Composite Sandwich construction

so sick.

Thanks Johnny - long time no hear. I see that you made it out to Tulloch, did you nail any of those 3 shuv's? That would be sick trick on a surfstyle board.

Out of the bag this morning and it looks like it's already been polished! When you run your hands across the surface you can feel the slightly raised bumps, so I think I'm just going to sand this with 220 thru 400 and call it a day on the deck.

Very nice. This will be a really dumb question. Where did you put the resin? Did you simply pour it on the cloth and then put everything in the bag?

Thanks Matt,

Not a dumb question - if you've got it, I know others who are following this build have the same question. If you don't mind, I'm going to answer your question and then go into a bit about resin infusion.

I mix up a batch of epoxy, fold the cloth into a nice square, then place the cloth in the bucket and let it soak in. After "mushing" it around I pull the cloth from the bucket, unfold it all wetted out and lay it out on the board. The vacuum won't pull the resin around on the textile with vacuum bagging like this.

After I position it, lay the peel ply, then the breather I slide the whole thing into the bag.

In order to maintain the 1:1 textile/resin ratio, I weigh my textile - in this case the fiberglass. I then want to match that weight with my epoxy mixture. The d-cell really sucks resin, so I only do the resin work on that material when I want it saturated. The skins do most of the work in strength/stiffness. Also, fiberglass is about twice as strong in tension as it is in compression, so I want the deck skin to have about twice as much glass/resin as the bottom.

One of the big drawbacks with this strict vacuum bagging is that the board goes in the bag in an oversaturated state - in the pictures above where you see the resin being pulled thru the peel ply into the breather that is excess resin. I attempted to be as careful as I could in the calculation of the amount of resin needed, but I missed by about 2 oz...which doesn't sound like much, but is almost 5% of the total board weight at that point.

Now resin infusion, which is done with a vacuum, PULLS the resin thru the textile. So you lay all the components into the mold or a bag and there are pickup line(s)/vacuum outlet that draw the vacuum thru spiral wrap and the textile.

Then a resin pickup line/vacuum inlet that is placed into a bucket of mixed epoxy when everything is ready.

This process then pulls the resin from the bucket, through the fiberglass and eventually out into a catch tank before it can reach the pump. When everything is wetted out, you close off the resin pickup line and go to sleep. The result is that resin to textile ratio is better than what you can do with a strict wet layup vac bag system.

Inland surfer uses this methodology on the boards. I don't know how long they've been using Resin Infusion, but I know that I saw it on a sticker on their boards for the first time in '07. From a production standpoint, not only do you get better resin/textile ratios, but there is less waste, less contact with the resin and the arrangement of materials is without the time pressure issue.

Hey Dennis, you're right. Dennis was commenting that the surface looked pebbled or grainy and it isn'•••••••• smooth, except for the little raised dots. The D-cell, underneath has a very porous surface, so I'm sure that is what makes the picture look deceiving. Interestingly, what you can't see is the little raised dots. The resin pulls thru the perforations in the peel ply and cures that way.

How about the lumps and bumps from the edges of the cloth? I taped my board number two off to cut down on the strands of glass and the bubbles and such. I sanded / ground those down last night. Very time consuming.

The edges where the cloth ends isn't bad. I got a little sloppy with the epoxy, but I don't think I'm going to have "much" of an issue with grinding, the pressure is so extreme that the edges look/feel pretty clean.

Awesome again Jeff!

I really wonder how this board will work on water.

But tell me how you do hot coat with Epoxy resin? I have no idea. I know that for polyester resin they mix some wax or styrene in resin and then apply it with brush. But wit epoxy I have no idea. Do you use just similar resin like for glassing or something different?

And what about gloss or matt finish?

(Message edited by hawaj on October 31, 2007)

Thanks Petr, I'm looking forward to a first ride also.

The hotcoat using epoxy is just like using polyester, mix up a batch and paint it on. The folks at Resin Research have a special additive F that is something like 2ml per 1oz of hardener. Typically the ONLY place I have a problem with the hotcoat with epoxy is on the rails. The viscosity of epoxy is such that it just runs off.

