Im hearing this more and more .
I can understand a slight negative rocker in a long board thinning to a Vd pintail , like a Mistral RB.
Otherwise probably not good .
Im seeing a manufacturing problem .
When planing I imagine half weight driving over fin and other half over mast base.
There has to be all the energy trying to bend the board between the two.
One of two things must be happening .
1 , it's bending during manufacturing , vaccing,
or
Its bending with use .
Im thinking it's bending with pounding use.
Next board I build , full stringer.
Imax1, negative rocker from MASS produced, over priced, undermaintained manufacturing methods. Surely??? No??
In boatbuilding its called hook or interceptor. INTERCEPTOR now that sounds FAAAAASSST!!
imax, I'm fairly certain it's not "bending" I think it's the core foam compressing. this also results in delamns eventually, if it goes too far.
And what will probably happen with a stringer, especially om wide boards, is a compression either side of the stringer, resulting in the sandwich cracking either side of it, unless there's extra reinforcing running along the stringer, out into the board.
Select to expand quotedecrepit said..
imax, I'm fairly certain it's not "bending" I think it's the core foam compressing. this also results in delamns eventually, if it goes too far.
And what will probably happen with a stringer, especially om wide boards, is a compression either side of the stringer, resulting in the sandwich cracking either side of it, unless there's extra reinforcing running along the stringer, out into the board.
50 mm 6 oz strip along stringer ?
And is this because when lamming it squeezes into the foam with resin and on the stringer it is hard pressed with less resin . Thin almost no resin over stringer ?
^^^ no its simple mechanics
resin absorption into foam does not increase strength. And more resin in a fibre makes it weaker. Enough is enough, too much is weaker. Thus why vac bagged minimal resin laminates are good. Less resin in the glass on the stringer is good, not bad.
Think about how a board breaks, and the shearing force applied longitudinally along the glass / foam interface of a traditional PU/ glass surfboard. The glass is making the strength, that's the limiting factor.
I agree with the board lady site when she says she realised that stringers add nothing as the tensile strength of plywood is less than that of glass and so it adds nothing. So by the time the glass breaks, the wood stringer broke long ago. =total failure.
Non- stringers styro core / epoxy surfboards prove that.
A stringer does not add strength, and the only we reason surfers cling to it is a traditional look / belief its better.
Anyway even if it DID make it stronger / resistant to bending, its just a strip along the middle. So in a hard jump for example, if the stringer resisted an upward bending of the board, the force has to go somewhere so it just induces a torsional force along the centerline, which means that force has to go somewhere so it delaminates the stringer from the foam.
I'm confused .
A foam blank wth a stringer , I could stand on with a heavy mate on my shoulder between trestles , and it won't bend .
A foam blank vaccd without stringer support will bend and twist.
How could a stringered blank not be stronger , and combined with shell also not be stronger , all materials , apart from stringer , be equal ?
And , for mathematics , which I love we know we shouldn't mix glass and carbon for the same reason , and yet we do.
I can see a problem vaccing over a stringer .
when wetting out on a bench then draping over blank into a bag ,pressure on the part over this stringer would be squeezed almost dry compared to the rest.
Ahh the carbon issue. From what ive read we only use carbon for its byproduct of lightness. Carbons real benefit is its srength in tension No use like that in a sailboard?
I've suspected it's to do with differential shrinkage. Like a bi metal strip. Residual stresses after the initial cure eventually come in to equilibrium over the softer core. Maybe not? But that 1mm hollow seems a bit too consistent and the hollow too much of a smooth curve to be associated with random failure of the insides.
www.compositesworld.com/cdn/cms/Paper_CompositesWorld_Evonik_Oct2017.pdf
Select to expand quoteolskool said..
Ahh the carbon issue. From what ive read we only use carbon for its byproduct of lightness. Carbons real benefit is its srength in tension No use like that in a sailboard?
Sounds good in brochures.
Looks good , I got to admit.
I hear good glass or even better good S glass , for our purpose is best .
Why is it a super expensive extreamly fragile light carbon board is acceptable. And if it was made in glass and dinged it was the glasses fault ?
