Sandwich springer construction

Tomorrow, I'll bag the bottom skin using a 2 oz Kevlar sandwich layer.

Thanks for showing the Tail block, I might have to try that on one of my boards. I defiantly like the wood look, that is sweet! To bad I probably won't get to ride them till next year! Dang!

Also, wouldn't you get a better bond if the surface is rough and porous? I thought this would give you more surface area to bond to? If you bond to the spackle, will you still have a good bond between the spackle and the foam? I can see where it would give you a better resin distribution though! Do you think some of the resin will still seep through the spackle, giving you a good bond to the foam?

Also, Thanks for sharing the board builds. A person can learn so much from these, I have!!

Jon T

some of the resin will still seep through the spackle

Exactly! You're brillant! Under the pressure from the vacuum, the spackle will act as a wicking agent. There is still a considerable amount of foam that will be "accessible" to the resin, but there is no longer any trapped air that would impede the resin's contact with the structural components of the foam, plus the resin will now penetrate to a uniform depth in all of the pockets.

The problem with the rough surface is that the epoxy will flow into those depressions and pool there, potentially starving the surrounding area of resin. In effect that area will have very poor adhesion, and there won't be a uniform distribution of the resin across the board...potentially creating a weak spot just waiting to snap! Also, I'm onloy going to be using about 2 oz of cloth and 2 oz of resin, so I need 100% contact (or as close as possible) to the bonding surface as my matrix is pretty minimal - no extra resin to add weight or fill pockets.

Thanks for following along Jon, I'm glad you are enjoying it and I hope to see your inspired creations/builds this winter!

I like pictures! I so need a new box of crayola's though.

This might give a better idea of how the resin will flow or be absorbed into the foam.

The air that gets trapped in the pockets will rise and allow the resin to sink, creating a weak area, whereas the spackle will displace the air and cause a uniform distribution of the resin and keep it closer towards the surface.

Is this great art or what?!

Well I don't know about brilliant, but I did get a degree in this stuff, so it helps a little! Thanks for the visuals, it always helps me out! If wakesurf boards don't end up being your thing, I am pretty sure Art might be your path less traveled

That's funny! Reminds me of Robert Frost's poem the Road Not Taken. The last line of the first stanza: "To where it bent in the undergrowth;" I can remember a discussion in some class about that representing the unknown either the future or a calling unstudied, etc. I think I remember responding - couldn't he just have lost the map? I think I failed that class. BTW, where is that art map, anyway.

Thumbs up on spackle , Ialso will keep fisheyes under control when you go to hotcoat.

I've found that I had a bunch of 2oz Kevlar left over so I decided to use that as a sandwih layer. It's not stiff like CF, but it's equal to about twice the weight in e-glass. Kevlar is miserable stuff to work with, it doesn't sand, it fuzzes and it degrades in UV so needs to be hidden or used with a good UV inhibiting epoxy.

My Kevlar was on a 50" wide roll, so I can get a top and bottom from the one length cut.

Another of the characteristics of Kevlar is that it doesn't cut. You need special shears or these electric cutters.

I trim the Kevlar so that it is inside the rails, because you can't sand it. I mark the fabric with a pen and then cut on the line to fit.

Supplies needed for the rest - gloves, mixing bucket, stir stick, squeege and a ratty paint brush.

Because the sandwich layer fabric doesn't extend out to the edge of the rails, I paint on a 1 inch band of epoxy all around the edge of the dcell skin to insure a good bond at the rail.

The residual epoxy from the painting, I use to wet out the Kevlar. Kevlar is pretty stiff in it's natural state and is easy to saturate and apply to the board. I lay it down on the core, making sure that it doesn't extend past the rails.

I lay the dcell skin on top of the core and wet out Kevlar and then attach some tape to keep the dcell in place while I work it into the bag.

I want the skin to adhere to the 'cave shaped earlier and here is my trick for doing that on the rocker bed. The board/skin combo is in the bag, but the rocker bed isn't. The bag will pull tight up into the 'cave and I'll lay the board down on the rocker bed to insure the rocker remains.

This gives a better shot of how the skin is forming top the 'cave under vaccuum.

The skin being attached, the whole mess sitting atop the rocker bed.

Out of the bag ready for trimming the bottom skin and then shaping the deck.

dont see a shoe in the last pic.

I wanted to go back over some of the design elements when considering sandwich layer fabrics. The deck of the board receives compression forces and the bottom tension. Fiberglass isn't great at anything, but it also doesn't have any glaring shortcomings - like Kevlar that can't be cut, sanded or exposed to UV. In general FG is about twice as strong in tension as it is in compression - it's one of the reasons that a typical shortboard will have double the amount of FG on the deck as on the bottom - it creates a balance.