So I do the flats normal, flow it on with a brush. The for the rails, what I do is make sure the laps are smooth, even if I have to sand into the cloth. Then I mix up a batch of epoxy and let it sit until it starts to thicken up a bit...just enough to "stick" on the rails. Then I paint it on.

Polyester uses the wax additive for the hot coat. The epoxy doesn't need anything...just a different application method for the rails.

Interesting, now its clear for me.
Thanks a lot Jeff!

nope didnt land any 3 shuvs, but soon enough. i have a different trick that ari recomended i try to get stock that i want to work on first. so in all what does one of these boards weigh when its completed?

Cool...can't wait to see the new bag o' tricks. I can build this as light as 2.5 pounds, but realistically 3 pounds is a good minimum amount. Depending upon the rider, 3 - 4 pounds is the optimum weight. What can be done, is build it out to around 2-3 pounds and then selectively add weight where it's wanted/needed - like along the rails...or whatever.

Out of the bag this morning. It's at 38.something oz. I got a little heavyhanded with the resin on the top 'glass. Hopefully I'll be able to polish that down a little.

All that's left is to do the rails, which I'll most likely do by hand and the finish sanding.

Something that occurred to me after a discussion with Dennis is the concept of the thickness of the sandwich. Anyone that's ridden the likes of a Calibrated, P5, IS 4skim knows that the thickness of the board doesn't have a huge impact on the ability of the board to allow someone to ride it. We don't have the bouyancy/wave catching issues that folks in the ocean do.

Dennis and I were saying that we don't need the thickness in a board, but that isn't entirely true.

Typically, when we want to stiffen up the ride of a board, we add another layer of glass. "Too flexy"? Throw another layer of 6 oz on top. However, there is a weight penalty for that. Maybe as much as another pound.

Another way that the stiffness can be improved - or maybe a better term is to say increased - is by increasing the distance between the surface skins.

What was the corrected calculation that Walove did - 1/8" increase in thickness amounts to a 14% increase in stiffness. I think that a 3/8" increase in thickness amounts to a 44% increase in stiffness.

Using the representative formulas from above:

1 x 24 x .125 x 3.515625 / 2 = 5.273

increase of 1/8":

1 x 24 x .125 x 4 / 2 = 6

increase of 3/8":

1 x 24 x .125 x 5.06 / 2 = 7.59


I'm using some approximations, but I believe that by using 1# foam, increasing the thickness of that by 3/8" over the size of a borad this dimension increases the weight of that "blank" by around 2 oz.

I'm not exactly sure how much glass would have to be added to result in a 44% increase in stiffness, my "gut" tells me that would be another layer of 6 oz glass. So figure, maybe 16 oz between glass and resin. I think that the same stiffness increase can be achieved by increasing the thickness of the foam by around 3/8".

It would be interesting to have some way to compare it.

Anyway...thickness DOES matter.

Just in time for tomorrow. I didn't want to use the front traction I had, so just wax and the kickpad for traction. A set of SB1's and the total weight is 49.9 oz...let's say 50 oz / 3 lbs 2 oz ready to ride.

What did that take 2 weeks? It could really use some art...the Goverment Issue olive drab is starting to grow of me, but a nice red or yellow would be nice, too.

Jeff you should give that thing some special forces name or something. I think it would look really neat in a camo print. What did the overall dimensions end up being? I laminated number 2 last night. Fins on today. Hot coat tomorrow. I'm picking up some foam today.

Special Forces Airborne - Death from Above. You're right a camo paint would have made that look cool. Maybe like you say with an Airborne insignia. I wish that I had even an ounce of artistic ability, if I pick up an airbrush or a paint can the result is just ugly!

Keep us posted on the progress, Matt, looking forward to the final product.

The final dimension came out to be:

loa: 4'6"
width: 20"
thickness: 1 3/4
nose rocker: 3"

The thickness is a little misleading. The deck has a concave, so in the middle it's close to 1" thick. The tail width is 10"


Congrats on the foam acquistion - it's the right thing to do.

Maiden voayage! It floats!!!!

First off, congratulations. It’s great to see a project from start to finish. Your doing a lot of "out of the box" thinking. Your on line posts are pretty inspiring.

