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Ben1973 said..

:
videos of cobra

Great video, I look forward to buying my next board from cobra
Most people I sail with use them and we are all very happy

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col5555 said..
Does Kinetic hand lay up ?
Cobra uses some kind of resin infusion inside a concrete mould don't they

The mould is for expansion/moulding of the polystyrene blank.

Most factories (including cobra for race sups) will machine a blank down, however Cobras point of difference is that they have moulded eps manufacturing inhouse.

They then hand layup and vacuum bag the laminate.

^^^
With windsurfers it doesn't seem they lam over the raw blank . It would be a good way of minimising waste . Also a blank has a tough , (heavy) , outer skin which would be removed first . Just thinking though , if the blank was perfectly formed it would save the need of a sandwich. I'm presuming it's not done that way because it's probably wonky with a crap finish . Weren't those older indestructible light boards completely laminated , ( including colour) , with a plastic skin , done in a mould with expanded foam inside ? Why don't they do it like that today , way stronger and just as light ? Is it because of the ugly seam ?

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Imax1 said..
^^^
With windsurfers it doesn't seem they lam over the raw blank . It would be a good way of minimising waste . Also a blank has a tough , (heavy) , outer skin which would be removed first . Just thinking though , if the blank was perfectly formed it would save the need of a sandwich. I'm presuming it's not done that way because it's probably wonky with a crap finish . Weren't those older indestructible light boards completely laminated , ( including colour) , with a plastic skin , done in a mould with expanded foam inside ? Why don't they do it like that today , way stronger and just as light ? Is it because of the ugly seam ?

The ASA skin boards were moulded and tough because of the chop strand glass and Plastic skin creating a strong outershell. BUT they would crease easily. So for beginners, weekend warrior freeriders and occasional bump and jumpers they were fine, but for slalom or hard abuse they had problems of creasing and a bit of a weight issue. At least that was my experience as an instructor back in the late 90's early 2000s.

They still had a polystyrene core, a foaming epoxy was used to fill in all voids, so they were cost effective to make as the blank could be relatively inaccurate, but the foaming epoxy would fill in all the gaps and actually help the strength.

Bic had a very clever one shot process where boards were blow moulded like bottles. Perhaps this is what you are thinking of. But those boards were heavy and were like soggy boiled noodles and changed shape in the sun.

The sandwich isn't there to hide anything. It is there to increase the stiffness (thickness) of the laminate without adding too much additional weight. Polystyrene is fried air and has the structural integrity of the goo at the centre of a custard cream, so just laminating on to that would lead to a very temporary board.

No Imax as sandwich is wayyyy stronger - the old i-beam analogy

I totally understand the sandwich. I live and love it .
But are some bottom laminates made with the pvc stuck directly on to the eps without cloth between ? I'm probably wrong . Ok , if you then sandwiched over a skinned blank it would have to be stronger again .???
After using my brain a little more , eps doesn't have much of a skin , not like the hard skin on a surfboard blank .
Ill shut up now

If EPS is moulded as a blank it does not have skin at all like PU does. Its just little balls melted together with heat. In fact, looking at some moulded cores and in particular one that a manufacturer wanted me to deconstruct and photo re warranty claim / QA - it could be worse than "properly" shaped. It will be more bumpy, with adhesion only on the apex (?) of the balls, whereas a shaped foam will have the balls sanded down and have more surface for adhesion. That was certainly the issue in the product I looked at - the outer laminate only touching about 30% of the actual core..... if that.


I've never seen a board with no glass between EPS and PVC foam - if only as the glass ensures resin is everywhere, it can flow, and air can travel. If you just used thickened resin it can still have voids when bagging the PVC on. But of course it adds tensile strength to the overall product also

^^ So you've been there and seen how they do it ?

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Imax1 said..
I totally understand the sandwich. I live and love it .
But are some bottom laminates made with the pvc stuck directly on to the eps without cloth between ? I'm probably wrong . Ok , if you then sandwiched over a skinned blank it would have to be stronger again .???
After using my brain a little more , eps doesn't have much of a skin , not like the hard skin on a surfboard blank .
Ill shut up now

Generally speaking there is glass or carbon between the pvc foam and the eps core. It usually experiences tension so some people use Kevlar or other materials that are strong in tension. I have seen boards made that don't have any fabric inside the sandwich, but they had a much higher density foam core. The best way I can describe the purpose of the sandwich is: most of the work of the laminate is done by the most outside part of the composite. If you wanted a laminate made completely of one material to have the same same stiffness as a composite sandwich it would take 10 + layers of glass. This would be too heavy. So accepting that most of the work is done by the outside of the laminate, using a dense foam to provide distance (web) between the outer layers of the laminate means you get stiffness without a huge weight disadvantage.
the distance / thickness of the sandwich is important for stiffness. The density and material is important for shear strength and impact strength. in part the distance between the outer laminate is why boards that are 15cm thick are less likely to snap compared to boards that are 10cm thick.