On the sandwich layers, both the deck and the bottom, are receiving some compressive and tension forces. The skin is acting like a very thin, small board so the deck sandwich layer has compressive, but because it's also under the deck skin there is a measurable tension force being applied.

It's possible to use straight 4 oz on all layers internal and external, or like me the Kevlar internally and something else externally.

The sandwich construction offers a unique opportunity, and challenge, to incorporate various design elements into the construction because the board is broken down into components.

@ jimbeam. LOLOLOL I forgot it! That was great fun.

arrgh those shoes really distracted me so I forgot to watch boards

(Message edited by hawaj on October 09, 2009)

lolol - the only thing you guys can see is the SHOEEEESSSSSS!

I try and take as much of the EPS off with a hotwire, the rest I just mow with a plane.

I will be adding 1/8" with the deck skin, so I shape the foil down to that much less. The only area that is tricky is the nose, the thickness is just over 1/4" with skins, so the core is very thin. I just go slow and set the plane depth at it's lowest setting.

One of the problems with shaping the blank with HD rails and a LD core is that the core knocks down much quicker than the rails...so I do the rails first, get them to spec and then bring the core down so it's flat and level.

This board looks like a squash tail I round the corners to make it a semi-roundtail. I also add the material to make the wings.

Tomorrow I'll do the rail bands, inset the springer and seal all the foam. Maybe, I'll get the top skin into the bag.

Currently the blanks weighs about 1.25+ pounds.

looks great , are you using a tucked under edge on the bottom

Thanks! Yes, I will, although I haven't shaped that in yet. The H45 shapes really easily and a Fred tool will tend to tear chunks out if I use too much pressure. What I'll do is, hit the bottom of the rail really lightly with the Fred and then finish up with 40/60/100 sanding blocks/paper.

It was a little early in the morning to run any of the power tools, so I cut the deck skin and sealed it.

I shaped a domed deck, I wanted to be sure to leave a flat'ish area down the middle to accomodate the springer. Then planed the deck and rails down.

Then I use a surform and sanding block to finish rounding the rails.

Now comes the fun part! I want to inset the spring so that it's flush with the top of the core at the deck. I align it down the center and mark the outline that I'll route out. Then set the depth of my router so that it is a tiny bit shallow.

I route around the outline, leaving the center in place as this will aid removing it later. After the outline is gone, I route side to side rather than lengthwise as the center section provides a bit of support as I remove it.

And test fit the springer into the recess.

I want the springer to be free-floating, I'm not sure how well I'm going to achieve that, but I'll give it a try.

I'm going to leave the recess unsealed and then I waxed the springer with mold release, I'm hoping that will be enough to allow the springer to move separately from the core and skin of the board.

I sealed the eps, save the recess and also fixed up two gouges. At the nose, I cut off a chuck of the corecell and something similar at the tail. A mixture of 'balloons and epoxy does the trick.

I like to put a deck patch under the feet. I used to make it shaped like the outline, but concluded that an hour glass shape did the same thing with less weight and waste. I save the offcut between the top and bottom cuts and use that as my foot patch.

Kevlar cut to size.

The assembly process - springer in, wetted kevlar down, then the skin and into the bag.

The springer seemed to form to the rocker without issue and it doesn't appear visible from the deck.

In looking at the rocker, it just seemed to be begging for a tad more nose flip, so I am adding about 1/2 in the last 3 inches or so. Fancy rocker tables that are adjustable don't need the wooden shims

how about wrap spinger in wax paper

That's a great idea brewkettle. I was looking for some PE and couldn't find any. I'll try that if I do another springer build.

Out of the bag and ready to finish shape.

I use a single edge razor to trim the excess skin, it saves a ton of sanding.

All shaped and ready to be laminated - it's about 2.25 pounds, the springer added about 6 oz net.

And NOW you know why no one makes these for retail. What is that, like 12 hours just to get to a shaped blank that using traditional close tolerance blank might take an hour?

Standard vac bag lamination, perforated peel ply, but I ran out of breather. You can find that at most fabric stores called batting and it's much cheaper than the breather. I use papertowels, about 1/3 of a roll does the same thing and is cheaper still.

I wrap the whole thing in a mattress topper foam. In molding with a film, they call such "stuff" intensifiers - it helps push laminations into deep corners where the bag might bridge the gap. My foam also allows the air to be drawn out and apply an even pressure across the entire lamination.

