The transverse sub-frames ( like formers in an aircraft wing) are the way to go, I think, though you might want to use something a bit harder and less compressible than balsa, perhaps the 1.5mm plywood you mentioned. It occurred to me that an easy way to go with that would be to hot-glue or otherwise stick a piece of the ply to the flat, cut foam surfaceand then run a bottom-piloted cutter along the surface of the foam, using that to cut the thing to the same shape. There are cutters available that are commonly used for Formica and other pressure laminate surfacing materials that’d be ideal for that job. -------- I want to use plywood for the joining surfaces…the inner structure will be 20mm wide balsa to get a wide and good bond to the shell. The whole strukture will be built and put together before installing in the foam to make sure perfect alignement. This way I can reshape the blanks surface before I take it apart again and glass both parts seperatly. -------------- Also, I suspect you might have an easier time of it on the longitudinals with a stiffer, denser foam than with balsa. You could simply glue them in and it’d be fairly straightforward. --------------- You mean foam instead of Balsa for the “stringers”? I don’t understand what you mean I fear. --------------- If you go with a left-right threaded screw setup, and if ( he wrote, enviously seeing the lathe and mill in the picture) you’re going to be making them from bar or rod stock, then a slightly larger diameter toothed wheel ( like a plain gear ) will make a nice, easy way to tighten it up. Are you thinking of using something like an Acme or buttress thread? ------------ we don’t use that mill [smile])) got 2 other bigger ones…only use the lathe. Acme thread is the joice I guess. Haven’t decided on Aluminium, stainless Steel or Nylon yet… My Prof. “the metall guy” doesn’t like Nylon but I am ok with it…the platic prof. also agrees… I have stainless and Aluminium (AlMg3) and maybe I am too lazy to get some PA. It wouldn’t hurt to have stainless nuts…they go together well with Nylon. In mechanics Nylon and steel are joined to make long lasting non degrading gearboxes at fast speeds. ----------------- I think o-rings around the tubes, between the board halves, those might be worth trying. I also like Pierre’s idea of using a thin sheet of cork or possibly a neoprene between the halves, would be a good idea, to keep some tension on the threads, like a lock washer. Otherwise, you might have some problems with things vibrating loose, say on a choppy day. Though the nylon screws would deal with some of that themselves. ----------------- I got cork… do you think it would work on the faceplates…not under the laminat? Does cork degrade in salt water if not imprignated? what about black cellular rubber…glued on the surface with double facing tape… ---------------- Aligning the tubes properly and all- a similar problem has been the downfall of many who have tried to reinforce broken board repairs. But, I see you have the answer right there. Attaching the halves to the carriage of that lathe ( you may have to remove the tailstock temporarily) using a simple jig ( and using the centerline and bottom of the board for reference points in attaching the jig to the plywood end-pieces) will not only give you perfect alignment, you can even have power feed. A boring bar chucked into the headstock and there you go. Thius might also be a good way to machine the cavities for the attachment screws, using the carriage cross-feed and milling cutters. -------------------- I’ aligne them before glassing…glue the whole completed and crewed together structure in the foam at once…did you mean that? ------------------- heee…this is fun. Cross-pollination, if you will. ---------------------- [smile])))) yeaa…really cool.
Hi GW. I don’t want to tape it…if I get it right it should fit perfectly [smile] I once tried a Styro Kayak Plug I shaped in the water (before I used CAD, only to see if the volume was right and if it would float me)…I did use carpenters glue to join the foamblocks…unfortunatly not the water fit. If it was summer I’d probably taken the shaped blank to go waterskiing [smile]) fortunatly (for the blank) it’s 4°C outside and snowing every morning. I am a warm water guy anyways… What would it cost to sent the board to the US or Oz for prototype testing and some feedback [smile])
I got cork… do you think it would work on the faceplates…not under the >laminat? Does cork degrade in salt water if not imprignated? what about black >cellular rubber…glued on the surface with double facing tape… I don’t know about salt water, but I know cork won’t degrade in contact with wine for many years… In any case, since it’s on top of your lam, you’re not taking much risk, you can always take it off and replace it with something else in case it wouldn’t work. Pierre
Hi Marcus, I agree with the plywood for the mating surfaces, glassed over. The balsa ( or, again, denser foam) strikes me as a very good idea. Foam instead of balsa for the stringers, yes. With regard to alignment, if you make the assembly up, check it for fit and all, then disassemble it and attach the plywood mating surfaces to the cut faces of the blank ( even temporarily) , then you’ll have something you can work off of to give you clean holes in the foam at 90 degrees to the faces of the mating surfaces and perfect alignment of both halves of the board. If your blank is made up, with denser foam stringers or balsa, shaped and ready to cut in half, I think you will find it easier. The saw kerfs removed from a shaped blank when cutting should be quite close to the ply thickness, so no flat spots in your rail or bottom curves. Otherwise, I think you would wind up with trying to align all the separate pieces of foam, balsa and all, stick them together and then do finish shaping, which strikes me as difficult. Nylon and stainless shouldn’t be a problem, or nylon and aluminum. I’ve used a number of what we in the states call locknuts or aircraft nuts, with nylon inserts at one end, in salt water for securing underwater hardware with no problems. Though finding aluminum or stainless nuts in anything other than a standard bolt thread could be difficult. Acme or buttress thread, especially reverse thread, very difficult. Something like that I’d think you’d have to make. Especially if you wanted to make it fairly long/deep, to give your threads as much bearing surface and as little stress as possible. It would also be a good idea to perhaps make a wide flange in those nuts, where the nut came up against the wood, to spread the pressure over a greater area. The cork, or rubber, well, Pierre answered that one better than I could. Considering wine is probably more acid than seawater, I think your main problems with it might be sunlight/UV and repeated soaking/drying cycles, which wine corks don’t have to deal with. Hope you are having as much fun with this as I am doc…