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Mr Hooper said..
^^ So you've been there and seen how they do it ?

No I have not.
I'm only addressing that EPS doesn't have a skin like PU.
The blanks seem to be sanded down from Cobra but one other I saw was woeful.

Thats all.

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Overner said..

Imax1 said..
I totally understand the sandwich. I live and love it .
But are some bottom laminates made with the pvc stuck directly on to the eps without cloth between ? I'm probably wrong . Ok , if you then sandwiched over a skinned blank it would have to be stronger again .???
After using my brain a little more , eps doesn't have much of a skin , not like the hard skin on a surfboard blank .
Ill shut up now

The best way I can describe the purpose of the sandwich is: most of the work of the laminate is done by the most outside part of the composite. If you wanted a laminate made completely of one material to have the same same stiffness as a composite sandwich it would take 10 + layers of glass. This would be too heavy. So accepting that most of the work is done by the outside of the laminate, using a dense foam to provide distance (web) between the outer layers of the laminate means you get stiffness without a huge weight disadvantage.
the distance / thickness of the sandwich is important for stiffness. The density and material is important for shear strength and impact strength. in part the distance between the outer laminate is why boards that are 15cm thick are less likely to snap compared to boards that are 10cm thick.

An excellent description

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Overner said..
Generally speaking there is glass or carbon between the pvc foam and the eps core. It usually experiences tension so some people use Kevlar or other materials that are strong in tension. I have seen boards made that don't have any fabric inside the sandwich, but they had a much higher density foam core. The best way I can describe the purpose of the sandwich is: most of the work of the laminate is done by the most outside part of the composite. If you wanted a laminate made completely of one material to have the same same stiffness as a composite sandwich it would take 10 + layers of glass. This would be too heavy. So accepting that most of the work is done by the outside of the laminate, using a dense foam to provide distance (web) between the outer layers of the laminate means you get stiffness without a huge weight disadvantage.
the distance / thickness of the sandwich is important for stiffness. The density and material is important for shear strength and impact strength. in part the distance between the outer laminate is why boards that are 15cm thick are less likely to snap compared to boards that are 10cm thick.

Good examples:

?t=68
?t=232

I don't think these videos are much good. They're mostly directed at boat building and don't have much relevance to board building.
A lot of the things he describes in a very complicated way are pretty much incorrect. For example I don't see why you would be smearing a thick coat of bog over a surface and then having to sand and flush it before you laminate over it ??? I've never seen anyone do that.
This is a big problem wit Youtube. Anybody can put whatever they like up there be it right or wrong.

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Mr Hooper said..
I don't think these videos are much good. They're mostly directed at boat building and don't have much relevance to board building.
A lot of the things he describes in a very complicated way are pretty much incorrect. For example I don't see why you would be smearing a thick coat of bog over a surface and then having to sand and flush it before you laminate over it ??? I've never seen anyone do that.
This is a big problem wit Youtube. Anybody can put whatever they like up there be it right or wrong.

Oh , c,mon ! NASA use YouTube . There's also some good stuff about lower back pain .

^^^ Now you've done it, nobody will come here to find answers to their chronic illnesses.

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Mr Hooper said..
I don't think these videos are much good. They're mostly directed at boat building and don't have much relevance to board building.
A lot of the things he describes in a very complicated way are pretty much incorrect. For example I don't see why you would be smearing a thick coat of bog over a surface and then having to sand and flush it before you laminate over it ??? I've never seen anyone do that.
This is a big problem wit Youtube. Anybody can put whatever they like up there be it right or wrong.

It was an example of why composite-laminating is cool. Not of board-building skills.

Youtube has actual experts - like Physicists, Engineers, sports people... and board-builders. Painting the whole platform as being terrible, would be the same as saying the human-race are all a bunch of death-merchants given one person decided murder was ok.

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mathew said..

