Sandwich springer construction

Last year I swiped an idea from Firewire surfboards and installed a springer into the neutral axis of the board. Well, what I thought was the neutral axis. In the last year there have been some changes and it seems the neutral axis on a surfboard has either changed, or been abandoned in favor of recessed on the deck side.

My build thread from last year is here

The changes in Firewire's tech is here

If you notice the propaganda from the Firewire site, they are describing layers, like the leaf spring of a car, which is the graphic also. Last year I just used a thick Balsa board, which was ok, but there really isn't much flex return as the minimal amount of flex we get with our boards didn't engage the balsa board. I needed to tighten up the response.

If you "glue" three things together, no matter what the material - say playing cards they become incredibly stiff resisting any forces that try and deflect it. Carbon has great flex return and retains that characteristic when included in an epoxy matrix.

So my springer for this build is 3 layers of 6 oz CF sandwiching 2 layers of 1/16" Balsa.

I'll be incorporating the sandwich springer into a composite sandwich board.

CF/Balsa/CF/Balsa/CF laminate stack:

The general location of Firewire's springer circa LAST year.

i wish you would use CF tape

I am too CHEAP! I am using up old scraps of B and CF.

and dont forget the vent

LOL yes mom! Reminds me of last night. Judy "gently" reminds me not to bring epoxy and EPS into the house. So I typically try and clean up before going inside. Last night I must have wiped my hands on my shirt and not realized it. I'm heading to bed and go to take my T-shirt of and I've laminated it to my stomach!!!! I effectively gave myself a stomach waxing instead, using epoxy You know...that hurts!!!!!

oops , i think it was the lighting that does it ( lack of ) , so now what is your status

That's a funny story. When I went to pull the T-shirt off, I truly waxed lyrical (pun sooooo intended ). Poopy! (or word(s) to that effect) I exclaimed. Judy, ever attentive to my exclaiming Poopy! (or word(s) to that effect) asked: What's wrong?

I explained the small matter of being one with my T-shirt and the epoxy. Upon hearing this, she went into some type of convulsion that included writhing on the floor and hysterical laughter. Poor thing.

I removed the slack in my T-shirt and on the count of three, pulled with all my might in a swift upward motion. THAT caused, once again, a waxing lyrical: Poopy! (or word(s) to that effect). And was also effective in separating the T-shirt and a certain amount of stomach hair, from my person.

So, for the time being, I am smooooooth as a baby's butt, slightly red and irritated in an isolated spot, but sans T-shirt.

Thanks, ever so much, for your inquiry, which allowed me to relive that glorious moment, once again.

This build will be a composite sandwich, utilizing corecell rails and divinycell skins.

I'm not a big fan of divinycell (cl pvc) in the 3mm thickness for the skins, preferring corcell (san). The more brittle cross-linked PVC foams crumble and shear under severe impact, and are better used in low-impact areas. Brittleness also lowers the resistance to crack propagation. Once there is a crack, such as the 45° crack
occurring under impact, it can easily propagate as the sandwich panel continues to flex.

This first picture is of some H-80 D-cell you can see the jagged edge - it tears like construction paper.



The next picture is A550 Corcell, 3mm and it's virtually impossible to tear.

Divinycell has a number of features, it's readily available, about 50% cheaper than the stronger Corecell and in comparable densities is "floppier" than Corecell - bending around tight corners is pretty easy with D-cell - a tight radius tends to just snap the Corecell.

I'm using H45 D-cell, it's a 3'ish pound foam. Anything less than 5 pound density isn't structural, so my H45 will basically crush unless I stiffen it up. Further, this low density d-cell offgasses like your grandfather after a mexican meal It will need to be sealed to reduce that OG and to increase the resin at the surface, which will help stiff the skin.

It's hard to see in this picture but the D-cell's porosity is so extreme that there are holes thru the 3mm cross-section.

The board in the background is this same basic construction, with the exception of the rails, which in this case were H45, also.

The skin will be sandwiched between two different fabric, the underlayment will be 4oz Zylon as on the exterior of the board above - Zylon in a epoxy matrix exceeds all technicals of aerospace grade CF and it comes in a 4 oz weight.

