Wakeboarder Forum Index

 
 FAQFAQ   SearchSearch   MemberlistMemberlist   StatisticsStats   FavoritesFavorites   RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages  Log inLog in 
BlogsBlogs   

Composite sandwich wakesurf build
Goto page 1, 2, 3  Next
 
Post new topic   Reply to topic    Wakeboarder Forum Index -> Wakesurfing and Surfing
View previous topic :: View next topic  
Author Message
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 7:45 am    Post subject: Composite sandwich wakesurf build Reply with quote

I haven't posted a build thread here on Wakeboarder.com, so I got permission from Ed and thought I'd litter this site with the details of a build, too. Smile

The last board I built is a divinycell composite sandwich. It has 1/8" d-cell H-80 skins and 1/2" d-cell rails. The core is 1# EPS foam. The methodology is super light, the board I described above weighed 3.5'ish pounds and 4 pounds 3 oz with fins and traction.

The final product:
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 7:54 am    Post subject: Reply with quote

This thread will detail the steps involved as I undertake the next build. The construction methodology is a sandwich, in that it has two facings or skins and a core that is light weight to allow shear. The physical construction was first used in WWII aircraft, refined in the 70's and 80's in windsurf construction and then popularized in surfboard construction by Randy French of Surftech.

Roughly, it's name (sandwich) comes from the core being sandwiched between several layers. The skins are attached to the low density EPS core with a light weight fabric, typically 2 oz e-glass. Then the skins have a layer of 4 oz s-glass or e-glass. Finally, the Surftech folks use several layers of urethane paint.

Most often thjose boards are molded (commonly referred to as pop-outs). I don't have that capacity in my garage, so I will duplicate the construction using manual techniques.

The very first step in the process is to make the core from 1# eps. EPS melts easily with a hotwire. The normal process for this is to create templates and then run the hotwire along those to cut the shape of the product. I will hot wire the rocker, but jigsaw or plane the rest.

Picture of the core with hotwire templates attached and then the core after hotwiring.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 7:59 am    Post subject: Reply with quote

I had an existing shape that I wanted to duplicate, so I drew a centerline down the hotwired foam, and aligned the existing shape over that CL. Finally tracing the shape on my core. In molding boards, the skin wraps the rails, but that takes a huge investment in the tooling and most likely an oven or autoclave to get the high density divinycell to wrap around the tight radius of the rails. Instead, I will attach a section of 1/2" divinycell and then shape the rails from that high density foam.

The core with the outline and final inset marked up for cutting.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:05 am    Post subject: Reply with quote

The line I've draw inside the outline is just a hair short of 1/2" the thickness of the rail material. Now is a good time to briefly talk about divinycell. There are a number of high density foams on the market that are used in composite construction. Divinycell or d-cell has encellent properties and comes in varous densities and flavors. I am using H-80 plain, which is a 5 pound density foam. D-cell is manufactured from cross-linked PVC. It allows the foam to comform to just about any shape in a cold molded process, but can also be thermo shaped such that the final product retains the shape.

D-cell cuts fairly easily using a razor or saw blade. I use the rocker hotwire templates shown above when I cut the EPS core, as a guide to cute the 1/2" d-cell rail material.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:18 am    Post subject: Reply with quote

I will be using a vacuum bag to attach the rails and skins to the core. The principal behind the vacuum is that all of the air is sucked out of the bag using a pump and the atmosphere outside the bag exerts a uniform and HUGE force down on the contents of the bag. It's used in wood working for attaching laminates and also in RC model airplanes when attaching skins to wings.

In this picture you can see the core, the rail material and also a rocker bed. The rocker bed is the offcut from a core. I have used a higher density foam, in this case 2# EPS and then loosely attached some formica to prevent my resin work from sticking.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:23 am    Post subject: Reply with quote

I my first build, above, I merely epoxied the rail material to the EPS core, but I decided I wanted to stiffen the board up but not rely on the external layers of resin or heavier material to achieve that. I will be using Carbon Fiber between the EPS core and D-cell rails, the sandwich layer will be a 1.7 oz Kevlar rather than 2 oz e-glass. The Kevlar is reportedly 2 to 3 times the stiffness of an equivalent weight e-glass.