Painting the whole platform as being terrible, would be the same as saying the human-race are all a bunch of death-merchants given one person decided murder was ok.

Does that make YouTube the AR-15 of the online world?

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mathew said..

Mr Hooper said..
I don't think these videos are much good. They're mostly directed at boat building and don't have much relevance to board building.
A lot of the things he describes in a very complicated way are pretty much incorrect. For example I don't see why you would be smearing a thick coat of bog over a surface and then having to sand and flush it before you laminate over it ??? I've never seen anyone do that.
This is a big problem wit Youtube. Anybody can put whatever they like up there be it right or wrong.

It was an example of why composite-laminating is cool. Not of board-building skills.

Youtube has actual experts - like Physicists, Engineers, sports people... and board-builders. Painting the whole platform as being terrible, would be the same as saying the human-race are all a bunch of death-merchants given one person decided murder was ok.

I didn't paint the whole of YouTube as being terrible. I said that people can put whatever they want up there regardless of it's accuracy. There are many good articles on all sorts of subjects. There are a lot more crap ones though.
I don't think that guy did a very good description of composite laminating at all.

He should do some back stretches first

I also noticed that guy did not mention Six10 even once .
Bloody amateur !!

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Mr Hooper said..
For example I don't see why you would be smearing a thick coat of bog over a surface and then having to sand and flush it before you laminate over it ??? I've never seen anyone do that.

Mr Hooper,

I am interested to know why you would not use an epoxy filler on the foam of a sandwich laminate.

Can I jump in and say - because you don't have to?

If I vac bag onto smooth sanded EPS a layer of already wet out glass and a layer of corecell, its all squished together and all air removed so the contact between materials is superb. You're putting a tonne of weight (literally) spread out over the whole board. Why add another step and possible weight?

Curious, if you sucked down glass and core to a perfect uneven bond , you would have to then fill after ? I've seen a pic of someone over vaccing a board and it would have needed a litre of bog to fix . I try anally to get every stage as perfect as I can because I'm gaining sooo much weight hand laminating, I try to get the blank as smooth as possible knowing every scratch or rough spot adds weight . I have sealed a blank squeegeeing thickened resin and then sanded baby butt smooth but couldn't tell the difference in the overall weight savings . I could try spraying a thin layer of resin over the blank ??? I think I've mastered the art of sandwich hand laminating as light as possible . A wheelbarrow load of stones perfectly pushes down 3 mm pvc over double concaves . Now you guys know my secret .
I know , I need a vac system ! I only build a board a year or so for myself and a vac system is the cost of another board .,
ps : any advice on making a hand laminated board lighter would be greately appreciated . About to start one soon .

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Overner said..

Mr Hooper said..
For example I don't see why you would be smearing a thick coat of bog over a surface and then having to sand and flush it before you laminate over it ??? I've never seen anyone do that.

Mr Hooper,

I am interested to know why you would not use an epoxy filler on the foam of a sandwich laminate.

Hi Overner,
It's perfectly fine to use an epoxy filler on the foam , wether it's the PVC or the EPS.
You just don't lay it on 3mm thick like that guy in the video. You would screed the blank or PVC and remove all excess before laminating. You would also do it in the same process as lamination so everything becomes integral.

Cheers, Hoops

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Imax1 said..
Curious, if you sucked down glass and core to a perfect uneven bond , you would have to then fill after ? I've seen a pic of someone over vaccing a board and it would have needed a litre of bog to fix . I try anally to get every stage as perfect as I can because I'm gaining sooo much weight hand laminating, I try to get the blank as smooth as possible knowing every scratch or rough spot adds weight . I have sealed a blank squeegeeing thickened resin and then sanded baby butt smooth but couldn't tell the difference in the overall weight savings . I could try spraying a thin layer of resin over the blank ??? I think I've mastered the art of sandwich hand laminating as light as possible . A wheelbarrow load of stones perfectly pushes down 3 mm pvc over double concaves . Now you guys know my secret .
I know , I need a vac system ! I only build a board a year or so for myself and a vac system is the cost of another board .,
ps : any advice on making a hand laminated board lighter would be greately appreciated . About to start one soon .

I'm feeling a bit uncomfortable about you talking about a litre of bog and trying anally to get it right. Perhaps this is a subject for another forum ?

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Imax1 said..

I know , I need a vac system ! I only build a board a year or so for myself and a vac system is the cost of another board .,
ps : any advice on making a hand laminated board lighter would be greately appreciated . About to start one soon .