I read the brouchures and see flex ,stiffness, twist controll , rail support , rail ding resistance , all on one board . Really ?
Could a good quality glass board be so close to the benefits of carbon at %10 more $ , not double even though the carbon is less work and so slightly more expensive in materials ?
Select to expand quoteIan K said..
I've suspected it's to do with differential shrinkage. Like a bi metal strip. Residual stresses after the initial cure eventually come in to equilibrium over the softer core. Maybe not? But that 1mm hollow seems a bit too consistent and the hollow too much of a smooth curve to be associated with random failure of the insides.
www.compositesworld.com/cdn/cms/Paper_CompositesWorld_Evonik_Oct2017.pdf
Yes , one has to break before the other, not at the same time.
As far as a board snapping , or at least flexing , a stringer would have to bend , ( which it won't ) , before the glass ,( or carbon ) takes the strain .
Select to expand quoteolskool said..
Ahh the carbon issue. From what ive read we only use carbon for its byproduct of lightness. Carbons real benefit is its srength in tension No use like that in a sailboard?
When the board flexes it is in tension or compression depending on what way and side of the board your talking about
Imax
Get two trestles and put a bit of 3 ply between them.
Do same with a piece of glass, 2 x oz laminated in epoxy
Clamp it, so it can't slide inwards, so all the weight applied will be in tension.
Which can you stand on? I bet I know.
So clearly when a board is loaded in such a fashion, the glass is taking the load. If the glass fails then the stringer does. The stringer adds nothing.
Are all the (quality) epoxy over stringerless styro cored surfboards failing at a far greater rate than the old stringered PU ones? No.
Are our sandwich construction waveboards failing at a greater rate than the old (double) stringered PU blank ones of the 1990s? No. They are a ****load stronger.
And yes carbon is more brittle so hitting it with hammer, not so good But in tension is extremely strong so don't fall for the salesman speak of some windsurf companies that want to sell you on $8 p/m s-glass vs $60p/m carbon. Carbon has a massive part to play in board construction. Do you suddenly see Airbus going for S-glass as they can halve the cost of a plane and have it perform the same?
The strength of a board is indeed a function of its skin taking the compression and tensile loads but the board breaks when those surfaces are over-stressed and at that point the top and bottom of the board try to come together. The board then snaps the bottom laminate rail to rail - with the deck then crumpling - or else the process starts with cracks at the rail.
The argument for a stringer is not so much to add rigidity to the hull, but to help keep the deck and hull bottom laminates apart - like the centre web of an I-section beam.
Without a stringer, the foam has to take all the compression when deck and hull boots try to come together.
But, on topic, I'm sure it's possible to build a board without stringers, and without vacuum bagging causing negative rocker.
Just an observation from mid last century. I was at Margaret river, and I guy had just repaired his broken in two surfboard. He'd peeled the glass back about 6 inches either side of the break, and butted new glass up against the old. I tried to convince him it wasn't a good idea, the glass needed to overlap. But he wouldn't listen. took it for for a surf, and the board broke in two again half way down the first wave.
YEP you guess it, a clean break where the glass was butted together, snapping the stringer 6 away from the previous break. That's when I first became aware how much strength a stringer added. Then in 66 I met Midget who was experimenting with stringerless boards. It made sense to me, dispenses with the weight of the stringer. When I returned to Perth I started making all my boards stringerless, and haven't put one in since. That's no stringers for over 50 years.
Select to expand quotemark62 said..
I wonder if Patrik's air in side boards suffer with this?
I'll ask him.
Select to expand quoteBen1973 said..olskool said..
Ahh the carbon issue. From what ive read we only use carbon for its byproduct of lightness. Carbons real benefit is its srength in tension No use like that in a sailboard?
When the board flexes it is in tension or compression depending on what way and side of the board your talking about
Ok so in yacht building the real benefit of using carbon is in the chainplate area where the shrouds are attached. Large loads in tension. A pulling load. Stiffness n lightness are the secondary benefits of the carbon.
I cant for the life of me see where in a sailboard it is used for its primary design benefit. Anyone??
