Wood Carbon Fiber

Either. You should study how the bond between glues/resins/adhesives and solids work.

The primary function of the core in foam sandwich construction is to resist shear. Shear is different than compression.

Unless the buckling leads to catastrophic hull failure which is entirely possible. Good design requires a balance of resistance to the various potential failure modes.

No one is claiming that "one layer of 6oz glass cloth is the only solution to the parameters" but it may be a better solution than replacing the glass with carbon fiber.

Are you planning to design a boat?

 

This topic seems pretty well covered up to this point, but I'll add my 2 cents worth.

First, regarding resins, polyester is porous and so lets water through the laminate which can get into the core if the outside skin is not thick enough or if not built with the right materials, which usually means you need lots of mat on the outside skin. Vinylester is much more solid, but not 100%, so there is a chance that a tiny bit of water can get through it. Again, lots of mat helps. Vinylester is used in things like underground gasoline tanks and other vessels that hold chemicals, so it is really pretty good. Epoxy is 100% solid, not porous, so water does not get through it. That is why it is used to seal the bottoms of boats that have blistered polyester laminates.

Brittleness: All composites are brittle materials, meaning that they don't have a definite yield point the way many metals do. Some are more brittle than others, and a lot of that depends on the resin. Most polyesters have an elongation of only 1-3%, which is really brittle--the resin breaks before the fiber. There are some polyesters and vinylesters that have an elongation of 4-8%, which are very forgiving and don't experience minor cracking as easily, either on the surface or within the laminate. A shining example is Mike Plant's very first boat, the Rodger Martin designed Airco Distributor, built in 1984-85 for the 1986 BOC. It was built with fiberglass over Airex foam core and Dow Derakane 8084 vinylester resin which has an elongation of 10-12%. Airco has been raced around the world 3 times and it has crossed the Atlantic 15 times, and it is still going strong, still competitive. Epoxy resins can have a wide range of elongation, and the WEST resins typically are in the 8% elongation range which makes them very suitable for working with wood or with fibers. The resin just holds together better. I have seen one or two suppliers who have very elongation epoxy resins, on the order of 20-30%, and in my opinion, these resins are way too rubbery.

Engineering: In the best of engineering, fiberglass cored laminates are engineered for the right thickness of skins and the right thickness of core. The strength and stiffness are both considered. Usually, compression strength is lower than tensile strength, and the highest stresses in a boat occur at junctures with bulkheads and stiffeners, or with stiffeners at bulkheads. The compression side (inside the hull) are where the usual failures occur. The stresses in the centers of the panel between stiffeners and bulkheads are only half those at the junctures. All of this is taken into account in the engineering. The core is always designed for the shear loads between the inside and outside skins. The denser the core, the higher the shear strength. The thicker the core, the lower the shear stress in the core. So the trick of engineering is to balance the right amount of skin thickness and strength with the right amount of core thickness of the density selected so that the structure carries all the loads evenly. Ideally, a structure will fail by compression in the skin and shear in the core all at the same time. But the loads have to be really high because we use safety factors in all of this. The denser the cores, the more expensive they are. Cost also follows thickness--thicker skins and thicker cores are more expensive than thinner materials, obviously.

So, which is best? Fiberglass/polyester and core, or wood-epoxy and carbon fiber? First, best in what way? You cannot make a generalization because the engineering of a boat is too complex. By far the first three things that come into play are the cost of all the materials, the complexity of the lay-up measured against the skill of the owner/builder, and the size of the owner/builder's wallet.

I will add that the study in the Gougeon Brothers book is all well and good, but remember that the testing that they do is highly specialized and really rigoruous compared to what a boat actually sees. Usually, in fatigue testing, the tesile test, for expample, is either full stress reversal cycles, or full stress to zero cycles, full stress being the stress level for the data point at hand. When you think about it, boat hulls don't really get stressed all that much. Most of the time, they are just sitting afloat and are not loaded at all. When sailing, it is usually for day trips or short excursions. A round the world voyage will age a boat about 10 years per year, but still, a lot of the time, the hulls are not loaded really all that heavily. So the conclusions that the Gougeons make about fatigue have to be taken with a little bit of reality. As PAR stated above, there are thousands of composite boats afloat that have not delaminated or failed.

You pick your materials commensurate with your skill and pocketbook, and you engineer and build accordingly.

I hope that offers some perspective.