On the exterior, I am going to use a carbon and kevlar hybrid. It offers the stiffness of CF and the impact resistance of Kevlar. I'm sure it will be a mess as the Kevlar won't sand, but I like the look of it.

It seems that mills are routinely dying the Kevlar different colors - strictly cosmetic, but I like the look.

[insert after crack propagation p ]

Klegecell, Divinycell, Herex are cross-linked PVC foams, they're actually blends of PVC and di-isocyanates, a very brittle urethane foam component. In fact, the PVC / di-isocyanate blend is a good compromise. It makes it easier to foam the PVC, and to produced different densities of that foam. The di-isocyanate gives the PVC two properties it lacks; good mechanical strength and better heat distortion. However, it imparts its brittleness in the process. Elongation in cl PVC foam is only about 10% vs SAN Corecell at 60% which is why I was able to tear the D-cell.

aha, and have you seen holographic CF? Board from it must be eyecatching

I've seen that stuff! So many interesting fabrics.

Examples of the holographic CF that Petr refers to. The website where I swiped the pictures indicates that it's hard to capture the reflective quality of the fabric in the picture.

looks like snake skin

just holgraphic

holgraphic, that's funny. It does that that irridescent snake skin look.

So I've been working with texturing the epoxy, on the deck so that I can reduce traction/wax, at least outside the area where the EVA traction will go and on the bottom to aid release.

The excellent idea about sand, I've used before and didn't care for the results, but I may go back to that. Instead I used a metal wet out roller after the epoxy started to gel just a bit. It left bumps, that are similar to sand, without any real sharp edges...I think that may work.

This is a close up after the texture coat and I shot some primer today.

Towards the end of last year, I built this board:



I shot the paint with three layers - black, white and red. So the red was proud from the rest of the paint. It didn't seem to slow the board any, but if it can go 14 and get there quickly, that's enough. What it DID do was release really well. The water didn't seem to stick to it at all. So I wanted to add a texture to the bottom of a board that didn't require so much paint build up.

Epoxy is miserable stuff to work with, it fish eyes and seperates and seems to be impossible to gloss...so I thought, how can I use that to my advantage here (and be lazy). I laid down a solid hoatcoat to ensure the fabric was sealed, then I got my hands dirty and oily using a tiny bit of baby oil and I rubbed and scratched my dog Woofie for about 10 minutes. After doing that I touched the hotcoat - just doing EVERYTHING wrong for a good gloss. Then I squeeged on a very thin gloss coat of epoxy so that there wasn't enough to self level and viola - a textured bottom. Oh! and a happy dog.

I hope to paint it so that the depressions are one color and the peaks another...my plan is to shoot the whole thing black, then go back and lay on a really thick wet coat of red, following quickly with a squeegee to strip the red from the peaks and if I'm lucky it will be a sort of mottled look, with the texture still in place...we'll see.

There is a similar concept in the kneeboard and surfing shapes - they are called jet bottoms, but they are actually shaped and glassed into the bottom of the board. A few simple pictures, there are some incredibly intricate shapes in the genre.






I can't even imagine shaping something like that, let alone glassing 'em.

I swiped two quotes from sway's about the theory of Jet Bottoms:

There's conflicting views out there but if you read carefully, it seems that the closer studies have found that micro-turbulence prevents macro wake turbulence behind curves by keeping the boundary layer energetic. This became a diminishing return when ridges or whatever extended beyond the boundary layer.


While not absolute proof, it gives credence to the claim that by deliberately inducing turbulence, you can break up the adhesion layer of water which sticks to your board, thereby slowing it down. Breaking up this surface tension may result in a faster, looser, more responsive board, which is what riders of these bottoms claimed.


