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!!

decrepit 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 ?

^^^ 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.

And , for mathematics , which I love we know we shouldn't mix glass and carbon for the same reason , and yet we do.

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?

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?

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 ?

I wonder if Patrik's air in side boards suffer with this?

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?

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.

Ben1973 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.

dragonplate.com/what-is-carbon-fiber

Imax1 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.