Divinycell cored composite

[stripperguy]

OK, don't any of you get too excited about another composite build, this one's a ways off yet.
Not to get too far off of my own topic but...

MDB and I have sold our house. We're building a new one next year, along with a 30 x 40 detached garage/workshop. In the meantime, we're finishing a bonus room over my daughter and SIL's garage.
Granddaughter has requested, for two years now, a canoe of her own. And it HAS to be pink. However, with no work space for the next year or so, this build be a thought experiment for the time being. Sorry.

The plan:
An all composite build, with 2 layers of 4 oz inside and outside of some 1/8" thick Divinycell foam. Glass wrapped foam gunnels. Hopefully end up with a light, stiff canoe, sized just right for a strong 6 year old girl.

The process:
Cut foam into wide strips, of sorts, and epoxy their beveled edges together in a female mold set. Kind of like a stripper build from the outside in. Glass the inside, part the pattern set. Sand and glass the outside.

The dilemma:
How to keep the foam in place??? I've seen videos of big sailboat hull builds, similar to what I've described, but with much thicker foam. The temporary fastening of the foam is less challenging with 1/2" foam...

If you've managed to read this far down, and have some input, I'd be pleased to absorb it. I really want to avoid building a plug or mold.

 

[Cruiser]

I was toying with something similar.

The plan was to cut into similar strips as a wood strip (say 3/4") and edge glue the pieces. Assembly would be pretty much the same as a regular strip boat, assembled on a strongback, using existing canoe molds etc. .... just substituting the DVF strips for cedar strips.

They have a special saw blade for cutting foam that reduces losses and cuts down on the foam dust ... the foam is compatible with our epoxies and wood glue.

In the end, I just couldn't swallow the cost of the foam here in Canada ... but I think your idea is totally workable (at least in the mind).


Brian

 

[stripperguy]

Thanks for the feedback, Brian.
I was thinking to cut the foam up to 2" wide, and build inside female patterns.
If you've ever you tubed videos of sailboat builds you'll know exactly what I'm thinking.

But either way, in a female form or on male patterns, the question remains:
How to hold the foam in place until it's glassed? Staples, tacks, screws, wires, all seem unworkable to me.

Uhmmm, wait a minute! Didn't Allen try some plastic staples? I remember he didn't like them for his build, but for foam...maybe!

Where are you Allen? I know you're busy with your new place, but can you refresh my memory?

 

[Cruiser]

I build stapleless ... so I didn't see that as an issue. I think I would just use some cam buckle straps at each form to hold the foam in place while the glue dries.

I actually did review a bunch of those videos, so we are on the same page .... at 2" I would be worried about making the turn at the bilge (assuming you have no tumblehome to worry about) .. maybe a few narrower strips to cover that area. I did see some videos on how to shape the divinyl, but that seemed like a LOT of work.

I guess you could go female molds, but it would seem that the male would be easier to devise something to hold them in place ... I generally find a convex surface easier than a concave to work with from a "hold down" perspective.

This a pic from my Freedom build, you can see the straps holding the strips snugly to each form ... the black cord is 3/16" shock cord I use to pull the strips tight ... obviously the key is to have the straps run along the forms, so they don't deform the strips.

Brian

 

[Jim Dodd]

I'm a little familiar with the staples you speak of, They were designed to be broken from the stations of a strip mold. I'm afraid you would destroy the foam. They are quite visible, and I fear they would be hard on the forms, as you hammer to break the staples. I never liked the idea, and don't think it really caught on in the Cedar Strip world.

Maybe a Thomas J Hill Lapstrake build, cut the foam 4" wide, and super glue, or that CA glue the planks together ? Build on male plywood forms.

I see troubles using a female mold ! How would you hold the foam against the mold ? And then how would you remove the hull from the female mold, unless it was split down the middle. That type of mold would be expensive to build, in my eyes anyway !

Jim

 

[stripperguy]

Jim,
Thanks for the staple input...I have no first hand experience, you just gave me the next best thing.
If I could buy the foam very thin, I could do overlapping diagonal strips, like a cold molded hull.