I cut the CF to the approximate shape and laid it on a section of polyethelene sheet which acted as my wet out table. I mixed up about 5 oz of epoxy and then saturated the CF.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:26 am    Post subject: Reply with quote

The CF I used is a commercial grade 5.7 oz fabric which has a Young's Modulous of about that of 1/8" basswood. This principally duplicates a perimeter stringer of basswood. In this picture you can see the CF laid up against the EPS core and the d-cell rail material alinged and ready to be attached.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:35 am    Post subject: Reply with quote

I roughly tape the rail material to the core and then that whole mess to the rocker bed before siding it all inside the bag. The bag is clamped on the two ends before the air is sucked from it. This picture shows the tail of the board and the green painters tape I used to keep everything in place as I managed it into the bag. Two different anges for clarity:
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:37 am    Post subject: Reply with quote

Picture of the pump I use to evacuate the bag and then the "blank" under vacuum.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 23, 2008 8:40 am    Post subject: Reply with quote

This morning, out of the bag the rail material and CF laminated to the core. The next significant step will be to shape the bottom concave in preparation for bagging the bottom skin with Kevlar.
Back to top
View user's profile Send private message Send e-mail
oshensurfer
PityDaFool Who Posts This Much
PityDaFool Who Posts This Much


Joined: 14 Aug 2003
Posts: 6325

PostPosted: Dec 23, 2008 10:42 am    Post subject: Reply with quote

surfdad, Awesome. Very different than the old school hand shaping. I've built/shaped surfboards and this is very interesting. Post the rest as it gets finished!
_________________
(insert funny chit here)
Back to top
View user's profile Send private message Blog
Rhawn
Wakeboarder.com Freak
Wakeboarder.com Freak


Joined: 14 Jun 2006
Posts: 3127
City: Richmond, V to the Izzay

PostPosted: Dec 25, 2008 1:04 pm    Post subject: Reply with quote

Awesome!
_________________
WakeSurf and Wakesurfing News
Back to top
View user's profile Send private message Visit poster's website
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 6:10 am    Post subject: Reply with quote

Thanks guys. I'll be working on the project some over this weekend.

oshensurfer, old school polyester over polyurethane (pupe's) is where everyone started! Shape the board on Saturday morning, glass it Saturday afternoon and ride it Sunday! Smile

The build I am documenting is substantially stronger and lighter, but the reality is that the problem with super complicated builds like this, are that the old school PuPe's go really well and are relatively easy to build.

My goal for the weekend is to get the bottom skin attached. This will require that I shape the bottom contour and also insert some high density foam for the fin boxes.

The core material is 1 pound eps, which by design is mostly air. When I sink the fin boxes in that material, it will allow the fin boxes to twist off under sideways pressure, as when pumping.

I will route out the EPS, then fill that cavity with a 4 or 5 pound Polyurethane pour foam. Some folks use the offcuts of D-cell but that takes a very steady hand to route the exact outline and depth. I prefer the pour foam because, it will fill every nook and cranny left by the routing process. Also, it will tend to expand out of the void, so when I shape the bottom contour, I also shape that high density insert.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 8:34 am    Post subject: Reply with quote

As I mentioned earlier, 1 pound EPS is mostly air. It's not a closed cell foam like d-cell nor the polyurethane that oshunsurfer shaped in the past. We need to protect the inner EPS from intrusion by water, otherwise it will suck water like a sponge. The rails are d-cell and that is a closed cell foam, so we are good there. The skins will also be a d-cell, so the vast majority of the board's surface area is protected. The last area that needs attention is the tail. This design has a slight squared off section of the tail, and I merely cut that back to allow adhering a small tail block of d-cell. I've chosen d-cell as the skin, but wood could just as easily be used - balsa, pawolina or the like. Then then tail block could be laminated pieces of different types of wood.

