pvc mast?

Discussion in 'Wooden Boat Building and Restoration' started by fishmonger, Apr 6, 2005.

  1. fishmonger
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    fishmonger Junior Member

    my 12 foot skiff calls for a 16 foot mast (sprit sail). I could easily build it out of laminated 2/4's but it wouldn't fit in the boat. Being the kind of guy who LOVES pvc, I'm wondering if a resonable spar could be made out of pipe covered in a couple layers of biax fg tape and epoxy? It would be cheap and easy. Because none of the materials are uv stable, I'd have to paint it. But that's no big deal. What do you think?
     
  2. Florida_mariner
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    Florida_mariner Junior Member

    I used a PVC mast for my 12'2" sailing Dory and for my 15' 9" Sharpie...in each case I put emt (electrical metallic tubing) inside for rigidity...it has worked well so far...the Dory is on it's third season with this rig...the Sharpie is new but working well with it...surely there are better set ups but price wise it's hard to beat...the total mast cost for the Dory was like 15 bucks or so...

    PVC electrical conduit is UV resistant but I used the white instead of the grey...I drilled and tapped the emt inside to keep it from shifting...
    the problem is at the coupling but larger mast hoops worked for me...

    the purists will no doubt cringe but us budget constrained types just need to get on the water :)
     
  3. fishmonger
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    fishmonger Junior Member

    purists beware!

    Nothing else about the boat is purist oriented, so I'm not to worried. I'm glad to hear that someone else has tried the experiment!

    What is the "emc" stuff? I've never seen it. And what size PVC did you use?

    Thanks!!!!!!!
     
  4. Florida_mariner
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    Florida_mariner Junior Member

    EMT is electrical metallic tubing...I worked for years as a construction electrician,that was where I got the idea...it's conduit to pull wires into/thru...you can buy it at home depot or any electric supply house..it's not as heavy as rigid conduit and it's not real expensive...

    I used 1' 1/4" pvc with 1" emt inside for rigidity...it allows some flex but not too bad...if you start getting into longer masts if it were me I would size up the pipes accordingly for added strength and rigidity...stays and shrouds help a lot too...

    after you get to 1 1/2" emt it gets quite strong and stiff....

    when using it of that size in the trade it takes a hydraulic bender to bend it :)
     
  5. PAR
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    PAR Yacht Designer/Builder

    I'm reasonably sure epoxy doesn't stick to PVC well. EMT is Electrical Metal Tubing, basically galvanized steel tubing stock. PVC is pretty flexible, gets brittle with age and exposure to UV (sun light) You could fill the PVC with polyurethane foam, which would make the pipe much more rigid, pretty much sealing up the inside, and it would float too. The polyurethane foam comes in different densities and I'd opt for the higher density stuff. The gray plastic (PVC) electrical tubing is UV stabilized, though will fade in time. None of the PVC's take impact well, but a foam filled PVC pipe would survive much better. EMT would add a good bit of weight to a mast.
     
  6. fishmonger
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    fishmonger Junior Member

    poly foam

    Yeah, I've heard that epoxy doesn't adhere well. I guess you can use polyester resin though. I also just heard about a guy who used wood veneer, contact cement, then epoxy to make a beautiful mast.

    Is the poly foam that pour in stuff?

    do you have to cut the EMT before you slide it in, or does it just fit in place? Did you have to rivit it?

    PVC. . . E=mc2. . . EMT
     
  7. Florida_mariner
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    Florida_mariner Junior Member

    1" emt (an alloy) fits nicely inside of a 1 1/4" pvc stick...of course weight is always a factor but two sticks of 1" is not real heavy in the scheme of things

    I think PAR's idea of foam to seal out water sounds good...but I doubt it alone would make it stiff enough...I can't see why you couldn't put pipe in pipe and then foam it?
    my 16' mast of this construction (although I haven't actually weighed it) doesn't make me grunt to step it...it just doesn't seem that heavy to me and as of yet (knock on wood) I haven't had a capsize with either of these boats...

    I would personally be afraid of cracking if you covered the pipe with polyester...seems to me it should flex some...the question would be how much?

    I have used miles of PCV conduit in outside applications in my electrical career
    and it is strong and wonderful stuff imo...

    I have added a pic of the Dory from two summers ago you can see the mast and poly jib...we had just sailed up the ICW from Marineland to Matanzas inlet area and dropped the main just before hitting the beach
     

    Attached Files:

  8. PAR
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    PAR Yacht Designer/Builder

    Foam (yes, the pour in, two part stuff) will make the PVC pipe very rigid, keep it light and permit it to float. The foam will prevent the column from deforming under bending loads. It will work for the same reasons foam core structures are so strong. The walls of the pipe actually change shape while a bending load is applied. This is pretty slight, but a measurable ovalish shape must be made for the pipe to bend. The foam will prevent this form happening.

    While you were using a heat gun to bend some conduit, during your electrical career, you would have seen a dramatically increased version of the effect. Ever bent some conduit, maybe in a curve that was tighter then usual or before enough heat was all the way through the pipe, just to see the round shape become flattened a bit? The outside of the curve has to stretch and the inside of the curve has to compress, leaving the sides to bend in conformity to the radius. This is the very concept, cored structures rely on for their rigidity. The core attachment to the outer skin (pipe in this case) will resist the change in shape under a bending load, which makes for a much stiffer structure.

