see is small rocker changes over a long period of time.

Different core material for boards. Glue or melt the materials for the sail; no sewing. something other then foam for the boom grip

100% automation for mast production. Because the bill of materials really doesn't add up currently.
what dollar amount is tied up materials wise in a fin?

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rtz said..
what dollar amount is tied up materials wise in a fin?

I don't know, but it is still a lot cheaper than the foil stuff....

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mathew said..

geoITA said..
in fact, we are not talking about elastic deformation, not at all.
I know that shape changes with time, quite quickly. Few years ago I had one of my boards re-shaped because of this reason. I asked a well known Italian shaper to take care of that and we talked about the problem. He told me that even his better built custom boards were prone to bottom deformation after just a few sessions. So I lean toward giving credit to his words.

I'll repeat for clarity - if the shape changes markedly within a few uses, then it implies one of..... a/ it will continue to change markedly b/ it will 'bed in" to stop changing.

If it is (a) then we would see banana-rocker or concaved-rocker everywhere... which we dont
If it is (b) then the board shaper didn't take into account the changes that do occur on first uses... in which case, why would you purchase from them.

What we actually see is small rocker changes over a long period of time.

Hi Matthew,
oh thank you so much for the engineering lesson and for the clarity.
We probably live in different universes. Here in mine, I almost always find altered rockerlines when I check. Note that the alteration is usually around a few tenths of a millimeter, so it's hard to notice without using a good ruler.
I also never heard of designers taking into account the future deformation in their boards. And never read this in any brochure or web page. If you know of any brand selling such boards, please let me know. Probably I'll become a faithful customer.
As for "small" rocker changes, in my experiences those small changes are enough to impair performances at speed. Also, when RRD used to do their boards development here in my place, I often saw PWA athletes such as Andrea Rosati (very very often around July), Finian Maynard, Arnon Dagan, and their boards. Expecially about Andrea: I never saw him on a board with its regular bottom paintwork, all of them were "finished" in grey putty. The guy in the RRD lab (Aurelio Verdi at that time) had those reshaped sistematically.
So from what I understand. Yes we see a lot of altered rockerlines, if we check. Most probable cause in my view (I will not explain this here, it would take too long, but I am sure that the eventual reader competent enough will understand with no need for explanations) is some crushing in the sandwich foam, that probably sets in and does not go on indefinitely. And best way to avoid it, is using extra heavy sandwich foam in the bottom in the area between straps positions, as this would cost a very marginal weight increase in order to obtain around 2x better strength.
Supposing the area surface is around 1 meter long and 60 cms wide, a 3 mm thick foam layer of 130 kg/m3 in place of the usual 80 kg/m3 would add just 90 gms.

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geoITA said..

.

Note that the alteration is usually around a few tenths of a millimeter, so it's hard to notice without using a good ruler.

Wow! You do realise that board manufacturing involves many, many manual steps and there will be much more tolerances in the specs than tenths of a millimetre?

I wouldn't be surprised if an identical board from the same factory can have changes in shape up to millimetres. Not sure what is acceptable from a quality control perspective but pretty sure it's more than 1 mm.

I think what you find are invariants in the building process more than deformation from use. Both will be normal but if you claim that you feel the difference when a board is a tenth of a millimetre different then I find that very hard to believe so why does it matter?

PWA riders select the "best" board out of a few and stick to the board for the season. If it would deform and have negative impact they would jump on a new one but haven't heard that before and they hammer the chop harder than any of us I guess.

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geoITA said..

mathew said..

geoITA said..
in fact, we are not talking about elastic deformation, not at all.
I know that shape changes with time, quite quickly. Few years ago I had one of my boards re-shaped because of this reason. I asked a well known Italian shaper to take care of that and we talked about the problem. He told me that even his better built custom boards were prone to bottom deformation after just a few sessions. So I lean toward giving credit to his words.

I'll repeat for clarity - if the shape changes markedly within a few uses, then it implies one of..... a/ it will continue to change markedly b/ it will 'bed in" to stop changing.

If it is (a) then we would see banana-rocker or concaved-rocker everywhere... which we dont
If it is (b) then the board shaper didn't take into account the changes that do occur on first uses... in which case, why would you purchase from them.

What we actually see is small rocker changes over a long period of time.

