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Old 25-11-2009, 22:20   #16
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Quote:
Originally Posted by kiapa View Post
nick, i think you might be oversimplifying things. aluminum is great bldg material, but taking care of it IS serious business. i've run across four beautiful aluminum boats while cruising, all run by very capable families. it's a small sample... but two of the four had undiagnosed problems that lead to dangerously 'think skins' in spots.

i'll take wood, plastic, with a can of epoxy on board any day of the week.
@Kiapa: as I said, there's bad ways to build an aluminium boat, no question about that. But when it's done right there's no problem. The looks of the boat are not the issue, it's the technical design and manufacture that make the difference.

@Barnie: polyester???? ughhh! no maintenance? tell that to Fish! No, vinylester at minimum but epoxy would be just great. Jedi is from 1994 and there's no sign of even the smallest blister... that's because she's built in vinylester instead of polyester.

@S&S: you can take that into space ;-) But it isn't new; Dashew put unidirectional reinforcements into Jedi and the hull was molded in 1993. I think TPI was about the only yard doing it at that time. SCRIMP resin infusion too, look that up as it's still high tech today.

But, in the end, if I was gonna build my own boat, it would be plywood/epoxy/fiberglass/carbon. If I would have it build: aluminium.

cheers,
Nick.
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Old 25-11-2009, 22:27   #17
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A post in boat design forums from 2005 by Eric W. Sponberg

I did a technical paper some years ago that was published in Marine Technology of SNAME, Vol. 23, #2, April, 1986, pp. 165-174 called "Carbon Fiber Sailboat Hulls: How to Optimize the Use of an Expensive Material". It was also referenced by Larsson and Eliasson in Principles of Yacht Design. One of my references for this paper was another paper that I did before that for the Southeast Section of SNAME, Sept 1983, called "Fundamentals and Practicalities of Carbon Fiber Composites for Marine Applications." It became quite a bible for a lot of people in the marine industry.

I did physical tests and engineering analyses on 5 different laminates using unidirectional materials over foam core (4 samples) and one with balsa core (1 sample). In all the samples, the fibers were always running in the same direction, that is, I did not have any laminates with non-zero orientations.

#1: 3-ply S-2 glass, equal thickness skins both sides of 1/2" Airex core.

#2: 1 x S-2 glass + 2 x Carbon + 1 x S-2 glass, equal thickness skins both sides of 1/2" Airex core.

#3: 3-ply S-2 glass skins one side, 4-ply Carbon other side of 1/2" thick Airex core.

#4: 3-ply Carbon, equal thickness skins both sides of 1/2" Airex core.

#5: 3-ply Carbon, equal thickness skins both sides of 1/2" balsa core.

I studied:
a. computer predictions for strength and stiffness
b. test results for strength and stiffness
c. weight per unit area
d. cost per unit area
e. specific strength vs. specific stiffness (i.e. strength and stiffness divided by weight)
f. a desirability factor
g. Impact tests.

The results were:

Laminate #2 was the overall winner when considering all of the factors above. The all-carbon laminate scored very high for strength and stiffness, but at the time, a very high cost. The cost is still pretty high.

Laminate #3, where the S-2 glass is one side of the core, and carbon is the other side, was the worst laminate. It is not strong or stiff, and it wastes the mechanical advantages of the carbon, particularly considering its price.

In my practice, I always advocate for the balanced laminate. When mixing materials of different strengths and stiffnesses, it is always beneficial to make the skins mirror images of each other either side of the core. You get the most efficient use of the materials. This mirror image technique is quite fundamental to general composite design, and has been proven innumerble times in engineering analyses and tests.

I don't always mix materials, and every design seeks to satisfy different needs. As you are aware, the science is complex, so you have to pick and choose the best combinations for any particular design.

I hope that helps.

Eric
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Old 26-11-2009, 11:50   #18
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Quote:
Originally Posted by s/v Jedi View Post

@Barnie: polyester???? ughhh! no maintenance? tell that to Fish! No, vinylester at minimum but epoxy would be just great. Jedi is from 1994 and there's no sign of even the smallest blister... that's because she's built in vinylester instead of polyester.
Well, my boat is from 1980, polyester, gelcoated. No blisters either. Maybe maybe because in Sweden they know (knew) how to laminate and use gelcoat properly. Or maybe they used high specs materials too. Who knows.

