You blokes jinxed me.

Broke my router today....................

decrepit said..
Nice and neat Mike, my freehand routing left a few gaps, I've been working more bog into them today.

Thanks mike. As you know tge tighter the fit tge less bog and less added weight, I used 60ml ogtr resin for 4 boxes and glueing more on to make thicker blocks.

^^^ from memory 14mm and 16mm segmented..... so two layers does a mas track nicely.

Then a big sheet of 25mm being saved for best :)

This is the outside skin thin probably 2 or mmaybe 4oz glass, wood, more 2 or 4 Oz glass, then paint. It's going to be tricky feathering such a thin layer of glass for my layer of glass to stick to. Very easy to sand through to the wood.

Dodgy pricks using XPS over EPS, would be nowhere near as strong.
Has it been previously repaired? I'd hope so as JP / Cobra would surely not do that?


(wouldn't bet my last dollar though, that's for sure....)

So the HD foam blocks are stuck in with Q Cell and Resin and weighted down?
Before you applied the bog was there a layer of glass applied, or the only layer of glass is the final layer(s) which you feather into the existing board structure before routeing out the fin box holes?

^^ I say it is wrong though as XPS tends to offgas and delaminate unless it is treated right (and the hurry hurry in Cobra will ensure it is not cut, offgassed under temp, then used....)

I'd love to see their advertising blurb from that year as the layup pics in the brochure re often very different from reality......
"Full carbon" - one strand end to end, patches under heels

lol

decrepit said..
Mike, how thick is the blue stuff???
Stiffness varies with square of thickness, and I guess it's a 1:1 ratio with density. So if it's 5mm thick and 35kg/m3 it's going to be stiffer than 3mm of 80kg/m3. And the timber looks after the impact problems. It obviously works, and it could be lighter. 3x80 = 240, 5x35 = 175 + timber?

Mike its 5mm thick same as the 5mm thickness i use on the bottom of boards, So as stiffness is related to the distance between the two skins dispite their density they would be the same stiffness, but one would be lighter and dent more easily hence the wood to stop dents and possibly resist compression of the outer skin when landing jumps. I googled pine "Radiata pine is commonly regarded as a 'medium' density softwood, with typical average tree basic density values of 400-420 kg/m3." Maybe the wood has better compression resistant properties than a thin layer of 160gm or 200gm glass. the wood looks to be between 0.5mm and 1mm thick.

Mark I've read about outgassing and epoxy not sticking well to XPS but the stuff is stuck pretty good. 2013 FSW

What we are all forgetting is the blue Dow XPS has some Polypropylene incorporated into it somehow which is why we have so many delam issues. Its not just the outgassing but the PP. If you have ever tried to stick stuff to PP you would know its almost impossible.

What Cobra are using must be using is a true XPS manufactured for this purpose, not a foam dedicated for insulation purposes that board builders have stolen and tried to use.

I was dubious when i first saw that construction but i can't say I've heard of bulk failures (or any tbh), and its used more widely now across the JP range especially in the SUPS so it must be working.

When considering the stiffness of the veneer it acts like a layer of unidirectional since the fibres run pretty straight if the grain of the wood is true. Agreed its impact strength and ability to handle compression is key in its performance.
The thickness if the wood veneer has the effect of bulking up the outer laminate which we all know will increase compression strength and stiffness of the sandwich.
0.8mm of wood is worth about 600GSM of glass to get the same laminate thickness in a wetlay which would add considerable weight.

As Decrep says Stiffness is not related to density, it is actually related to the Young's Modulus Mike.

Bertie said..
What we are all forgetting is the blue Dow XPS has some Polypropylene incorporated into it somehow which is why we have so many delam issues. Its not just the outgassing but the PP. If you have ever tried to stick stuff to PP you would know its almost impossible.

What Cobra are using must be using is a true XPS manufactured for this purpose, not a foam dedicated for insulation purposes that board builders have stolen and tried to use.

I was dubious when i first saw that construction but i can't say I've heard of bulk failures (or any tbh), and its used more widely now across the JP range especially in the SUPS so it must be working.

When considering the stiffness of the veneer it acts like a layer of unidirectional since the fibres run pretty straight if the grain of the wood is true. Agreed its impact strength and ability to handle compression is key in its performance.
The thickness if the wood veneer has the effect of bulking up the outer laminate which we all know will increase compression strength and stiffness of the sandwich.
0.8mm of wood is worth about 600GSM of glass to get the same laminate thickness in a wetlay which would add considerable weight.

As Decrep says Stiffness is not related to density, it is actually related to the Young's Modulus Mike.

Thanks Alex always good to have your composite and engineering knowledge on here. Do they need a layer of glass between the wood and XPS or could they have taken that layer of glass and put it on the outside and added to the other outside layer?

Sanded through paint down to the glass

Template matching the jig.

R1DER said..
Freehand routing, I know my lines are a bit wobbly.

Mine aren't any better.
But I get the best results dragging the router towards me, so my eyes, the line and the edge of the cutter are in the same plane

Today mixed 45 ml resin wet out 3 layers 4oz on plastic also mixed some of same batch with qcell to bog up air holes, layed glass over boxes squeegeed down left to dry. 1st layer meets up with boards sanded layer.

How will you get the fins in?