Nice video. Note the author indicates 'don't mix & match unless you know what you are doing' and is mainly referring to break points/loads of hybrid laminates [SIC]. At an industry level, 21st century board construction has been fine tuned for many decades by pros+composite engineers who mostly know what they are doing. This includes the hard earned knowledge of required bend patterns/reflex characteristics and abrasive/impact resistance not covered in the vid, all essential for getting punters across lumpy water quickly, controlling turns and generally allowing enjoyment of the product until boredom or breakage kicks in. Today's production boards are pretty good with the right laminate being on the right boards and in the right places, certainly more carbon will creep in over time much like we've seen with the rigs we use.
My bet is structural cores will be the next area to bring weight down without reducing longevity. But as with anything new, it will be pricey and primarily for wealthier early adopters in the first instance.

I don't like it. Well not in the context of WS board. The video is correct of course but he only addresses strength. He does not address abrasion resistance, or wanting to conform to a weight limit.

(1) at 2:30 he is talking about stretching. Things are stronger in compression than tension so the value (or lack thereof) of carbon on the deck of our boards is different to on the bottom of our boards. The deck is in compression and the bottom in tension for the most part. (neglecting the sandwich layer that also has its own tension and compression areas but I'm trying to keep it simple....) But then under the heels we are back to tension again as we try to dent it downwards. So it is not as simple as just looking at elongation as he says. Essentially: He is talking about just plywood. We have plywood - foam - plywood all glued together. Its different. In some ways...

(2) 5:20 ish he is talking about a layer of carbon over 3 layers of glass. Yes of course it is correct, but it neglects items where one is trying to achieve a weight limit. ie: yes, bunging a layer of carbon over a glass laminate adds no strength (as many assume it does). BUT if you are trying to make a board that is under 7kg then the use of carbon makes sense as strength to weight ratio is high.
That is my main issue here - to a casual observer this video makes it sound like carbon is useless. No, he is just saying adding it for no reason is useless. They still choose carbon to build aircraft wings and windsurf boards for a reason.

(3) 5:59 ish - he talks about reversing the layers being better..... 3 of carbon and a layer of glass over the top. Well, that is what we do in windsurfing boards. Everybody can switch off now

(4) at about 6:32 he says why not use carbon for all of the laminate and forget glass. Again, he is only addressing strength. Glass (and even better, aramid or innegra) offer amazing abrasion resistance. Anyone who has sanded carbon fibre will see how fast it disappears. Its shocking.....
So some outer glass can be a major help.

Then, he makes reference somewhere to how carbon fails completely and glass will break but stay together a bit to limp home - VERY valid to us.

So, no, your carbon and glass board is not crap. He is talking about carbon added for wank factor only.

Back when I was building whitewater racing Kayaks, we quickly learnt that mixing Carbon into fibreglass was a waste of money.

However, mixing fibreglass with Aramids (Kevlar) was a great benefit as long as you used the much stronger bonding Epoxy or Vinyl-ester Resins. Using them with Poly-ester resins was also a waste of time and money.

IMHO, there is definitely a very large marketing-wizz/wank factor in the advertised use of Carbon Fibre in windsurfing boards, where high strength glass, Aramid fibres or wood would achieve better results. (Aramids are very light, like Carbon, but have far superior tensile strength).

Massive stiffness is something I actually don't want in my windsurfing boards!

One huge reason Aramids have not gained favour in the surfboard and windsurfing custom build industry is for that which Decrepit mentioned. It is impossible to sand! Therefore, it can't be used on any external surface that is subject to sanding in the construction process. For internal layers between core and sandwich foam it is very useful, and can be used under a layer of sand-able glass with care.

Carbon fibre may make sense under foot pads if done correctly. And it has a huge place in fins and masts!

buzzy said..
Marks on the money in relation to compression loads. Carbon slightly outdoes glass in this area as it is about 5 times stiffer than glass. This also means that failure of carbon is catastrophic. (still maybe need a bit of glass)
Carbon under the heels takes the weight of landing etc. due to its layup with the pvc core and inner cloth. when weight is applied the core bends downwards the layers under the core are under tension and the outer layers are under compression. the correct layup of carbon and glass, etc. on the outside helps prevent buckling of the fibres that lead to delamination and laminate breakdown.
Compression is not a force that is at right angles to the cloth. It is a force that is internally applied to the fibres on the outside of a composite that has a force applied externally. Below image shows those forces. If the compression layup cannot handle the forces it will buckle or wrinkle and fail leading to delamination and cracking of the core.

Compression has nothing to do with sharp impact or knocks and bumps, this is impact forces that carbon does not like.


Board makers are putting carbon around the rails to help stiffen the boards while keeping weight down, not for impact resistance.
Carbon has become more popular in board construction due to it have approximately twice the strength to weight ratio than glass, assisting to keep boards light and hopefully kind of strong.....well maybe.......ok, sometimes, but not if it says Textreme on the label.
This video has no relevance to sailboards as you do not make a board by just laying up layers of glass and carbon. Proper core composite layups have a lot more going on than what this video is about.
P.S. I'm not a carbon fan, you can make a decent board without the use of it.

Yep. I recon the best sandwich will have extra glass on top to resist crush and deform', and kevlar under for tension strength. And maybe a double layer sandwich of lots of deck grip, closed cell foam of you jump to the clouds!

Just wasted 6 minutes of my life
My latest carbon waveboard is holding up fine.

Heres another vid , if you could be bothered
More to make your brain hurt .

Sailquick said

Massive stiffness is something I actually don't want in my windsurfing boards!