So, since the boats I like (I would like) are all low effort designs I think any mechanically adequate resin would do. If vinylester is better/cheaper, why not.

My main concern is the fear that we may hit something minor (say a log) hence the idea of using some extra materia,l better than glass, in vulnerable areas. May be more costly to build still probably cheaper than a new boat.

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Old 26-11-2009, 11:55   #19
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To lancelots:

Do you think it is possible to mix glass with something that reduces impact damage? (kevlar?) - in order to build a plastic boat that would be more difficult to damage in contact with heavy floating objects?

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Old 26-11-2009, 14:23   #20
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Funny you should ask, I found this as I was wandering the web.


High performance, carbon nanotube strengthened epoxies


Epovex™ is a new line of liquid epoxy resins from Zyvex Performance Materials (ZPM). Epovex resins are high performance, carbon nanotube strengthened epoxies ideal for numerous composites and adhesives applications. ZPM’s patented and proven nanotube dispersion technology gives Epovex superior performance. Epovex processes as easily as unfilled epoxy resin and can be cured with a wide range of curing agents. Epovex is available in both bisphenol-A and bisphenol-F types.
Arovex™ is a high performance prepreg using Epovex resin. The use of Epovex, optimized for use in a prepreg, offers dramatically superior mechanical properties over conventional prepregs without CNTs. Arovex is available in standard, intermediate, and high modulus carbon fibers, glass, and as a unidirectional, woven, or knitted material. Large custom material orders for Arovex are also available.
Engineered Solutions are available for custom applications of our technology.


Zyvex Performance Materials • Carbon Nanotube (CNT) Prepreg, Epoxy Resin, and Adhesive

Does anyone care to comment?

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Old 26-11-2009, 15:17   #21
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Interesting thread. Barnie, you shouldn't sell that boat because it is unusual to get away without blisters after that much time. But I also have a feeling that you're not in the tropics which might help. I've seen many Swedish built boats with blisters in Holland, also built in the 80's and even earlier. But indeed some builders have much more trouble than others and quality of lay-up and discipline are key.

Vinylester is more expensive and more difficult to use. but it's better when done right. Vinylester resin is good for fixing polyester boats (the 3M fillers are still vinylester) but the price of epoxy has come down to a level that epoxy makes more sense for repairs. But building a hull is different and vinylester would be great. Many years ago a good vinylester was better than a bad epoxy but I don't know any bad epoxies anymore. But epoxy is at least twice the price...

About reinforcements. I always first think about the stiffness of the hull. I hate, really hate flexing hulls. Like the Morgan's: they don't go through the waves, the waves go through the boat. So, I'm thinking about the area around keel, rudder, prop-strut and stringers for carbon reinforcements. Abrasion and impact resistance is a science on itself. Metal rules there: if a rocky point want to come through during a grounding, the metal just changes shape to accommodate that point without springing a leak. For anything not metal you need to look at sacrificial material because it's gonna grind away. I look at watertight bulkheads, integral tanks etc. and only after that to reinforcements and sure kevlar is king there. But you would need it on the outside of the hull and the problem is that I hear it's a bitch to work with. Dashew took a different approach: he offered the buyers an option for extra material at the turn of the bilge and every buyer took that option. All the info you ever want to know is in his encyclopedia, incl. diagrams of each layer of fabric with full specs of the fabric.

My biggest fear would be ice I think. Not just floating pieces of it but also freezing in a marina.

cheers,
Nick.
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Old 26-11-2009, 16:36   #22
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I used i.a. Kevlar, Spectra in sail making and i know some of their properties. I also know that some polyethylenes, Kevlar and Spectra/Dyneema are part of ballistic armours. Hence the idea that they could be applied towards similar use between layers of lamination. I remember at a time Catana advertised sthg (aramid?kevlar?) inserts in front portions of the hulls where collision damage tends to be be highest.

I like the idea of watertight bulkheads and I have seen it applied even in small boats. I just think the bulkheads AND some form of trying for a stronger hull shell should be applied at the same time rather than either / or.

It is easy to imagine that the ultimate will probably be neither vinylester nor alloy but something newer that will come from those areas of technology that develop faster than sailing - like the space things, cars or military. That's the way it has nearly always been.

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