Hi Matthew,
oh thank you so much for the engineering lesson and for the clarity.
We probably live in different universes. Here in mine, I almost always find altered rockerlines when I check. Note that the alteration is usually around a few tenths of a millimeter, so it's hard to notice without using a good ruler.
I also never heard of designers taking into account the future deformation in their boards. And never read this in any brochure or web page. If you know of any brand selling such boards, please let me know. Probably I'll become a faithful customer.
As for "small" rocker changes, in my experiences those small changes are enough to impair performances at speed. Also, when RRD used to do their boards development here in my place, I often saw PWA athletes such as Andrea Rosati (very very often around July), Finian Maynard, Arnon Dagan, and their boards. Expecially about Andrea: I never saw him on a board with its regular bottom paintwork, all of them were "finished" in grey putty. The guy in the RRD lab (Aurelio Verdi at that time) had those reshaped sistematically.
So from what I understand. Yes we see a lot of altered rockerlines, if we check. Most probable cause in my view (I will not explain this here, it would take too long, but I am sure that the eventual reader competent enough will understand with no need for explanations) is some crushing in the sandwich foam, that probably sets in and does not go on indefinitely. And best way to avoid it, is using extra heavy sandwich foam in the bottom in the area between straps positions, as this would cost a very marginal weight increase in order to obtain around 2x better strength.
Supposing the area surface is around 1 meter long and 60 cms wide, a 3 mm thick foam layer of 130 kg/m3 in place of the usual 80 kg/m3 would add just 90 gms.

You think it's pvc sandwich foam that deform or eps core that be definitively compress ?

It's the soft EPS that deforms . Same as when a deck soft spot happens. The EPS crushes down a lot and the join between the EPS and sandwich separates when the sandwhich pops up again. On the bottom the EPS only squashes a little bit and the sandwich stays stuck to it creating the negative rocker. There is no way that the sandwhiched foam crushes. That's my take on it.

So what we need is hollow board. Lighter, stronger and possibly greener.

That s the main improvement I see on board in the future.

For sails, I guess it's dyneema (uhmwpe). Like Aluula and others.

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Nicko29 said..
So what we need is hollow board. Lighter, stronger and possibly greener.

That s the main improvement I see on board in the future.

For sails, I guess it's dyneema (uhmwpe). Like Aluula and others.

Patrik has the air inside boards but not sure how good they are though.

On old surftech surfboards, those made with pvc (pink) sandwich, pvc compress because fiberglass over is so thin so you can see lot of dimples. Those boards where light, stiff and ding fragile. New ones with thin wood betwenn heavier fiberglass on same foam are less stiff and so have less buckling strengh but lot more ding/dent r?sistant.
From my small experience, eps density play more than i though for dynamic compressive strengh over time. Something to look at...
For sure hollow could be good but whit is one problems.

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Imax1 said..
It's the soft EPS that deforms . Same as when a deck soft spot happens. The EPS crushes down a lot and the join between the EPS and sandwich separates when the sandwhich pops up again. On the bottom the EPS only squashes a little bit and the sandwich stays stuck to it creating the negative rocker. There is no way that the sandwhiched foam crushes. That's my take on it.

But then if you were right, on boards with stringers to contrast deformation (the stringers are embedded in the EPS) and nonetheless some bottom deformation, then one should be able to clearly detect the stringers, which is not the case: the bottom of such a board looks perfectly smooth and solid, to the point that someone believes it's OK, unless one checks properly by using a ruler.As I said earlier: the PVC is covered by a thin layer of laminate that will flex easily and not provide resistance against compression (it's the whole sandwich that does it, external laminate + PVC foam + inner laminate), while the EPS although much weaker is protected by the whole sandwich.
And anyhow 15 kg7m3 or so EPS is so weak that it cannot be taken into any account as for resistance.
Sorry if I appear too much assertive, I do not own the truth, only trying to better understand.

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ptsf1111 said..
Wow! You do realise that board manufacturing involves many, many manual steps and there will be much more tolerances in the specs than tenths of a millimetre?
...

PWA riders select the "best" board out of a few and stick to the board for the season. If it would deform and have negative impact they would jump on a new one but haven't heard that before and they hammer the chop harder than any of us I guess.

Your point about PWA athletes makes some sense.
Nonetheless it's not uncommon to see boards used in PWA with the bottoms "repaired". As said before, I don't remember seeing Andrea Rosati (I talk about him because I know him and used to meet quite frequently in my spot) using a slalom board with its bottom showing its production graphics.

