Firewire knockoff - compsand build.
 

I want to earn some WW points, so a build thread is in order! :)

Want a stiffer board? Add a stringer - wholesale cost of 1/16" basswood is like $0.60. This build is my interpretation of the corecell skinned, balsa railed Firewire's. Only I am swapping basswood for the balsa, the basswood is slightly stiffer than balsa without much increase in weight, maybe an extra 3 oz for the six layers i'm building up.

I swiped this from the Firewire site.

I like to start with the rocker hotwired in as it's easier to use my rocker bed as a saddle as I assemble the bits an pieces. Pictures of the rocker and outline.

I've previously cut the rail material using my rocker template. I'm going to glue up 3 pieces of the basswood on eash side and build up any additional width I need with balsa. Just to be safe, I always mark the inside of each piece with R or L so that I quickly identify which side of the wood needs a coat of epoxy. If I don't I swear I wind up with an extra R side coated and then a huge mess as I try and wrestle it into place.

I mixed up 4 oz of epoxy and as can be seen in the previous photo, I just paint the epoxy on using a cheap bristle brush. I reserve about 1 oz of the resin to paint on to the EPS core, which is 1 pound density. I paint everything very lightly, it's more than enough to keep things together.

I didn't get any pictures of it, but I lay up each rail individually, but all three pieces at once. I tape the basswood to the core, in the middle and then work my way from the center to the nose, and then from the center to the tail - very similar to lapping a rail with the external lamination.

Once everything is in place I slide the mess into the bag to hold it tight while the epoxy cures, which is where it is now.

Oh! Always be sure to have a trusty shop dog to stand guard over any loose EPS pellets.

Very Nice, I just noticed that Wakeworld has the points system going! How does this work? I can't seem to find the information on it! Glad to be back on Wakeworld though!! The ice has finially melted here in MI! Should be on the water soon! Love that Woofy likes the pelets so much!! hahahahahah

Hey Jon,

Thanks for following along. Isn't woofy a kick? He's always out in the shop with me and typically I'll find him in the eps! :)

I don't really know how the points work, I just know that when you hit 200 you can score stuff in the store:

http://www.wakeworld.com/forum/showthread.php?t=776982

I was hoping that posting a build thread would give me a ton, but it seems only 2 points :)

I'm not sure what I did to this new camera but it has a sepia tint to it. I should NOT be allowed to touch a camera! :)

Out of the bag this morning, rails/stringers glued up.

Mowing foam - not quite finished with the concave, still needs a few touches, but this is the general concept.

That looks like a single concave. Are you going to go with that all the way to the tail of the board? It also looks like it is a deep concave, are all of your boards like that?

Hey Jon, good eye - it's a single, I normally fade to flat or a V out the tail. I think the picture distorts the concave a little, it's just a hair over 1/4" deep.

It's hard to tell, but the bottom shape is done.

I was reading some propoganda about the materials creating stiffness and I was reminded of an article that talked about the difference between strength and stiffness. Strength is typically an attribute of material - steel is stronger than aluminum (all things being the same), but that stiffness is an attribute of the structure. Triangles are stiffer than a rectangle because to deform the triangle you have to bend one of the sides and the corners, whereas a rectangle just needs the corners to bend or deform.

The standard example is a magazine. Standing on end and flat, it's not very stiff, it won't support anything as it tends to bend under it's own weight.

The can of hardener has about 10 oz total weight - the magazine folds under the weight.

But roll it into a tube and it easily handles the weight. A cylinder offers a very stiff structure.

Same material, but the structure is different and becomes stiffer, at least in the one plane.

I swiped a section relating to structure of sandwich construction from boatdesign.net:

http://boatdesign.net/articles/foam-core/

The vast majority of wakesurf boards are built as a single skin laminate, which is where the relevance comes into play.


Sandwich Principle

The sandwich concept is based on two main ideas: increasing the stiffness in bending of a beam or panel and doing so without adding excessive weight. The general term for bending stiffness is flexural rigidity (D), which is the product of the material(s) elastic modulus, and the cross section moment of inertia (I). For a symmetric sandwich beam (both skins have the same thickness and material properties), the formula for flexural rigidity is:

With:
Ef = Elastic Modulus of the Facings (Skins)
Ec = Elastic Modulus of the Core
b = Width of the Beam
d = Distance Between Facing Centroids
t = Thickness of a Facing
c = Core Thickness

If the skins are relatively thin compared to the core (d/t > 6) and the core material is considerably weaker than the skins (Ef/Ec . td2/c3 > 17), the equation can be reduced to:

From this equation, it is apparent that the core material does not directly contribute to the stiffness of the panel or beam, (at least in lower density cores) but it's the distance between the skins that is the overwhelming factor. Increasing the "d" variable will have a much greater effect on the flexural rigidity than any other component in the equation, since every other variable has a linear contribution. (I added the emphasis - thicker is stiffer is the readers digest version :) ) When dealing with higher density cores (usually > 5 lb/ft 3 ) and thicker skin laminates, the full equation must be used in order to properly predict the stiffness properties. This is due to the high-density core contributing stiffness in the first case, and the thick skins absorbing more shear stress.