In my experience, there wasn't any speed increase or degredation for that matter. So, speed didn't seem affected by the a roughened surface - whether I had just scratched the bottom with 60 grit, of the traverse ridges from the paint. However, I have consistently found the boards released better, so there was less adhesion of the wtare to the board.

look at shark skin - there answer - it is milion years of development

http://swimatyourownrisk.com/wordpress/wp-content/uploads/blogger/blogger/7194/799/1600/42-15442272.jpg
http://images.google.com/images?client=opera&rls=en&q=shark%20skin&sourceid =opera&oe=utf-8&um=1&ie=UTF-8&sa=N&hl=en&tab=wi

http://www.sharkskincoating.com/newse.asp?newsid=239

The structure of shark skin has another function besides protection. The streamlined shape of
the scales decreases the friction of the water flowing along the shark's body by channeling it
through grooves.The grooves are so closely spaced, they prevent eddies from coming into
contact with the surface of the shark's moving body. This reduces the amount of "drag" as the
shark swims, enabling the creature to glide farther on a given amount of energy.
Scientists have found that the ridges created by shark scales can reduce drag in the water by
as much as 8 percent. Golf balls and many military aircraft and vessels employ similar
drag-reducing principles.



I think its kinda nanotechnology (geckos already use it)

Also new fabric of Speedo wetsuit for British Olympionics was banned because of speeding effect. Call Speedo, buy some and glue it on bottom


NASA`s riblets
http://www.nasa.gov/centers/langley/news/factsheets/Riblets.html

http://www.springerlink.com/content/p8746pq28732p1t5/
http://www.freepatentsonline.com/4706910.html

http://coachsci.sdsu.edu/swimming/bodysuit/fiveauth.htm

http://coachsci.sdsu.edu/swimming/bodysuit/Image13.gif

http://www.swimming-faster.com/

Or you could go Shark Fishing!!!!

LOL! Shark fishing! I can't even catch a bluegill!

I have read "some" of that literature Petr, but around the 6th paragraph my eyes glaze over From what I have been able to glean is that the sharks skin is a ORGANIZED channeling of water - so something TOTALLY unlike my desk. Whereas the jet bottom and my separation bottom are chaotic, JUST like my desk. The organized channeling tends to speed things up, while the chaotic channeling, I think, really only loosens things up...but there are those that same the chaotic does both.

Sorry Jeff even I dont have time and energy to read it all but its very interesting so I posted all I found.
Shark skin is compound of hard ribleted sheets inserted in soft underlay. But I dont know real size of this texturing which is crucial for proper function. If tis in mm, microns etc.?
These hi-tec swimsuits provide also some floatation becase small air bubles catch in riblets.

look at this drag reduction product KISS-COTE
http://www.kisspolymers.com/Products/products.htm
http://www.kiss-cote.com/Products/marine.htm

they talk about 1-2% or 4% reduction

drag science - very interesting and short text
http://www.kisspolymers.com/Science/science.htm

Its all about directed turbulence

(Message edited by hawaj on September 29, 2009)

Here we go - that film is made by 3M and each V-shaped groove measures 150 micrometers across -- approximately twice the width of a human hair. So we can imprint this pattern from some film to gloss coat. I think that maybe some PE or PVC thin plastik sheets are made with this texture.

http://researchnews.osu.edu/archive/riblets_closeup.jpg

http://researchnews.osu.edu/archive/ribletspics.htm#anchor77852
http://www.innovations-report.de/html/berichte/verfahrenstechnologie/bericht-15278.html

Its all about directed turbulence
they talk about 1-2% or 4% reduction

I don't doubt that for a minute. I think that in Olympic level swim events that can be decided by 1/1000 of a second any advantage is helpful. I'm not so sure that has any practical application behind the boat.

In the picture below - I'm in the realm of 16 mph, but I'm pumping like mad and have to be careful not to engage the rocker on the face of the wake. That REALLY is the fastest that board would go with me riding it. The increase in speed with the organized flow is possibly TO 16.16 mph up to a maximum of 16.64 mph. I'm not sure that's even a perceptable difference, let alone usable difference.

