Hopefully a quick question for the board builders..... i intend to make a 3mm pvc sandwiched float'n'ride board, and i have a visualisation problem with the sandwich. What i assume is the process is: 1.hotwire the rocker and deck. 2. template. shape in any bottom contours, but leave the rails square? 3. vac on the bottom pvc (plus glass/reinforcements) so that that it reaches the square rails? 4. shape the deck and rails top and bottom, but leave an 'edge' running through to the nose, where it would normally be soft??, but shape the tuck through to the tail. 5. sandwich the deck, with the pvc and glass lapping onto the bottom pvc? 6. fine shape the rails, softening the pvc join in the front of the board, but obviously leaving the rails harder in the tail.
My visualisation problem is the softer rails in the nose, and the risk of shaping through the pvc, or do i literally only have to take the 'corner' off the pvc? Cheers all, great forum!

Yes, leave bottom square, vac the PVC, then shape the rails, allowing for the extra 3mm to go on top.
With the top PVC, run masking tape around the perimeter, this helps stop it from cracking when you preform it round the rails.
Leave it about 2cm bigger than needed, this helps the vacuum bag pull it in. You can then cut the excess off after wards.
Some people fix a strip of PVC along the bottom where the edge of the top wrap comes, to prevent possible cracking from the tight bend, but I haven't found this necessary with adequate preforming.

Gluing pvc around rails is the best way to go. Not easy, thermophorming and masking is tha way to go. An alternative that can be acceptable even more for a personal garage build is to not warp rail with pvc, add fiber strip renforcement instead then be carreful to warp rails with all fiber layers. After full shape finish I warp rail with biax glass 300gr/m2, epoxy mastic, let cure, sand prep then i bag top and deck skin, sand flush, then lam warping rails.
Many cobra boards build i repair don't have sandwich material warping rails and no fiber add, over sanded instead. No good.

4. shape the deck and rails top and bottom, fully shape them so the bottom tuck is rounded like a finished board. 5. Pre shape the PVC around the rails with a heat gun then sandwich the deck, with the pvc over lapping about 10mm onto the bottom pvc.

Yes that works as well, but you always have to allow for the extra 3mm.
If you fully shape the rails then put the bottom on you're going to end up with extra tuck, that's why I glue the bottom PVC on flat, then shape the rails. I then only have to allow for the rail thickness and not the tuck.

Decrep i reckon he was talking about bottom already on as per the OP...
I am sure the 3 of us do it the same, based on your previous posts. Unsure what you mean about allowing for the 3mm in rail shaping?

The only allowances i make are obviously 6mm or 8mm thinner cutting the blank and 6mm narrower cutting outline.
Then as per Jontys list, once the bottom is on, shape deck n rails starting with tuck and finishing very carefully to not fk up rail apex. Then the only other allowance is made - a tiny bit more tuck to allow for bagging the deck sandwich as the pvc around rail will always sit a bit proud and you dont want to have to shape in more tuck later as you thin the pvc... bad bad.

Jonty i have no idea what you mean by point 4 or the question
There should be no sanding back the pvc on deck or rails, save for a little smoothing and filling some relief cuts you made. The best way i ven describe it is once out of the bag and the excess deck sandwich is cut off flush with the bottom, it looks 100% like a finished board. To a non watersports person its all homogenous they wouldnt know there is stryro in there. If it's ideal! But there will always be cracks or relief cuts u made, maybe a wrinklw bubble with lack of adhesion onns difficult bit

Its hard to do... but soooi rewarding and i am thus not a fan of shortcut rail techniques, gluing bits on to avoid the hard steps
So much strength is in the rails so why do it surfboard style (sorry lemat)

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Mark _australia said..
Decrep i reckon he was talking about bottom already on as per the OP...
I am sure the 3 of us do it the same, based on your previous posts. Unsure what you mean about allowing for the 3mm in rail shaping?

The only allowances i make are obviously 6mm or 8mm thinner cutting the blank and 6mm narrower cutting outline.
Then as per Jontys list, once the bottom is on, shape deck n rails starting with tuck and finishing very carefully to not fk up rail apex. Then the only other allowance is made - a tiny bit more tuck to allow for bagging the deck sandwich as the pvc around rail will always sit a bit proud and you dont want to have to shape in more tuck later as you thin the pvc... bad bad.

