Carl and Gareth,
I found your post about impregnated aluminum very interesting this morning, not for the boating community, but for the transportation community. Specifically, using the sandwiched aluminum and even more importantly, the composite aluminum as bridge components. Since I have not been in the bridge community for a few years now, I forwarded on your posts to a US bridge expert in high-performance materials for his consideration. He should know whether we have already tried it, are considering trying it, or should consider trying it. Thank you for sharing the information. You may be revolutionizing bridge design and construction with you posts here on Catsailor.
So Darryn,
If I wanted to build a pair of lightweight beams or whatever, I could use, say, some of that very thin aluminium boiler flue piping from a builder's merchant and coat it with carbon strip bandage @45 degrees for layer 1 then, say, laid lengthways for layer 2 and then @45 degrees the other way for layer 3? Then I'd have a light and very strong beam? (I realise I'd have to vacuum bag it).
Can I ask what kind of glue and surface processing you use to make that combination stick together? It would also be good to know how you deal with electrolysis if you use carbon.
I know that you need special glue films and autoclaving, or great amounts of epoxy-filler to make alu-honeycomb stick to glass.
I got a tip some time ago, to sand the alu with 80grit sandpaper and apply the epoxy immediately before oxydation starts. Is this what you are doing?
Using 2024-O aluminium, roughed up with sandpaper, cleaned with MEK, West System epoxy,600Gsm woven Carbon, keep it warm with a light bulb, the aluminium helps here once again.
I only vacuum bag when I've finished prototyping, my prototypes usually get tested to destruction unless I cant destroy it when I overload it to a degree that I am satisfied with, then it may become the finished product.
I use this process for fairings/brackets, I dont deal with electrolysis apart from sealing the item well and inspecting regularly, so far I haven't had corrosion issues. My plan is to use well bonded conductive foil in the laminate, similar to what is used in aircraft fairings to dissipate static electricity build up if it becomes an issue.
Darryn
If I wanted to build a pair of lightweight beams or whatever, I could use, say, some of that very thin aluminium boiler flue piping from a builder's merchant and coat it with carbon strip bandage @45 degrees for layer 1 then, say, laid lengthways for layer 2 and then @45 degrees the other way for layer 3? Then I'd have a light and very strong beam? (I realise I'd have to vacuum bag it).
You could use that as a former, anything really but if your going to use it for a beam the former might as well have some structural integrity. Aluminium can be quite heavy for its strength when it is formed into a tube and you will loose its benefits when its wrapped in Carbon. I've used balsa but found I had to use so much Carbon it was quite heavy and also expensive due to the amount of carbon I used. Balsa laminated was better. The best so far has been Canadian Spruce, same quality that is used in aircraft spars. Its light, cheaper then the aluminium/balsa I was using and very nice stuff to work with. I've made some Laser Tillers using Spruce wrapped in carbon that have stood up to years of punishment, none have broken. You could build a box section spar from spruce then wrap it in carbon.
I'm sure there are even better products to use as a former out there somewhere, I'm always on the look out.
I wouldn't worry about vacuum bagging until you have built something that might do the job, once you have the processes involved in building sorted out and a prototype that has been tested and looks like it will stand up to the job you can then build the final piece with the object of maximum strength and least weight. Testing it against the prototype will give you confidence when its used in the final application.
I've done alternate layers of carbon wrapped at various angles, seems to work out well, its going to be very messy though.
You need to keep in mind that the info I'm giving you is the result of experimentation in my spare time, I like to tinker, see what I can get away with, I dont get to concerned if something fails as I will just build a better, stronger one.
Work out what you are aiming for by testing what is in place now.
Darryn
Mosquito 1704
South Australia
Thanks for the description of your process Darryn!
What I was discussing is not a sandwich. It looks like al alloy. The fibers are contained in the metal.
Al carbon sandwich is another story. I general it does not work well. They delaminate. I have tried it and I have a Marstrom Al/carbon rudder crossbeam. The results are the same, delamination. M&P handbooks list 2 problems. Unstable surface on Al. The Al oxide surface finish forms over time and the epoxy bond breaks. Also there is a problem with the difference in stiffness and response to load unless the Al is foil thick.
Thank you Darryn,
I'll try some experiments soon. I've been toying with a few ideas for building my own boat for some time, but I want to be sure that I can do it a) as cheaply as possible and b) the way I want it rather than having to incorporate proprietary extrusions etc. that might not be ideal to the way I want it. In particular I wanted to try and develop a 'one piece' style of construction where the beams are blended into the hull once all is bolted together and avoid the current appearance of all catamarans where at best the hull is faired to allow the beams to sit into the trays and give a smooth appearance.
I've just read what I've written and I don't know that I've made myself clear..... 
I want the beams to form the fairing at the hull junction not the other way round.
Anyway it's just a sort of idea at the moment.
Thanks again Darryn.
What about the new material GLARE (Glass reinforced laminate) used for airplanes (airbus) and developed at Delft, the Netherlands ? Could this be used in the catscene ? 
I think you have this backwards- kevlar on the outside and carbon on the inside. Otherwise the carbon is doing ALL the work as it's the stiffest of the three.
With a Kevlar/Wood/Carbon layup, the kevlar distributes the load to the wood, which in turn distributes the load to the carbon.
With the Carbon/Wood/Kevlar layup, the carbon takes all the load and the wood only absorbs load when the carbon cracks.
What do you think of that Mary? Delft now famous for crocheting up glass fibre?
With a Kevlar/Wood/Carbon lay-up, the Kevlar distributes the load to the wood, which in turn distributes the load to the carbon.