To me, acceleration or squirt are more important once you have a board that can operate in a speed range above your wake speed. Theoretically, our boats are running around 11 mph. If your board can operate at 12mph easily - at trim, then that's probably enough, but you'd want to get from 11mph to 12mph instantaneously...you attempt a 3 and you're fading out the back, lean forward and you automatically are going faster than the boat - THAT's usable squirt or acceleration.

As for the difference between organized and chaotic flow. Personally and this is just my opinion, organized flow, while quantifiable, isn't practical in this application. If chaotic flow doesn't degrade speed by more than that .16 to .64 mph and DOES have some impact on the release of the board, THAT is a more useful application of the texturing.

OR not. So much of this is subjective and may even be unrelated to the texture itself. Although I do enjoy the discussion of theory. Thank you for your input Petr! I wish that I had a better grasp of it all.

ooops - picture below

yep increase is not so big its good to know something more

I like to think about all posibilities and unconventional things around that other peoples are scary off

(Message edited by hawaj on September 29, 2009)

yes - you've always been way ahead of the curve!

I was just organizing some of my notes and remembered finding some info on Tom Morey's Air Lubricated boards. In one of the articles Tom is quoted: "Once I knew for a fact that a wide board given freedom from drag would really fly, I was mentally free to think in terms of wide flat stone-skipping proportions, which in a way led to the development of the first boogie boards, which, in fact, given decent size waves, really scream along."

I was thinking about Shred Stixx and Inland Surfer - both Jerry Price and Jeff Page are exceptionally innovative and will forget more than I'll ever learn. They both seemed to grasp on to that wide board with no drag pretty early on. I think both of their companies are constrained by perceptions - you can't sell something that is TOO advanced otherwise it scares people - like you mentioned Petr.

Anyway back to the Air Lubricated boards of Morey. He put steps in the boards, these pictures illustrate:




I wonder if surfcraft being partially submerged and partially airborne have a greater reliance on that boundary of water and air. Shark's are fully submerged and so there really isn't the introduction of air into the boundary layer as would be possible with surfcraft. It seems to me, and I'm probably all wet here (I loved that pun ), that there is a potential for reducing drag and thereby increasing speed and acceleration, by trapping or creating air bubbles in the hundreds of recesses.

I tried something over the weekend. I have a tsunami pump with cheap clear tubing. You can see the water flowing through the tube, but mostly because of the occassional piece of gunk that zips by. I pinched the tube, just a bit, enough that it created a convex shape in the path of the water. On the trailing edge of the convex there was a turbulent distruption and the formation of bubbles - lots of air. It was funny, because there didn't seem to be any air in the flow before the convex...my guess is that it's there and not magically created, but probably along the surface of the tubing and the restriction mixes it into the flow of water. If that's the case, I'm hoping the same thing can happen with the "dimples" and the result will be a more slippery board.

I think that NAVY after riblets developed some system which distribute air thru small holes under body of ship to decrease drag of water.

Read this article:
http://www.innovations-report.de/html/berichte/verfahrenstechnologie/bericht-15278.html
... very interesting

That is interesting, I just scaned the first little bit, I'll read it in a bit - thanks for the link Petr.

NOT the dramatic effect I was hoping for, but fun nonetheless.

From that article: The optimal arrangement, Koeltzsch said, is when the distance between the peaks of the riblets is half the diameter of the vortices. In this case, the fluid caught by the vortices only contacts the peaks of the riblets and not the walls of the pipe, so friction is reduced and the fluid moves faster.

How does one determine the diameter of the vortices?

he he you must simply measure it lets say from photography


Call some hydro lab where they have hydro tunnel put board there and lets water flow and take picture. Maybe colored streams will help.

Or wakesurf in very clear water and put camera under board.


