PVC Structure and Laminations

Discussion in 'Materials' started by JCFARER, Oct 8, 2004.

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What is the greatest concern for PVC Skinning?

Poll closed Oct 23, 2004.
  1. Feasability

    0 vote(s)
    0.0%
  2. Cost/Weight

    0 vote(s)
    0.0%
  3. Structural

    100.0%
  4. Cons

    0 vote(s)
    0.0%
  5. Weight/Strength

    0 vote(s)
    0.0%
  6. Aesthetic

    0 vote(s)
    0.0%
Multiple votes are allowed.
  1. JCFARER
    Joined: Sep 2004
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    JCFARER Junior Member

    Hello all:

    I just wanted to throw this out there because I haven't seen a discussion on it. Some will kill it, some will explore it. Hmmm, this must have been out there at one time or another.:idea:

    PVC pipe comes in a plethora of lengths and wall diameters and are usually resistant to all kinds of chemicals. In the smaller diameters, they are quite flexible and once filled with a substance, they can either be very stiff (foam)or almost indestructible (cement).

    What if a vessel were to be skinned with 1.25 diameter pipes of this material filled with foam, attached to each other and frame members mechanically, radius outlines filled with virgin glass filler and then glassed on the outside to provide further reinforcement and protection? The inside can be filled in the same manner and the skinning can be plywood for aesthetics. This sounds like it would be super easy and fast since lengths can be attached with fittings if they are not long enough to skin. Also, it sounds like it would be easier because a 6 pound length of 30 foot PVC would be easier to handle and maneuver into tight radiuses single handed than a 40 pound scarfed piece of lumber or plywood. I also think that the circle would add to the structural strength of the skin.

    What does the pros and cons look like?

    Jay :D
     
  2. PAR
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    PAR Yacht Designer/Builder

    Glue up some sections of pipe after you've hard fastened them with screws or bolts, filled with foam and test to destruction. You soon find out why . . .
     
  3. JCFARER
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    JCFARER Junior Member

    Hello Par... :idea:

    Between you and the poll, this seems to be the second structural concern.

    Okay, but before I do I will need something to compare against. I might as well publish this test for everyone.

    1. I will construct 3 mediums:

    1/2" plywood with 2 layers of 6oz cloth on each side.

    1/2" foam with 2 layers of 6oz cloth on each side.

    1" pvc, with 1/4" wall mechanically fastened and filled with foam. The grooves on the outside and inside will be filled with silica and epoxy to make flush with the pipe and 2 layers of 6oz cloth on each side.

    All three will be 18"sq. and I will document certain data before testing to destruction. The data will be cost, weight, flotation, difficulty to construct.

    2. I will build a jig to test the mediums.

    It will have iron plates on end which will be placed on the 12"sq. perimeter of the medium as resistance for the medium which will be placed on top of a tire jack. The tire jack will be placed dead center on the medium with a 1"sq plate to test the loads at 1"sq. The tire jack will be sitting on top of a scale to measure lbs. per 1"sq.

    3. Loads will be measured and events will be documented at different milestones.

    Loads will be recorded everytime there is any crunching, splitting or cracking noise and the medium will be inspected. Visual failures will be documented under load (the load on the medium will not be eased for inspection)and if the load has decreased that will be documented. Loads will continue to be applied until destruction of the material.
    Destruction will be defined as any crack that is completely cross sectional in nature irrelevant of whether it is perpendicular or angled, or if the jack plunges through the medium.

    Okay... does this sound objective enough? I will of course first ask if any study exists out there so that I don't have to do this.

    Before I begin, I am going to open up to any and all suggestions or further data study requests that anyone would like to have incorporated.

    Jay :D
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I would be helpful to make it a fair test and compare apples to apples rather then what you've suggested.

    Currently you are making two 18" sq. x 5/8"~ panels and comparing them to a 18" sq. x 1 1/4"~ panel, each of differing construction.

    First of all the engineered structures you're trying to make require some concessions (engineering) in regard to differing tensile, compressive and flexural strengths of the different materials used. Attention also will be necessary to the modulus qualities, distortion, moisture absorption and structural orientation in the matrix.

    Panel 1: The two layers of cloth over the plywood will provide very little additional strength to the structure, providing only a limited amount of abrasion resistance. Puncture resistance will increase a slight amount, but not enough to warrant it's use for such.

    Panel 2: The thin layers of cloth will be the structure (in sandwich) in this panel and couldn't be asked to provide a lot in strength compared to the others. The density of the foam and the type of foam will determine the abilities of this panel. The skins would have to be much thicker to be a fair test, as the plywood core used in panel 1 is far stronger in every way we can measure, making panel 2 a weak kneed sister at best. Not a very fair test of a proven construction method, though will be the lightest of the lot.

    Panel 3: You will have a bunch of reinforced epoxy running in one direction (filling the grooves between the pipes) more then I think you realize. This will provide a good bit of strength in one direction, but not much in the other. The 1" pipe having an over 2:1 advantage in thickness seems rather unfair. Not much sticks to PVC. It can be chemically welded and can be welded with heat, but epoxy doesn't stick to it well at all, so you'll be relying on mechanical leverage in it's application (Liquid Nails would be a better way to go in this application) rather then the qualities epoxy is known and used for. You may be better suited by using polysufide as your binder, but then you'd have a flex issue between the core filler and the sheathing, which is the worst thing in cored structures. Again, the foam type and density will be an issue.