Andrew, I have to disagree with you a bit here. Using the core polystyrene foam as a shock absorber doesn't make good engineering sense, it's not really suitable for that job.
If the sandwich flexes, the core foam will fatigue and compress a bit, leaving you with negative rocker under the feet. Exactly where you don't want it. The boards lift moves aft behind the rider, forcing the nose down, and increasing wetted area. The next stage of course is collapse of the foam and delam.
Guess it depends how long you want the board to last?

And as I said earlier, if the carbon cloth is laid on the bias it doesn't add to the longitudinal board stiffness any more than the fiberglass.
If the ride is too harsh you can always experiment with different foot pads.

sailquik said..
That video is extremely straight forward. If your brain hurts when trying to understand it, you should leave composite construction alone.

Excellent presentation from a person who actually knows what they are talking about, and yes, those principles are directly applicable to windsurfer construction, in the right contexts.

Have to agree with you here Andrew, I learnt a few things from it, didn't realise how good s glass is and how bad kevlar is in compression.

Mastbender said..

decrepit said..
Sailquick said

Massive stiffness is something I actually don't want in my windsurfing boards!

Andrew, I have to disagree with you a bit here. Using the core polystyrene foam as a shock absorber doesn't make good engineering sense, it's not really suitable for that job.
If the sandwich flexes, the core foam will fatigue and compress a bit, leaving you with negative rocker under the feet. Exactly where you don't want it. The boards lift moves aft behind the rider, forcing the nose down, and increasing wetted area. The next stage of course is collapse of the foam and delam.
Guess it depends how long you want the board to last?

And as I said earlier, if the carbon cloth is laid on the bias it doesn't add to the longitudinal board stiffness any more than the fiberglass.
If the ride is too harsh you can always experiment with different foot pads.

I agree with your disagreement, also the more the board flexes, the more speed is being scrubbed off, stiff = fast.
One of the reasons you don't see the plastic boards of the 80's anymore, they were slow, too much flexing, but they lasted a long time. Shock absorption should be done with the foot pads alone, one of several reasons they have improved over the years with laminated pads.

I'm not talking about the floppy soft plastic boards at all. I am referring to the difference between a well made non carbon sandwich and the same type with heaps of carbon. Big difference!

I am well aware of the difference even the slightest negative rocker can make in an out of shape board. You definitely don't want that to happen, but good sandwich construction with wood and/or S Glass should prevent it. I like your strategy of laying the Carbon fibre on bias if that has the effect you describe.

I have a ten year old Isonic wood that has had an absolute pounding all it's life. It is still 100% sound and the rocker is still as new. It is still my go to, all round board in it's size. The harshness of the full Carbon boards is body breaking and out of control in comparison.

Comfort, control and confidence = fast.

Imax1 said..
Interesting video,

I agree. He never mentions windsurfing, so it's clearly not a critique of how current windsurf boards are built. It is, however, helpful for someone who makes occasional board repairs. Fixing a nose with some glass layers for better impact resistance, and a carbon layer on top to match the looks, seems reasonable at first. Not that I ever did that, but I'd now definitely shy away from that, since it only adds weight, not strength.
I also found the numbers about tensile strength interesting. I think they explain the well-known difference in impact resistance: glass can stretch more, absorbing and distributing the load.
So for a nose repair of a carbon board, I'd be tempted to use only glass instead of carbon. Stiffness should not be much of an issue in the first few centimeters of the nose, impact resistance often is. Is there a problem with this approach?

He didn't mention Basalt, which sits in between S-glass and Carbon. Stronger than S-Glass but has similar properties than S-Glass , not brittle like carbon, so if you want the matrix to be similar to S-Glass but stronger use Basalt.

boardsurfr said..
>>> Stiffness should not be much of an issue in the first few centimeters of the nose, impact resistance often is. Is there a problem with this approach?

In my opinion stiffness is only an issue aft of the mast, I only use carbon in that area, mainly under the sandwich so it's protected from impact.

I certainly would never do a nose repair with plain carbon. I do use carbon/kevlar under glass, and that seems to lessen nose damage significantly

decrepit said..

kato said..
Yes sanding Kevlar is crap but cutting it is easy. Just run tape where you want to cut and cut through the tape and cloth. I tend to use cheap scissors which last a good 6 mths

Good one Craig I'll try that next time.

Ot
kevlar tricks...
A trick we use in RC modelling is to blunten scissors by running them past a belt sander at 90 degrees. Cuts Kevlar really easy - pretty well stuffs the scissors for anything else

ive also seen multiple layers of Kevlar cut with industrial cutting fabric cutting wheel - imagine a oversize Olafa disk in an angle grinder. Cut through Kevlar into a waste sheet of polystyrene

info go in this thread...
www.rcgroups.com/forums/showthread.php?795224-Sharpening-Kevlar-Scissors

Sanding kevlar...
we sand exposed Kevlar with fine wet and dry used wet ie 400-600 gets a very smooth finish

we also firm up frayed Kevlar that has been trimmed in a laminate with superglue before sanding

cheers Jeff

jirvin4505 said..

A trick we use in RC modelling is to blunten scissors by running them past a belt sander at 90 degrees.

I buy the serrated on one side dressmakers scissors at Spotlight that are "guaranteed to never blunt" and lifetime guarantee.

There's an assumption in his video which no one appears to have questioned. He says the carbon adds no strength after it breaks. But who says the carbon is going to break? The carbon does add stiffness to the total construction, and if the design does not subject the carbon to forces that will break it, then it will continue to do so.

The takeaway point is that the carbon will fail first under excessive loading, so the additional carbon layer is giving you extra stiffness, but not additional strength or toughness. Be aware of it.

Maybe the phrase 'Carbon Reinforced' is misleading...perhaps 'Carbon Stiffened' would be more appropriate, not leading you to thing the carbon is making it stronger.