: TOOLING: Why would you need different tooling to lay up foam strips instead
: of wood?
First, I know of no boat building technique that uses strips of foam. Expanded PVC cores like Divinycell and Airex are sold in sheets made up of segments blocks of the foam held together with a fabric scrim. The segmenting permits the blocks to follow the compound curves of the hull while the scrim holds them in position. The PVC products were developed to compete with balsa core materials. In "traditional" production glass building a female mold is used and the hull is built outside-in. It starts with the gelcoat followed by roving, mat, the core material, and more mat. Resins may be applied as the layers are built up or drawn into the built up laminates by vacuum. A good producer can get a boat or two a day out of a mold. Crew size of three to twenty will depend on boat size. In this type of production the female mold tooling represents thousands of dollars in capital investment. The tooling pays because of the labor saved by producing a finished hull exterior without much further labor. It does this by presenting a continuosly smooth surface which holds and supports the laminates during cure.

: All that is being changed is the core composite. Wood or foam-it requires no difference in "tooling".

One-off foam building with sheet PVC products requires the construction of a male mold to support and hold the shape of the laminates during cure because unlike wood strip the laminates will not hold their shape without almost continuos support. The mold is constructed much the same as a strip built boat. If mat is to be applied to the mold first the surface of the mold must be continuous. If a core material is applied first then some gaps in the surface strips of the mold are permitted as the core blocks will bridge the wood strips. The proposed strip foam method would require almost continuos support to prevent sagging between frame stations. The one-off method is more time consuming than the production method as the foam has to be mechanically fastened to the mold, the hull has to cure before being removed from the mold and then the interior laminations have to be built up. Lastly, the exterior finish will take days of filling and fairing to come close to a production hull.

Frankly, I can't imagine any one person lofting, cutting, erecting, and trueing the building frame of a 20' hull in 18 hours. Much less assembling and laminating a cored hull. With the tooling in place, a Binks chopper gun and a couple friends who don't mind the stink of styrene, an unfinished one-off could be pulled in this time. If this story is true Genmar ought to give this guy a million for his secret. But Genmar has decided to expend its capital developing tooling to build up to 24' hulls out of polyethylene using rotocast techniques-because in the end production fiberglass boat building is still very labor intensive.

: I will concede, that foam requires fewer power tools, since foam is softer and easier to
: work.
I think you wanted me to concede this point, but whoever said this hobby was about having fewer tools? Yes, foam is somewhat faster to fair, although some PVC cores are quite hard, but I think wood starts out fairer and deflects less under sanding pressure. Generally, there is little sanding of the foam core materials as they conform quite well to the lines of mold.

: If you are cutting your own strips, you need to figure in the cost of several
: bandsaw blades or circular saw blades. Strip cutting of the foam and there is
: virtually no wear or tear on your blades. Heck - you can even cut using a
: hot wire and save all the lost sawdust from the saw kerf!

I generally get about 600 board feet out of a blade before it dulls to the point that production slows. That's about 7000 lin.ft. of 1" strips. Which should be enough for a couple boats. Re-sharpening is $6US.

A friend asked me where he could get 1/2" styrofoam to laminate up some landscape for his HO setup. I grabbed a blue Dow billet, threw it on the band mill and cut him 10 sheets. Next log on the mill didn't cut so well. I guess it couldn't have been the plastic that dulled the bale. I think you'll find that a hot wire consumes some material during the cut, but your right this method does cut down on that terrible plastic dust.

: TIME: Same or less with foam than with wood. A block of sandpaper and an
: Xacto knife and you can quickly shape and fit foam. Wood requires a plane,
: saw, sandpaper, etc. and a set of special router bits if you want to bead
: and cove the wood. Of course, you can do that with foam too.

: I had posted in an earlier thread, a detail of a guy building a power boat of
: twenty-some feet in length. His estimated time, including cutting of
: template/stations was 18 hours as I recall. Don't think you would come
: close in 18 hours with a wooden stripper. Heck - I don't think you could
: hit that time with a hard chine panel boat either.

I really don't consider strip boat building to be a particularly useful activity adding any substantial benefit to the general welfare or gross national product. We could probably put an end to it tomorrow and only a few hundred people would be out of work. I guess it's just one of those activities that is for no good reason more meaningful and pleasurable than other aspects of our lives. I realized last week that I had got a great deal of satisfaction out of spending a day on the tractor cutting the brush back to the tree line. When I was done there was all that smoothness to show for my effort and a deep comfort, perhaps coming from some ancient knowledge that I had pushed back the cover for any potential predators. I could have done without that nest of ground hornets, though.

You want or need a quick and dirty boat go with stitch and glue. Some designs require no tooling. You could building the 6 hour (plan on 30) canoe, for example.

: MATERIAL COST: Again - wood (cedar) is about triple what you would pay for
: the same lineal feet of extruded foam. Let's see, as I recall, a 4x8 sheet
: of foam, 3/4 inch thick runs about $10 - $15.00 at the local lumberyard. I
: haven't seen anything on the low side of $25 - $30 for some red cedar
: boards. We won't even discuss the outrageous cost of redwood.
My wood is free, after real property taxes, capital investment in chainsaws, tractor and a $5000 sawmill. Hemfir, spruce and white pine can be had in rough cut 4/4 in my area for $1 a board foot from small mill operators.

My response assumed that the foam to be used was designed for the purpose. These foams run about $10/sq.ft., depending on thickness. I'd question the appropriateness of blue board for marine use. Even Airex and Divingcell foams have been known to fail in sheer and tension in some applications. Unlike wood, plastic foams have little inherent strength. They strengthen the hull by separating the stressed skins. Like the web of an I-beam this strengthening only exists as long as the joint between the core and the skins retains its integrity. If the core fails in sheer or tension the hull is mortally compromised. Its you money and time, but I think it's a mistake to spend $150 or so on glass and resin and a couple hundred hours with such a questionable core material.

As I mentioned the PVC core foams are segmented, meaning the sheets are razor cut into small blocks. As these blocks are laid on a curved surface the cut lines open up. To assure a proper bond with subsequent laminations Divinycell advises the use of a propriety resin to fill the opening and properly bond to other laminations. Balsa wood block cores are laid down with the end grain exposed. This permits the normal laminating resins to deeply penetrate the blocks which produces a much stronger core bond. For this reason builders still prefer balsa as a core material even though it is more subject to degradation from water intrusion.

So I'm still not convinced this is a viable material for boat building.