    I'm not sure about polyester's ability to stick to PVC. I would think that the stiffness of the cured resin coating over the flexible PVC would cause sheering load issues pretty quickly, unless it was a pretty heavy application of polyester and cloth. If enough poly and cloth was used to provide the strength necessary, then you'd be better off making a 'glass tube without the PVC insert.
     
  9. Florida_mariner
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    Florida_mariner Junior Member

    I appreciate the physics lesson I know exactly what you mean about the pipe flattening out and I can see and concur that foam alone would no doubt add some stiffness and that it's properties combined with the shape of the pipe would compliment each other strength wise but I'm not sure I'd trust it alone...foam and the emt inside the pvc sounds like a worthy experiment to me...seems like having re-bar...and seems like foaming it in would help protect the metal from the brine as well...you could probably size down the emt with the foam combo maybe saving a little weight but emt in these small sizes is just not that heavy anyway...PVC is bouyant but I'm not sure if a PVC/foam/emt combo would be...but it still wouldn't soak up water...

    I agree with you on the impracticality of laying that much glass on the pvc...
    even if you could get good bonding,
    seems like unless it was pretty thick it would be in danger of cracking and the mast hoops would wear off paint pretty bad too probably causing uv damage unless you were painting it a lot...
     
  10. PAR
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    PAR Yacht Designer/Builder

    The physics of this principle have been well proven. It seems funny, but it works.

    I was working on an engineering degree when I saw my true first stitch and glue boat (early 70's). I couldn't believe it could work, without most of the fasteners and major structural members, like frames. I now understand the concepts and time has placed it's mark on the techniques.

    Build a test piece if you like, or the full size version, it's not a lot of materials there. The worst that could happen is your mast will be to flexible and you can heat up the end of the EMT and shove it down into the foam. I have a 10' section of 3/4" EMT here which weighed four or five pounds when I picked it up yesterday. The foam will weigh a few ounces. Any weight you can save in the rig, especially on small craft, will benefit the boat.

    I haven't punched up any numbers for this, but I'm reasonably sure a foam filled 1 1/4" PVC pipe will support several pounds. The buoyancy of the foam is pretty easy to calculate, once the type and manufacture is selected. It will likely have a guide printed on the can for this purpose.
     
  11. Florida_mariner
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    Florida_mariner Junior Member

    I think you have me convinced to give the foam a try...the stuff should be "closed cell" type eh? or would that matter in this application ?

    wonder how you could tell how much you would need to fill the pipe?

    and do you think canned stuff would suffice or two part would be the only way to go?


    how's the water levels down around Lk Eustis lately?...all the recent rain has them quite high around here for a change..
     
  12. PAR
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    PAR Yacht Designer/Builder

    I think you'll use a surprising number of the caned foam (Great Stuff and the like) to fill your stick. I only know of the two part, closed cell polyurethane foam. I have little experience with the other foams. I get mine in three differing densities from FGCI (Fiber Glass coatings Inc) out of St. Pete. I use there 2 pound stuff for these applications, though they sell less dense grades for floatation.

    The lake levels are great, though St. John's, in their infinite wisdom, has been drawing down the levels already (they usually wait until May to do this) in expectation of the rainy season. I had trouble doing sea trials on a 25' hardtop last week. The water levels were so high I just barely got under the railroad bridge crossing the Dora Canal. Been good sailing weather, lots of fair winds (if from weird directions) and very pleasant temperatures. St. Augustine is a beautiful town, lots of water fun and plenty of collage age women hoping to get lucky. You should try the "want to see my boat" line on them. They kissed mommy and daddy goodbye and are 1,200 miles form home, looking for more then the boneheads they share class with . . . Ain't life grand . . .
     
  13. Florida_mariner
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    Florida_mariner Junior Member

    St Auggies is a Jamming place...loaded with history and awesome places to exploit water toys to the fullest....St John's county is choice with two inlets too...three of it's four lines border on water...ocean, inlets,ICW,St Johns river,Pacetti creek and so on but we don't have much for lakes that aren't private...

    unfortunately the fishing has declined in recent years imo...and in spite of ever increasing fees and taxes the need for more boat ramps is getting worse
    especially with the blistering development and people coming from miles for the inlets...

    the local boat building co's Luhrs Mainship and Sea Ray as well as smaller outfits seem to be going full throttle...

    I'm hoping for a shot at sailing my sharpie on the kissimmee chain or at least Apopka in the summer....(if I haven't sold it by then)

    la touristas and co eds are thick around here and it makes for eye candy especially at the beaches, but you know what they say,just because you may be on a diet you can still look at the menu...I'm a lucky man with a good hearted wife and family :)
     
  14. sronicker
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    sronicker Junior Member

    old school

    I am a young (but happily married) college guy just getting started in the boat-building arena and call me a wierdo but I think I would prefer to use wood over pvc or anything else any day! I cherish the though of building my own completely wooden boat some day and not use all the fancy new products. I have been pondering and studying about building a cedar strip canoe but all the books I have found use the fiberglass/epoxy coating. Doesn't anyone build completely wooden boats anymore? I know this is not entirely related to your topic but this seems like a good thread to reply on.

    Thanks,
    Sam
     

  15. Florida_mariner
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    Florida_mariner Junior Member

    I like wood too but I'm not a total purist...for me it's about getting on the water economically mostly ...but maybe you should check out Woodenboat mag...there are a lot of old school stories and opinions there...I think it's a great mag myself and I have learned tons from it...


    http://www.woodenboat.com/
     
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