While the core keeps the skins an equal distance apart from each other thereby increasing the stiffness, it also bears most of the shear loading. In bending, the lower skin is in tension, while the upper (or inner) skin is in compression thereby putting the core in shear (See Figure 1). In order for the sandwich to function correctly the adhesive layers between the skins and the core must be able to transfer the loads, and thereby be as least as strong as the core material. Without a proper bond, the three entities work as separate beams/plates and the stiffness is lost. This is why proper core/skin bonding is so critical.

Sandwich vs. Single Skin Fiberglass

Exactly how much stiffer is a sandwich structure versus a single skin laminate, and what are the weight savings? As noted above, the flexural rigidity of a structure is dependent on two factors: the material(s) stiffness or modulus, and the cross sectional geometry or moment of inertia. The material properties are often difficult to change (and sometimes expensive), so a change in the geometry can be done to increase stiffness while not compromising on strength or other properties of a single skin laminate. Figure 2 shows.the difference in stiffness, strength, and weight when a core material is placed between the plies of a single skin laminate (all attributes are approximately normalized).

From just increasing the cross sectional geometry, the stiffness increased 48 times, while the flexural strength increased 6 times, and all with a marginal increase in weight. The increase in strength and stiffness allows builders to use less skin materials, resulting in considerably lower weight structures.

The Sunova's have a few different skin options - balsa and corecell. I'm using the corecell skin for this build. Corecell comes in sheets 8' x 4', so I have the retailer cut the sheet down to 5' x 4' which is what's in this picture - it will net me 2 pieces and the remaining 3' x 4' sheet can net one skin.

Using the core and rail as a pattern, I trace the outline of the corecell sheet and cut it with a pair of scissors. This corecell is A500 Plain, which is a 5 pound foam.

I'm using 2 oz eglass as the sandwich layer. It comes in a 50" x 3 yard size. I trim it slightly large, so that I don't have to struggle when laying it up. The eglass trims/sands easily so it's not an issue to clean it up.

I'm all organized and ready to bag tomorrow night.

Jeff, thank you for taking me back to College in my engineering days.. WOW,, Equations and everything, but I do have to say that you explained it better than my professors did. Either that or I just understand now, because it is on something that I enjoy!! With that said, are you going to increase the cross section of your boards?? Even by .5 of an inch could make a difference it seams. Also where do you want the most stiffness out of the board? Seeing that most surfboards have less material at the nose it must not matter as much in that area, but between your feet, would you want to increase the cross section in this area? would that help make the over all board feel more stiff? Thank you for your teachings, keep it up,,!! I hope I understood this correctly also!!

PS, all of the blanks I have already hotwired might be hosed... I might have to get some skins to add to my blanks so I can bulk up the cross section.

Dr. Walker presents 500 ways to build a surfboard.

You already knew the formula, there's nothing I did that made it clearer! :) Your understanding is excellent, the further the distance between the center of the skins, the stiffer that area will be compared to a thinner section. It does get you rethinking where to place the foam, doesn't it? Surfboards in the ocean, which we've modeled after, have foam under the chest for paddling/flotation and we don't really have that issue. James has snapped a few (lots :) ) of boards and they almost always break just ahead of the fin boxes...that is mostly associated with a lack of flex directly behind the break.

I snuck a peek at the new Elevation from SS - Chase's signature board and the tail thickness is enormous, but there is a lot going on there also - channel and the board I saw had like a stop behind the tail pad shaped into the foam and glassed over. Picture of the tail, I'm not sure if that is a production model or not, I swiped it from some site. :)

If you look at the tail, the channel stiffens that area up - like the creases on the sheet metal of car doors, plus that board has a center stringer and with the extra thickness all combine to have the effect of stiffening the tail up.

Building to take advantage of the principle would seem to indicate that is the path you should take if you want a stiffer tail. Our little wakes don't really have much power behind them, and we don't really "flex" boards to fit into those tiny pockets.

I need to think more about how to engineer the board to take advantage of the structure and also what is most useful for our wakes, I've actually been thinning some boards down - but placing the foam under the feet.