    Engineered structures are a complicated lot of formulas and compromises, not easily done without completely understanding the properties, mechanics, physics and chemistry involved.
     
  5. JCFARER
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    JCFARER Junior Member

    Par,Par,Par... You're raining on my parade. :D My initial post was to establish feasability of the pvc skinning and you're reply was to build it and test to destruction and I would then come to some kind of understanding. I assumed that it would be an unhappy understanding, so I figured I try a test.

    My comparison of the different panels is actually only to measure the plywood with 2 skins (which is typical of boat construction) and the panel I am suggesting would show some promise. I know that the foam with two skins is not going to stand up to the test because the skin is not thick enough, but I don't care about the panel. You may however, tell me what layup you would like to see on the foam and I will test it.

    The thickness of the panels just happen to work out that way and should bear no consideration for the test because I wanted to simulate inside diameter and not outside, in this case, 1/2"ply...1/2" foam, and 1/2" inside diameter in the pvc filled with foam. The outside of the pipe is in my belief only for neatness and the wall can be any size you please. The skins obviously only simulate a water barrier as it would in any layup and who cares about abrasion when we are testing for strength? Besides, we all know Dynel is excellent for abrasion.

    But, an open mind is a good thing...so if you want, specify exactly how you would like to see the panels as long as the inside diameter is the same for all panels and the pvc panel is still constructed as I said. I am still of the belief that the glue will bond well.

    Okay, I'm awaiting your designs so I can start...and any other suggestions. Wow, lots of views and little response. It looks like maybe only we are interested in the results. :confused: Maybe it isn't worth the trouble.

    Jay
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Sorry about the rain, but epoxy doesn't stick to PVC, so what's the point? I've heard that hot glue will stick somewhat, but I know of no one relying on hot glue to hold their structures together in boats, planking or otherwise.

    The whole point of testing one material or method against the other is to find a better way, cheaper way, more efficient way, etc. Engineering cored structures isn't difficult, unless you want to get the most out of the structure for the least amount of effort, materials and cost. It makes little logic to build heavier then necessary, nor more costly then necessary or require more effort then necessary, unless the gain (proven through testing after the math) can provide reasonable offset. These are the basics of engineering. The concept seemed interesting right up to the part where you learned that binder (epoxy) doesn't stick to the core material, which is the worst case for a cored structure. Now your options are to use a different binder, core or both, possibly treat the core so the binder will stick, etc.

    Don't get back in the box, keep on thinking outside . . .
     
  7. nero
    Joined: Aug 2003
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    nero Senior Member

    excellent attitude!

    A great idea to try something different. Let me know what happens. I have used a quite a bit of PVC pipe in residential plumbing. The stuff we use in France is different from the stuff we use here in the states.

    The French stuff is thin walled ... 2 mm. It explodes when it is hit with a hammer or bent to much. It is excellent for plumbing because with a bit of heating it can be stretched and bent. Because it is so flexible perhaps you could chink the joints with PU foam in a can. Would not give a lot more in structure but would keep water out. Incedently, pole vault poles are foam and balsa cored tubes.

    I am interested in extruded polystyrene and expanded polystyrene granuals. The extruded stuff is available in 600 psi compression. Maybe this could be cut and bonded into a matrix with epoxy and fiberglass cloth to make some sort of stripping material?

    The granuals are used (in france) to make light cement for use under tile floors. I busted some of this in a remodel and was amazed at the stiffness and toughness. Maybe this could be used with a resin to make strip planks.

    I would like a core material to replace WRC. (The stuff is overpriced now and the wood traders are more like horse traders) In other words a core material that is structural not just transfering loads between skins.

    Can these ideas be of interest to your study?
     
  8. Buckle
    Joined: May 2004
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    Buckle Composite Engineer

    Going back to basic?

    Can I just state that the whole point of a sandwich concept is to increase the second moment of area, thus increasing panel stiffness, without much increase in weight.

    So can anyone please tell me why there is need to fill the insides of the pipe with heavy fillers etc. With all sandwich panels, 99% of the time, the core fails first in shear. However going back to basic's,the point of using a light weight core is too primarily increase the second moment of area (bd^3) of the structure. Therefore the load is carried in the skins of the hull. So why, why,why do you want to use heavy fillers inside the pipe. I cannot see not advantage. Its just added weight, cost, and labour.
     
  9. nero
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    nero Senior Member

    For me it is cost reduction.

    Using a stuctural core (like wood stips) means a distributed load support. The skins do not take all the load.

    So I can use materials that are less expensive (maybe even cheap), do not require hiring a mathmatical genius (generaly interesting fokes).

    Allow me to have a strong, durable boat by doing the working with my hands and inexpensive tools.

    Allow me to realize something interesting not a hard chined crate.

