Ian K said..
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?

geoITA said..






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 ...

Ian K said..
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 alittle hollow?

Ian K said..
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?

Chris 249 said..





I agree that sail deformation limited the top end with the old sails and that the new ones have a vastly better top end. Manufacturers still seem to try to sell sailors just as many sails to cover the wind range. As your figures indicate, a lot of what it gained in top end handling with modern sails is lost due to their lower power at the bottom end.

I can't completely agree about your wind range figures since the wind range you quote for an ancient 6m slalom sail is way out of what I would have used at that time, and since I was top 20 at the slalom world titles at the time I wasn't particularly shyte. No one at the worlds or during the Aussie pro circuit at the time (which included Robby, Bjorn, Anders etc) would have used a 6m slalom sail in 8 knots because the lower wind limit was 15 knots and even in that a 7.8 or perhaps 7.3 was the standard sail.

Top end deformation and C of E shift were a problem, but that is to a significant extent a matter of technique, harness lines and back hand strength. Where those old sails did lose out, as we agree, was by having high aero drag that limited their top speed. I had an ex Pete Cabrinha Gaastra team 7.3 or 7.8 custom with foam/glass or carbon sandwich battens and something like 6 camber inducers and it, and similar sails, actually seemed to have amazing stability - at the cost of having a tight leach and deep upper camber that reduced the top-end speed. It would never make it as a production sail because it was also extremely unforgiving through gybes, although personally that suited my style very nicely.

I think essentially it's an issue about how we define range. We can have different (but equally valid) measures. Those of us who have done a lot of sailing on various OD longboards have spent a lot of time looking for power in light winds and practising holding onto a sail far over the top of its normal range, so our feeling for range is probably very different to that of other people.

I'll also say that I'm unsure how many people these days use a 6 in a true 35 knots. That is hitting well over 50 knots in the gusts. In such winds, people find it difficult walking, the water is covered in spume (not just white caps), things ashore are breaking, etc etc. I sail Sydney-Hobarts where we have sophisticated wind instruments so spend a lot of time getting real windspeed info and with respect, what many people call 35 knots is a wind that may hit 35 knots for very short times at the peak of the gust. That is actually a true 20 knots, by meteorological definition. Some people may be capable of using a 6 in a real 35 knots, but not the average sailor in what I would call normal conditions, with normal chop and gusts.

Imax1 said..





I could imagine that the EPS core could get harder and more crumbly over time.Or is it that boards that are a few seasons old are built better than newer ones ?

lemat said..




When i open old eps (surf)boards and recently old (1995/1998) f2 windsurf store outside i find eps core in perfect condition, like you imagine core retracted and crumbly like eps you find on the beach. Skin around protected it. I don't know if old boards built better but it really seems that epoxy continues to harden over time although resin manufacturers say not.

hardie said..
WE that love windsurfing want to find ways to make it grow, I think thats what we have in common, some of these arguments here even if resolved wont contribute greatly to the growth of windsurfing. Let me digress only slightly. In human psychology, there are what is known as the big five personality factors. One is openness. Openness is a positive attitude toward new ideas, experiences, and solutions. People who are high in openness are often curious, imaginative, and creative. Those high in openness want to continually try new things. So when kiting, SUP and Winging emerge windsurfers high in Openness will move to the new sport. Those low in Openness will windsurf till we die, coz we know how good it is. Now for non-windsurfers, it is how to get those high in Openness try windsurfing and get hooked. One disadvantage is that windsurfing has been around 40 to 50 years so those that havent windsurfed before have had many years to try it but never found it appealing, so we cant win them over. Its only the odd straggler of a certain older age we might get, or its the young to give them an experience. The difficulty with the young is that windsurfing is no longer cool, kiting and Winging are cool. I dont think any great innovation in windsurfing equipment is going to attract the young. Its young sailors in Yatching Clubs who are taking it up for Olympic selection, but thats a Foiling discipline. Wish I could be more optimistic, but these are the barriers, its more psychological barriers than equipment barriers that prevent large growth in windsurfing anymore. Decisions to participate and invest in sport are made inside our brain and filtered through our personality lens. My 4 cents or is it 2 cents?

Ian K said..
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?

SchobiHH said..





oh! now you are talking. Unaware of "what I am talking about beeing totally illatere". You are quite insulting and give no proper argument. I like that type of person. Blaming others to be stupid because the are questioning there profound argumentation....
I still can not image that you have a mechanical engineering degree.

There is one principal concept about "elasticy", you a apply a force to some body and the elastic deformation is of a "tensorial" kind. Which is nothing than stating, that the body reacts with shear and tensional stress. (forget my statement about torsional stress, that was wrong. Got abit rusty and have it looked up again. Because I want to sure I am stating the correct) Obvisously you are not aware of that fact.
Fatique is btw the special situation where the material encounters its limits of elasticity because of period loads...

Your statement "fatigue leader to sudden failure, not to a tiny yet important deformation that somewhat tende to "set in" is total nonsense.

Fatique is something what starts slowly and evenutally ends in total failure.

Your statement
"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."

is also wrong (because of the simple fact that the compression strength of a stronger PVC is nothing compared to the compression strength of the laminate. That is why there is sandwich construction. That is something every mechanical engingeer should have learnt is its undergraduate classes But you don't care because to you all others who not comply to your flawed ideas are stupid.

Can you please give me the calculation fo the 2x better strength? I really would love to see that. BTW the strength indeed can be calculated. It is not so complicated. You just need to know that is the correct formula to apply, i.e. the right theory that models that effect. You might share your indefinite wisdom with us.

geoITA said..




My best suggestion to you is the following.
Take 20' of your precious scientific time and do the test:
test.mensa.no/home/test/en
Obviously the result will not be certified, so it's nothing one can brag around; but it can be extremely useful for you. Once you will know exactly where you sit among the general population, you will also know how you do appear to others every time you speak your mind.
Just 20'. And leave the tensors alone.

P. s.: as for the 2x better strength in heavier PVC, no need for calculations, it's in the charts already (www.3accorematerials.com/uploads/pdf/TDS-AIREX-C70-E-08.2022-ex-Europe.pdf).
P. p. s.: as for "the compression strength of the laminate", apart from the fact that you don't seem to understand how the sandwich structure works, do you really think that the thin outer laminate will resist compression by itself?
P. p. p. s.: maybe you didn't notice, but fatigue is out of question here, as we are not talking about "total failure" of hulls, but just about possible deformation of the rockerline.
P. p. p. p. s.: you can study deformation by means of tensors, but there is no such a thing as a "tensorial kind" of deformation.

SchobiHH said..
ohhh, know you say that I lack intelligence. What of an insulting person are you. Obviously it is only argumentation can can deliver. Mankind has to feel sorry, that all your wisdom never came to use.

geoITA said..
Insulting? Me? Why? Did I state anything wrong about you?
To say that is the "only argumentation" is a false statement, as I answered to a few of your points, those that could be answered to briefly. And one should be grateful to be explained, for instance, that the mechanical properties of most commonly used (in sandwich boards) PVC foam are readily available in the data sheets so that he needs to make no calculations, or that fatigue is not involved in the alteration of a rockerline.

Doggerland said..
only a split-toe booties duel can restore honors here