First, a practical matter, It is very hard to sand and fair Kevlar, it fuzzes. So you put it on the inside so you don't have to finish it. You can cover kevlar with glass or microballon epoxy to fair it but that is dead weight
Second, Components of a laminate do not take load individually. It is the strength of the whole. Once you exceed the strength of the whole, it starts delaminating, becomes about as strong as wet cardboard and and the whole thing falls apart.
Third a Carbon/wood/Kevlar can be made lighter and cheaper than a carbon/wood/carbon. Plus Kevlar has great impact resistance and tension strength. In case of a sharp impact, like a collision, there are a lot of cases where the carbon would break but the wood/Kevlar will flex or not break clean so the hull would hold long enough to go home and fix it. That is the theory plus panel testing plus hear say from white water kayaks anyway.
Fourth, for a homebuilder Kevlar is easier to laminate and a lot cheaper. I have bought it for as little as $2/yd on eBay. Carbon is ridiculous on eBay. To make carbon junk for their car, people are paying more than they could buy it from a real dealer like Fiberglass Supply Company.
Carl
Imagine if we could build our boats like this, 1 piece, the technology is already out there.
"The Premier I composite fuselage consists of 2, filament wound cabin sections (1/8th inch carbon fiber filament that is pre-impregnated with epoxy) that are bonded together."
Check out the pic.
I like the Kevlar on the outside idea. Makes good sense.
Darryn
Mosquito
1704
South Australia
Darryn, now you are getting closer to my crocheting idea, because I was thinking about how to make it as one piece, like a big sock, whether crocheted or knitted or woven, around the hull's internal structure and bulkheads. I'll bet a good basketweaver (or hatweaver) could make a REALLY light boat using palm-frond leaves (or whatever they use) -- and those are available in huge quantities for FREE.
Let me be blunt. Don't put Kevlar on the outside of a core composite. It is likely to fail.
In general, near worst case, for a catamaran the outter layer of a core composite is in compression and the inner layer is in tension. Kevlar is strong in tension and weak in compression. Look at what happened to the Kevlar/foam core Tornados. The Kevlar failed in compression. This also applies to similar materials like Specta/dynema/Vectran/etc
I hate to keep this thread alive BUT I don't want anyone to spend time building something that may fail.
I believe the Taipan 4.9 comes with optional Kevlar hulls, and I had assumed (although in complete ignorance) that it was on the outside. Anyone know?
I believe Boyer uses Kevlar on the inside and glass or Kevlar/glass on the outside. In any case Boyer has done suffient engineering to make sure their hulls hold up.
The real problem is a homebuilder substituting
Carl and Mary
Your crochetting idea is already in production, Forte RTS http://www.forterts.com/per.html uses a computerized braiding machine to make carbon parts. This technology is directly from the weaving industry. The carbon (or whatever fiber) is wound around a mandrel, so you need a mandrell in the shape of your part. As its being wound, it is impregnated with epoxy. It is then put in the autoclave, and cured at elevated heat and atmosphere. The result is strong, light and very reasonable priced parts. I bent 4 aluminum booms (falling on them) before I got a forte boom. I have beams, spin poles, booms and tiller extensions, and tiller connectors. The only thing is that the outside "skin" is an "uncontrolled surface" so its not smooth, it has texture and it needs to be UV coated. Tony will make you spars to your specs for very reasonable prices.
also, ebay carbon is a rip off. Go to carb.com for the best prices that I have found on the internet. 5.7 oz carbon weave 30 inches wide is $14 per linear yard at carb.com. 50in wide is like $20 and I have seen it at over $45 per linear yard other places. Ebay was even higher, its some guy selling his scaps, or selling sheets with epoxy already hardened to people for accent parts in their cars. Carb.com is in Hawaii. They told me prices were going up. Order now.
I also found good prices on nomex from http://www.plascore.com/ they were about 1/2 the price for 1/4,5lb,ox - a 3x8 sheet was $50. The lead time is 6 weeks.
I talked to Wade.
Wouter, Your 14kg figure for an A cat sounds low. 17kg-18kg target is what at least 6 new home built A cats are shooting for - check out the pictures http:/
Any ideas on lightweight hull finishes? How about wood veneer? How about wood printed paper? How about a hawaiian print fabric? All white is boring.
Bill
The Taipan 4.9 can be ordered to have a glass/kevlar hull skin. If memory serves me right this means that the sandwich construction from outside to inside is :
Gelcoat
Glass
Kevlar
Foam
Glass
You don't want Kevlar on the outside of the outer layer as well as it forms a vary rugged fluffy surface when is touches something abbresive. Glass wears down alot more smoothly.
The kevlar is only in the hulls to give it extra impact resistance. If makes the hulls alot harder to dent. It is not in there to improvement tensile strength or stiffness of the whole hull.
Wouter
14 kg was taken from Marstroms webpage
http:/
I know that homebuilder used to build A-cats for as little as 45-50 kg's before the 75 kg rule came into effect. However if you pitchpoled one of these than you would break the hulls. I think they used 3 and 2.5 mm marine ply for these hulls.
I'm often amazed of how light you can actually build when using marine grade ply. It is pretty good boat building material and it is very impact resistant.
Wouter
There is a very good description of the layup of the Shadow hulls in the following sail test under "Design and Construction"
http:/
Damn, my boats going to fall apart, its double Kevlar so it probably wont even make it to the water before the outer layer fails in compression and then, because its platform weight is 55kg it will break up when I pitch pole, dont know how it has survived the last 16 years 
Darryn
Mosquito 1704
South Australia