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Bomb proof board from XPs insulation foam

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DartBoard
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Bomb proof board from XPs insulation foam

Postby DartBoard » Thu Jan 12, 2017 4:14 am

Office was closed for 3 weeks so I had a chance to get in an build a new board to replace the re-purposed twin tip I've been using for 6 months. The main aim was to make something with a bit of volume and to make it strong enough to take a beating while I learn how to ride in the surf. My old board cracked when I hit a sand bank at speed and over the last month of so its taken on a lot of water!

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Its 125 x 43 x4cm with about 80mm of rocker starting just after 1/2 way. Core is XPS foam insulation board bought from our local hardware chain called Bunnings. $12 for a 30mm thicksheet that we enough to do the board and then some. I put 3mm ply top and bottom over 2 x 7 mm marine ply stringers. With 20mm Tasmanian Oak blocks where the foil connects and where the footstrap inserts go. Then to top it all off 10z stiched e-glass top and bottom and q-cell/resin filler (because the stiched glass has large, random voids between the weave. Final step was to use sugar/resin to create the grip on the deck.

In hind sight I think the ply was unnecessary and leaving them and some of the extra reinforcement out would would have saved a whopping around 1.3kg. In the end the board ended up the same weight as my other one so no gain there - 4.3kg. Too heavy to be a last attempt at a board but great to have something with enough rocker to recover from a touchdown and some volume so i don't spent nervous time dangling in the water waiting and hoping it will float back to the surface.

Here's some snaps of the construction as it progressed.

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I haven't had it out on the water yet but tomorrow looks promising!!

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downunder
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Re: Bomb proof board from XPs insulation foam

Postby downunder » Thu Jan 12, 2017 7:44 am

Hmm,

I did not have much luck with Bunnings and xps. Maybe in NSW is different market with building standards at.al.

Cheers

D.

max
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Re: Bomb proof board from XPs insulation foam

Postby max » Thu Jan 12, 2017 8:05 am

downunder wrote:Hmm,

I did not have much luck with Bunnings and xps. Maybe in NSW is different market with building standards at.al.

Cheers

D.

Great effort Matt. Joke is that I have bought the same foam and am in the process of doing a similar build . . . well . . . the core foam part at this stage. I had not considered using stringers but it seems a good idea . . . helps set the rocker and should provide a bit of structural integrity. I was going to try the kerning method for the rocker so maybe the foam will not be under stress before glassing.

So did you use the glass between the ply and the foam and none on the exterior?

Will be keen to see how it holds up.


Downunder: this is the stuff I bought. It comes in 50mm thick also I think.

Knauf Insulation 1200 x 600 x 30mm XPS Multi-Use Foam Board.
Last edited by max on Thu Jan 12, 2017 8:13 am, edited 1 time in total.

RalfsB
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Re: Bomb proof board from XPs insulation foam

Postby RalfsB » Thu Jan 12, 2017 8:12 am

Last winter I built my bombproof foilboard using the xps core (2 cm thick) and 3mm plywood on both sides plus wooden reinforcements inside. Works fine but is quite heavy.
foil-in-making.png

DartBoard
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Re: Bomb proof board from XPs insulation foam

Postby DartBoard » Thu Jan 12, 2017 10:38 am

RalfsB - love ya work! That looks great and good to that it has held up. I like the stringer arrangement you've got. It didnt' show in the pictures that I posted but I also had short stringer section running across the board and located around where I will place my feet. I took a leaf out of the book of some of the hollow board builders and created effectively a torsion box with the foam being there to prevent compression of the deck. Maybe the ply layers are more important that I thought.
max wrote:
Great effort Matt. Joke is that I have bought the same foam and am in the process of doing a similar build . . . well . . . the core foam part at this stage. I had not considered using stringers but it seems a good idea . . . helps set the rocker and should provide a bit of structural integrity. I was going to try the kerning method for the rocker so maybe the foam will not be under stress before glassing.

So did you use the glass between the ply and the foam and none on the exterior?