This is what the tail looked like after emerging from the bag - the green is the painters tape I used to hold the rail together as I pulled a vaccum.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 8:38 am    Post subject: Reply with quote

I squared up the tail and cut back into the core so that I can attach my tail block. I measured a small section of d-cell and then glue it up using 5 min epoxy. Epoxy is the adhesive of choice for this construction. While the d-cell can tolerate epoxy, polyester and vinylester, the EPS will melt with exposure to styrenes, which eliminates the polyester and vinylester options.

Ready for gluing:
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 8:40 am    Post subject: Reply with quote

The weather here is a bit cold, so my tail block will need more than the 5 min's the epoxy claims. I'll tape it to hold it in place then come back later to start my high denisty fin block inserts.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 9:49 am    Post subject: Reply with quote

The board I am using as a guide is my son James, TWP. This picture is from the WWSC. The second picture is a close up of the fin box configuration. The ong boxes are standard futures rail boxes. The smaller C-5's are a Rusty design that was incoorporated into the Rusty C-5 Smile. We stole that concept, rearranged the placement a little and eliminated the trailer.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 9:56 am    Post subject: Reply with quote

I don't care about the cosmetics at this point, because all of this will be covered by a layer of Kevlar and d-cell skin. We want to be sure that the integrity of everything is sound, but I don't care about markings.

I lay out a temporary centerline so that I can mock up the fin placements. Next, I mark off 1" around all of the boxes. This will give me a solid foam block to insert my fin boxes. At this stage you have a choice about depth. I want a solid point of attachement between the deck skin, high density foam insert, rails and bottom skin. In that way, all of the power from the surfer's feet will translate directly to the fins. However, as a design element you may wish the deck skin doesn't contact the HD foam, nor the HD foam contact the rails - which would allow more flex in the tail of the board.

I want that hole section ocked up tight, so I routed deep enough to insure contact with the deck skin AND the carbon lining the rail material.

The outline of the cavity:
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 9:58 am    Post subject: Reply with quote

Using a router, I freehanded the cut. Next I cleaned up the rail joint to insure good contact with the carbon.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 10:02 am    Post subject: Reply with quote

I used Foam it's 5 pound pour foam. It's a pretty good quality foam and comes in various densities. Pour foam's denisty, after curing is highly dependent upon expansion and being forced into a small space. I make some disposable covers that I use to hold over the foam as it expands.

The covers, liquid foam in the cavity and the final expanded insert awaiting final curing and bottom shaping.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 11:07 am    Post subject: Reply with quote

I quickly knocked down the high density foam so that I can accurately measure the bottom depth as I shape the single concave.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 11:11 am    Post subject: Reply with quote

I mark the measurements of the concave directly on the foam, for a quick rough out by planer.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 11:14 am    Post subject: Reply with quote

After the quick rought out, the concave starts to take shape. You'll still want to finish shaping, so leave enough material that you won't over-shape the concave. I bring it to tolerance using a sanding black and surform.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 11:15 am    Post subject: Reply with quote

The concave shaped and the blank ready for the inner Kevlar and skin.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 3:44 pm    Post subject: Reply with quote

The skin's will be vacuum bagged on. The bag material is fairly strong, but can be punctured. Tiny pin holes eventually make the bag unusable.

Carbon, once it's been cured in epoxy can create very sharp needle like points. I run the planer over all exposed carbon to help reduce the chance of a puncture.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 3:50 pm    Post subject: Reply with quote

The skin will be 1/8" d-cell. I have it shipped all rolled up to minimize shipping costs, but still get the full 4' x 8' sheet.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 3:59 pm    Post subject: Reply with quote

I am using 1.7 oz Kevlar as the sandwich layer. In the original board, I used 2 oz e-glass. The Kevlar is significantly stiffer than e-glass. It also has proven to be easier to wet out and work with. However, it does have a few drawbacks. One is that it doesn't cut...a special pair of shears are required to cut it and the blades only last for about 8 hours of cutting before requiring sharpening or replacement. Another is that Kevlar doesn't sand. With the e-glass I could be rather casual with the cut. Any excess that was left over would just sand off. I had to carefully trace the outline I wanted, that was 1/4" inside the final outline.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 4:00 pm    Post subject: Reply with quote

Oops I forgot the picture! Smile
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 4:14 pm    Post subject: Reply with quote

Once the material was cut, I lay it on a piece of polyethele sheet. Nothing sticks to PE, so it makes a great wet-out table. This is where this construction methodology shines. In composite construction, like aerospace parts, a resin to fabric ratio of 40:60 is a typical goal. For folks that have built a Polyester surfboard the idea of using less resin weight than fabric weight is probably hard to imagine.