As for the other points: please bear in mind that I am talking about slalom boards used at full speed by experienced riders. Nothing noticeable at reduced speeds typical of wave or freewave or freeride boards.

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mathew said..

geoITA said..
.... This results in bottom shape changing after just very few sessions, expecially in fast riding boards, and developing a "spoon" shape (negative rocker curve, concave) under hull just where it would be important to keep the right shape....

That isn't quite how "elastic deformation" works - there are youtube videos which will explain it better than I ever could.

The shape certainly does change over time, but not that fast and usually not aggressively. It changes because the elasticity-limit of the material has been exceeded, which in the case of foam will be crushed.

If there was a major change to shape [ within the first few uses ], then the designs would take this into account. For example the first few uses of a sail causes the material to stretch somewhat - it is quite normal to have less-than-recommended downhaul for a few sessions.

...once crushed it stays crushed, even if just slightly so, but we are talking few/10 mm or so, which is enough to impair high speed performance and control...

Definitely agree that the material gets crushed over time - the material-limits are exceeded. Also agree that small changes to shape -particularly the rocker - will have some effect.

A solution to this but a few light passes of epoxy-paint will solve this problem. We change a ropes, tendons, and so on -> maintenance of other gear is usually required too.

Saying it another way -> the choice of materials does indeed ensure that changes to the shape do not occur easily. We could use foams which don't crush (aka staying in the elastic-deformation region of the material), but then the final board would be significantly heavier.

"elastic deformation" is an oversimplification. There are 3 types of elastic stresses "shear, tensile and torsion stresses. To have a good construction you need to understand the way they occur and then you understand where they happen. And then you need to understand how to mitigate them. These stresses eventually cause the fatigue of the used materials and in the end the breaking of the construction. This is everything but easy to do in windsurf boards. The construction on a windsurfing board allows only very limited mitigation. What makes it so complicated is the fact that you want to have a "high flex" of a board as this reduces the compression peaks. And compression is actually the number 1 killer of that kind of construction, because the thickness of the "walls",i.e. the laminate is so thin. But if you have a "high flex" i.e. low tensile preak forces you end up having high shear forces. As if one of the stresses goes down annother one will go up.... So it is hard to keep all 3 stresses in its limits :-( That is the reason why in over 30 years there is no real progression in this area. But to often you see a degression in the production of boards. Because the people just do not understand the physics.... And therefore come up with stupid lay ups of fibers...

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SchobiHH said..

mathew said..

geoITA said..
.... This results in bottom shape changing after just very few sessions, expecially in fast riding boards, and developing a "spoon" shape (negative rocker curve, concave) under hull just where it would be important to keep the right shape....

That isn't quite how "elastic deformation" works - there are youtube videos which will explain it better than I ever could.

The shape certainly does change over time, but not that fast and usually not aggressively. It changes because the elasticity-limit of the material has been exceeded, which in the case of foam will be crushed.

If there was a major change to shape [ within the first few uses ], then the designs would take this into account. For example the first few uses of a sail causes the material to stretch somewhat - it is quite normal to have less-than-recommended downhaul for a few sessions.

...once crushed it stays crushed, even if just slightly so, but we are talking few/10 mm or so, which is enough to impair high speed performance and control...

Definitely agree that the material gets crushed over time - the material-limits are exceeded. Also agree that small changes to shape -particularly the rocker - will have some effect.

A solution to this but a few light passes of epoxy-paint will solve this problem. We change a ropes, tendons, and so on -> maintenance of other gear is usually required too.

Saying it another way -> the choice of materials does indeed ensure that changes to the shape do not occur easily. We could use foams which don't crush (aka staying in the elastic-deformation region of the material), but then the final board would be significantly heavier.

"elastic deformation" is an oversimplification. There are 3 types of elastic stresses "shear, tensile and torsion stresses. To have a good construction you need to understand the way they occur and then you understand where they happen. And then you need to understand how to mitigate them. These stresses eventually cause the fatigue of the used materials and in the end the breaking of the construction. This is everything but easy to do in windsurf boards. The construction on a windsurfing board allows only very limited mitigation. What makes it so complicated is the fact that you want to have a "high flex" of a board as this reduces the compression peaks. And compression is actually the number 1 killer of that kind of construction, because the thickness of the "walls",i.e. the laminate is so thin. But if you have a "high flex" i.e. low tensile preak forces you end up having high shear forces. As if one of the stresses goes down annother one will go up.... So it is hard to keep all 3 stresses in its limits :-( That is the reason why in over 30 years there is no real progression in this area. But to often you see a degression in the production of boards. Because the people just do not understand the physics.... And therefore come up with stupid lay ups of fibers...

