Composite Sandwich Wakesurf build - 2010 :)

[Nooga678]

No worries. Still just following the build. I asked because I thought most surfboards the concave got deeper towards the back rather than fading away to flat. I may have just throught wrong, as I don't have access to any actual surfboards.

Have you every experimented with single to double, or are our boards too short to make it worth while?

[surfdad]

There are a bunch of theories about how concaves work. The typical feel is that the boards are faster down-the-line and also rail-to-rail. The rail-to-rail response is pretty consistently felt to be because there is less volume out at the rails and so it's easier to sink one rail or the other, creating that responsiveness.

As for concaves - some say greater wetted surface area, some say introduction of air into the area just under the board, another and this is the theory I subscribe to, is that it flattens the rocker down the middle of the board and a more relaxed rocker tends to be faster. Could be that all of them are applicable.

With all that said, I shape my concaves to create a flat running wetted surface when the board is trimmed. As such, it will be deepest at the apex and fades at the entry and exit.

I have done single to doubles and a double INSIDE a single (which is a major PITA to shape and glass! ) The double through the tail tends to loosen the tail up and made the boards too skatey. We have failrly wide tails to begin with, which already makes them somewhat loose and skatey, I haven't found any reason to increase that feel.

Thanks again for following along.

[surfdad]

I'm jumping ahead for thisone picture. I finished shaping the deck and rails and this gives a good view of the amount of corecell in the rails.

[surfdad]

Back to the sequence. The composite sandwich uses a textile between the core and the skin. The weight of the textile, as well as, what it's made of will affect the stiffness and toughness of the final product. Surftech boards, which uses the construction, use a 4 oz egalss. The newest iteration of the construction is using 4 oz warp glass. For this build, I am striving to build the stiffest board I can, so I am using 4 oz Zylon. Zylon is a ballistic fabric - that doesn't stop bullets after a while! In composite build, it has physical properties better than aerospace grade carbon fiber.

It's not a good product for production for a number of reasons. One is that UV light will destroy it over time, it is MISERABLE to cut and I have a special pair of electric shears, lastly it doesn't sand, it fuzzes!

Nothing beats it for stiffness though, so that's my choice.

The fabric unrolled and cut to shape.

[surfdad]

For the skins, I am using 3 mm Corecell A500. It's a 5 pound foam, about 1/8" thick. I have it cut into 4' x 5' pieces for shipping.

For the bottom, I merely trace the outline on the sheet and then cut it with a pair of shears - it cuts like thick construction paper.

[surfdad]

I didn't get many good pics of this segment, but I place the Zylon piece on my wet out table and wet it out with about 4 oz if epoxy. I had mixed up a total of 7 oz of resin and with the reserved resin I mix a blend of microballoons and cabosil into the resin and then spread that "sludge" on the surface of the EPS core and on the inside surface of the corecell skin.

I then assemble it all - core first, Zylon aligned and squeeged down, then I carefully align the corecell skin on top of the Zylon. With all the pieces in place, I lightly tape the skin down so that I can handle it and slide it in the bag.

I am not placing the rocker bed in the bag, as that would press out the concave I shaped earlier, instead I rest in on the rocker bed and the weight with highly sophisticated weights.

[surfdad]

Out of the bag. I intentionally leave the bottomn skin a tad "fat" so that I can be "less than" accurate when I place the skin on. I then trim it up using a razor to get it close and then a sanding block to make it flush with the rail material.

Pictures: fresh out of the bag and then trimmed up.

[surfdad]

Shoot I lost a post - I shape the foil of the deck by hotwiring as much off the deck as I can. Then I measure and mark the thickness from the bottom up and free hand the foil. Hit it with the planer and make sure the deck is level. Crappy picture, but you can see the foil taking shape.

[surfdad]

I'm adding wings to this board. Wings do a couple of things, one is they allow the outline to remain straighter - longer. Conversely, they provide a rapid way to step down a wider tail to a narrower tail.

A wider tail provides extra flotation, but that also prevents sinking and this gives a more skately feel. This board will have a fairly straight section of the outline through the fins to give it some extra drive, then step the tail down to a medium width to aid in turning.

The wings don't really carry any load and as I mentioned extend the straight on the outline. The corecell rail materials follow the natural curve of the outline and I add material to effect the wings.

I'm using some scrap divinycell for the wings. The blue material is 1/2" thick H45, which is a 3 pound density foam and shapes like soft clay.

[surfdad]

I rough out the area that I want the wings to cover and then cut a section from the H45 to glue up to the rails.

I'm adding the wing material at this point, which is AFTER the deck has been brought into tolerance, but before shaping the rails so that the wings will be shaped to the rails, but I didn't waste too much of the scrap divinycell, making it just tall enough to cover the foiled deck.