I carefully measure out exactly 2 oz of epoxy, then after mixing I pour it out on the fabric that is on the "wet out table". Once the fabric is wet, I transfer it to the bottom of the core. Smoothing and making sure no threads poke out.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 4:20 pm    Post subject: Reply with quote

I have already cut a rough shape of the bottom out of the d-cell to form the skin. It cuts easily with a pair of scissors, alomst like a thick construction paper. I lay that on top of the wet Kevlar. The epoxy and Kevlar will hold the deck skin to the core.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 4:31 pm    Post subject: Reply with quote

This next shot is a secret. If you've seen skimboards or other vacuum bagged boards, they typically have a flat bottom. Not so much because they perform better, but because it's easier to build. If you notice in this picture the skin and core are in the bag, but not the rocker table/bed. When I pull the vacuum, the skin will be pulled tight to the concave, leaving the skin with the same curvature of the concave we shaped.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 4:36 pm    Post subject: Reply with quote

By pulling the vacuum against the core, there is a chance that the rocker can be changed. To avoid that, I lay the blank and bag combo on top of the rocker bed and then weight it so that the rocker is maintained. I leave the board in the bag until the epoxy cures - several hours with a fast cure epoxy.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 27, 2008 4:39 pm    Post subject: Reply with quote

That's about all for today. Hopefully tomorrow, I will trim and clean up the outline, shape the deck and then bag the top skin on by the end of the day.
_________________
Buy my kid's board! Smile

FlyBoy Wakesurf - the most technically advanced wakesurf boards
Wakesurf
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 28, 2008 7:29 am    Post subject: Reply with quote

Out of the bag this morning and I've trimmed off the excess on the bottom skin, sanded the surface to check for imperfections and to remove any EPS stuck to it. You can also see the bottom concave in the last photo.
Back to top
View user's profile Send private message Send e-mail
surfdad
Soul Rider
Soul Rider


Joined: 21 Oct 2005
Posts: 381
City: Stockton

PostPosted: Dec 28, 2008 7:39 am    Post subject: Reply with quote

Without getting too boring or technical I want to touch briefly on the concept of the sandwich. In this construction there is a low density foam core that is sandwiched between two high density foam skins and attached with resin and in this case Kevlar. Engineers first applied this tech in WWII and they discovered that the stiffness of a panel (the board in this case) is increased exponetionally by the distance between the skins. So, by increasing the thickness of the board, the stiffness increases. Additionally, by placing the high density skins between layers of glass...or more appropriately separating the two layers of fabric that is normally on the top of a board there is also an increase in the stiffness. This stiffness increase allows using lighter weight fabrics and less resin, while still achieving the same stiffness as the old school double 6 oz fabric on the deck.

Lastly, a typical old school PUPE board is a 2 pound polyurethane foam. by using a 5 pound high density foam skin, this board is less prone to heel dents as that sandwich layer is much harder to dent or deform. As you can see in the first few photos, I put my buddy Dennis on the board. Dennis weighs 270'is and the board sans traction and fins weighs about 3.5 pounds. No heel dents or deformation of the board.

Back to the build, today I hope to shape the deck and bag the deck skin.
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    Wakeboarder Forum Index -> Wakesurfing and Surfing All times are GMT - 8 Hours
Goto page 1, 2, 3  Next
Page 1 of 3

Add To Favorites

Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum
             


Copyright 2012 - Wakeboarding - Wakeboarder.com - All Right Reserved
Powered by phpBB © 2001, 2005 phpBB Group