Disclaimer : If you learn something here, it is my fault; if you don't, it is yours. If you get offended by something, tough. Oh yeah, guess you modern types will just have to deal with the screwy measurement system used.
 

Design and Material selection:

Based on my work at the time and my need for mobility, I settled on the F9-A as THE design of choice.  If not for the need for quick relocations up and down the west coast, I probably would have built John Shuttleworth's 32' cat.
The next dilemma was 'what material?'. Being a firm believer in the concept that wood and water don't mix, foam seemed like the best choice - especially after my analysis showed foam & carbon to be a bit cheaper than duracore & glass. This was about August 1992 - the F9-A was still relatively obscure. Speaking at length with Ian Farrier (great, supportive guy - buy his plans), I broached the subject of foam & carbon. He was rather resistant to the idea, but had the sense not to try too hard to talk me out of it. So here, then, is her saga:

Materials :

* Divinylcell rigid foam, 1/2" x 4' x 8' sheets, density about 5 lbs/cu ft
* Epoxy from the Erskine-Johns proprietary label until I found a better supplier in Rich Mouton at Applied Poleramics in Benicia, CA (Yes, this is a plug - he deserves your business - buy from him, too)
* Carbon from Erskine-Johns (I was one of the beneficiaries of the post Reagan aerospace industry crash - super deals on surplus carbon and honeycomb panels from Boeing). Layups detailed later.

Workshop:

I was fortunate enough to be able to claim a 40' x 100' warehouse, more-or-less abandoned by my employer, for a shop.  It all came together one day & I bought plans. Talking with a few people (CREDITS : Wayne Gorrie of nanaimo, British Columbia - F9-A Red Shift, Ian Farrier, Graeme Bird of Erskine-Johns), I decided to stiffen the strips so they wouldn't sag between the frames by laying uni-directional carbon on one side of them before placing in the frames. My layup ended up as this : outside was 12oz satin weave carbon (plans called for 9oz, but 12 was dead cheap and more impact resistant); inside was two layers of 3oz uni-directional at (approx) 90°.

The steps:

Build a 32' long table for layups and cover with plastic. Place four sheets of foam on table, then edge glue (butt joints) with thickened epoxy to create a 4' x 32' sheet. Weigh down join line to keep flush (I used a 4x4 piece of timber and some plastic).  Mix up a slightly thickened (with micro-balloons) batch of epoxy and squeegee onto sheet to fill the broken pores in the foam's surface and prevent epoxy starvation of the laminate. Roll out four lengths of 3 oz uni-directional carbon downthe 32' long sheet (each roll was about 1' wide). Wet out the unidirectional and squeegee (using an auto-body bondo spreader) epoxy down length of sheet. Cover with peel-ply as you progress. Once all cured, peel off the peel-ply. Be careful not to remove the carbon with the peel-ply; it will peel off the foam if pulled on hard enough.

Now for the fun part - making strips. I started with a makita cordless saw and 1/32" wide blade but eventually got impatient enough to move up to a regular skillsaw and 3/64" wide carbide blade. This will cut the foam as quick as you can walk.  Wear one of those disposable tyvek suits to catch all the carbon fibers being blown out off the saw; they HURT!  Attach a jig to the bottom of the saw & cut until you are a peppered mass of carbon bits.  I primarily used 2" wide strips and could rip a whole 4' wide sheet very quickly. Result : 2" x 1/2" x 32' strips with carbon on one side. Ian's plans call for (female mold) frames on about 24" centers, to which I attached the strips with 1" drywall screws (wonderful things, no?). The carbon layer was on the inside and stiffened the foam up admirably, but it was still quite flexible, so I got creative again. I took some rebar tie wire (well, it was an ex-construction site and all this shit was free...) and wrapped it around a 4x4 then cut each strand at an angle in the middle of the flat side. Result : Hundreds of 1/16" wires bent into L shapes with sharp pointy ends. In between the frames, align the strips by hand and 'toenail' them together with one of these Ls. When the epoxy has cured, twist the L by the part sticking out & remove it. Once all the strips are laid up, trim to top of frames. Wet out interior with roller (probably not necessary if using glass instead of carbon) and place inner unidirectional layer. Pop out of mold. Go to start.

Miscellany

Hard points were created by routing out foam to inner laminate & filling with a peanut-butter consistency mix of epoxy, microsilica, and balloons (bog). Sand to proper level. Holes in honeycomb were done in a similar manner - set router to just clean the inside laminate & cut a 1/2" wide slot around cutout. Fill with Bog, let cure and run router inside same jig with a 1/16" pin bit. Result is 3/16" high density edge on all holes through the honeycomb.

Observations:

• Foam was great to work with - cut with knife, moisture insensitive (in terms of swelling), cheap.
• Carbon was the most incredible pain in the ass to work with - hard to cut (I went through so many pairs of scissors), hard to wet out (or tell when it was).
• Boeing makes a damn good honeycomb (I would hope so - it was aircraft flooring), but I have not been able to find any since I bought this batch.
• The foam strips make great fairing boards (if only one side is glassed) - glue a wood block to each end and cut a belt sander belt into a strip.

• Put glassed side of strip on outside - the foam is stronger in compression & would thus be more fair.  There might be some more fairing of teh exterior ofthe hull required, but I think it would all work out to the better.
• Use fiberglass instead of carbon (except in special areas)
• Use vinylester instead of epoxy
• Pull a Tom Sawyer & convince someone else how much fun this is so they want to help.
• I like Ian's idea on using large pieces of foam - I would use his new & improved method

So go build it already!