[surfdad]

The H45 conforms to the rails like a wet noodle. Simple tape will hold it in place while the epoxy cures. I use a fast room temperature epoxy for the "glue"

What the tail and the wing material looks like in the last picture.

[surfdad]

Before and after pictures. I use a jigsaw to cut the outline on the wings and block sand them to flow from the main part of the rails. When those are shaped and smoothed out I start shaping the entire rail. The wings are not blended to match the curvature/shape of the rails.

[surfdad]

The deck and rails are shaped and ready for the attachment of the deck skin. That completes the foiling of the deck and shaping of the rails.

[surfdad]

A short discussion on Zylon and also a note about the hype spewed by some of the board manufacturers. I swiped these bar charts from Soeller composites:

[surfdad]

Those charts are relative, that is to say that if you could get a sheet of steel .004" thick, a single layer of Zylon in epoxy would be 16 times stronger and 4 times stiffer. Of course you can imagine how soft and week a sheet of steel .004" thick would be. Don't be mislead by the claims some board manufactures make with their Carbon board boards being stronger than steel - EVERYTHING is.

If you look at the chart you'll see two different Carbon Fiber materials. The AS4 is what is used in commercial applications, like boards.

Zylon is stiffer and stronger than commercial grade carbon, plus it comes in a 4oz weight that is about 1/2 the price of carbon of the similar weight.

[surfdad]

Attaching the top skin starts with marking the outline on the Corecell skin material. Again I cut that with a pair of shears.

[surfdad]

As noted earlier, Zylon is tough to cut and doesn't sand at ALL, so I attempt to cut the sandwich layer of the Zylon such that it won't exceed the top sheet of corecell.

[surfdad]

I roughly fit the skin and zylon to see if I need to trim some more from the Zylon. Once I'm satisfied that I have it trimmed neatly, I wet it out using the same method decscribed for the bottom skin and tape the top skin down for ease in handling while I bag it.

[surfdad]

I want to add about 3/8" more nose flip in the last 6 or so inches of the board. I do that by shimming the nose on the outside of the bag. This concept of shims allows me to affect just about any aspect of the bottom shape - nose and tail rockers, concaves - anything that I want to change.

[surfdad]

Out of the bag with teh skin attached. The rails need to have the excess skin removed and blended.

[surfdad]

Back to it.

I am going to bag the top lamination of Zylon. Zylon is very stiff and won't lap without being bagged.

I place - I think they are called darts - in the fabric to avoid bunching when the material laps the rails. I also bag the deck first because in want the bottom 100% perfect, so the bottom lamination will consolidate over the lap on the bottom.

[surfdad]

I have two peel plys. The lighter green on the left is a perforated peel ply, but it doesn't stretch too much, the darker green is actually a bagging film Stretchlon 800. I poke a few holes in it to make it a perforated peel ply.

[surfdad]

I don't trim the Stretchlon at this stage, I just cut it wide enough to cover the lap. When applying a peel ply over a wet fabric, it tends to stick and pulling it up, often lifts the wetted fabric. So I don't trim the peel ply until it's ON the wetted fabric so that I don't have to be super accurate laying it on the wetted fabric.

[surfdad]

I wet the fabric out on a wet out table using 4 oz of resin, which is the weight of the faric so that I get a 1:1 ratio. The Zylon on the shaped blank.

[surfdad]

The Stretchlon 800 stretches 800%, I use it to avoid bridging on the rails and compound curves. I pull it tight, which consolidates the fabric very well and then tape it down - ALOT

Lots of blue tape and then a picture of a rail under the stretchlon - the fabric pulled tight.

[surfdad]

I wrap the board in a mattress pillow top foam so that when I am pulling the air out of the bag, it distributes that vacuum evenly - as the vacuum gets stronger the foam compresses.

Foam on the board and slide the mess in the bag. Once the vacuum is pulled I wrap it in an electric blanket to keep the eposy at or about room temperature for curing.

[surfdad]

Out of the bag this morning, you can see there is no bridging or wrinkles in the lamination. Pictures of the deck, right rail and left rail at the trailing edge of the wing.

[surfdad]

A quick discussion on the supplies used in vacuum bagging. The peel ply demonstrated above is is used on the surface of a wet laminate, typically, to impart a surface roughness for subsequent lamination or a smooth finish if it is the final layer of lamination. In most instances vacuum bagging is perfomed in a mold or tool. The surface of the part that is pressed aganist the mold surface is normally glossy. As such, the peel ply would be on the inside of a part not the exterior as I have used here.

Another thing that peel ply does is separate off the cured laminate. Most peel plys are treated with a release agent or are made of a material that nothing sticks to like polyethelene and the "peel" off of the finished part.

The parformations in a peel ply will allow excess resin to be squeezed out during the consolidation process, eliminating excess resin.