Eric

 

As Usual Eric Sums it up very well. If I could add another $.02.
The use of Uni Carbon Fiber can make good engineering and economic sense when the load path is clearly understood. The most obvious is when laid on top of stiffeners. Since the higher modulus material will pull the neutral axis upward away from the hull shell making the stiffener more efficient due to less "bulk" having to be added for equal stiffness. A hat section made from +-45 Fiberglass roving making up legs and webs with 0 deg. Carbon uni in the cap is an example of materials working together in a logical manner. The uni taking the brunt of the tension or compression due to bending and the +-bias fibers carrying the shear loads. The bias material also conforms well to varying shapes, and the uni lays well along straight lines. all IMHO.

 

I don't believe they are opposites. In foam sandwich, the foam acts to keep the skins separated, giving the laminate its strength. In sheathed cold molded, the wood does act to keep the skins separated, but the wood itself is actually providing most of the strength. Foam is not a strong material when compared to the other materials used (fiberglass laminate, carbon laminate, wood.) You can cut H80 divinycell with a steak knife, can't do that to any of the others.

I know how they work. I work with them. Enlighten me, what glues or adhesives do you use in hull construction?

Or to separate skins.

True. Foams will fail in shear. Foam compression causes reduced separation of skins followed by, buckling of laminates and/or failure in bending. Skins will fail in tension of compression, which are also different. There is also the problem of face sheet delamination, which is also different.

You are describing failure in bending. Which would require one to exceed the ultimate tensile or compressive strength in one of the skins, crush the core by exceeding its ultimate compressive strength, shear the core by exceeding its shear strength, exceed the ultimate tensile strength of the core laminate interface and cause face sheet delamination, or a combination of any of the above.

Stiffness is needed for calculating deflection or reducing deflection, but if ultimate strength isn't exceeded in one way shape or form, imho it shouldn't be considered a failure. Umiak construction comes to mind. Seal skin over wood or bone planking. Lots of deflection, no failure.

Very true, and more than likely right, depending on what is considered a "better solution" Basically I was hoping to check the logic was those here to see if it follows, and to come up with a ball park weight savings/$ or labor savings/$ relation. Obviously it is not that astonishingly valuable, because I'm sure I'm not the first one to think of the idea. But the discussion does serve a great purpose as a vehicle for gaining knowledge.

I'm building one from the hull up as of right now. But little design. Very utilitarian.

B.S. in Mechanical Engineering and a current Westlawn Student. I would like to design someday, but only time will tell.

I think you added more than 2 cents worth. Thank you. Much cleaner than my discussion.

Is it safe to assume that in the powerboat sector the Gougeons' studies are more applicable?

As an aside, Eric did anything ever become of that House Boat idea of yours? We met at IBEX 2011, I really liked your presentation.

 

No, I didn't describe failure in bending.

If a structure is not stiff enough then there can be buckling, either global or local even with "high strength" material and stresses well below maximum allowable at the onset of buckling. When a structure buckles deformations can become large enough for failure as described above. Sometimes the failure due to buckling will be localized; other times it can become catastrophic.

This is a different situation than the "classic beam in bending" as taught in introductory structural mechanics courses where there local deformations are assumed to be small enough to be negligable, ie no buckling either global or local. That assumption as well as some others allows stiffness and strength to be considered separately. But those assumptions are not always valid. This is one the ways that linear stress analysis may not be sufficient and can be mis-leading or worse.

See comments above. Stiffness can be very important to prevent buckling and other structural instabilities which can lead to failure.

Umiaks have frames with sufficient stiffness that they don't buckle. Very different construction and irrelevant to this discussion.

 

Certainly, with powerboats, the loads are higher and more frequent, so boat structures have a much greater likelihood of fatiguing, actually no matter what type of material they are built from, and composite structures in powerboats will be as susceptible or more so to fatigue failure, than say sailboats or dinghies and small craft like canoes and kayaks. So the solution to engineering usually is to increase safety factor for highly loaded structures, and/or apply any direct experience one may have on the scope at hand. For example, I remember listening to a lecture by an industry racing powerboat veteran who said, "Build them strong, then add power." That was his overall design guideline, and I think it still applies. He knew roughly when his boats would break, and he would do laminate testing, so applying all that knowledge he knew how to build his laminates, then whatever the boat weight turned out to be, he would follow Crouch's formula and decide on the power package. I'm sure he went through the design spiral like we all do, but he had practical experience that let him know what his overall strength and fatigue strength had to be. The easiest way to get there is to have a sense of the basic safety factors you need over the max load so that the boat will survive the fatigue phenomena it will experience.