Will be keen to see how it holds up.


Downunder: this is the stuff I bought. It comes in 50mm thick also I think.

Knauf Insulation 1200 x 600 x 30mm XPS Multi-Use Foam Board.
Thanks Max. That is uncanny !Yes, it Knauf multipurpose board , the 30mm thick. I think the 50mm would be good for making a board with the rocker carved in. I wanted a lot of rocker for the waves and exactly as you said one of the roles of the stringers is to bend the rocker into it rather than curing the laminate on a rocker table. I was able to bend about 80mm rocker over c. 500mm. I felt like this was about the limit as in one test piece I did the foam did split when I tried to bend it around a tighter radius than that.

I read quite a few posts on swaylocks about using XPS. It was mixed in terms of success people had but those people that did get it to work ( and work really well) seemed to all say that it was important to really rough the surface of the foam up ( a solid sanding with 40 grit after shaping it) because it is genuinely closed cell and so resin can't penetrate like it can into the pores in EPS foam.

Yep, I did use a layer of glass between the core and the ply. 4oz, reasonably resin rich and with a few small holes drilled in the ply to let excess flow out. I also put glass over the exterior. I used 10oz stitched glass because I happen to have it on hand. I did the top and bottom laminates in separate passes so the rails have 2 x 10z glass. Because I was thinking of it as an XPS foam assisted hollow board i figured having solid rails was important to creating the torsion box 'effect' that wooden rails do on hollow boards.

One other thing I found at Bunnings is they now sell Sika polyurethane glue which I used for bonding the foam to the stringers. It came highly recommended by some boat builders who used the ply/XPS sandwich to make quite large structural panels. It requires a lot of clamping pressure to get a strong bond so I only used it on the stringer/core bonding where I could clamp it like a mofo.

Good luck with yours and I'm keen to see some pics as it progressed.

max
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Re: Bomb proof board from XPs insulation foam

Postby max » Thu Jan 12, 2017 12:43 pm

DartBoard wrote:
Thanks Max. That is uncanny !Yes, it Knauf multipurpose board , the 30mm thick. I think the 50mm would be good for making a board with the rocker carved in. I wanted a lot of rocker for the waves and exactly as you said one of the roles of the stringers is to bend the rocker into it rather than curing the laminate on a rocker table. I was able to bend about 80mm rocker over c. 500mm. I felt like this was about the limit as in one test piece I did the foam did split when I tried to bend it around a tighter radius than that.

I read quite a few posts on swaylocks about using XPS. It was mixed in terms of success people had but those people that did get it to work ( and work really well) seemed to all say that it was important to really rough the surface of the foam up ( a solid sanding with 40 grit after shaping it) because it is genuinely closed cell and so resin can't penetrate like it can into the pores in EPS foam.

Yep, I did use a layer of glass between the core and the ply. 4oz, reasonably resin rich and with a few small holes drilled in the ply to let excess flow out. I also put glass over the exterior. I used 10oz stitched glass because I happen to have it on hand. I did the top and bottom laminates in separate passes so the rails have 2 x 10z glass. Because I was thinking of it as an XPS foam assisted hollow board i figured having solid rails was important to creating the torsion box 'effect' that wooden rails do on hollow boards.

One other thing I found at Bunnings is they now sell Sika polyurethane glue which I used for bonding the foam to the stringers. It came highly recommended by some boat builders who used the ply/XPS sandwich to make quite large structural panels. It requires a lot of clamping pressure to get a strong bond so I only used it on the stringer/core bonding where I could clamp it like a mofo.

Good luck with yours and I'm keen to see some pics as it progressed.


A bit ridiculous but I also read everything that i could on Swaylocks forum about the XPS issues and ways around it. Not recommended to leave in the hot sun but usually only develops issues if foam has been compressed like underfoot. This should not happen with your build.

As for the glue, I have used the Aquadere Poly . . . same thing.