However - Is that all, "It Floats"? I mean when I made the 25 pound recycled board that was a serious issue. You’ve made a board from materials that are almost lighter than air, I’m surprised it didn’t blow away.

So that's not a very comprehensive review! How does it perform, do you think your efforts are working in the right direction, or is a significant redesign needed, or worth while?

I've already got #2 in the oven. Bottom skin, contour mat and rails all in one operation. I'm getting better.



AND I have 3 more "blanks" already cut and calling my name: "Jeff, we want to become wakesurfboard cores, tttttttoooooooooooo"

I didn't notice before we went out, but I had ground through the rail laps...so my prized effort was taking on water. I wound up with some under the lower skin. I "think" I can save it, but I'm not sure. I was able to get almost an ounce of water out of it this morning.

The build methodology is cool, certainly opens up a BUNCH of variables...if I had a better handle on some, it wouldn't feel so "out-in-left-field".

One of the things that I did notice was that designs that work in PU with a center stringer don't translate exactly into sandwich construction with perimeter stringers.

The stiffest part of the board was the nose, because the perimeter stringers are so close together. Referring back to the "stiffness" formula, you can make the nose flex more by thining it down, OR by making it wider...anyway...it's a very interesting build and technology.

It's hard to see, but there is a concave in this new board. What I did was create what is referred to as a contour mat. The mat is is aligned on the rocker bed and then the blank to be cooked is placed on top of it, or on the rocker bed as normal.

Then when the vacuum is pulled, the contuor mat is pressed INTO the blank. In this instance I wanted a single concave and you can barely see it in the picture:

What is interesting from a shaping standpoint, is that I have YET to use a single shaping tool on this board. I cut the rocker and outline with a hotwire, and the concave was pressd in with the vacuum. Things like grab rails can be pressed into the deck using rope, or a half round wood trim, again without using a tool.

Pretty interesting when you start looking at using the vacuum to replace certain tools.

How about shaping and blending the rails?

The d-cell takes a pretty strong pull to shape. If we did just the 1# foam, you could pull it in into a mold of some kind - then do just like surftech and wrap the entire board with a d-cell skin, soak it in epoxy to stiffen it up.

I would think the way I have it done, with the d-cell rails, that the pressure it would take to vacuum form the d-cell would crush the 1# core.

Hey Matt,

Thermoforming! Check this technical memo:

http://www.fiberglasssupply.com/pdf/core/ThermoformDiab.pdf

I'm not sure how I would heat the d-cell up to 212 degrees F - anyway...that would be one way to achieve what you were talking about.

I would guess that these folks have some form of an autoclave. I tossed an e-blanket over my project, but the max temp I could get was around 72 degrees. I don't know the exact temperature that EPS melts, but I think it is somewhere around 300 degrees F. I wonder if the D-cell would soften up at a lower temperature than the EPS core, such that you could form the d-cell skin, but not distort the core?

mmm baking surfboards - Jeff's Surf Bakery

I know...Petr, you have to see my "frankenoven" for this If I build it, which no doubt I will because it's sick and twisted, I'll post pictures.

sounds like some scary surf helloween

LOL - it does, doesn't it Petr.

Matt, I had to see if the D-cell would thermo form. It does. I tried a heat gun...I think some people call it a hair dryer - I'm unfamiliar with that term...nonetheless, it didn't do anything.

SSOOOOOOOO...I broke out a butane torch and viola! It shapes pretty easily. Now, d-cell is highly toxic when it burns, so I wouldn't recommend what I just tried.

This is the bend after heat:




This is a before and after without heat. The 1/2 h80 d-cell just returns back to it's original shape.

So...if this thicker piece of d-cell can be thermoformed, I'm sure that the 1/8" skin can be also...there are films available for vac bagging that can go up to crazy high temps. I was reviewing the airtech catalog and saw a film that could withstand 480 degrees F...so I'm sure that it's possible to heat the skin somehow and then pull a vac to bend 'em.

My first foray into thermoforming

Hairdryer? What is this "hairdryer" you refer to?

The next compsand will have balsa rails rather than the d-cell rails. The second compsand, pictured above has a round tail with a piece of 1/2" d-cell an inch tall bent around the EPS. The radius is about 11 inches. I single piece of 1/2 thick balsa won't make that curve, so it has to be built up.