We use it for its secondary benefits, stiffness n lightness. It has a much higher tensile strength than the glass but has poor impact strength. This is why we use a layer of glass a layer of pvc a layer of carbon n a layer of glass. To try to spread the loads which the carbon cannot withstand. Its s tricky product to work with to gain the full benefits of its properties.
Select to expand quoteImax1 said..
I hear good glass or even better good S glass , for our purpose is best .
Why is it a super expensive extreamly fragile light carbon board is acceptable. And if it was made in glass and dinged it was the glasses fault ?
I read the brouchures and see flex ,stiffness, twist controll , rail support , rail ding resistance , all on one board . Really ?
Could a good quality glass board be so close to the benefits of carbon at %10 more $ , not double even though the carbon is less work and so slightly more expensive in materials ?
I had bought the story that glass can be better than carbon. With respect to ding resistance, that is the case, so if you often have the mast fall onto the nose, the nose may last longer before it needs to repair. But nose repairs are easy!
If you plan to use a board a lot and for a long time, the ding resistance matters little. What does matter is flexing. Glass flexes a lot more than carbon. The same is true for a glass-PVC sandwich. That means the cores gets compressed a lot more in a glass board. If you sail in chop, you can rack up so many compression-expansion cycles that the EPS will give up. With a carbon sandwich, the core compression is a lot lower, so the core should last a lot longer. That pretty much means that the board will last longer. A "crushed core" delam repair with PU injection won't last; you pretty much have to remove the crushed core and replace it. That's too expensive to have done professionally. If you do it yourself, it's a lot of work. If you don't remove lots of EPS (under all load-bearing areas), then the section next to the one you just repaired is likely to go next. On the plus side, it's a good way to gain repair experience 
.
But for my next boards, I'll pick carbon over glass, if I can afford it.
Select to expand quoteMark _australia said..
Imax
Get two trestles and put a bit of 3 ply between them.
Do same with a piece of glass, 2 x oz laminated in epoxy
Clamp it, so it can't slide inwards, so all the weight applied will be in tension.
Which can you stand on? I bet I know.
So clearly when a board is loaded in such a fashion, the glass is taking the load. If the glass fails then the stringer does. The stringer adds nothing.
Are all the (quality) epoxy over stringerless styro cored surfboards failing at a far greater rate than the old stringered PU ones? No.
Are our sandwich construction waveboards failing at a greater rate than the old (double) stringered PU blank ones of the 1990s? No. They are a ****load stronger.
And yes carbon is more brittle so hitting it with hammer, not so good But in tension is extremely strong so don't fall for the salesman speak of some windsurf companies that want to sell you on $8 p/m s-glass vs $60p/m carbon. Carbon has a massive part to play in board construction. Do you suddenly see Airbus going for S-glass as they can halve the cost of a plane and have it perform the same?
Im not sure what your experiment proves ?
The stringer is not laid flat but in an upright position . On a large board it is 8 to 10 cm high . Virtually unbend able .
That has got to help hugely . If the board doesn't flex to start with there must be way less tension on the glass . There would be less compression of the foam as its trying to bend and also less sideways shearing force between the glass and foam .
Im not saying a stringer is necessary , it obviously isnt . But it has to be stronger . Is it worth the extra weight ? , probably not .
And you cant compare the older boards to the newer ones because we now use sandwich construction which is hugely different .
Id bet if you made a board with a stringer-ed PU blank with sandwich construction it would be sooo much stronger , with the harder foam and all.
Also a lot heavier .
Getting back to the original problem of negative rocker forming with the continuous pounding in that area between the front and back straps ,
Having some sort of stringers , even a few shallow ones in that area would have to help hugely , not add nothing .
Select to expand quoteImax1 said..
>>>>
Having some sort of stringers , even a few shallow ones in that area would have to help hugely , not add nothing .
That's how the mistrals were made, but the stringers are d-cel glass not timber. Maybe they should have used more glass on the stringers, because I've seen a few blown bottoms where the mini stringers have broken under the delamn. It's not due to a dry layup either the resin goes further into the blank than I've seen anywhere else. And the foam has separated a long way down.
I feel a carbon sandwich with no mini stringers would have survived longer.