Either a female or male set of patterns would have batten strips between the forms, to better shape the foam. Maybe I'm hung up on female molds after seeing so many sailboat builds.
In any case, I'm still stuck (see what I did there?) on the method of holding the foam in place firmly enough to allow some sanding and glassing, yet weakly enough to allow release from the patterns.

If I were a rich man (maybe, more accurately, if I were willing to spend the money) I would make a male plug, and hot vacuum form a pair of foam sheets to the desired shape.
I have built vacuum formers before, but not with heat, and not this large. That would be tricky.

Anyway, all this discussion is causing me to think of many ways to create that little canoe.

I'm open to any and all suggestions. Thanks, guys.

 

[BWCA66]

I've found that contact cement works well with different foams, not sure it would work for what you're doing but it might be worth a shot.

 

[Alan Gage]

Jim is right about the composite staples. I think they'd damage the foam pretty badly. They tended to break out the sides of my wood forms when I beat them out. Sorry, I don't have any good ideas on holding the foam in place until it's glassed.

I still think this method is a bit overkill for canoes. Production canoes have had thin sides of only a couple layers of cloth for years and it just doesn't seem to be a problem. I say keep the foam in the bottom of the canoe where it's most useful. But then there's still the age old problem of how best to build a one-off composite canoe.....

I'll be interested to see how this turns out.

along with a 30 x 40 detached garage/workshop

I've seen pictures of your current shop and all the different projects you get involved in. That's just not enough room. Once you park all the jeeps and motorcycles in there there's hardly enough room to work on anything else. Make sure you leave enough room for a vehicle hoist too.

Alan

 

[stripperguy]

Alan,
Thanks for chiming in...
The reason I'm thinking all foam core is the reduced number of cloth layers which should result in reduced cost and weight, and high stiffness and strength.
I was incredibly surprised at the flexibility of my carbon copy (before the Divinycell).
Samples that I laminated with glass and foam only were many times stiffer than any laminate with carbon and glass only.
This will be a little boat for a little girl, I want her to be able to lug it around by herself.
BWCA66's mention of contact cement has potential.

Now the garage. We bought 34 acres a few years ago, splitting it with my daughter and SIL.
They built on one side of the property, we'll build on the other--about 1/4 mile away.
Our house plan has an attached 3 stall garage, that should handle the Jeep CJ5, a couple of motorcycles and MDB's Volvo of the week. Other vehicles can stay outside (currently 08 Element, 05 LJ, 2011 S80, and a future Sprinter based motorhome)
The detached garage will have a carport off the back, to keep my K19 sailboat during the sailing season, and my Exmark mower.
As for a lift, daughter and SIL are building a 40 x 60 detached garage/barn for their collections and added work space. SIL is a former Volvo mechanic, he does side work now at home. So I can always use their lift when needed, I think.

 

[sailsman63]

Sounds like an interesting challenge.

Disclaimer: I've never worked with the foam at all, the following are thoughts I've had after watching some of the same youtube that you seem to have been looking at.

---

If I were a rich man (maybe, more accurately, if I were willing to spend the money) I would make a male plug, and hot vacuum form a pair of foam sheets to the desired shape.

Why go all fancy for a one off? Try this on for size:

• Standard canoe forms on a strongback, with battens.
  • Battens perhaps 2-3 inches spacing in flatter areas, closer to 1 inch in tight curve.
• Single sheet of foam. May need the start of a gore for the stems.
• On top of the foam, a canvas tarp or strong (low flamability) sheet, a bit larger than the foam.
  • Weights suspended along the long edges of the tarp, start light. Perhaps a 14 oz water bottle every 2-3 feet to start.
• PVC deforms around 100C. (boiling water) This can easily be reached with judicious use of a heat gun. The weight on the tarp will tension the foam onto the curve of the hull.
  • Gentle, in several stages. Add weight to the tarp as needed.
• Add/Lengthen gores as needed. The ones for the stems may be possible to calculate ahead of time. May need a couple more near the shear if there is tumblehome in the hull.

If you have some tumblehome in the shape, you will get to the point where you need to cant the strongback over about 30 degrees, and focus on one side, then go the other way to finish. The only place where I really think this would never work is if you have a reverse curve in the tumblehome.