@ Show - I need to go back to college and do a dissertation on determining the finite number of different board construction methodologies. Dr. Walker - YES! :) Phd in wakesurfconstructionology. :)

'Glass wetted out and spread out on the core.

Corecell skin with a sludge applied to fill the pockets.

I flip the skin on to the core with the 'glass and the tape it in place so that I can pick it up and slide it into the bag.

...and in the bag with the vacuum pulled.

Out of the bag this morning all glued up.

The 2 oz eglass is easy to cut even after the epoxy has gelled.

Super crappy picture, but what I was attempting to show is the corecell on the bottom has been trimmed flush with the basswood rails.

I've trimmed the deck down to my desired foil using the planer.

I only accomplished one side, I glue up some balsa to shape the wings into.

First wing rough cut, ready for final shaping and the material glued up on the opposite side.

And the other side rough cut.

Jeff, I know you have probably answered this before, but what advantage does the wing give to the board? I know you have this detail on almost every board you make.

Hey Jon, more than anything all of the boards I've built are just different materials or bottom contours on the same shape/outline. The concept is to compare all the materials to see what gave the best performance and durability.

The concept behind the wing tough, is that it steps down the width of the board at the tail, quickly. If you look at the picture with the wing on the right side of the board you can see that the wing straightens out the outline around the fins. That parallel part of the outline helps with drive and also release.

The abrupt change also seems to assist with release when the board goes vertical. I don't seem much support of that, but I have witnessed it. I think a severe hip does the same thing.

In a general sense, they also give a pivot point, an definitive area where the board can turn.

The wings and rails attached and shaped, rail bands shaped in and the core is now ready for the deck skin.

Thanks for the explination!! That makes sense. As always it is great to watch your builds. Do you have a top two or three builds that have given you the most durability and performance that you like? What is your best combination so far? Also how did your hollow carbon board turn out. I must have missed that thread.

We rode the Hollow Carbon this past Sunday and in a word: "sucked" is probably most accurate. :) The design specifically allowed the bottom to morph, creating concaves - or maybe it's best to say - the concaves change to adhere to the shape of the wake. Our wakes are so small and powerless that the "morph"ing either didn't happen or happened so late that it wasn't effective. I can see in an overhead wave in the ocean, how doing a massive bottom turn would shape the bottom to give the board some speed out of the turn. For my purposes, I used 6 oz Carbon because it's the cheapest. A 2 oz cloth might have perfoormed better, but I'm not going to invest $100 a yard for the stuff. :)

Also, in order to build up the stiffness the boards weight was not light. It was heavy like an 8 pound board, but it wasn't light like a 4 pound board. Overall, I can see any advantages to the concept behind the boat. Carbon has a great look, but being black it would absorb heat like crazy which would mean venting a ton out on the boat. It's stupid expensive. You can't see through it, so it makes working with it a pain. Not much to recommend pursuing that construction.

Of all the stuff we've built, the balsa wood has the POTENTIAL to be amazing (don't tell Ed or Petr they'll give me grief for years! :) ), but it's so inconsistent piece to piece, that it's hard to get the right balanced combination - I'd build one where the left rail was amazingly lively and the right one dead. :) Was great turning left! :)

Really love the perimeter stringers, but on a foam board, the deck glass tends to rip at the stringer under the heel at the tail and then the board is done. That happened to James the weekend before the World's in '08. The fix just didn't work. So that construction tends to have a life span of a few months. Then again wood...the inconsistency in the stringers would make one board magic and an identical one average - the only thing we could attribute it too was the stringer wood.

We've had the best luck with the high density foam compsand with carbon wrapped rails and high density foam frame. They come out very light, like a 4/4 x 4 epoxy board, but they don't get heel dents. The carbon on the rails gives that liveliness of the perimeter stringered boards, without the headache of tearing the glass under the heel at the tail. The high density foamrails and extra carbon out there at the rails give the board some perimeter weighting, which helps with rail set. That's been the best in terms of both performance and longevity...the drawback being it's a major PITA to build. It requires 5 trips into the vacuum bag and the board is almost shaped twice, once for the core and then once again, lightly, when the skins are attached.

I say PITA - I love to build, so it's fun for me, but it's exceptionally labor intensive.

Carbon Build Thread is here. Me riding it! :)

Jon, I'm sorry to be so rude, thanks for the props and for following along.

The deck has two layers of 2 oz under the deck. I cut two pices of fabric and then fold them to get ready for wetting out.

I use the remainder of the sheet of corecell for the deck - simply tracing the outline and cutting with a pair of scissors.

I mix up two batches of resin, rather than 1 large one so that I have more time to work. The second batch I don't mix until I'm ready to use it.