In this picture I am using 1/16" balsa strips CA glued together to form a 1/2" thick band. I've made the radius a little tighter than the 11" as when I remove the band it relaxes just a bit.

My fingers are coated with CA glue!

Excellent, I bet this is more lively than the d-cell.

The reflex is certainly quicker than d-cell. I also have two other foams that I'm going to skin with, while keeping the balsa rails.

One is core-cell A500, it's a little "snappier" than d-cell. The other is Rohacell IG 71, it's the skin material that Surftech is using in their new TL2 construction, I do believe. Bright white and fairly rigid/snappy so less external resin is needed.

The funny thing is that it will be 6 weeks before it will arrive as it's coming from Germany!!!!! Sheesh.

Airex doesn't come thin enough for what I want to do.

I love the reflex properties of Balsa, but the variations from one piece to another make construction difficult. To achieve a balanced board, you truly have to weigh each piece and match it left and right.

I did a bit of work with carbon on the second compsand...quite stiff after lamination. Lots of different materials with different properties.

Test fitting the tail band. The rails will have the same thickness and height. The tail band is 8 layers of 1/16" balsa. I was thinking that alternating with a darker wood, would look sweet.

The bottom skin is attached. I really like the look of this so far.

Hmmmm, I have some constructive criticism or a suggestion. I think I would have made each end of the balsa ring a slot or tab. If it were say a tab you could join the rest of the stringer with a slot and use a dowel to secure the joint.

so jeff i figured out how fire wire does their boards to some extent if this helps with the construction.

first they cut the rocker into a giant slap of eps, then they cnc out the outline, and lay the balsa wood on the rails with the rocker the same as the blank. this way there is no spring back from the flat blank being bent into shape. then the rest of the process is basicaly the same as you do but they paint the skin white, and do a hand lamination with no bagging for the final glass.

Ed, you are a master woodworker. I can shape anything into foam, but I can barely even spell wood, yet alone cut slots!

How would I do what you are saying? Cut all the piceces to the same length - but somehow allow for the increase in radius as it gets further out, OR size each peice and cut before gluing it? Sheesh - I have to tell you the wood is GORGEOUS and the reflex properties and weight are perfect - but what an incredible PITA to work with!

Johnny thanks bro. This blank is hotwired with the rocker and the outline. So I am "there" with that part of the process too. Are they gluing the rails up before the skin?

I want to try something different with this board, which I thought necessitated doing the skin first, but maybe not.

The FW's have the bottom skin free-floating, but I only want the front half free-floating. I'm going to try attaching the skin over the rails from the front foot back.

I figured they were doing the exterior lamination by hand - I did that with my last compsand - if the deck and bottom are sealed, it comes out about the same as a bagged lamination.

Ed, I almost forgot! Can you suggest a dark wood that comes in a 1/16th thickness? I'd love to have the tail cap alternate colors.

You could make the slot or tab in the ring by cutting the individual strips before gluing. Start by form the ring and holding in place with pegs or clamps. Then mark a line across the ring. Measure from that line back an inch or so and draw another line. Repeat on the other end. Now each strip has two lines. Number the strips as you remove them. Cut the strips that are part of the outside at the first mark. Cut the remaining strips that are on the inside at the second mark. When setting up for gluing use the second mark on the outside strips to align the inside strips.



Balsa is pretty soft. You should be able to saw a grove. What I do on something like that is I make cut multiple closely spaced cuts in one direction. The cuts leave a bunch of Halloween pumpkin teeth. Then I take a chisel and hammer the “teeth” out. You’ll probably need to follow up with a file to clean up rough spots. Seems like a router would work well too.



The easiest way to add color is with stain, at least that’s what I would do first. Whatever you do don’t by African ebony, that stuff is heavy like a rock. There is a specialty wood store in Columbus. I’ve only been there once. They have all sorts of really interesting wood. I’m sure there are similar stores out west. I remember seeing Purple Heat wood, that’s really cool looking. http://curiouswoods.com/wood--Purple-Heart--PH It could be really cool to use an exotic wood on the outer strip of the ring, http://www.curiouswoods.com/cat--Exotic-Woods--Exotic.html

I suspect these woods are going to be pretty pricy. Most furniture is stained, that’s much cheaper. If you want to go that rout then look for specialty hard ward stores in the yellow pages or specialty lumber. If you call one and they don’t cater to your needs they’ll probably know who does.