I suspect that single-sheet would save you a few pounds from not having to glue it all together with thickened epoxy. It would also reduce how much you need to sand....

If the above is not clear, I can try for some drawings....

---

Have you considered going a little thicker with the foam? Perhaps 1/4 or 3/8?

At the scale you're working at, I doubt even a 6 year old would have trouble with the weight, and this would add some positive buoyancy to the hull, which could be important. (You know that she will end up capsizing many times. Sometimes, it will even be an accident...)

---

Dynel on the stems. Less for the 6 year old, more for the 8-10 year old that she'll be fairly soon.

 

[sailsman63]

And a parallel thought chain:

How does one select or design a hull for a 6 year old?
What qualities are required, and how would they differ from an adult's boat?

 

[stripperguy]

Mr sailsman,
I've had similar thoughts about forming the foam...

Let me jump to the design first. Mostly, a canoe for a child needs to be right sized, IMO, with adequate narrowing of the beam at the paddling station. We're talking solo here, a tandem for kids is a no brainer. Anyway, sufficient tumblehome, or maybe even a crease, with some bow flare and a wide enough waterline to provide comfort and safety. Not that any of the kids would be paddling Lake Superior, but no reason for them to be intimidated by larger waves and water. Remember, everything looks bigger to kids...

Now, back to the foam forming. When I was adding the foam stiffening to my carbon copy, I very unsuccessfully attempted to heat form the foam with a heat gun. Between the thermal properties of the foam and the lack of heat capacity of air, I couldn't get enough heat soaked into the foam to shape it to my hull. And that was a relatively small piece of foam. A heat source with a higher heat capacity (water) should certainly help. I do like the simplicity of larger sections of foam. I may have settled on male forms with batten strips, it does to be the most elegant solution. Ultimately, the hull need not be perfect, she'll outgrow it in a few years anyway, and a first attempt might be just practice for further build refinements.

Someone upthread mentioned expense of the foam...I did the comparison a while back and the Divinycell cost is similar to the cost of a boat's worth of cedar, at 1/4 of the density! And the stiffness provided by a full hull's worth of foam trumps the many, multiple layers of carbon, kevlar, basalt and other fabrics du jour found in most high end canoes. Just speculation here, but maybe the production boats use foam only in selective areas is due to the complexity (read: expense) of heat forming an entire hull sized sheet (s) of foam.

In any case, I appreciate all the alternate viewpoints, lots of good ideas offered.
Thanks to all so far...

 

[Cruiser]

SG ... I did the same cost comparison .... it did seem a lot cheaper in the States, but I am in Canada and the foam was several times the cost of cedar .... so location probably matters.

I tried the same idea with a heat gun and bending cedar strips .... I heated them up to 225F for more than 30 minutes and the strips just won't bend ... so air heating seems to be a bit problamatic.

I do have a steam generator now, I wonder how that might work to just heat the foam in place or where it needs to bend ... of course that depends I guess on whether 100C is enough. Heck, maybe just steam box the whole setup, lol


Brian

 

[Jim Dodd]

And a parallel thought chain:

How does one select, or design a hull for a 6 year old ?
What qualities are required, and how would they differ from an adult's boat?

This perks my interest also !

At 6 yrs old, I wonder if she could paddle a canoe ?

I've built a few Wee Lassies, and in my mind, this little hull is suitable from kids to 200# adults, and then some. It can be double or single blade paddled, and sitting in the bottom gives it great stability !

Yes. I'm curious to see a design !

Jim

 

[stripperguy]

This perks my interest also !

At 6 yrs old, I wonder if she could paddle a canoe ?

I've built a few Wee Lassies, and in my mind, this little hull is suitable from kids to 200# adults, and then some. It can be double or single blade paddled, and sitting in the bottom gives it great stability !

Yes. I'm curious to see a design !

Jim

I've got a few vague ideas for the boat, think of a scaled down Kite, but maybe a little skinnier.
This past summer, she paddled my carbon copy Kite, MDB's Swift packboat, and did bow work in my Sawyer Cruiser...so I think she'll have no problems.
My own kids were paddling from age 4, wilderness tripping from age 5, so the granddaughter is a little behind. But then again, my kids weren't riding motorcycles at age six...