No its not, if you wanna pay post I'll send u one (minus pump)

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Imax1 said..I know , I need a vac system ! I only build a board a year or so for myself and a vac system is the cost of another board .,
ps : any advice on making a hand laminated board lighter would be greately appreciated . About to start one soon .

Yes, my advice is get a vacuum.

Finally built my own rig and the savings in masking tape alone make it worthwhile. And while we are on the subject, let's heap praise on peel ply - why I never used the stuff in the past escapes me even without a vacuum. It's worth ten times its weight in sandpaper.

At least in the States, we can get affordable vacuums for hobby use on ebay or hardware store notorious for selling less expensive imported products. Some (sturdy) hose from the hardware store, landscape T connectors and valve, cheap pressure gauge off ebay and poly sheeting for the bag. I did pay up for a nice bag connector. Yes, it's a bit of an expense but the improvement in being able to get stuff tight is amazing. Got to be easier than shovelling gravel on top of hand-shaped EPS. It may be enough of a difference to encourage you to build/mod more.

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Mr Hooper said..
.... I'm feeling a bit uncomfortable about you talking about a litre of bog and trying anally to get it right. Perhaps this is a subject for another forum ?

Waiting for a forum post "Do you get enough fiber (not the carbon kind) for windsurfing?". You know it's going to happen, it's just a matter of when. The youtube videos will be mint in that thread.

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Mark _australia said..
Can I jump in and say - because you don't have to?

If I vac bag onto smooth sanded EPS a layer of already wet out glass and a layer of corecell, its all squished together and all air removed so the contact between materials is superb. You're putting a tonne of weight (literally) spread out over the whole board. Why add another step and possible weight?

Mark _australia,

I hear your argument. But don't agree, which is why I asked Mr Hooper why you wouldn't use an epoxy filler.

Where is the resin going on your laminate? I would suggest it is filling all the holes and gaps. So you have to make a resin rich laminate to allow for the migration of the resin. This may not be a big problem with Corecell, but with balsa and PET I think it would be as they are both thirsty. I know when I use Nomex honeycomb you can see the resin create micro fillets within each cell.

There was a surfboard company Bufo(?) Hydroflex that called this type of bond 3D glassing. It was a 'thing'. But all they did was vacuum their EPS boards and found the epoxy penetrated about a cm into their blanks, so they marketed that as a positive. It may well be, but I cannot see how other than a waste of resin and an increase in weight that need not have taken place if the blank had been sealed.

Greg Loehr 20 years ago advocated sealing blanks on swaybacks.

IMO if you scraped on an epoxy filler you fill all all the gaps so you have less resin migration, I haven't noticed any particular weight penalty. At least that is my line of thinking and I am sticking to it... like... glue... Oh dear. I have noticed a concerning anal trend to this thread so perhaps I should have said sticks like sh**... Sorry.

Like Mr Hooper suggests I scrape off the vast majority, but have found, for me at least, a reduced risk of delam and general mishaps in the lamination (I guess because I know everything has glue on it) but I haven't noticed a weight penalty.

I will agree it is a PITA though.

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Overner said..

Greg Loehr 20 years ago advocated sealing blanks on swaybacks.

Swaylocks... bloomin' autocorrect

I do use peel ply , for it is good Gives a great finish and sucks up a little resin .
Yes I use a ton of masking tape ,including graphics , around 10 rolls of cheap stuff $25 .
For those that are horrified and picturing me tipping a wheelbarrow of stones on my board , I should explain . This is for the bottom of the board with concaves. The top is mummified with tape . No sunken decks for me .
Firstly the blank has a layer of glass so is already stiff . I do half of the board at a time . On a bench I support the board very well then make a cardboard well tight around the board . Using a ribbed squeegee apply thickened resin to the 3 mm core and place on board . Cover in plastic then a thin blanket . Then I gently shovel on a 2 inch layer of clean small pebbles . Works a treat . Totally eco friendly as the garden gets its pebbles back when I'm finished .
On the topic of some resin seeping into the blank compared to a sealed blank , wouldn't the seeped blank have a stronger stiffer skin ? What would the weight and strength difference between a bogged and seeped blank be ?

ps: yeah , I know , " sucks ", " bottom " , " stiff " and " ribbed " was used in this thread.
pps : for Hooper , I also used " tape " and " cover in plastic "