I'm building a 6'4'' Hollow Core Cardboard Fish

I will say this, hold the board up to the light and it looks friggin awesome.

Was that you guys (shrunkenhead) in Foam E-Z the other day getting some fins and Probox inserts?  If so, the board looks great and I have to agree with Yarnes that when we held it up to the light the board looked friggen awesome!

Good build!


here's a hasty shot of the board at Ray Bay which shows more of my happy son (father-son project) than the build.  He was super stoked to finish it, and yes, he brought the board into the guys at Foam-EZ "to match the color of the fins we're gonna buy just right"


What kind of vent thingy is in the center there?  Gore-tex by chance?


Center vent IS the Gore-tex vent that is the "retrofit" version we got from FoamEZ.  We glassed over the edges of the vent as well as the (couldn't stop my son) FOUR proboxes. 

Gotta say doing the fin boxes is much more tricky than in a standard foam board.  Had to cut out the "bottom", glass it in (since there was nothing to stick it to), then stick the box in.  We decided against making a supporting bottom block or gluing more cardboard onto the other side so we could keep with the translucent effect as much as possible.  Since we (I) was worried about the board being watertight and strength (he is 14 after all) , I put glass over the boxes too.   

End result is a cool looking board.  Stops people when they see it here in Seal Beach.  It's not really super light (since it has like 14 oz glass on the top and 10 on bottom),, but if I were to do it again, I could make  it lighter for myself (just two glass-on fins), stingier on resin, etc.

My son is smiling, and that is more than worth it.  Just gotta see how it does when he gets slammed.  Concerned about Gore Tex, since I used to mountain climb a lot and know its limitations. 

Son's choice onthe vent--was worried he'd forget to close the vent, since he sometimes forgets to put his leash on .  Did I say he was 14?


Good point.  I went with 2 plugs, and Pete C has been on it, letting me know what to expect from this vent.  I believe we are pushing its boundries a bit, 2 should help.  And, this is sways, pushing boundries is what we do.   I stuck on more glass than your board, but used 4oz S-cloth.  4-6-4 both sides.  We have jagged reef out here.  The water is more floaty due to how close I live to the equator, so I should get good buoyancy.  The next Sheldrake build will have less glass, and be cut lapped.

Heres the posts for the Gore-tex vents you can get from Foam EZ, by Pete C.



Your sons 14?  This site should be good for him, if he were to ever want to learn board making.  Treatosea as well.  And other sites…

The fins, on my son's board were tricky,,the Proboxes are usually pretty easy...but on this board, we had to carefully trim the core once we cut through the lam.  It was easy to get through the skin, but I made the mistake of pretending the cardboard core was like foam and used the router.  Large mistake, since the bit easily handled cardboard as long as you didn't try to router the cardboard from the flat side.  If you did, it would jump and I chunked a good slice from the lam and significantly enlarged the hole on one of the boxes. 

After trimming, such as it was, I laid in 4 oz e glass and 6 oz s glass in each hole with a small overlap all around the hole's edge-- over the board's bottom surface (like 3/8 of an inch, or so)---  and carefully resined two boxes at a time in.  I was trying to make a little pocket in each hole to work with.  I took an insert and covered it in plastic wrap, then placed it (gently) into the fiberglass pocket while it was curing and flattened out the edges of the cloth that were above the hole. 

 I kept a long aluminum level with a weight on top  touching two boxes at a time so that the pockets would level, wouldn't float up, and be easy to do the final glue in.  It is important, because during the lam stage, it is actually hard to figure out what level on the board is...the bottom really isn't completely flat, and the core kinda gives you a little bit of an illusion.

Once the pocket was hard, I sanded and feathered out the overlap on the board's bottom, then... I resined in the box (again with the level across two boxes at a time) and waited for cure.  After that, I took a pull-saw and flush cut the flashing on the box, rather than traumatizing the board again with my router or sanding through the lightly resined bottom lam. I then used my younger son's play doh to cover the grub screw holes

Then we put another, carefully trimmed 4 oz oval piece directly over each box and resined each one over, covering the slot and overlapping the initial glass for the bottom of the box, so the oval piece overlapped like three quarters of an inch away from the plastic around the box.  We kept some wax rubbed in the main slot to keep resin out ( mistake, we found out later, since we didn't fully wax every slot).  .

