Mmmmmm..... I want to laminate the coach roof too, prob use Divinacell - AU$280 a 20mm (3/4 frozen inches) sheet..... wot? and eithe r3mm ply sandwiched or perhaps glass direct to the foam, want to have the roof back a fair bit to cover us from the Perth sun and those 40 deg daz.... really not keen on any framing below the roof, and insulation is also a real concern so prob bight da bullet (lol) and buy 4 sheets - 2.050 x 1200 x 20mm, maybe another for the cuddy roof too.....
Do you have to vacuum bag that stuff if you are laminating layers of wood onto it? Seems like it would make sense and I know there are 'hacker' ways of doing it with shop vacs and what not ...if you don't already have the equipment. I've never tried it, nor have I looked too deeply into it. Another option is to create a sandwich roof that's filled with standard polyurethane or polyethylene (my preference) foam. I think Renn Tolman's book has details on doing it this way, and/or you can contact Neal Schlee at http://www.lasertechalaska.com and he'll send you pix on how he did it ...the guy's a craftsman. Cheaper than the divine-o-cell fancy shmancy stuff... Tell him I sent ya...
Brian
Yea vacuum bagging is simple Brian and and yes I will vac the coach roof, vac really makes for building all sorts of elements in the build if you are a ditherererreer like me.... never been keen on Polyurethane - slightest movement ova time and it crumbles at the veneer layer to dust an oh heck the pain when a little mountain size gets in ur eye!
I agree on that foam too.... plurry expensive AUD$280 a 2M sheet 3/4".
Bean thunking, perhaps 2 x 3/16th spaced apart with 30H x 15mm W 'stringers' @ 200 centers fore'n aft, BUT still needs cross 'frames' @ 2 ft centers, to hold the curve, under it's own weight it will sag ova time. Perhaps polystyrene foam infill for insulation - we need that here.
Inexpensive and in the water I say!
You can use the compressor off an old fridge for smaller work like veneering doors, foam sandwich hatches, even sandwich panel with 1/8th ply and foam for that 800mm wide hatch on the cockpit sole (deck a'la Alaskan) this stops that springy feel to 1/2" ply even with the cleats you designed in. Generally people don't like 1 to 2mm floor movement....
Looking at a woodworker machine shop today - fatal o the wallet! out the back they had various wood veneers, got to thunking, Mmmmmmm nice transom look..... easy to vac on see.... just the maintenance Brian, even with the space-age tech in coatings these daz, high uv here and NZ too aye Muzza.
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... They called it Gopher wood in them days, now we know it was resin made by the go-for(apprentice). Thats probly why it took 50yrs to build it, continually cutting it up and adding length as more animals was discovered and he musta had your BBq eating and beer drinking mates to turn it over.