Dowels? Chisels, hammers and files? I can't do it with a surform? and/or a sanding block?

The cut and glue would work for me on the next one. Also, thanks for the link on the wood and insight on staining it.

I'm curious as to what the tongue and groove with the dowel gives me in the end? The tail block doesn't really have a function other than ding resistance and the rails will be glue to each other and the underlying foam, plus the top skin will overlap and be epoxied with a slight amount of 2 oz glass. The the whole mess will be covered with some 4oz glass. I want some movement of the rails. Not alot, but some and I want them to act in concert with the width of the rail.

So...what would this procedure provide for me?

It would extend the stringer to the end and it would make the end and stringer one unit. I don't think you want the stringer to float but you do want it to behave like a spring. I think it might be helpful if the ends of the spring were terminated. Otherwise you might develop fractures in the skin from independent movement of the two, really three parts.

I HATE wood!!!!

5/16" of rail attached on one side. Blue Painters tape to hold it, saran wrap to pull it tight - Tomorrow, hopefully, it comes off nice and clean.

PLUS I still have another 1/4" of plank to attach on this side and the ENTIRE other rail!

}}

The second compsand. Just needs the bottom glass to cure and it'll be ready to ride. I set out to make this one as TOUGH and as STIFF as I could. So it has 5 layers of 4 oz e-glass, a 1/4" x 4" horizontal "springer" located on the neutral axis and a section of 5.7 oz carbon tape running lengthwise down the middle.

It weighs in at 78 oz with this bottom layer still wet. It's under 5 pounds and that is in line with any performance production board.

The one thing this board has that a typical performance board doesn't, though, is that the entire epidermous is 5 pound density foam, as oppossed to 2 pound density foam AND 5 layers of 4 oz glass.

We'll see how it rides, hopefully next weekend.

I've been looking for alternatives to gluing up the balsa rails and ran across this site - check the gorgeous nose and tail blocks with the intricate inlays - the fin blanks are just as goregous.

http://www.the-fin-guy.com/Block.html

Have you ever seen how they make the rosettes, decorations, around guitar sound holes. They stain long 1/16 by 1/16 square wood strips. Then they arrange them in a pattern and glue. Once glued the assembly is a long tube. Then they slice the tube just like you slice deli meat, - thin strips. Each thin strip bears the intricate pattern.

http://www.sempleguitars.com/index.php?seiten_nr=187

Don't you just love wood!

No, I HATE wood! But I do love the way it looks.

Speaking of looks...the artwork on the top is done Walmart Red, Ace Hardware Brillant Yellow, Krylon Rose and CHROME! Do THAT in wood!

I just have a love of the industrial look of the d-celll, so I am going to leave the rails naked and probably a panel on the top and bottom - proud of the heritage!

My third skin material arrived today (the first was d-cell a cross-linked PVC foam, the second and most nightmarish - [evil] balsa, the third which I am discussing here is core-cell a SAN foam, the fourth - should it ever arrive, it has a 4 to 6 week lead time and I had to sign a consent and waiver to allow it to ship!!!!!! is Rohacell a PMI foam).

The core-cell I ordered was A500 pl - which I thought was a pale blue, the stuff I received today is yellowish, which I thought was the higher density A550...anyway, I received the yellowish stuff.

I intend 3 builds. One with this SAN foam skin top and bottom and dcell rails. Another with the SAN foam skins top and bottom and the evil balsa rails. The final a single top skin of the SAN foam and dcell rails.

Depending upon what source you are looking at, the cross-linked PVC (dcell) is better than the linear SAN (core-cell). And vice versa

I stole this from the Bluebird Electric Composite Bodywork website:

Styrene acrylonitrile (SAN) co-polymer Foams

SAN foams behave in a similar way to toughened cross-linked PVC foams. They have most of the static properties of cross-linked PVC cores, yet have much higher elongations and toughness. They are therefore able to absorb higher impact levels.