I have bagged the external lamination here because the Zylon is too stiff to lap the rails by hand - it would just straighten back out before the resin could cure. So in this instance, bagging an external lamination makes sense. However, most often it does. The drawbacks of an external lamination are that it is very time consuming taking several hours longer than a hand lamination. It consumes a great deal more supplies and lastly tends to produce a dry and spotty laminate. Sometimes intended, bagging the external laminate often times results in print through - the sections of tape that I placed over the wet laminate are imprinted in the final lamination, you can clearly see the outline of where the tape was place. I'll remove that with a quick hit of the sanding block, but it wouldn't be necessary with a hand lamination. However, this CAN be used to advangate if the intent was to impart grooves or something.

[surfdad]

Flip and repeat.

[surfdad]

Out of the bag and now I have to remove all the tape - pile of tape to the right in the picture.

[surfdad]

A few posts ago I talked about insuring that the weight of the resin and fabric was equal. The reason for this is that resin by itself isn't stiff or strong and fabric by itself isn't stiff or strong either, but together the resultant matrix can be both stiff and strong, depending upon the ratio of resin and fabric and the choice of resin and fabric.

If the ratio of resin to fabric is high - say twice as much resin, by weight, to fabric the matrix will tend to take on more of the characteristics of the resin and it will be brittle. Vice versa if there is too much fabric by weight, the resultant matrix will be weak and floppy - taking on more of the characteristics of the fabric.

Pre-preg carbon fiber is used in aerospace applications. The dry fabric is impregnated with the resin by passing it through a roller system with the resin being spueezed in the fabric. Then it's frozen to prevent the resin from curing. That roller system can get resin to fabric ratios close to 40:60 by weight. I could never achieve that accuracy by hand, and so I strive for a 50:50 or 1:1 ratio by weight...which gives me a good balance of the resin and fabric characteristics.

[surfdad]

Surfboards typically have 3 layers of resin. The first I've done above, it's the lamination coat. Expert laminators can lay down a layer of fiberglass by hand that achieves the 50:50 / 1:1 resin and fabric matrix.

After the lamination is cured, the next layer of resin contains no fabric and is typically called a hot coat, filler coat or sanding coat. This a very thin coat of resin that fills in any exposed weave of the lamination it also gives a layer of resin that can be sanded to smootrh out any imperfections in the lamination.

Two layers of resin tend to be more durable and stronger than a single thick layer also.

In surfboard construction there are principally only two resins used, the old school Polyester and new'ish school Epoxy. Polyester is much easier to work with than Epoxy, but isn't as strong. Polyester has toxic fumes (VOC's) that require a respirator to when working with it, most Epoxies have very low VOC's. Polyester also tends to be cheaper and cures much quicker.

Epoxy requires an absolutely clean surface and can't have debris in the epoxy itself. Any dust, even a finger print will cause separations on the surface and any debris such as dust will cause "zits" in the epoxy. It's really just miserable stuff to work with when trying to get a smooth glossy finish.

As noted earlier, Zylon breaks down in UV, so I will paint the exterior to prevent any UV intrusion down to the Zylon. I am doing a fill coat on the bottom tonight and that will be the end of the resin application for the bottom.

One last thing about Epoxy, it is an exothermic reaction meaning that it gives off heat as it cures - in fact just for giggles, if you mix up 4 or so ounces of epoxy and leave it in the mixing container it will smoke, it gets so hot. One of the issues with this exothermic reaction is that it causes bubbles in the resin any air trapped in the resin expands creating a hideous surface.

Typically gloss coats of epoxy are laid down on falling temperatures to minimize the bubble formation. That is why I laid down my hot coat towards early evening.

[Nooga678]

So no gloss coat for the bottom?

Do you hot coat with a brush?

[surfdad]

I hotcoat polyester with a brush, but epoxy tends to froth if worked too much - brushing epoxy creates that frothing. I used a fairly slow cure epoxy on this hotcoat so that it would level and still cure in the fairly cool temps I have to work with here. I mix up the desired amount, pour it directly on the board and then spread it slowly with a squeegee. Once width-wise and once length-wise and then I leave it. I check on it every so often to knock down any drips on the rails, but mostly with epoxy, I've found don't mess with it after it's laid down.

As far as a gloss, no, I actually leave a textured surface. A "speed finish" is sanded typically in one direction (not circular) running in the direction travel of the board. What I've found is that the textured surface doesn't appreciably enhance speed - I'm sure there are folks that can feel a speed increase but I couldn't, however, the effect on "release" was noticable. There is an experiement that "I think" demonstrates this. If you take two pieces of plate glass and wet the surface of one and then lay the other on the first one, it's super hard to separate them. However, if you score the surface of the piece on top, they separate with relative ease.

I've heard all sorts of discussions on WHY that is and I don't understand the physics behind it enough to reiterate them, but I know that I can feel the difference.

That said, the bottom will be textured and painted.

[lakewakes]

Bice job SD