I think stupid layups is a two fold thing. Catalogue who haa and a new better modification. Each year has to be better. But it's not. In my mind , without a doubt, if you want something, talk to a local board builder. Everything above makes sense. And can be done. My opinion comes from my hack backyard builds and the repairs I do. Just look at the foiling mast track issue in the foiling section . This is what we are dealing with, and spending our hard earned cash on.

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SchobiHH said...

geoITA said..
.... This results in bottom shape changing after just very few sessions, expecially in fast riding boards, and developing a "spoon" shape (negative rocker curve, concave) under hull just where it would be important to keep the right shape....

"elastic deformation" is an oversimplification. There are 3 types of elastic stresses "shear, tensile and torsion stresses. To have a good construction you need to understand the way they occur and then you understand where they happen. And then you need to understand how to mitigate them. These stresses eventually cause the fatigue of the used materials and in the end the breaking of the construction. This is everything but easy to do in windsurf boards. The construction on a windsurfing board allows only very limited mitigation. What makes it so complicated is the fact that you want to have a "high flex" of a board as this reduces the compression peaks. And compression is actually the number 1 killer of that kind of construction, because the thickness of the "walls",i.e. the laminate is so thin. But if you have a "high flex" i.e. low tensile preak forces you end up having high shear forces. As if one of the stresses goes down annother one will go up.... So it is hard to keep all 3 stresses in its limits :-( That is the reason why in over 30 years there is no real progression in this area. But to often you see a degression in the production of boards. Because the people just do not understand the physics.... And therefore come up with stupid lay ups of fibers...

It seems to me you are a bit confused. I suggest you to study some engineering before trying to explain things to others.
Anyhow, you are 100% right about those stupid layups we are used to see even from the most famous manufacturer(s).

Well as you can read on the pages and opinions posted one of the main problem are the Windsurfers themselves . The Industry Mantra of new is better smaller is better bigger is better you name it has found to much followers. Yes you can limit gear and yes you can build Boards and sails with a much bigger Range. Obviously you would sacrifice performance Points here and there. So what ? the main objectif should be to grow the sport and bring the fun back of beeing on the water. You can see the success of one design classes .
What i mean is, i wittnessed a beginner / intermediate talking to a long time Windsurfer why he is planing and for him it seams unreachable. And there you go ... Boardsize sailzize finsize boom stiffness .. thats all fine but we should instead try to offer him some advice and help instead of a sales pitch for the industry. So if the industry would build something in those lines the real question is : would anybody buy it ? As a majority still believes to much of the marketing . And if you a wingfoiler you better get a downwindboard or a hybrid before everybody thinks you are oldschool .. and do not forget a stiffer Wing... just my five cents

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geoITA said..

SchobiHH said...

geoITA said..
.... This results in bottom shape changing after just very few sessions, expecially in fast riding boards, and developing a "spoon" shape (negative rocker curve, concave) under hull just where it would be important to keep the right shape....

"elastic deformation" is an oversimplification. There are 3 types of elastic stresses "shear, tensile and torsion stresses. To have a good construction you need to understand the way they occur and then you understand where they happen. And then you need to understand how to mitigate them. These stresses eventually cause the fatigue of the used materials and in the end the breaking of the construction. This is everything but easy to do in windsurf boards. The construction on a windsurfing board allows only very limited mitigation. What makes it so complicated is the fact that you want to have a "high flex" of a board as this reduces the compression peaks. And compression is actually the number 1 killer of that kind of construction, because the thickness of the "walls",i.e. the laminate is so thin. But if you have a "high flex" i.e. low tensile preak forces you end up having high shear forces. As if one of the stresses goes down annother one will go up.... So it is hard to keep all 3 stresses in its limits :-( That is the reason why in over 30 years there is no real progression in this area. But to often you see a degression in the production of boards. Because the people just do not understand the physics.... And therefore come up with stupid lay ups of fibers...