As for the Modular Catamaran Houseboat, I still get inquiries from time to time, but no one has stepped up to the plate to buy into it. I think we are still suffering the effects of the great recession and the mortgage crisis. There is not enough cash around amongst real estate developers and investors to move into new houseboat marina construction, the central core of my idea. Also, I think that not a lot of developers have tuned into the idea yet that living right on the water in a houseboat is an easy sell. Judging from the inquiries I get, that kind of lifestyle is on a lot of people's minds. No regular marina, even with a fair percentage of liveaboards, is going to let in houseboats (I get a number of inquiries from people who want to do just that--"There's a marina right here in town, can't I put a houseboat there?" Uh, no, you'd better ask first what kinds of vessels they accept. And check with your local ordinances regarding houseboats and liveaboards.)

And just so that we can get this thread back on track, houseboats of course can be built out of composite materials, but I would use, and have used, plywood and fiberglass, I would not use carbon fiber. The loads in the hull are really tiny and carbon fiber would be a waste of money. And there is no fatigue in a houseboat hull.

All this said, my sailboat design Saint Barabara, 37.5' LOA,is strripped planked Western Red Cedar with carbon fiber skins either side. The wood strip planking is 3/4" thick, the carbon skins run at +/-45 deg to the strip planking and are less than 1/32" thick. The laminate was developed by the owner with the help of The Gougeon Brothers and built by Van Dam Custom Boats in Boyne City, Michigan. It's a great lightweight boat. Without the carbon, the strip planking likely would have been about an inch thick, and fiberglass overlays would have been thicker, the whole boat would have beed commensurately heavier.

By contrast, my very first commission, Corroboree, was 35' LOA, was designed and built to Lloyd's scantlings in Kauri in New Zealand, again for a Michigan owner, and her hull planking is 1-1/2" thick. The strip planking is 1-1/8" and the +/-45 Kauri veneers are each 3/16". The outside is coated with a layer of 10 oz. fiberglass in epoxy as a finish barrier and base for the fairing and paint. She's 24 years old now and still owned by the original owners on Lake Erie.

All food for thought.

Eric

 

1. I have used US Composites epoxy and after 4 seasons in my Bayliner I feel I can say that it is a quality material. Cost per gallon is less than half the cost of west system epoxy from west marine.

2. I have bought roving in surplus auctions on ebay...I picked up two orders of 18 yards of 18 oz roving for $40 per order.

I do not see fiberglass losing that much strength over 800 hours. There are plenty of Chris Craft Commanders from the '60s that are very much still seaworthy. My Coho shows over 3400 hours. If strength diminished to only 19% over 800 hours I would be safer in a cabin cruiser made of paper mache and the boat couldn't support itself on blocks.

3. it is my personal opinion that more laid up layers make for a more water resistant construction. I feel better having 3 layers of thinner glass over say wooden stringer (in a fiberglass boat) than 1 layer of say 40 oz glass. I am not a professional and this is simply a personal feeling.

My experience is more from fiberglass boats than wooden boats so much of what I said is probably pointless here, but still

 

Incorporating a model for a hull with non-developable surfaces and multilayer stress-strain relations of both anisotropic and isotropic materials supported by a super structure... I doubt that would be covered in an introductory structural mechanics course. I'm not sure there are any courses that would cover that except maybe an advanced nav arch course, but even that is doubtful because foam sandwich is not a construction method preferred by commercial ships. Not to mention inclusion of FEA would be mandatory.

As for the Umiak being irrelevant to the discussion, I'd be careful saying that. The newest advancement in composite boat design is actually just that. Check out what Scott Lewit, president of Structural Composites Inc. has done in designing a RHIB. "It [Carbon Fiber/Polyester laminate] functions like fabric-covered wooden wings once did on vintage aircraft."

To be honest, my father in-law is a contractor and specializes in higher-end builds and I've been trying to pitch it to him for a while, because I think he would enjoy the challenge, but I haven't come up with the guts yet. He doesn't care for me much as it is and I don't want to take a chance upsetting the fragile relationship. But someday.

And there we have it... Thank you.

The reason the chris craft commanders from the 60's are still seaworthy is because they were built with conservative safety factors, likely greater than 5. In other words, the hulls were at least 5 times stronger than they needed to be when they were built. All boats are built this way today, although at times less conservatively, especially in the race sector.

It is my understanding that it is actually the opposite. Glass fibers act as a channel allowing water to move in the laminate.

Built to Last: The Lifespan of Fiberglass Boats By Eric Greene
This is a great reference that discusses both the area of water penetration and fatigue.

 

what ??