I then took a razor and sliced out the cloth away from the slot with when the resin was set enough, but not completely hard.  At the end, I took a Dremel (but a drill would've been fine) and ground out the grub screw slots.  I knew I was deep enough with my Dremel when pink Play Doh showed up

Two pic's highlighting the mistake and recovery.  One is the munched hole (the one with the fin in the box) as evidenced by what looks like extra white stuff outside the plastic box.  The other is what happens when you try to dig resin out of a plastic finbox. The resin extraction kinda scarred the plastic, but it is fully functional.   

Speaking of fins, thanks to Nick for hitting me up about making some customs for this board.  I've been looking for a good reason to make some hollow wood fins for a while now - just haven't gotten around to figuring out the bracing.  Here's what we'd agreed upon so far:

After taking a look at a close-up shot of the bracing pattern for the Sheldrake design it became apparent how the joints work - twice as many notched on one side (SS) as those with alternating notches (DS).  I had a chance this morning to do a quick mock up with some 1/8x3/8" strips of cardboard testing that idea, and yeah, it went together like buddah. One tough, rigid little sample . . .hmmmm . . .  

I'll have a chance to repeat with wood this evening and let you know how it goes.  As you know, there is some flexing that needs to take place in order to put those last strips in and that could determine which wood is to be used.  On the other hand, it might not be a problem at all . Until then . . . 

Yo, Camplus. Your fins are going to out-do my board for sure!

Just a minor update on the build.  Brads package from Foam EZ showed up today.  Tomorrow I will start the install of the Lokbox fin system.  Wish me luck.  Also, Pete C’s Gore-Tex vent plugs arrived.  Im thinking about where to install them at the moment.  Probably near the tail, both sides???  There is some debate to why they should go towards the nose, but these puppies never have to come off.  So, I think it should be ok to put them there. 

-Anyone do custom board bags? Im looking for a hollow core design.  Something along these lines, only in honeycomb translucent styling… Just kidding :wink:




AW SNAP!  Literally! This one's going in the "old enough to know better - too young to resist" file.  5mm birch ply strips, 3/8" wide with the notches cut 90deg. through like the cardboard. 

The smart side of the brain was telling me that I wouldn't get enough flex to put that last run of strips in without snapping the grid.  The hasty side of my brain that told me to go ahead and try it anyway . . . No worries though Nick!  I'm setting up the jig for 60deg notches tomorrow and moving on to phase 2 (halo casting) shortly thereafter.  I'll keep you posted.   


Woody-O wanted an entire board made out of balsa.  I figured balsa would need an angle cut like you just discovered, at an angle of approx 45-60 degrees or so. to allow the board to shift into position, or align from a grid pattern to the Star of David honeycomb.  The cardboard allows for flex, as shown in Post #5, on top.  But, perhaps Im missing something, and your doing it a different way.  Either way, im just going to sit back and enjoy the show! These fins are going to be sick!!!

Yep.  Wood is a whole different animal. Cardboard will allow for enough compression on the edges of the joint to get that ‘shift’ you mentioned above.  A 30deg. notch would probably be enough to get wood to shift that little bit more and 60deg. would be a perfect fit.  I’ll go with the 60deg. joints and have it looking as straight as Taylor Swift’s new hair-do.  And like Rhianna’s new tat reads: ‘Not a failure but a lesson’ (is anybody else’s mind being consumed by useless informaition like this every time they log into their email?)

In the meantime we need to see some shots of those fin boxes going in.


Notches being cut in 1/8" x 3/8" paulownia strips (8) on the radial arm saw.  They're taped together on the underside with masking tape to keep the index accurate. Also blocked on the front side to keep the sections from blowing out while cutting.

Single-sided, notched at 30deg strips come together to make a skewed grid.  Intersections @ 60deg (or 120deg depending on how you're looking at it). 

I figured out last week that it would be easier to cut the second notch in the double-sided strips in place, while the grid is assembled.  Getting the double sided strip to match up perfectly using prefab/hand methods was not happening. One slightly off cut or misaligned strip in the group, and the whole run is off.  In order to be able to cut the grid like this, without all of the sections blowing out, I spanned each cut path with masking tape before cutting. Note top LH corner - first cut, first blow-out before using tape. 

Here's the finished blank I'll be using to cut the fins from.  Right now it's being laminated to a layer of 9oz e-glass with RRblue epoxy and weight-clamped. I'll leave it overnight and hit the wood with a cheater coat of epoxy in the morning and let drain upside down while laminating another layer of glass on the flat side. All stuff that has to be done at some point in the process, but now makes the most sense in terms of stabilizing the grid for cutting and foiling.  Until then . . .