SAN foams are replacing linear PVC foams in many applications since they have much of the linear PVC's toughness and elongation, yet have a higher temperature performance and better static properties. However, they are still thermo-formable, which helps in the manufacture of curved parts. Heat-stabilised grades of SAN foams can also be more simply used with low-temperature curing prepregs, since they do not have the interfering chemistry inherent in the PVC's. Typical SAN products include ATC Core-Cell's A-series foams.

Core-Cell is the first structural foam designed specifically for the marine industry. In the context of our project, the properties apply equally to vehicle body production.

Not only does Core-Cell offer better handling and machining characteristics, it surpasses all previous limits of stiffness, impact strength and heat distortion temperature. Core-Cell does not out-gas and is compatible with all resin types.

Being closed cell, Core-Cell adds safety, comfort and reassurance to ocean going passages and reduces condensation through insulation. Core-Cell is preferred by professional builders and has an excellent reputation with amateurs for being easy to form around tight curves, but stiff enough to strip plank between temporary frames.

For in-mould applications Core-Cell reduces resin usage and weight by its unique double-cut and triple-cut sheets. The invisible knife cuts open less than other contourable foams when curved meaning less chance for voids and/or delamination.

Impact tests repeatedly produce failures of PVC cored panels while Core-Cell remains undamaged.

In my UNscientific testing of scrap material I found that core-cell didn't absorb as much resin as divinycell during lamination and that the test panels "felt" slightly stiffer.

I haven't been able to get my hands on any PMI foam - apparently I'm not "good enough" to acquire any. Boeing and Cobra get it by the boatload. I wonder if their purchasing departments have to sign a waiver and release to ship?

so i have a source for my carbon fiber now jeff, all along my good friend ryan was using it to laminate some of his boards. he makes amaizzzzzzzzinggggg boards, and is just a young dude cant be any older than me, shapes all his stuff himself, laminates himself, pinlines himself, its all done by him. you should take a look at these babies.

http://www.pointconceptsurf.com/

You just have to love a young man that invests in his future - like you with your education or Ryan building a buisness.

I loved this board with the concave deck and carbon wrapped rails. Nice pin lines too.

That's just pure board porn. I love the resin swirls he's doing on some of the boards in his gallery.

wow johnny - your buddy has some amazing artwork!

One of the drama's associated with vac bagging is that eventually the bag's develop small pinholes and need to be replaced. Typically you can get about 10 vac's per bag, anything more than that and you are living on borrowed time.

Let's see...this WOULD be my 14th vac. I kept meticulous records, but if you ignore them they don't do any good. My bag has a hole, I couldn't chase it down, even though it would seem that every square inch of the exterior is covered with sealant tape.

This sequence of builds will result in a duplicate of the current firewire structure.

http://www.firewiresurfboards.com/

I'm starting with a core-cell top sheet, no bottom sheet and d-cell rails. The second build will have a core-cell top and bottom with d-cell rails and the final will have core-cell top and bottom and evil balsa rails.

The balnks that I am using for this are all 1# denisty with the rocker hotwired in. That dictates a different cut in the d-cell rails. For this purpose I use the masonite template that I used to hot wire the rocker in the foam and then used an X-acto knife to cut around the template.

I am making a few changes in this board. The first is that I am moving the fins outward a bit so that I can connect the high density foam inserts with the rails. Further I have made the inserts deeper so that they will connect to the decking, in this case the Core-cell.

I also chose to "thermoform" the tail block. In the tight curves, the d-cell wants to spring back. Trying to make the stringers curve around in the back under vacuum wasn't successful.

What this also lead me too was heating the d-cell skin, which is 1/8" thick. With a slight amount of heat, it easily conforms to the rail shape. It would seem that it would be easy enough to heat the skin and shape the rail before bagging it.

So, you've bagged 14 boards? Where do you put them all?

Jeff, this is a really interesting thread. You keep experimenting and finding different things to try.

Put them? Is a person supposed to put them someplace specific?



Thanks for the compliment Ed. I have always enjoyed the prospect of asking "why not?" over the more common "why?"

Sorry that I wasn't more clear. I have only completed 3 boards, I have 3 more in-progress and my raw materials inventory is probably sufficient for 10 additional boards.