I think that maybe some students at university can by interested in this and you can make some colaboration project. You get accest to hi-tec lab and some answers and they will get interesting theme

fin tip vortexs

http://4.bp.blogspot.com/_5hQ00FJXHtA/Sdp7JLF7HsI/AAAAAAAAAe0/Hcpbc7NYf70/s1600/0904_typhoon%2Blagoon%2Bexport%2B-_148.jpg

low speed hydrodynamic tunnel

http://4.bp.blogspot.com/_5hQ00FJXHtA/Sdp7JLF7HsI/AAAAAAAAAe0/Hcpbc7NYf70/s1600/0904_typhoon%2Blagoon%2Bexport%2B-_148.jpg

vortices
http://www.pmmh.espci.fr/~ramiro/images/flap_fluo_BKI_ASYM.jpg

beware Jeff - surboard science!!
I dont read it! Just posting

http://users.tpg.com.au/users/mpaine/thesis.html

http://mysite.verizon.net/res7n5pu/id7.html

(Message edited by hawaj on September 30, 2009)

I love the intro to your last post beware Jeff!

In looking at one of those articles, I read this:

Even the slightest roughness such as scabs of wax on the bottom of the board can make the difference in avoiding a wipe out. These small imperfections cause enough friction with the water that a turbulent flow results, decreasing speed.

I guess my position is I don't believe that, or perhaps my position is best stated as; Yes that's true, but the degradation in speed is so minute as to be imperceptible. However, the increase in release or looseness is significant and easily felt, if not easily quantifiable.

I need to find a fluid dynamics class interested in surfboard design.

In looking at the vortices in the one picture, I would think that only the first one is significant, because that's where you want to place the second row of tips - or actually at the mid point. It seems, though, that there is a leading ramp, which has to be based upon speed - slower the speed the less that lead in and possibly the larger the diameter of the vortex. I wonder if there isn't some formula to predict the diameter of the vortex given the height of the tip, density of the fluid and speed of the tip through the fluid...sheesh then there would also have to be some angle of attack. OK OK OK, I give up!

Interesting Jeff, I must read it all after my work is done ...

And please dont forget that we are at field of water mixed with air bubles (plus foam at sea) and not only in pure water, so it can make difference than pure fluid dynamics.

What I like from that first article is that sharks which move quicker have different skin than others and that scientist started to study pinguins and seal fur - ie how fibers can decrease drag

Wonder how looks speed fishes skin like swordfish etc. Do they have that fish skin slime like other ones? So what about to put some slime or vaseline on board? Only measuring and testing can show the difference

and if you can find it ...

Hendricks, Terry. Surfboard Hydrodynamics, Part 1: Drag. Surfer Magazine January 1969.

ok here it is
http://www.rodndtube.com/surf/info/Hydrodynamics.shtml

(Message edited by hawaj on September 30, 2009)

Another concept from Bourton - cathedral hull

http://www.mesurf.com.au/ProductDetail.aspx?id=774&name=bourton-fat-bullet

and Jeff do you know this Findesigner software

http://cetic.swan.ac.uk/surfs/products/findesigner/

they promised some add modules but it was long long time ago
- Comparative flow analysis and pressure distributions add-on modules
- Comparative drag and lift analysis add-on modules

All done, we'll see if the bottom texture theory is 'all wet'

I ordered a few sections of nomex, I think it will give a uniformly "dimpled" surface rather than the random surface pattern with the separated epoxy. I'm also interested in how the honeycomb will work as a skin.

How are you going to use Honeycomb as a skin. Are you going to have at least one layer of fiberglass over the honeycomb? My friend used honeycomb as a core for some speaker enclosures he built, with a couple layers of fiberglass. He used a vacuum bag technique, and he was left with little dimples in his end product. This could be a good idea! Can't wait to see the end result. Jon T

In both the d-cell and hc skins I'll have fabric over and under the skin core. My general approach is to shape the 1# EPS core and then bag the bottom skin to that shaped EPS. I intend to use 4 oz zylon as the sandwich layer in both of the builds. I'll do a few test panels to make sure it's all working, but I think I can achieve the results I want with 10" of vaccuum.

This picture is a from a few years ago where I was discussing that it wasn't necessary to bag to a tool of any kind, just lower the vacuum and leave the EPS core unshaped on the top, so that it's thick and will resist bending, and the 3mm skin will conform to the shape.

I'll then go back and laminate the exterior, most likely again with the bag.