Hey Nick!  Thought I'd spare you the boring update from yesterday's lamination and cheater coat on the blank, and show something a little more exciting today . . .

Here's a shot of the paulownia grid with 9oz glass just pulled from the platen.  The translucency gets even better with a hotcoat, as I found out putting that cheater coat on the yesterday. 


I decided to cast the halo independently of the grid in order to get a really clean inside line, and not worry about one of the joints somewhere leaking into an adjacent cell (absolute nightmare scenario).  I made plugs out of 1# EPS so that I could dig them out of the cast halo instead of trying to pop the halo off of a rigid plug and snap it.  It's cast with the same RRepoxy I'm using for glassing, only with copious amounts of milled fiber, pigment, and strategically placed roving added. 

The mold that I cast into is the same one I use for casting halos on solid wood fins.  Yep, silicone and marine vinyl are pretty useful for epoxy applications. Here's the EPS plug being dug out of the center of the halo, which was then carefully pulled from the mold.  I definitely did not skimp on the mold release on this one!

Now we're getting somewhere, eh?  Just the raw castings here (flashing removed) on top of the grid, but the realization is a bit clearer now.  I'm clamping these halos to something flat and running some post-cure cyles on them this evening in a craft oven (130-150F) before messing with them anymore.  Next step will be to fit and fillet glue the grid in, then foil.  Until then . . .

those are going to be some sick fins… very very cool

Wow, I am impressed and very happy that these are going to be on my board.  I must say, you have talent!

Thanks guys!  I'm having a great time making them, and have to admit I'm a bit jealous that Nick is getting the first-of-a-kind of these. However, they were his idea so . . .I got a chance to foil them this afternoon.

Used the 3" disc with 80 grit paper on the angle grinder to rough them out, then switched to 120grit and the orbital sander to blend.  Pretty much like foiling solid material, but a lot more pulsing the grinder than actually running it.  That material comes off quick!

Being able to look at the cross-sections of the foil while shaping was pretty interesting, and made matching them up that much easier.

Here we are (again) figuring out how to glass the tops while spanning the voids, trying to avoid sagging, pooling, dry-weave, etc. . . . I put the fins in a vac bag and tried pulling different levels of vacuum on them to get the desired effect. As you can see, the bag cups pretty readily into the hexagonal voids.  Decided to just laminate a layer of 6oz glass onto my platen, peel, cut to shape, and vacuum bag to the fins as a cheater laminate.  I have a sample of a single layer panel like this that I made for another project and it looks like it will take the form easily without sagging in the voids. We'll see. . .    

Looking good Camplus, impressive stuff!

QUOTE: "Thanks guys!  I'm having a great time making them, and have to admit I'm a bit jealous that Nick is getting the first-of-a-kind of these. However, they were his idea so . . .I got a chance to foil them this afternoon. "





Alright, seriously...I imagined fins that would match the board, but this is just too much!  Camplus, you have taken a single idea-my thought from seed- and turned it into art.   I don’t disserve any credit here aside from pushing the ball into your arena.  I think these are the coolest fins I’ve ever seen, period!

Aw c'mon! We'll just call this one a product of collaboration.  Besides, I'm surprised one of the elder Swayfolk hasn't piped up yet and said something like: "Yeah, me and Barney Dingleberry made a bunch of these in the mid-50s' for Jimmy Witherballs Surfboards.  They worked ok but . . ."  Anyway, here's a shot of them in the bag getting those cheater laminations put on.

So, the single layer 6oz glass panel works. As you can see, I cut the skins smaller than the halo frame they're being glued to. When I tried a test run with over-sized skins and the fins raised for the overhang to clear, I got a pretty good look at how the compound curvature made the edges very wavy (think lasagna noodle).  I figure it's only necessary for the first layer to seal and bond to the grid anyway, so I cut myself some slack and got rid of the extra material and riser blocks.  The edges of this first skin will be feathered into the halo frame before adding subsequent layers. 

Good thing about those glass skins is that they're able to resist cupping into the voids under the vac-bag's pressure.  That nice, smooth, spanning transition here should mean they'll glass up like solid wood fins once they're out of the bag and cleaned up.  So, looks like the next update will include the tabs being cast on and a look at the finished product . . .