I was referring to actually pulling a vacuum, so I HAD (the bag is past-tense ) pulled 14 jobs on the old one. The wood in the last pull killed it. Have you noticed that wood is evil?

Some of the projects took several pulls. The first board took one for the rails, one for the bottom, one for the deck and then one additional for the exterior lamination for a total of 4 pulls.

In a production environment, I would think that folks could attach rails, top and bottom skins in a single pull, or like the surftech and firewire people, the entire assembly in a simple pull.

I am hypotizing, but my guess is that Inland Surfer probably has their technigue and molds down so they do everything in a single pull, also.

One of the concerns I've had with the composite's is that the you need to insert a higher density foam for the fin boxes. As in the above photo's I've connected that insert to the rails, but I'd rather have a more substantial connection to the rails, and also to the top deck. The design isn't finalized yet, but what I was thinking was to use some 8 pound pour foam to create a chunk that would incorporate the fin box inserts, a FULL connection to the rails and also a web between each box. I am NOT an engineer, nor an artist, so don't bust my chops on either count - but recommendations on design change would be most welcome. Except, the inclusion of e.balsa.

I'd rather create a cavity in the board before attaching the deck, so that I'd have perfect conformity to the rails, and shape of the cavity. However, I'm a little concerned with blowing out the bottom skin and properly containing the expansion with some type of lid that would allow the excess to escape.

Next I thought about making a mold, but if I keep the web, I'm concerned about getting the foam out without destroying the mold.

Lastly, it just feels easy enought to buy, or make an 8 x 24 x 2 block and then route the web and shape to fit into the board outline. I think that will wind up being the easiest.

Before insertion, the block will be shaped to find the cavity.

I'm still leaning to pouring directly into a cavity in the board and somehow containing that to fill the shape and eliminate trapped air bubbles.

Is it just me or has nobody offered to buy a board from Jeff.. I would be interested.. I just got my boat at the end of this season and would like to try Sufing.. So how much would one be Jeff?

I was kidding Mark Sher the other day. He was saying I should give up bean counting and going into shaping $2,000 and the baby is yours! Realistically, the way I am doing it is so labor intensive as I experiment, that I couldn't really sell them at a price that I could cover my costs...so, I'll make you a deal...

After I am done with all the experiments, have have got my measurements, I sell you any of the "leftovers" for my cost of materials. That would put them in the $125 to $150 range, except for the Rohacell IG 71 (when and if it arrives) that skin by itself is close to $125 per board.

If you are really interested in a board right away, we have a brand new Inland Surfer Yellow, pre 07.5 that has never been ridden. James won it at the Tulloch event and he'd sell that for $250.

PM me if you want me to keep you posted, after I'm done.

I cut the first skin out of the core-cell. It is substantially more stiff than the equivalent thickness of divinycell. In this picture you can see the d-cell curved and limp. The core-cell won't bend like that from it's own weight, it snaps back, straight up.

It has a similar stiffness and memory as balsa...not quite as much, but very close.

Compsand #4 (#3 is an all balsa that is under construction, which at the rate it is taking shiuld be done next year at this time ).

One of the issues that folks have with the surftech construction is that the boards are too stiff. This ISN'T an issue with composite sandwich construction, but in the build that Surftech uses.

This next build will have only a single deck skin and h80 d-cell rails, no bottom skin. I've also kept the thickness below 1 7/8". This board will no doubt be too flexy to be ridden hard. It will however demonstrate that composite sandwich construction can produce a board that is exceptionally stiff, like Compsand #2 or exceptionally flexy - like Compsand #4. This experiment will lead into a board that has core-cell skins connected with 2oz glass and covered with 4oz glass and balsa rails. It is the same construction that Firewires are made with.

Cooked and out of the bag. Just need to feather the skin on the rails and then the final outside lam. I think I'll do 4/4 top and bottom, hopefully I'll get enough decent weather for the epoxy to cure.



(Message edited by surfdad on November 18, 2007)

I've been out of the loop a little lately. My 5 year old is in the hospital with pneumonia right now. Anyway, are you going to have to put a "vent" into it? Those rails look really boxy too. Have you found that boxy rails hold an edge better? I know when I rode my longboard behind my boat (it's got 50/50 rails) it felt a little less stable side to side. By the way, that board looks nice. And nice buckets of spray on the compsand #2 in the other thread.

