My boyfriend an I have an interesting plan. We want to build a foam core fiberglass kayak, no woodworking or molds involved. I want this to be a rolling boat, so it will be a Greenland style kayak, Designed by Björn Thomasson. It's called the 'Black Pearl'
http://www.thomassondesign.com/choosing/my_kayaks/black_pearl.aspx

The plan is to cut out a foam shell out with a CNC hotwire. This would be done in sections, and the sections would then be glued together.

I'm a visual person, so I drew some sketches to help me explain. Figure 1 shows how the foam would be cut to give me the shell, Figure 2 shows the shell with the excess foam removed. Figure 3 shows the deck and hull of a mid section of the boat. From here I would glue the shell together, giving me a foam boat with the deck and hull separate. Next, I would turn the hull shell upside down and place the plug (which would be cut out from Figure 1) inside, this is shown in Figure 4. I would then sand the hull smooth while it's resting on the plug, so that the foam doesn't fracture. Fiberglassing would be done with the shell still resting on the plug, again for strength but also to keep it from twisting. This would be repeated with the deck.

Ok, to clear things up about the CNC, it's computer guided and it bridges the gaps between two cross sections here is an example of an mold that we are using to create a fiberglass Greenland paddle: http://3.bp.blogspot.com/_Be-o6_unLIs/TNWfYJkc0CI/AAAAAAAAAgM/F0f8L58kXW0/s1600/PB050131.JPG

Very cool. How thick of a piece of foam can you cut?

*****

Outstanding. The machine is a lot more capable than I thought originally. So Figure 5 shows the sections that'll be cut out separately and then joined together? Looks like you thought it through,can't wait to see the build in progress.

It can cut pretty much anything you want, we will probably use 5-10mm thick. I need to do some more tests.



Yes, that's right, the CNC can only cut straight lines, but if you make multiple cross sections and glue them together you can get curves. It will still have to be sanded a bit to smooth it out.

Alana,
There are many who have built airplanes using a similar method. However I recommend that you DO NOT use the beaded polystyrene foam. It is far more flexible and much weaker than the rigid polystyrene that is used for airplane wings. The rigid foam is available in home improvement stores and is used for insulation. It is usually blue or sometimes red (pink) I think. If you want larger pieces, houseboat pontoons use a big block that is orange (at least the stuff I saw was).

The stitch-n-glue plywood boats are essentially the same kind of structure as what you appear to be thinking about. The difference is that wood is used as the core of the sandwich instead of foam. There are some advantages to using wood rather than foam. The wood is more dense and is stronger. This allows for a thinner fiberglass facing and probably a lighter boat. A higher density foam would also work like the wood, but styrene is not available in high densities (and the foams that are available in high densities will emit a toxic gas when cut with a hot wire).

I can relate to wanting to find a way to use your CNC foam cutter to make a kayak (I have two CNC metalworking machines). Just be aware that a stitch-n-glue kayak will be easier to build and likely a little lighter. I also understand that there are those that like making things with fiberglass and don't like using wood.

At any rate, your approach is certainly viable and a quality boat can be made this way. Boats take a lot more pounding than airplane wings (there are no rocks or beaches up in the air), so keep in mind the strength of the materials you are using....

Rookiebuilder, the foam that we have is the higher density stuff used for surfboards and windsurfers. I'll look around for the ridgid foam, but we have a 4'x8'x2' block of foam that needs to be turned into something

I realize that this isn't the most practical method of building a kayak, but we want to experiment and I'll be happy with whatever we end up with.

Alana,

The foam you are using is polyurethane, not polystyrene, isn't it?

I am struck at the boldness of your project, particularly compared to similar builds incorporating more rigid, less compressible core materials (e.g., plywood or cedar strips). I know that balsa core/GRP-sided laminates are common for sizeable ocean-going craft. Those laminates set the grain of the balsa perpendicular to the GRP enclosures, to prevent "denting," and subsequent failure when the hull gets dinged.

I wonder if there are stiffer grades of PU foam in use by surf board manufacturers which might help prevent that sort of weakness?

I really love the whole concept of cutting the foam and laying the whole thing onto a male mold for layup, as Mick has described. Quite a project.

Keeping everything aligned, achieving a smooth surface, as well as having a foam core will be most difficult - but determined people can certainly achieve difficult tasks. In my opinion, going for a foam core while keeping weight down (ie minimum to no filler during fairing) might be compromised.
However, here's what i'd say was a good example of using a foam blank such as you have - for a short yak such as for ww or surf. The point here is that shape can be adjusted by adding filler or clay or more foam without fear of adding eventual weight as it is all dug out later. In this case, some of the foam may have been left in for floatation but all the glassing was on one side.
http://www.ptone.com/boatbuilding2002/page1.html
hotwiring the shape:

If you are using the kind of foam used for surfboards, it is NOT polystyrene as Dave points out. It is superior to polystyrene in almost every way. BUT IT WILL EMIT A POISONOUS GAS WHEN CUT WITH A HOT WIRE!
Hot wire machine are intended to ONLY cut polystyrene for this reason.

One layer of 6 oz glass is not very impact resistant. I would make some test panels. You could then compare different constructions (cedar strip/glass, plywood/glass, foam/glass, ect.) Rig up a way to drop a heavy object on the test panels.
Gravity, mass, and a tape measure, you can't buy a better testing device.
If you make all the test panels the same size you could also compare weight.
I am only suggesting this because you will might invest 400 hours building the boat. After all that work you probably don't want to test the boat on a rock.
The great thing about using foam is that it is easy to shape. With foam you can create a shape that you could not duplicate with wood strips, play wood, or sticks and cloth.
I can't wait for the photos of this project.
Roy

Wow, very cool. I had an almost identical idea last spring after finishing my first stitch n glue boat. I was thinking about how foam core (poster board laminated stuff at craft stores) was structurally very similar to the marine plywood used in all commercial kayak kits and how perhaps it could be substituted with additional layers of FG to make up for the weaker material. Then I thought about my college days in an industrial design program, where I spent years in a studio laminating sheets of blue foam, shaping them with a hot wire, and sculpting them into product designs or small vehicle shapes.

I bet it would be pretty fast and easy to build a stitch n glue with a few 4x8 thin sheets of insulative blue foam. You wouldn't even need a hot wire (the gases are toxic) and just use a fine tooth jig saw or even a carpet knife to slice big arcs. The walls would be thicker than foam core, but it would be easy to bevel the joining edges with a razor or sand paper. You could just use hot glue or even packaging tape to stitch the edges together long enough for a fiberglass layup...

In fact I once made an experimental sculpture using those thin sheets of blue foam as a 8 ft tall weather vane.

Wow, very cool project! I'll be following your build with some interest, that's for sure!

link to a Guillemont customer gallery page showing construction of a foam planked kayak.
http://www.guillemot-kayaks.com/guillem ... _mystery_1
The builder used female forms to lay up the foam strips and glassed the inside first so he could "fair" the outer surface.
Roy

Some info on the foam used in carbon fiber greenland paddles:
novorca