Ok, so time to get down to business. These boards will be a composite sandwich - a low density core 'sandwiched' between high density skins. The skins get the tension and compression forces and the core some compression and sheer. MOSTLY the core just keeps the skins separated and prevents them from bending.

This illustration shows the various forces on the components of the sandwich.

I use 1 pound EPS for the core. It's low density gives it great sheer properties and lowers the weight close to 40% when it's complete.

There is a fairly new "flavor" of EPS referred to as EDRO that makes EPS virtually impervious to water. EPS is a closed cell foam, but in this low density it's most air and pentane, the blowing agent inside the pellets. The gaps between the pellets can fill with water in the case of a puncture.

For my purposes I use the cheaper non molded EPS. I get the EPS in billets that are 4'x8' and I typically have it cut 4" thick.

I use a simple circular saw to hack the 4'x8' into 3 pieces, 2 - 2'x5' and the residual 3'x4'. Depending upon the rocker I can net 3 to 6 cores from that, which is about $4 to $8 each. The 1# foam is super cheap.

I hotwire the bottom rocker and leave the deck unshaped at this point. I have a set of rocker templates made from masonite. That material allows the hotwire to slide along the cirve of the rocker smoothly and melt the EPS as it goes.

I put alignment marks on each side so that the hotwire templates match and I'll create a flat rocker. I attach the templates to the foam using simple wood screws.

I have a 28" Tekoa hotwire bow and transformer - they call it a thermal generator

The 1# pound foam melts like butter under a hot knife. After making sure that the rocker is square, I remove the rocker templates and hang them up.

So, the textured bottom doesn't seem to have impacted the speed either positive or negative. My guess is that it does add drag, but it's so negligible as to not be perceptible, but it does have a definitive sense of release. The board isn't loose, due to the fins, but it's not stuck to the surface. I'd like to try it with a less chaotic texture.

Jeff, the with you on the board it still looks stuck to the water.

LOL! I represented that it released really well, NOT that it was magic. The magic board is slated for construction in January.

After hotwiring the core I shape the core to accept high density rails. I like to glue them up with a single layer of 6 oz Carbon Fiber that acts somewhat like perimeter stringers.

I take an existing shape and lay it on the core so that I get a rough idea where the final outline will be. In this build I'm using 1/2" A550 Corecell for the rails. I want to leave just a hair of the rail material beyond the final outline so that I have some excess to play with when I go to shape the rails. Once I have the general outline drawn on, I lay an outline template on the centerline and mark my cut line.

I use a jig saw to cut along the outside of the cutline and a sanding block to square the cut up, as well as, bring it down to the inside of the cut line. In this situation my foam is a tad thicker than the depth of my jiggy blade so I use a hand saw to finish that part up. Lather, rinse and repeat on the opposite side.

I forgot to mention, that I don't trim the tail back where the tail block will go. The HD rails are bent into the curve of the tail, and I don't have the ability to size those accurately during the prefab, so I cut the core and rails after glueup so that I get a straight cut for the tail block.

The rail material, as I mentioned is corecell. It's very stiff and has great shear resistance, but when stressed too much it tends to snap. Attempting to bend the rail material both INWARD to follow the outline of the board AND UPWARD to follow the rocker tends to put too much stress on the 1/2 thick material. So, I cut the rocker into the rail material and then only need to worry about the bend in towards the outline.

I use a simple single edge razor to cut the corecell, using the hotwire template as a guide. The rocker will be slight different when it is finally shaped, but it's pretty close at this stage.

I was going to glue up the rails, but I seemed to have stocked out of bag! Anyway...while ordering the bag, I thought about peel ply to give the bottom surface some texture. Peel ply is non porous and leaves a slight texture to allow secondary bonding, I'm hopeful that will give me the release in a more uniform/less chaotic fashion.

My intention will be to lay it over a wet gloss coat and leave it to cure.

While I'm waiting for my nomex, bagging film and peel ply, I got my rails ready for glue up. In the above photo you can see the rails are @ 2" wide. Up at the nose, that will exceed the thickness of the EPS core. When the bag starts to consolidate the rail material, the area that is proud of the core will tend to bow inward and force the bottom away from the core. It's a little hard to see, but I've trimmed that area even with the deck of the core.