I'm sorry to hear about your child. Is everything ok? That has to be so scary for you as a parent - I can't think of anything worse.

I don't think the rails are all that boxy, it's just the angle of the picture. The tail is vertical, but once it's up around the fins, they actually blend from about the center line out. I haven't done anything with the skin yet, so there is about an extra 1/8" that needs to be blended.

Unless you completely seal the 1 pound EPS, it needs a vent. This one isn't sealed and so would need a vent, but I doubt I will actually put one in, as this is just a prototype. As I build the firewire replica and the all balsa construction, those will have vents.

Thanks for the compliments on #2

Matt
Sorry about your 5yr old. Hope everything works out soon.

Looking good Jeff!

By far the best post I have ever seen on Wakeworld! I've been tossing around some similar ideas but at a much lower tech. level. You have really got me thinking at a higher level and you're knowledge of foams is amazing. My background is in woodworking and I have been looking at making an ultra light balsa board but by creating a honeycomb of balsa using a CNC machine to rout out a precise pattern in the material. My biggest concern is that it will become too stiff. I've been researching making the top and bottom skins parallel to increase flex. I was also wondering about making it a quad. I'm way out of my league with surf board construcion and how it relates to wake surfing but generating speed is something I hope to do with bottom shape and fins and increasing flex by making top and bottom parallel. Thoughts.......

Ya, Jeff is doing some pretty neat stuff, great to watch.

Scott, I just completed an ultra light balsa wakesurf board a few months ago in response to a challenge that Jeff issued. http://www.wakeworld.com/MB/Discus/messages/87668/497879.html?1192119812

I see you're in that state up north. If you’re not too far north we should get together some time next summer and surf. I’ll be running a wake surf comp in Dayton next year and another venue to be named later. Also just to poke a little fun, I think a school teacher should be able to spell school.

Hey Scott,

Thanks so much for the compliments and for sharing your stoke! I'm glad that I have stirred some enthusiasm and from someone with a different background.

I am NOT a woodworker and quite frankly I HATE wood! Evil Balsa = e.balsa. From what I have seen, and you may have a better handle on sources of material, contest grade balsa came in at 6 pound density - that's pretty heavy in comparison to foam. Many of the skim style boards are shaped from 5 pound density cross-linked PVC. MOST of those are in fact STIFF.

Stiff isn't a bad thing, but it really chages the way a board rides. Longitudinal flex, but only moderately, is really great for our small "waves". Too much flex and the board is a pig. I don't think that you can really go wrong with TOO stiff except in a contest board, or a board for an expert. However, it's easy to make it too flex'y. If you were asking my opinion on that, I'd opt for too stiff on the first build, then if it's TOO STIFF, adjust for the second build.

I just posted a thread on quad's:

http://www.wakeworld.com/MB/Discus/messages/87668/521144.html?1195615948

I'm in love with the "idea" of quad's, but I have to be honest, I haven't ridden that many and of those that I have, I haven't found a set up that I am in love with. I think that it's really easy to make a crappy quad, but much harder to get all the elements correct for decent peformance. It seems that at the speed we are at, the quad setup is really finicky. I'm sure that boards like Johnny Stiegs pro model work well...I just haven't had one of those under my feet (yet ).

In terms of bottom shape...I really am of the opinion that a flat bottom is the fastest design available to us. Even a single concave is an attempt to remove the continous rocker and make a flat bottom.

I can't believe that there are TWO of you woodworkers though first Ed and now Scott - sheesh, I'm outnumbered!

Speaking of foams...something I failed to mention is the PMI foam - the Rohacell IG 71 is also Radar Transparent. I'm going to do some stealth surfing on that prototype.

Compsand #4, single core-cell 3mm A500 deck skin. 1# eps foam core and no bottom skin. D-cell h80 rails.

The core-cell blended and the board is ready for final lamination. Current weight is 21.8 oz. I'm guessing an aditional 2 pounds for final lamination and hot coat. Which should keep us under 4 pounds.