Is a parabolic rail solid balsawood ? Thinner strips curved around outline then shaped ?

Is the blank glassed and sandwiched , then rails stuck on , then clear glass all over ? How and where does the sandwich fit in ?
Would love to know the build process .

Overner said..
All depends on whether it is hand shaped or preshaped, pu or polystyrene.

but if you search up Bert Burgers 'Compsand' on swaylocks or Greg Loehrs WMD with warvel foam you should find a technical outline of something fairly similar to what I do.

But if you don't have a rocker table (which I don't) then ply stringers are a must, in my opinion, as there is a tendency for the boards to warp in the bag even in fairly low pressures. I have used rocker sticks for years and they are just not up to the job.

Or have a look at Mark Stones vid of Jaegar's 60litre board. I found it on Vimeo / Contenent 7 website.
I have my own idiosyncratic parts to the process, but everyone builds boards subtly differently based on their skills and general competency. I know my failings and have found workarounds. Thin ply stringers being one such crutch.

I can't find the build on Continent 7, Do you have a link or title? Cheers . If there's a way of making a sandwich construction without wrapping the rails, I'm keen!

Thanks, Overner, build threads are the best!

Imax1 said..
Good vid , but I still want to see how parabolic rail is done on a EPS windsurfer with sandwhich construction . A surfboard over a PU blank seems simple enough .

I watched Bert do his, top and bottom bagged on, with square rails, strips of balsa wrapped around and glued and shaped the glassed over the top

Mark _australia said..
Many ways to skin a cat.
Personally I vac corecell on with a rocker spine and no bending or warping. If I'm being reallllly fussy like for a speed board the back 1/3 has moved by 0.5 - 1.0mm and needs a bit of tidy up with some filler before and after bottom lam.
No longitudinal twisting that I can measure.

Interested in all the other ways though as they can really help with surfboards and really light SUP builds that do want to bend lots

Ah now, this is the competency I talked about earlier. If you've got it, flaunt it! Go Mark!

Rocker sticks are a constant frustration for me. This latest freestyle board being the last straw. I am going back to what works for me. Now there is the possibility that the rocker stick did its job, but the blank being a PU Blank, which I bent to shape in the bag was the problem. It may have returned to shape after I pulled it out the bag. I am not dismissing that as a possibility. But I used the rocker stick at each stage of bagging and the rocker is not what I planned - it should be flat from tail to 120cm point. It has 8mm of rocker over the last meter of the board, which should not be there.

My problems with rocker sticks may also have something to do with my vac bagging etiquette. I am making this up as I go along, so my technique may be shockingly bad. I don't know.

I live right next to where Corecell is imported in the UK, and over the years I have tried different materials to decide what I like best. The importer would always steer me back towards Corecell, despite having PVC (cheaper), PET and Balsa (cheaper, brittle, heavy) on offer. The importer always said that for frequent low load impacts (like we get in general sailing with windsurfing) Corcell is the best performing foam. It is also ductile and easy to use.

Personally, I found Airex C70.90 is a little bit better in compression (it feels a bit tougher and absorbs a lot less resin) and Airex R63.80 is bendier for rails. But this is a personal preference, rather than anything based on actual scientific data.

I have, in the past, bent the Corecell around the blank, but... I made mistakes. Things like over heating the foam and it goes a toffee crispy yellow and collapses. Or overheating the foam and melting a bit of the polystyrene so the shape needs fixing. Or parts haven't stuck down in the bag properly, or I have added too much pressure to get the bits to stick down and give the board a monoconcave that it really should not have had...

Too many mistakes. So in a typically British way I have gone; "Sod that for a game of soldiers." and figured out a way that means I cannot make the mistakes I know I have made in the past.



Mark,

Out of pure nosiness, and please feel no pressure to tell me if it is a commercial secret, what thickness of sandwich do you use?

I tend to use 8mm hull and deck on wave boards, 5mm on freestyle / flat water boards, and 8mm on foil boards. This, in part, is the reason I don't bend the foam around the rails. When I have had success bending the foam it has been 3mm thick, but then there is the need for double sandwich and it all gets heavy and mistakes double.

Te Hau said..
Hello Overner,
Lucky man, you can still get Airex, it's so easy to wrap and vac.
It dried up in NZ years ago.
I still have some left and so I have been building using Corecell for the straighter mid 150-180cm of the board and Airex for the front and back 30cm. No heat forming necessary.
That's mighty thick skins you're using. 3mm is plenty I reckon since the modern PVCs are so strong.

Hi Te Hau,

I thought as much, given no other builder seems to have a problem getting the foam to wrap.
The thicker foam or honeycomb does come with advantages though.

Gestalt said..
VERY recently picked up some 3mm 100kg and 30mm 250kg recycled pet material.

The 3mm sandwich core is flexible and about $11 per sqm. Ticks a lot of boxes. Gotta ise it to see how it works.

Hi Gestalt,

PET, especially the recycled stuff, is in my experience a bit of a variable mixed bag. You may find it brittle compared to pvc or core cell. I also found that there was variable structure, lots of holes that needed filling in the foam. It was also resin hungry and bit heavy for our purposes. The SUPs I made with it were a bit on the 'big boned' side.

You may also find sanding difficult as it is also very tough. The glue lines also present a problem and you will get some show through in your laminate, which will need filling.

I also cannot remember if you can thermoform it, as I don't use this technique in my builds. If I remember rightly it does Hotwire very nicely, and this I found helpful in shaping my rail bands.

Overner said..

Gestalt said..
VERY recently picked up some 3mm 100kg and 30mm 250kg recycled pet material.

The 3mm sandwich core is flexible and about $11 per sqm. Ticks a lot of boxes. Gotta ise it to see how it works.

Hi Gestalt,

PET, especially the recycled stuff, is in my experience a bit of a variable mixed bag. You may find it brittle compared to pvc or core cell. I also found that there was variable structure, lots of holes that needed filling in the foam. It was also resin hungry and bit heavy for our purposes. The SUPs I made with it were a bit on the 'big boned' side.

You may also find sanding difficult as it is also very tough. The glue lines also present a problem and you will get some show through in your laminate, which will need filling.

I also cannot remember if you can thermoform it, as I don't use this technique in my builds. If I remember rightly it does Hotwire very nicely, and this I found helpful in shaping my rail bands.

I suspect we are not talking the same stuff. What i have comes in a roll, is not heavy, has no glue lines and is treated to prevent resin uptake. It does seem brittle if bent to far or against the roll curl.

Whilst it May not be exactly what jp use i'd bet its not far from it. Plus its good for the world.

I had many conversations with the australian importer whom also used to supply products to cobra.

Still i need to actually laminate it to fully know.