Rotomolded composite surfski process

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1 year 4 months ago - 1 year 4 months ago #38793 by Steve Hansen
I'm trying to wrap my head around how one makes a rotomolded composite surfski. Is the carbon/kevlar cloth minimally layed up on the two halves of a mold, bladder inserted, then mold halves put together, resin inserted, mold spun, bladder pumped up to create a vacuum? Is this the future of surfski manufacturing ?
Last edit: 1 year 4 months ago by Steve Hansen. Reason: spelling

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1 year 4 months ago #38794 by zachhandler
I think “rotomolded composite” means they have mixed another material such as finely chopped fibers into the molten plastic prior to doing the rotomold process. 

Current Skis: Epic v10 g3, NK 670 double, NK exrcize, Kai Wa’a Vega, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy

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1 year 4 months ago #38796 by Steve Hansen
I was specifically thinking of the Kai Wa'a skis. I was under the impression they were somehow rotomolded because they are seamless. They are seamless, right ? Anyone familiar with how they are manufactured ?

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1 year 4 months ago #38797 by TomVW
I also wonder how these seamless surfskis are built. Nelo is also building seamless skis, using what they call the "Unico" technology. From the name, they seem to imply it is a "unique" shell instead of hull and deck, but I don't know how they do it. I googled it in the past and came up empty handed.

I don't think it is quite the same as rotomolding plastics. My guess is that it must still be two parts, but that the seam is invisible, perhaps simply recessed and gelcoated? I tried peeking inside through the breathing hole of my Nelo 550, but couldn't see anything...:-(

Perhaps Ranga could tell us more?

 

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1 year 4 months ago #38798 by Steve Hansen
Exactly. The process for rotomolded plastic kayaks is relatively simple. Ranga was the first person I thought of too !

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  • MCImes
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1 year 4 months ago #38799 by MCImes
Replied by MCImes on topic Rotomolded composite surfski process
Im not exactly how they do the initial layup so would be interested to know how 2 halves become one, but I heard for Ozone boats, they use an internal bladder that is inflated, then the boat is cured in an autoclave. After curing the bladder is removed via a triangular hole left in the hull just behind the bucket (or seat on an OC1). The triangular hole is then carbon'd over as the last construction step before sanding, priming, and painting.

I do know that there truly is no seam on Ozone boats (and probably nelo as well). Its not hidden, it does not exist! I would be very curious to see a layup layout of how the Uni/Prepreg carbon is oriented

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  • Jef58
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1 year 4 months ago - 1 year 4 months ago #38801 by Jef58
Replied by Jef58 on topic Rotomolded composite surfski process
The inflated bladder has been around a long time and is used in some carbon bicycle frames. I had one manufactured like that and they can be very light and strong. I suspected that was how those skis were made and is very conducive to work on the shape of a surfski. The layup of materials can still be controlled to give strength, flex, etc where needed. It would be nice to see more of this concept out there. 

Typically on a bike frame, the triangle is final bonded to the stays, but a ski has one nice fluid shape.
Last edit: 1 year 4 months ago by Jef58.

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1 year 4 months ago #38803 by Ranga
Rotor molded is a closed mold process with powdered plastic put inside before closing the two or multiple segments then heated and rotated and rocked like a see-saw to disperse the plastic throughout the mold which then melts and forms the shape.
One piece skis are quite different to that. Difficult to find any info because the process is confidential and not something you want others knowing how to do it. Nelo surfskis used to be one piece but are no longer, their kayaks are still one piece.
The process is similar to conventional two piece manufacturing that is top and bottom half is laminated as usual and then as mentioned before a bladder or balloon is inserted before the mold is closed, obviously the seam material is added before closing and then the bladder is inflated to move material to the mold surface, mostly the seam and then a vacuum is pulled to compress the laminate which is then cured under heat. The same bladder then becomes a vacuum bag as to get enough pressure with inflation will make the mold way too expensive to make strong enough, no problem with round tubes for a bicycle frame and small parts but quite expensive for a 6m long ski, it would have to be a solid aluminium mold to stop it exploding hence the vacuum which essentially needs no strength as the forces are equalised from inside to outside as you are only using atmospheric pressure. You will however still have a seam or join line where the two halves join together which still has to be finished off.
The following user(s) said Thank You: Steve Hansen, Watto, kvort, MCImes

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  • Jef58
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1 year 4 months ago #38804 by Jef58
Replied by Jef58 on topic Rotomolded composite surfski process
Yes, the molds are very expensive. I am impressed that someone actually put a ski out there made like this while keeping the price competitive. 
As far as bicycles go, the new flavor is bonding tubes together to eliminate the cost of the various sizes needed for the triangle. So the one piece are limited to very untraditional looking frames like time trial and tri bikes. A ski can get by with 2 or 3 different molds depending on what type of ski they want to build, but still an initial cost. Maybe he will only do the 2 models...

I'm not sure how expensive a traditional mold for a ski is, but the one piece is definitely a much more costly process, especially given the size/length.

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1 year 4 months ago #38826 by bradgross2013

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