I use about 2-3 oz to wet out each piece of eglass. I reserve the rest to mix up the slop to seal the underside of the deck skin.

I lay the deck skin on the core with the two layers of wetted out eglass and then tape it down just enough to keep it in place while I slide it into the bag.

Out of the bag this morning and ready for trimming the deck skin.

Thanks for the reply on the boards, and sorry the carbon did not turn out, but at least you know now. hahah Good test to never do again! Also did you end up adding thickness to this board compared to your other boards?? I like the look of the rails!

No...no thickness added here, the rails are made of the same material that a center stringered board uses - the basswood. It's like having a total of a 1" thick stringer! :) I have a feeling this board will wind up too stiff - which, IMO, makes a board feel dead. Just the right amount of flex gives the board a significant amount of "pop" and liveliness.

Back to it after Good Friday. I leave the skin wide, so that I don't have to wrestle with it when I am attaching the deck skin. I bring the Corecell over the rails close using a single edge razor. The razor also makes quick work of any errant fiberglass.

I block sand to blend the deck skin with the rails using 50 grit.

I still have some more work to do on the rails, but they are mostly shaped and the deck skin is blended. I tried to be careful and blend the deck even with the first layer of the basswood.

The rail and deck skin blend.

surfdad, that board is looking beautiful. i cant wait to see the finished deck

Looks nice SD. Seems like you're always working with wood:)

Thanks guys.

@ Show, I'm sure that you're mistaken about the frequency of my use of wood, SELDOM is a more accurate description. :)

The tail block is next. I had intentionally left the tail long, and I trim it and square it up, shortening it enough to add the tail block to get to my proper length.

I built up the tail block using 5 layers of 1/8" balsa strips. I picked the end piece for the character of the grain. The balsa shapes easily, so I just cut it relatively close and then glue it all up with 5 minute epoxy.

A few passes with the hand plane brings it down close and then the sanding block to match the rails, deck and bottom shape.

Most high density foams have a surface that is filled with craters. The foam is closed cell, so the craters don't go through the foam, but this surface poses a few problems. The first is that craters will trap air under the external lamination - when that air heats up like we'd have out on the boat, a delamination is almost assured. Another is that if the craters aren't filled, the external lamination will only be attached to the high spots between all the craters - substantially weaker than if the entire surface was uniform.

To address this most folks fill the craters with bondo or a resin and micro balloon mixture. I opted for the epoxy and microb's mixture. It only took about 2 oz, so not very much. The key is to work it into the craters hard. The Micrb's sand easily after the mixture cures.

I wanted to preserve the wood, so I taped it off and then I didn't have to be overly careful with working the mixture into the craters.

It's really hard to see, but I've spread the resin and microb's across the entire surface of the deck.

Flip and repeat. The process is basically the same, the only difference being the taping of the wooden wings.

As before, I'm using an epoxy and MIcroB mixture. The mixture has the look of really think mayonaisse.

I pour about 3 oz on the surface and then squeegee it in which removes about 1 oz.

All squeegeed and I'll leave it to cure.

Crappy picture, this is from the Firewire site. On the board to the left if you look closely, under the FCS fin plugs, you can see dark circles. These are high denisty foam that are set into the low density foam core. The fin boxes are then set into that high density foam.

I cut some scrap H-80 Divinycell about 1/2" wider than the box that I'll sink into the insert. I went with 1/2" wide so that the rear outside would contact the wood rail material to stabilize the material even more.

I measure and mark the location of the inserts - tracing the outline so that I can freehand rout the cutout for the inserts.

As I mentioned, I freehand the hole for the insert, the picture shows a test fit and then in the last picture, I glue the inserts in with 5 min epoxy.

I might freehand my install. Scary stuff on my balsa board.

I've been meaning to ask how your build was coming along. On the foam it was easy - the wood will be tougher. Maybe you can try clamoing a straight edge to do the center deeper cut and then move that for the two long straight sections. Then you'd just have to freehand the curved ends.

This evening, I installed the boxes and got organized for glassing the bottom.

I hit any high spots with the sanding block and it's ready to measure and mark.

I measure and mark the centerline of the boxes and then place one of the boxes upside down flush with a mark I've made for the rear of the box and align with the centerline and then trace the outline of the box onto the foam.

The rear of the rail boxes have the Futures logo on them, the set screw threads are at the front. The base of the fins looks centered lengthwise in the box, bit it is actually offset about 1/16" of an inch forward. I can't see any offset on the round part of the flange, but I always mark the box outline by placing the front forward.

The Futures fin box installation kit. Aluminum guide, round black collar, router and clear plastic alignment tool.

It didn't show up, but the alignment tool has the nose marked.