Brian,
Don't laugh, when I first read your mention of 100 C, I thought of steam too! It actually might be easier to build a box around the entire hull and just let the steam pour in.

 

[saltandsky]

For what it's worth: My 2cents and a few pointers if you want to heat form Divinycell;
In a prior career I was a custom boat builder (large one off sailboats). We regularly steam formed divinycell. We had a large steam box that used a kerosene fired hot pressure washer as a steam source. Typically we used H80 Divinycell about 1" thick cut into 8" wide strips. Divinycell is produced in a big block then cut to thickness. Properties are not perfectly even through the block so when steamed for a while the foam will naturally bend/bow in one direction. You can use that to your advantage when fitting it on the hull. The amount of bend depends on how long you steam it. For the 1" thick we would leave it in the box for 5 to 15 minutes. We would screw the steamed foam to the mold, leaving it for about half a day. After it cools mark and take off the pieces off, then spread them out for a couple of days to make sure they dry. For tight bends like at the stem a heat gun works but you can easily over heat it so you need to be patient and careful. When laying out foam pieces on the hull don't just think fore and aft or side to side, sometimes a diagonal lets the foam bend easier.

 

[stripperguy]

Mr sky,
I was hoping someone with just your experience would chime in!
I just looked at DIAB's data sheets, they have some limited data on thermoforming, but they do stress the need to quickly (seconds) transfer the foam from heat source to mold/pattern.
I have some left over 1/8" H80 that I could experiment with but other commitments (sold house, rental vacancies, finishing room to live in) are pulling at my time. In a month or two things should slow to the point where I can fiddle with this, in the mean time, keep the ideas flowing.
I promise to display and divulge all of my results for the benefit of everyone that's interested.

 

[Mrindy]

I wonder if you could try sailsmans method but with a steam bag? Basically, wrap the foam panel in plastic like a vacuum bag, steam it up and then shape it to the mold while maintaining the heat. I did something similar for the 1 in. uniwales on my Kevlar build. Cool project SG! Looking forward to hearing how it goes!

 

[stripperguy]

First things first, I apologize for the lack of photos, my meager descriptions will have to do for a bit...

I had some scraps left over from the carbon copy Kite, so I experimented a little bit.
I boiled some water in a 3 qt sauce pan, and immersed an H80 scrap in the boiling water, NADA, all I got was tender fingertips! I thought for sure with the enormous heat capacity of the water that this would be sooo easy. Maybe I need a molten salt bath.

Next, I used a Harbor Freight heat gun on its lowest setting, marked 430 F? Didn't measure the actual temperature of the heated air, but whatever it was, it was adequate in small areas. I could easily form complex curves that held shape after a quick cool down to ambient temps.

OK, so the H80 is extremely formable (is that even a word?). But, how to introduce heat over a broad area in a reasonable amount of time? Maybe infrared heating elements?
In my former life, I've built too many ovens, environment chambers, and heated test rigs to remember them all. Tubular heating elements, cartridge heaters, air process heaters, induction heaters...the list goes on.

How about this:
Standard male forms, reduced in size by the thickness of the batten strips.
A series of batten strips across the forms, like a stripper with missing strips.
A series of flexible bands to apply some load to the H80 draped over the battens and forms.
An infrared heat source to soften various areas at a time.

Maybe. I think key is the rapid introduction of sufficient heat, that can be just as rapidly removed. I wouldn't want to heat all of the battens and forms, that would just take longer to cool and lock in the curves in the H80. I'm just now thinking of a small hand held quartz infrared heater, with a reflector behind it, kind of like a magic wand that is waved over the future hull. What was that company I used to buy elements from...Ahh, WECO. Wait a minute!! Why not just use a quartz lamp work light? Already has the reflector, electrical connectors, etc. Something around 1,000 watts...

Gentlemen? Ladies? What say you?

 

[latremorej]

Man, late to this party!

I haven't read the entire post yet but thinking outside the box....

would it be possible to run a strip of steel over the male forms and use some magnets to hold the strips of foam down? Maybe some counter sunk screws in the forms instead of a steel cap? I dunno... ... ... ... ....