If you want to learn about glass and boats go spend a year doing boat repairs before you even consider building a fibreglass toilet of your own . I been using composites for more than 35 years and seen more high tech carbon failures than i ever want to think about
Mixing materials is most of the problems .if you start with glass you stay with glass if you use polyester resins you stay with polyester . you want to skin a wooden boat you use the glass to protect what its covering and epoxy resin because it made to stick to wood .
throw away all the books you been reading and take up a job in composites and get some dust in your lungs , go stand with a roller in your hands and sniff the fumes for a while. i travel to differant countries and teach and show workers how to do there jobs better . looking at what you've written you know very little ! get some practical exsperiance !!

 

Maybe you should lay off the fumes, and repurchase the books you through away. I have practical experience, however I choose to wear a respirator.

I'm discussing design, not repair. As for "you want to skin a wooden boat you use the glass to protect what its covering and epoxy resin because it made to stick to wood." This is true, this is proven method. However not all design objectives are the same. In high speed applications, weight is very critical. Carbon fiber skins may provide the strength needed to drop some weight.

I can see with all your experience, you know so much. Next time I need some toilet work done, I'll be sure to contact you.

 

YOU SOUND LIKE YOU FIT IN THE 25 TO 40 AGE GROUP JUST AT A ROUGH GUESS !!

iF YOU HAVE EXSPERIANCE THEN WHAT ARE YOU DOING HERE ASKING QUESTIONS ??
I DID REPAIR WORK TO SEE FIRST HAND WHAT OTHERS WERE DOING WRONG AND NOT TO REPEAT THE SAME MISTAKES THEY WERE MAKING .
I DIDNT NEED TO READ BOOKS, BECAUSE I HAVE WRITTEN A FEW AND MADE VIDEOS .
iF YOU ARE SERIOUS ABOUT DROPPING WEIGHT GO ON A DIET AND HAVE A BIG DUMP BEFORE YOU GO BOATING EACH TIME !
YOU INTO POWERBOATS OR YACHTS ??
SPEED WILL COME FROM CLEVER DESIGN AND DRIVERS WITH BRAINS !!!BEING SUPER LIGHT WEIGHT HAS A VERY LIMITED APPLICATION ,SO AS YOU CROSS THE LINE IT SELF DISTRUCTS IS THAT WHAT YOU WANT ??

wHAT IS ONE OF THE FEW THINGS CARBON IS REALLY REALLY GOOD AT ?? DO YOU KNOW ??

 

Carbon is fantastic for masts. Light, stiff and most important no corrosion so cheap over the long term.

Whomever invented the carbon mast needs a nobel prize.

 

Ok you are looking at carbon with blinkers on and only seeing all the good things !! now you need to take the blinkers off and look for the down side and it really has some down sides as well . Because its light and stiff it snaps and breaks like a carrot . its widely missused and overloaded and thought of as being indistructable and if engineerd and used how it should be it does all those good things !!,people exspect to much from it !! Its just another building material and yes its light ,and yes its strong BUT !!!!glass can do amazing things as well if used properly with the right resins . Glass has durability and it will show signs and tell you when its overloaded and before it breaks and can be made to hold on till the last strands let go , carbon is there one moment and oops shes gone !!! usually with no tell tail signs its about to leave and you left scratching you head as to how did that happen . :?:
Long time ago i worked on progressive distruction of items used in the safety industry and kevlar was the tops for somethings but just your everyday glass off the shelf won out hands down finally over all !!,carbon was way down near the bottom of the heap !!
Progessive distruction is really interesting its a test of not only the building materials and combinations of all the differant fibres and resins but how they can be used and why they should be used in such a way as they progressivly break yet hold on even when they are crushed ,bent and cracked and almost broken .
Like i said i did glass repairs and saw and took particular note of what worked and held together ,and what simply parted and came fell off really easy . Its a reall eye opener thats for sure .

 

I have no doubt that correctly aligned , compacted and cured epoxy glass is a fantastic material. I often wonder about this carbon fascination with home boatbuilders. Carbon is double the price of glass and home builders could never expect to achieve its theoretic physical properties.

Oh and my trusty carbon mast has been standing for 20 years. Only painted once. An Alloy mast would be painted ever 5 years and be a mass of stress cracks and corrosion after 20 years

 

For the most part when we talk about fiberglass were talking E glass but people seem to forget about S glass and go straight to carbon when they could get a pretty good improvement in physical properties just going to S glass, i guess its just not as sexy. Where vinylester falls in between polyester and epoxy in both Physicals and price so too does S glass between E glass and carbon.

Steve.