It seems to me you are a bit confused. I suggest you to study some engineering before trying to explain things to others.
Anyhow, you are 100% right about those stupid layups we are used to see even from the most famous manufacturer(s).

I am a physistist and mathematican. What are your trying to tell me? I am all ear! But if this confusing to you, then it tells me you simply do not understand that complexity. Which is fine, because you need the engineering background for that. But this whole discussion about building better boards is an engineering task. Unfortunately you read everywhere comments of people who believe they understand how to make boards better with lacking that background. You can make up your own mind of what to think of these comments after you hopefully understood from my comment, that the topic is to complex for simple solutions.

Select to expand quote

SchobiHH said..

geoITA said..

SchobiHH said...

geoITA said..
.... This results in bottom shape changing after just very few sessions, expecially in fast riding boards, and developing a "spoon" shape (negative rocker curve, concave) under hull just where it would be important to keep the right shape....

"elastic deformation" is an oversimplification. There are 3 types of elastic stresses "shear, tensile and torsion stresses. To have a good construction you need to understand the way they occur and then you understand where they happen. And then you need to understand how to mitigate them. These stresses eventually cause the fatigue of the used materials and in the end the breaking of the construction. This is everything but easy to do in windsurf boards. The construction on a windsurfing board allows only very limited mitigation. What makes it so complicated is the fact that you want to have a "high flex" of a board as this reduces the compression peaks. And compression is actually the number 1 killer of that kind of construction, because the thickness of the "walls",i.e. the laminate is so thin. But if you have a "high flex" i.e. low tensile preak forces you end up having high shear forces. As if one of the stresses goes down annother one will go up.... So it is hard to keep all 3 stresses in its limits :-( That is the reason why in over 30 years there is no real progression in this area. But to often you see a degression in the production of boards. Because the people just do not understand the physics.... And therefore come up with stupid lay ups of fibers...

It seems to me you are a bit confused. I suggest you to study some engineering before trying to explain things to others.
Anyhow, you are 100% right about those stupid layups we are used to see even from the most famous manufacturer(s).

I am a physistist and mathematican. What are your trying to tell me? I am all ear! But if this confusing to you, then it tells me you simply do not understand that complexity. Which is fine, because you need the engineering background for that. But this whole discussion about building better boards is an engineering task. Unfortunately you read everywhere comments of people who believe they understand how to make boards better with lacking that background. You can make up your own mind of what to think of these comments after you hopefully understood from my comment, that the topic is to complex for simple solutions.

You are a "physistist and mathematican". Not an engineer. That's all.

I think 3D printing will find a role in board and sail construction at some stage and it will be driven by reducing manufacturing costs.

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kato said..
I think 3D printing will find a role in board and sail construction at some stage and it will be driven by reducing manufacturing costs.

That's a way away, to slow and expensive at the moment

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Ben1973 said..

kato said..
I think 3D printing will find a role in board and sail construction at some stage and it will be driven by reducing manufacturing costs.

That's a way away, to slow and expensive at the moment

If you can 3D print an autonomous drone with a 5 meter wingspan that can fly over 2000 km and hit strategic targets then 3D printing a board is not that difficult. With a large print bed size and topographical optimisation 3D printing a board is pretty simple. Hardest bit is finding the time to do it!

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geoITA said..

SchobiHH said..

geoITA said..

SchobiHH said...

geoITA said..
.... This results in bottom shape changing after just very few sessions, expecially in fast riding boards, and developing a "spoon" shape (negative rocker curve, concave) under hull just where it would be important to keep the right shape....

"elastic deformation" is an oversimplification. There are 3 types of elastic stresses "shear, tensile and torsion stresses. To have a good construction you need to understand the way they occur and then you understand where they happen. And then you need to understand how to mitigate them. These stresses eventually cause the fatigue of the used materials and in the end the breaking of the construction. This is everything but easy to do in windsurf boards. The construction on a windsurfing board allows only very limited mitigation. What makes it so complicated is the fact that you want to have a "high flex" of a board as this reduces the compression peaks. And compression is actually the number 1 killer of that kind of construction, because the thickness of the "walls",i.e. the laminate is so thin. But if you have a "high flex" i.e. low tensile preak forces you end up having high shear forces. As if one of the stresses goes down annother one will go up.... So it is hard to keep all 3 stresses in its limits :-( That is the reason why in over 30 years there is no real progression in this area. But to often you see a degression in the production of boards. Because the people just do not understand the physics.... And therefore come up with stupid lay ups of fibers...