I've also trimmed the two pieces where they'll meet at the nose to about 45 degrees. Also, it doesn't show, but I've kerfed the last 4 inches of the rail material where it bends the tightest.

I have also cut two strips of 6 oz CF that I will sandwich between the rail material and the core.

I'm ready to glue as soon as the bag arrives.

TAPE

LOL! $

I didn't get pictures of the assembly, but a quick overview is: I mix up about 3 oz of epoxy, paint a very thin layer on all of the foam that comprises the rails. I use the residual epoxy to wet out the CF strips. With the resin spread, I smooth the CF on the EPS core, align the Corecell and tape it in place. With boths sides glued up and taped up, I place it on the rocker bed and tape the "blank" to the bed so that I can slide the whole shee-bang into the bag.

The blank, in the bag, as the vacuum is being pulled.

The blank with about 1/2 an atmosphere being pulled. It's enough to hold the rail material to the EPS without deforming/crushing the EPS. Probably the most troublesome area is up at the nose. The curve of the nose rocker tends to fight the curve of the rail inward towards the point of the nose. As the vacuum is being pulled, I work the rail material in and down against the rocker bed. If it's fighting me, I can stop the vacuum just long enough to work the foam into place and then start it back up again.

In place and I'll leave it like that overnight.

Surfboards or surf style wakesurfs have long had perimeter weighting and stiffening. The process of lapping the rails (where the fiberglass from the deck is "lapped" over the rails to the bottom and the reverse with the bottom to the deck) puts extra glass and resin on the rail and, as such, the perimeter of the board. The perimeter weighting helps sink teh rail in the wake and reduces rail twist-off some.

The high density foam rail material will aid this perimieter weighting AND help protect the board as rail dings are one of the most prevelant types of "injury" to a wakesurf.

The rocker bed I use is oversize from the shape I normally make. It allows me about 4 inches of apex adjustment and @ 1 inch of nose rocker and 1/4 inch of tail rocker adjustment. I can make changes to the rocker by adding shims under the nose or tail, as needed, as I am bagging the deck skin. In this build, I am moving the apex forward a few inches, by sliding the board backwards on the rocker bed.

The "blank" out of the bag this morning and ready for shaping. I'll shape the deck last, as the extra thickness helps when trying to mow the 1 pound EPS - it's floppy.

I'll attach the tail block next and then shape the bottom 'cave.

Jeff, Can you explain the tail block and what its purpose is?? Thanks Jon T!

You bet Jon and thanks for following along. I think most typically you'll see nose and tail blocks with HWS construction. These blocks make it easier to align veneer's or more appropriately elimiate the need Also, they help protect the nose and tail from damage by inserting more robust material. Lastly, as you can see in the images - they can add aesthetics.

Some examples of nose and tail blocks - the nose block is from a Paul Jensen HWS.

In my build, I will be embedding the springer into the deck of the board before laminating the deck skin down. I want something in the tail to help keep the springer "located" so that it can be loaded up and "hopefully" will unload with some extra pop. One of the advantages of the sandwich build is that the board can be broken down into constituent components and different materials used. So for my build the rail material is different than the core and skins, I could have used different rail material for the left and right sides of the board.

I don't know that such flexibility is useful, but it's possible

Tail block attached! I use 5 min epoxy and slather it everywhere.

I shaped a single 'cave in the bottom.

I'm going to skin this board with Divinycell H45, it's a 3 pound foam. I buy it in 1/4 sheets from Aircraft Spruce, so I have to cut the outline diagonally. The shear of d-cell is poor, so it cuts with a pair of scissors easily. Just be careful at tight corners as it will rip.

D-cell has a very porous surface. It's a closed cell foam, but the surface is basically tons of tiny crevices. If the surface is left unprepared, the epoxy will pool in some depressions more than others and create an unbalanced and possibly poorly glued skin. I also want to trap as much of the resin at the surface as possible. I seal both the the d-cell and EPS core with spackle.