I just finished a paipo style board . . . using 15mm Divinycell core . . . 160 by 46 (with about 9 to 9.5cm scoop) and it floats my foil well enough. Decided to build a small 120 by 46 and felt that I needed to go thicker to support the foil. I also know too well that anxiety at times when the board attached to the foil takes a while to surface and when it does, only a foot of the nose would sit above the water. Certainly easy as to water start strapless :D

I have been toying with just glassing the XPS (after inserting a few stringers and reinforcements in certain areas) and double wrap the rails for sure just as a first attempt using this foam. Weight is something I would like to keep to a minimum . . . say around 3 kg as maximum.

I also have a couple of pieces of ordinary polystyrene 20mm thick that I am looking at trying a skinned build like yours . . . again with certain area reinforcements. One of the XPS advantages is the fact that it will not take on water if the outer skin is damaged.

Just wish I had more spare time available at the moment to get further with each of the planned builds. Priority goes to foiling after hours if there is wind. I will make an effort to take some pics along the way with any new builds.

TomW
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Re: Bomb proof board from XPs insulation foam

Postby TomW » Fri Jan 13, 2017 9:25 pm

Guys, Ive built a kite surfboard with xps. You don't need the stringers or wood on the bottom. Shaped the xps, out of 2" xps, had extra 2" layer at nose to get sufficient nose rocker. Used a planer, sureform and 40 grit sand paper.
DSC_0493.JPG

I glassed bottom with rail lapp with 3x 6oz. Deck with 6oz under 1,5 mm Abachi veneer+ 2 x 6oz over wrapped over rails. You want it stronger, adding laminate is most effective gram for gram.
You would need reinforcement around strut attachment.

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Re: Bomb proof board from XPs insulation foam

Postby DartBoard » Sun Jan 15, 2017 8:59 am

TomW that looks freakin' awesome! A couple of questions:

i) Did you use denser foam around the fins or just set them straight into the XPS
ii) Did you do rough the surface of the blank up for better bonding? Did you do anything else to improve bonding?
iii) vac bagged?
iv) How long have you been riding?

Matt

TomW
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Re: Bomb proof board from XPs insulation foam

Postby TomW » Sun Jan 15, 2017 5:04 pm

Yes, I have Divinycell H80 around boxes.
Entire surface of foam is sanded with G40 sandpaper. To bond extra layer I roughed up surface with 40 g sandpaper and used polyurethane glue ( the kind that uses moisture to cure and foams up). Just put some paving stones on it to press it down.
Then using a rocker template on each side I cut it with a hotwire. Same for outline.
But it's totally possible to use saws, planer and sureform. Especially if you keep shape simple.

It's hand layup. First I laminated bottom and rails to stiffen it up. Pigment in the epoxy. Then I v-Bagged the glass and wood on the deck. Then hand layup for last 2 laminate layers.
Using future boxes so those go in before glassing.

Forgot to say I have 2 carbon fiber tow tapes on bottom. 15mm wide each. They run from between boxes to tip, following the edge of the double concave. I have no idea of they are needed.

Been building stuff all my life, made my first skimboard in 1967 ( I was 8 years old) and my older brother taught me how to make a surfboard when I was 14 yrs old. Grew up in Los Angeles....

Been kiting since 2002. Winter here at 56N is a struggle, so building keeps me sane.

DartBoard
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Re: Bomb proof board from XPs insulation foam

Postby DartBoard » Mon Jan 16, 2017 9:09 am

TomW - your experience shows. Its a very slick looking board. Like Max suggested I think I'll try making one without the ply on top and bottom. Maybe thin veneer to help with heal damage. Will probably still add stringers because they are very handy for anchoring the footstrap and mast boxes rather than forking out for carbon and minimum quantity of 80kg foam which local suppliers charge like wounded bulls for.

Max I think your goal of 3kg with this build will be pretty easy to achieve. My beast is 4.3 kg of which the ply is 1kg+. With smaller stringers and not using hardwood blocks around the mast connection and footstrap inserts (Tasmanian Oak) I am sure mine would have been well under.


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