my pleasure Doc. I will go with Balsa…the foam is very stiff anyways…it’s XPS. 20mm wide (maybe even 30mm) Balsa won’t compress too easy and gives a lot of surface for the epoxy to bond. 5mm Balsa Stringers are also used in poly boards…my LocalMotion got one, very nice. Which Foam would you have taken? Which Foam is better than Balsa? I will machine the nuts and bolds anyways…nothing is more satisfying than using handmade parts. [smile]) 20mm hollow Niro screw in the middle. 5mm marina quality plywood will work for the faces. I can’t wait to finish the board… Tomorrow is the last day before monday I can work on it [frown] Got so much other work to do… Which cloth would you use for the board? Is it not a problem for a sandwich if the top layer and the bottom layer isn’t symetric? Isn’t a sandwich that is identic on both sides better? what is 6oz in g/m²? 6oz is like 170g…is it 6oz/squarefeet or 6oz/m²? I hope the last [smile]) What about 2180 top and 1180 bottom? I’ve never glassed a board before…
Hi Marcus, While I can’t give you a better idea of how much glass to use than you’ll find out in the archives or from one of the guys that’s doing it regularly, I can say that the cloth is weighed per square yard, within about 10% of weight per square meter. 6 oz, let’s see- 2.2 lbs/1 kg x 16 oz/1 lb, 33.2 oz per kg or about 30 gm/oz - multiply by six and add 10%, so that’s something like 200 gm/m^2, very, very roughly calculated. 2180 deck, 1180 is typical for a new board in the 7-9 ft range ( 2-3 m ). I wouldn’t hesitate to add 2-3 more layers over the area of the joint to really reinforce it on both sides and tie the plywood plate into the skin so it won’t even think about moving on you. Maybe chamfer the holes in it some so you can tie the glass into the glass tubes as well? Foam- I would have used the same XPS you’re using, just go up a density level or two, though maybe experiment a little to see what it would deform when some heavy stress was put on it, drill a hole in a piece, set one of the tubes in there halfway, clamp it to a tabletop with clamps and a piece of lumber the same length and width and hang a weight from it or something to see if it crushes or anything. Have fun… and get some sleep, it must be late there doc…
Any reasons why a deck mounted idea wouldn’t work?
don’t know… I want something in the middle of the faces to hold it togeter better… Pope uses a deck mount+ a bottom mount. Now I will go with Pierres idea maybe… you can use a standard screw and nut on the other side…I will use a stainless hollow screw for weight reasons… If it gets lost it can be replaced easily by a nylon or stainless screw… If you put a big enough enddisk on the screw you can tighten it by hand… The opening on the deck (in a small wood block) is getting narrower as it gets down…trapez shape… M10 or M15… I have also bought one of these today http://www.mauritz.de/all/abspannmaterial/seilspanner-1.jpg if you cut it in half and weld together the screw it would make the part I was suggesting all the time…a true inline screw. But it hit me today that this is really to complicated… so here is the final…the most convinient…foolproof? version… it would even be suitable for mass produktion… I could sell ready tubesystems and scew and nut parts [smile]) For the tubing I would use aluminium the next time…carbon tubes are also available at sices that fit into each other (for a price)at almost any desired diameter and wall thickness. http://www.compositespars.com/1_5%20mm%20wall.htm A cool site for carbon/epoxy tubing! ok…heres a rendering of the final? thing. Only the nutpart and woodblock are missing in the pictures. I have also bought plywood today, 5mm, really good hard one. I got every part now… Have no time for assembly this week though [frown]( but next week… cheers Marcus thank you all for the great design critic and ideas!! http://www.compositespars.com/1_5%20mm%20wall.htm 
I’m sure you could make up something that attached only to the deck, but it would have to be very rigid, and so would the deck it attached to. The thing is, something holding two halves of a board together has to withstand bending stresses from plain old floating around with somebody on it, turning and of course the occasional hit from the lip. To do that , with something that is thin enough to deck mount without being very much in the way, means it’s going to involve something heavy or expensive or both. As an example, maybe oversimplified, 'cos it’s not quite this simple but it’ll show the main points - take a couple of wood blocks, put them together, then fasten some thin plywood to the top of 'em - say 1/4" lauan, not especially rugged stuff. Then, set a couple of other blocks under the ends of the assembly. Push down in the middle, see how the space between the blocks opens up? The bending stress on the ply is more than it can resist. If you had something like, say, a metal plate the same thickness as the ply, that might do it, biut it’d be awfully heavy. Now, try it with two pieces of lauan ply, one on top and one on the bottom. Try the same test - nothing happens. See below for an illustration. The piece on top is in compression, along with the blocks in between, while the ply on the bottom is in tension - and you have a whole lot more rigitity in the system. So, you would prefer to do something that involves the full thickness of the board, that you can make pretty rigid easily.It also means that you can have relatively lightweight mechanisms of fairly cheap materials. Try the same experiment above, and instead of ply, glue on some cardboard. You’ll be surprised at how much the two blocks set together, with just cardboard on both sides, resist bending. Then there’s the question of how to hold it together. If your system is top-only, it has to both resist bending and hold it all rigid enough that it doesn’t open up at the bottom and give ya a banana board. If, however, you have something top and bottom, the one on top is in compression ( no prob holding that together, the stress is doing that for you) and the other is in tension ( so you can use a few fairly strong fasteners) - cheap and easy. hope that’s of use doc… 
the hole is not too big either…ca. 2,5cm long and 6cm wide to get good access to the screw and to put in a new screw. http://www.compositespars.com/1_5%20mm%20wall.htm