Airex PVC core foam using ?

I wish to know if PVC core foam Airex sheets can be used same like the plywood in a planking on frames or I should have mandatory a mold. Could I curve the PVC foam in a stich and glue boat building process and a hand lay up lamination with fiberglass and resin?
If I need to build a male or female mold which is the best and cheapest material for mold.
I would appreciate any answer in this matter.
Can anybody help me?
Thanks.

Victor

 

Cross linked PVC foam is quite brittle and breaks if the bend radius is too small. To enable bending the foam usually has knive cuts or grooves which would leave ridges on the surface.
It is possible to strip plank a hull using foam strips. There is some info at http://www.spsystems.com/solutions/corecell.htm. CoreCell is less brittle than cross linked PVC and it is also supplied in bead and cove strips.
Another posibility is to thermo form the foam sheets. You can heat them up and then bent them without breaking them. Laminating over the foam is no problem. It's done all the time for one-off boats.

 

Victor,

Alcan makes several grades of Airex foams, their R63 foam is a non-crosslinked, "linear" foam, it's very tough and flexible, you can just about bend it into a pretzel shape.

While I'm sure you're all thoroughly tired of me harping on this, I would recommend you get a sample and try some experiments with it.

I'm sure you can use it for "planking", but I would either space the stations closely or use a fairly thick foam. (yet again, experiment with it!)

Yoke.

 

Thank you both.
I already have some samples of Airex R 63 and C 70 suitable for marine use, but the samples are too small to 200 x 100 mm to flex them in a complex curvature. I will experiment anyway to see how it's working with fiberglass and epoxy lamination., but for a planking on frames the sample is too small.
I think that having those square kerfs would help it to flex and to take the curvature over frames.
Do you think I should use a mold ? I want no mold.
Victor

 

try nidacore easier to use.

 

Most stich and glue chine hull designs do not have much bend as they were designed for use with plywood. In plain sheet PVC foam it would bend these designs and shapes easily. To be sure you could glass one side of the foam only (maybe the outside) and then stich the panels together with wire or whatever as usual. The glass on one side would still leave the foam quite flexible with much less risk of it breaking too. When the whole shape it set in place then glass the glass the inside and the boat it set strong.

For a round bilge design you can pre laminate boat length sheets of foam with just a light glass then and cut into 1-2" strips for strip planking over temporary frames just as you would with timber strips. Then a quick sanding and the rest of laminate goes on each side. Fair and paint as usual. This gives a foam boat with very minimal cost for frames compared to other methods.

Contour foam (with the squares) is really only meant for solid surface moulds whether they be male or female moulds.

 

Signum, I have been in the planning stages of building a gardener pram of corecell. I have also worked with Airex. The sheet stock is a little more flexable in half inch corecell than is quarter inch lauan plywood. I have made up sections of ribs with half inch corecell laminated to make one inch and they hold the curve when the adhesives have cured. (about a six inch radius.) Airex core is much tougher than corecell. You can twist a half inch thick, one inch wide, two inch long piece 180 degrees without fracture. I plan to build the pram just as I would if I were working in wood but taking care to not get "heavy handed" before the first layers of glass are in place.
In terms of corecell strength, a 4x8 sheet of half inch corecell can be lifted from one edge with fingers under and thumbs on top without breaking. It saws on the band saw as fast as you can push the sheet.

 

Foam Planks?

Hi Folks,

I recently spent lotsa hours and $s on a trailerable power dory which I hoped would be capable of going 10-15 nm offshore and still coming home if things turned nasty. She is GOP, 18ft with 4ft chine beam at the transom, with a cuddy and lotsa built in buoyancy underfloor and in side cockpit tank/lockers.

The sea trials were good in terms of speed and economy (12kt with 15hp OB fully laden, adequate ability to maintain it in a short head sea, and she lay well to wind and swell both at anchor and while drift fishing.) She is very tender, but I expected she would be and was willing to accept that in the interests of an easily driven hull. Since she has lotsa flares in her topsides, I thought we would be able to perch a small elephant on the gunwale without putting water over the cockpit coamings. We can't. A standing, lurching, listing, slipping, falling mishap with crew weight and trim managed to put water in the cockpit on a flat calm day.

She won't do. We have to get her terminal stabilty up, and altering the hull shape seems the best way. Would it be practical to:
1. Attack the area immediately below the gunwale beltings with a grinder to prep it.
2. Glue (epoxy) on planks of Airex or similar foam, bending them as we go.
3. Fair with a surform or similar.
4. Glass and resin over the faired foam.
5. Sand, fill, sand, paint etc.
6. More sea trials with small elephant.

I would appreciate any advice
Thanks
DEF

 

There is one of the old timey builders in the U.S. called Huckins Yacht that built many laminated hulls during WWII, as PT boats, which they are very famous for, using the principle of double planking on a diagonal, that was one of the first to build in Airex during the transformation from wooden hulls to fiberglass. Building one off took a hit to compete with conventional fiberglass in a mould constrution.

The key to most any design in foam cores, using sheets is very simular to using sheet plywood in the working properties of compound twists and turns, with a little bit more brittle. The hulls need simular longituals, but a few more of them.

Heat can bend it in a complete circle. Getting it fair in small strips, required in some hull shapes, but not unworkable. The key is where do you draw the line of needing excessive framing, to make it rigid, with additional work and weight in framing, too.

Here is what can be done with divinycell and even a heat gun, all with proper planning and a bit of extra work. The scored cores can do a better for some twists and turns. BUt it requires some extra resins to fill the slots and backing that hold the scored pieces together.













Airex construction jig

 

Victor and Yoke, et al,
It is now 2009 and I am wondering what you have found out or accomplished with the pvc sheets or strips. Were you able to use it as planking? I am thinking of building a skiff but a large skiff like the ones we use here in florida for oyster boats, clam harvesting and crabbing. I was going to use plywood when I happened on an article in Boat U S, January 2009 edition page 48. There is a skiff there that is built entirely of pvc. I just can't figure out what kind of pvc product it is. Is it the foam core or airex like you are using or is it something else, like a solid starboard or something. Do you guys have any idea what this is?
Also, where can I get it and where can I get a sample of what you are using?
thanks,
Terrycshan

 

Update on fix to dory

Hi Folks
In 2006 I asked about the practicality of using polystyrene foam and glass to fix a stability problem.
This thread has just become active again , so I thought I'd update ya.

1. Extended bottom past existing chine from point of max beam aft to transom. Chine beam increased 135mm each side.
2. Stripped back to ply, offered, faired, and epoxied layers of HD 50mm polystyrene stacked on edge up to the existing gunwale beltings.
3. Faired, epoxied, bogged, glassed and painted.
4 Sea trials with small elephant - dropped 3 kts, but stability very much improved and have spent lotsa time up to 10nm offshore and coped with the odd bit of nasty(ish) weather.