    I guess it all depends on how you look at it. smile
     
  10. JCFARER
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    JCFARER Junior Member

    Hello Buckle...

    I'm glad that there is some interest in this thread finally...it was just me and PAR for a while. Par was playing devils advocate, but it kept me thinking honestly so kudos to him.

    Well, as you have already stated, it increases the moment of the area, but I can think of other things that pop to mind:

    1. It was experimental and I wanted to test panels that would be almost equal to compare with 1/2" of core.

    2. The hairs on my body stick straight up thinking that the pipe has nothing in its inner circle, which if empty has lots of room for flex, implosion etc, then the only thing between the deep blue sea and me is a hole in the boat. :eek:

    3. The pipe can fill if punctured and then you have an x length of pipe by x inside radius full of water...imagine 10 or 20 of these full of water that you cannot evacuate on one side of the boat...internal ballast? :confused:

    3. Flotation

    4. Stiffness

    Jay :D
     
  11. JCFARER
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    JCFARER Junior Member


    Hello Nero...

    Thought I throw something out there because I also have experienced the compressive strength of the material. Also, the pipes can be filled with air under compression for super stiffness after they have been placed on their frames but I'm discounting this because if they do fail, you will have water intrusion that cannot be evacuated and depending on damage, listing, capsize, sinking and dead.

    I was kind of hoping that someone would maybe mention pipes that are filled with other pipes to increase compressive strength...just throwing that out there... remember that pounding will be high on the water, but it will be spread out over the entire area instead of 1sq" so I still think that there is a possibility.:D

    How heavy are the granules? Yes I'm interested, but at this time...the opinion that PVC and epoxy don't stick is out there and that has to be tested first. But yes...I am totally interested and if you read the entire thread you will see that I am open to all suggestions before I execute the test.

    One more note of theoretical importance is that in clinker hulls, the edges are exposed...so in all reality, If the PVC pipe can be mechanically fastened then it does not have to have its grooves filled or skinned with glass...the problem here would be making sure that it is water tight, which would mean filling the inside grooves and glassing, and the mechanical attachments which would mean making the fitting location solid such as with an epoxy slurry with the rest of the pipe filled with foam...just another thought

    Oh by the way, one of the strongest cements is ground sea shells because of their high lime content...but very heavy and it lasts forever, but is is very nautical...

    Jay :D
     
  12. JCFARER
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    JCFARER Junior Member

    Hello Nero...

    I'm starting to get used to you... :D

    Saw your gallery and stuff and we have quite a bit in common...I like your design, but why so big? Care to share the specifications? I'm almost finished designing a 30 foot trimaran, demountable that is blue water capable. It is however, all mathematics because I just can't deny my teachings. :D

    For me its cost also...why fall prey to accepted (albeit they are someone elses acceptance) super costs if you don't have to?

    Jay :cool:
     
  13. nero
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    nero Senior Member

    expanded polystyrene granuals

    The stuff I get in france is called Betostyrene. It comes in hugh 200 liter sacs (makes a lot of light concrete). In the states, it is a tough thing to get?? I have found expandable polystyrene beads. This is the stuff they make the white foam cups and insulation out of. It is a HAZMAT because of the difficult clean-up.

    One way to get the granuals would be to grind up scrap expanded foam products. It breaks apart easily. I do not know if this has a binder already on it or if the stuff sticks together under the molding process.

    About my boat being big? I thought it to be the smallest length for crossing oceans. (my other responce was my wife and I don't always get along so I need the extra hull spacing) smile

    The other reason is weight. The bigger boat can be more forgiving on overbuilding than a smaller one. (did I say that correctly) What I mean is there ia bigger target payload and if I loose some of that to using a heavy wood, then I still can have enought payload to cruise with.

    My idea is to make all the plans and build details of the boat for possible give away/or less than $1,000 US. But this is after the boat floats and stays together. The only plans I liked were from Shuttleworth. But they are expensive. (Thinking they were not so expensive as time goes on.) smile
     
  14. lprimina
    Joined: Jan 2004
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    lprimina Senior Member

    PVC is great stuff as long as it isnt in direct sunlight. It becomes brittle and looses strength.
    We have used it building clam grading stations. about 3 seasons is all you get out of it.
    I dont know if the salt water has any dire effects on PVC or not.
    Of course the PVC we use is standard schedule 40.
    but I would be interested in the results of your experament.
    Ben
     

  15. nero
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    nero Senior Member

    more alternative core ideas?

    Was thinking ... dangerous as that is.

    The PVC pipe needs to be abraided (sanded) because it is slick from manufacturing. This will help the epoxy stick. I think this idea came from West Systems.

    Nida Core not sure what plastic it is, has a thin micro fuzzy film applied to it so the epoxy can grab hold of it. (this is what i understood from their brochures)

    Maybe if 60 grit paper was used the scuffs would let the resin key in better.
    Or maybe use Monocomposite PU. (love that word mon....) We use it to stick terra cotta rooftiles on in france. It has different formulas with different amounts of flexibility. Sika makes something called Flex-o-tuile. It sticks to everything. It takes a few days but eventually seems to have less flex that the others.

    I posted this on some other threads.
     
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