Jonty i have no idea what you mean by point 4 or the question
There should be no sanding back the pvc on deck or rails, save for a little smoothing and filling some relief cuts you made. The best way i ven describe it is once out of the bag and the excess deck sandwich is cut off flush with the bottom, it looks 100% like a finished board. To a non watersports person its all homogenous they wouldnt know there is stryro in there. If it's ideal! But there will always be cracks or relief cuts u made, maybe a wrinklw bubble with lack of adhesion onns difficult bit

Its hard to do... but soooi rewarding and i am thus not a fan of shortcut rail techniques, gluing bits on to avoid the hard steps
So much strength is in the rails so why do it surfboard style (sorry lemat)

For sure warping rail nicely with sandwich material is the best way to do. Need time and technic no short cut here to do it, that's way guys should buy custom made by a caring craftsman.
My alternative of reinforced fiber rails is just an "acceptable"(for me) way to compensate a garage builder lack of technic. It's easier to shape without bottom sandwich set, after rails fiber reinforced board is stiff, far easier to bag skin even more without rails warp.
To do this i use to make a small step on flat to compensate renforcement thickness. Here on a surfboard lap.

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Mark _australia said..
Decrep i reckon he was talking about bottom already on as per the OP...
I am sure the 3 of us do it the same, based on your previous posts. Unsure what you mean about allowing for the 3mm in rail shaping?

The only allowances i make are obviously 6mm or 8mm thinner cutting the blank and 6mm narrower cutting outline.
Then as per Jontys list, once the bottom is on, shape deck n rails starting with tuck and finishing very carefully to not fk up rail apex. Then the only other allowance is made - a tiny bit more tuck to allow for bagging the deck sandwich as the pvc around rail will always sit a bit proud and you dont want to have to shape in more tuck later as you thin the pvc... bad bad.

Jonty i have no idea what you mean by point 4 or the question
There should be no sanding back the pvc on deck or rails, save for a little smoothing and filling some relief cuts you made. The best way i ven describe it is once out of the bag and the excess deck sandwich is cut off flush with the bottom, it looks 100% like a finished board. To a non watersports person its all homogenous they wouldnt know there is stryro in there. If it's ideal! But there will always be cracks or relief cuts u made, maybe a wrinklw bubble with lack of adhesion onns difficult bit

Its hard to do... but soooi rewarding and i am thus not a fan of shortcut rail techniques, gluing bits on to avoid the hard steps
So much strength is in the rails so why do it surfboard style (sorry lemat)

Point 4 means rather than completely shaping the rails soft all the way to the nose, once the bottom is on, if i left a chamfer, the deck pvc would sit better, avoiding causing a thin strip when i trim it back...... i think. I meant trimming and tidying the pvc rather than reshaping.
I do intend to make an 'elevated wing' which would be difficult to wrap in pvc, so think I'll shape it in a thicker piece of pvc, rather than eps and glass it in.
Thanks for all the advice from everyone, I'm hoping to take the build slowly, as i normally have no patience, whick leads to f..k ups!

Oh so this is boxy or rail bevels and u mean to take the bottom sandwch part way up rails...? Thus trimming at a line where meets deck sandwich..?

I think jonty means whether the front rails need to be soft or can he get away with chamfered to make it easier to build? Not sure if that's what you are getting at jonty.

my vote is for soft forward of mast track if not earlier

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Gestalt said..
I think jonty means whether the front rails need to be soft or can he get away with chamfered to make it easier to build? Not sure if that's what you are getting at jonty.

my vote is for soft forward of mast track if not earlier

yes, definitely going for soft rails , surf style, but just cant really visualise how the pvc wraps without either making a hard edge, or thin spot. I guess I can try on some foam scraps.

After making a drawing, showing the layers, it makes more sense, and the deck pvc just changes the rail shape a bit, and moves the apex out slightly..... i think. Sorry for the confusion, and my inability to explain....

We should make a new rule,

post all build photos , "and drawings"

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Gestalt said..
We should make a new rule,
post all build photos , "and drawings"

But I never make any drawings, just scribble on the wall.

But yes it certainly helps to draw the rail profile, with the inner core and the d-cell around it.

That's what I meant by allowing for the extra 3mm when shaping the core. The rails will end up 3mm thicker, than the core shape, on edge and top.

Yes - helps to make a rail template then a different template to use when turning the rails - with bottom on but no deck sandwich on

Jonty now i know what you mean.... yes you will need to remove the tiniest bit at the bottom 'seam' for rounded rails. But not much

And you remove the bit that overlaps the bottom PVC anyway. PVC should remain full thickness over the core