It seems to me you are a bit confused. I suggest you to study some engineering before trying to explain things to others.
Anyhow, you are 100% right about those stupid layups we are used to see even from the most famous manufacturer(s).

I am a physistist and mathematican. What are your trying to tell me? I am all ear! But if this confusing to you, then it tells me you simply do not understand that complexity. Which is fine, because you need the engineering background for that. But this whole discussion about building better boards is an engineering task. Unfortunately you read everywhere comments of people who believe they understand how to make boards better with lacking that background. You can make up your own mind of what to think of these comments after you hopefully understood from my comment, that the topic is to complex for simple solutions.

You are a "physistist and mathematican". Not an engineer. That's all.

Do you have something constructive to say? I don't think so.

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SchobiHH said...



Do you have something constructive to say? I don't think so.

I already told you something constructive. Go study some engineering or, better, quit explaining things you do not know. Sorry, but I am not going to explain things to a total illiterate. Grab a book or two instead, or even use Wikipedia. You do not even imagine how much far away from reality you are when you talk about "fatigue" in this case, for example.

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geoITA said..

SchobiHH said...



Do you have something constructive to say? I don't think so.

I already told you something constructive. Go study some engineering or, better, quit explaining things you do not know. Sorry, but I am not going to explain things to a total illiterate. Grab a book or two instead, or even use Wikipedia. You do not even imagine how much far away from reality you are when you talk about "fatigue" in this case, for example.

There's always been a bit of chipping going on between engineers and physicists. You've taken it to the next level.

Which of the points made by SchobiHH do you disagree with?

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Ian K said..

geoITA said..

SchobiHH said...



Do you have something constructive to say? I don't think so.

I already told you something constructive. Go study some engineering or, better, quit explaining things you do not know. Sorry, but I am not going to explain things to a total illiterate. Grab a book or two instead, or even use Wikipedia. You do not even imagine how much far away from reality you are when you talk about "fatigue" in this case, for example.

There's always been a bit of chipping going on between engineers and physicists. You've taken it to the next level.

Which of the points made by SchobiHH do you disagree with?

Too many!!!
Just talking about "fatigue" clearly indicates he is totally unaware of what he is talking about. Also stating that "... There are 3 types of elastic stresses "shear, tensile and torsion stresses" is totally naive, and explains that our friend makes some good confusion between the kind of stress(es) an object may be subject to, and the way (more or less elastic) it reacts to those stresses.
And, by the way, who cares about "elastic deformation", as if deformation is elastic then it gets back to zero when the stress ceases ...

Don't want to play wich have the biggest but elastic deformation play in material fatigue. When you calculate a part most of time you use elastic limit of materials. Not easy to explain it well in english, i am mechanical engineer, i teach mechanical engineering.

I am a mechanical engineer too and I do understand what you say. But fatigue still has nothing to do with what we are discussing (bottom shape deformation). Just a hint, fatigue leader to sudden failure, not to a tiny yet important deformation that somewhat tends to "set in".

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geoITA said..
I am a mechanical engineer too and I do understand what you say. But fatigue still has nothing to do with what we are discussing (bottom shape deformation). Just a hint, fatigue leader to sudden failure, not to a tiny yet important deformation that somewhat tende to "set in".

Yes and a deformation that set in is no more an elastic deformation but a plastic one, most of time not wanted like for board bottom (and deck).

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lemat said..

geoITA said..
I am a mechanical engineer too and I do understand what you say. But fatigue still has nothing to do with what we are discussing (bottom shape deformation). Just a hint, fatigue leader to sudden failure, not to a tiny yet important deformation that somewhat tende to "set in".

Yes and a deformation that set in is no more an elastic deformation but a plastic one, most of time not wanted like for board bottom (and deck).

Of course.

Do engineers consider epoxy shrinkage? How long does it take for boards to fully cure? Have you noticed that the slightest bump on a new board leaves a ding, but once they've done a few seasons they are immune to minor bumps? They've always go a mm or two hollow between the footstraps. That's the thinnest section of the board but shape and layup are different top and bottom. Has anybody measured the flatness of a new board and measured it again having not sailed it? What about old stock? Is it a little hollow?