I forgot the most important shaping photo!

Deck lamination out of the bag, I probably won't get to the bottom until Monday evening, then all that's left is boxes and my superlative artwork!

I was able to get the bottom in the bag. The temp's are dropping, so I draped an electric blanket over it just to be safe.

I had some trouble resizing this picture, but the board is fully laminated!

I'm trying something with the hotcoat on the bottom. I want to apply a texture, but in a less random fashion that the "failed" gloss coat test. I applied a layer of peel/release ply on the wet epoxy hotcoat. This peel has an extra coating of release agent, but it's still a PITA to remove.

In vacuum composite construction a peel ply is used to impart a texture so that a second layer of resin and/or resin fabric matrix has something to adhere to.

I've left a bunch extra so that I have some leverage to get the release started. Once it's going, it's just elbow grease to yank it apart.

whoa free moving springer!

Is there any concern of the free moving springer adding concentrated stress points in the board? Maybe the top sheet, or the foam? Could it move enough to where it might move even more than you expected over time?

Umm, no.

I was just giving you a hard time Jon! Good questions and again, thanks for following along.

I'm using 1 pound EPS as the core and it is something like 92% air and pentane (the blowing agent trapped in the eps beads). It's pretty interesting stuff, you can walk on it and the foam will compress, but it regains it's shape in a few minutes. Unless you rip the beads apart, after a day you can't tell you walked on it.

The flex that we are talking about here, is also incredibly minute. Maybe, 1/4" max deflection upon landing or loading up in an aerial. That load is distributed pretty well along the length of the springer. The deck side is a double 2 oz of kevlar and so has great impact resistance (bullet proof! ) The core side of the springer is in tension and so isn't really exerting much in the way of force on the underlying eps, with the exception of landing from aerials. My "hunch" is that will be like walking on the EPS and won't permanently deform the EPS, to the point of disabling the springer's effectiveness - ASSUMING it's effective to start with.

Great question, I appreciate your thinking the structural elements through.

If the springer is effective, I'd like to develop a tray like device that would allow interchanging different springers. Possibly stiffer for bigger wakes with a great lip (or mybe it's softer) and then softer for something else. We've been to numerous contests where the wake is significant different between practice and the contest, perhaps being able to tailor the "pop" of the board could overcome a soft wake on contest day.

Hahah point taken!! Thanks for the explanation, and the tray idea sounds cool/complicated.

Also, My buddy has a new AR-15. If you want to send us the board after you are done with it, I am sure we could test that bullet proof theory for you!!:-)!

LOL - gives me a great theme for a graphic! I think that Kevlar vests have a minimum of 8 layers up to 25. I'm doubtful my 5 layers would stop a .223. I'd bet a .22 short wouldn't exit, though. That's funny...test the boards for exit wounds.

Fin boxes curing. All that's left is to hotcoat the deck, then paint!

The secret to productivity: hotcoat at 4:30 am.

Looks like its snowing

It's 80! Definately not snow.

This board was exceptionally drivey. The springer aided pumping - it would squirt forward powerfully. I was able to fiddle around at the back of the pocket, basically one leg in the curl/wash and it would pump forward. There isn't any useful body of knowledge as to what works or doesn't when incorporating a springer into the onstruction...I don't think I want to be the CREATOR of that info!

I have a few additional CRAPPY PICTURES! They do give a rough idea. We used these cool camera mounts for an HD video camera. Dennis also had a remote so that he could turn the cam's on and off. The mounts are interesting because they have a suction cup base and you can place them anywhere on the boat with a relatively flat surface.

The two cam angles and Dennis with the remote.

The cam's save the video in an .MOV format and my FREE MS Moviemaker application doesn't recognize that so I had to convert from MOV to WMV and the image quality went to crap. Also the one angle we used, probably wasn't a good choice as mostly we got the image of the back of a hairy beast!

Anyway - just for fun, some additional images

So did you like the board? I read this whole thread to not even get much of a review.

Fool!

The springer adds drive when pumping, you can feel there is some sort of pop or snap at the end of a bottom turn or when James was popping off the lip. It wasn't worth the extra hassle of building, but what I don't know is if it can be improved by changing the construction of the springer or by relocating the springer closer to the neutral axis (or for that matter where the neutral axis actually IS in the board. )

I liked how snappy it was, how much squirt the springer added. It was a HUGE PITA to build and I don't know if this is the best that could be achieved, or if there are improvements that can make the responsiveness better...and I don't think I want to build a bunch to check.

Better?

Much better