Novice fiberglassing pvc pipe needs help

Discussion in 'Boatbuilding' started by VictorVictor, Nov 20, 2015.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Sounds like a good idea ( the cable up the guts of it) to give a clear go at it, and hold it reasonably straight, though inevitably it will have a bend. It is really a job for two people, the bloke that does the glassing, and a psychiatrist to treat him when it sends him bonkers !
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I assume the copper is a coated cable, why does it need this PVC mast to cling to, to be attached in turn to the mast. ?
     
  3. upchurchmr
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    upchurchmr Senior Member

    VV,

    It would be relatively simple to glass and epoxy the whole "mast" then insert / wrap plastic or wax paper at the saw horses.

    The points where it sits on the saw horses will be distorted due to the pressure of contact, but the glass/ epoxy will still be one piece and not stuck.

    An alternative is to just cover the top of the saw horse with packing or mailing tape. It is quite easy to break an epoxy bond free of the packing tape at these points. I do it all the time taking kayak mold forms out of a kayak hull.

    I believe as everyone else does this will be a difficult experiment to succeed at.

    1. how thick will the glass/ epoxy coating end up being? A thin coat of glass does not guarantee enough strength to hoist up the small end without breaking the glass

    2. The joints between the sections will typically not allow the glass to be directly against the pipe so that the glass will not buckle and break at a very low load. If you could put a tapered collar of PVC at each joint so the glass changes direction minimally and rests directly against the PVC everywhere you will have a stronger system.

    3. The weight of PVC, Glass/ epoxy, and wire will be multiple times that of just wire.
    The load on the mast will be significantly higher, defeating one of your purposes.

    4. How will you attach the PVC/ glass tube to the mast? That joint seems to be very weak without more information. A simple pinned joint looks like it will tear out with out a significant amount of reinforcement. Slamming or jerking of the boat at sea will cause increased loads at the top. Just the weight being jerked back and forth at sea will cause large loads. Have you done a test to see if your upper joint will support just the load of the "antenna"? I would suggest a short section of the upper section of antenna, hooked to about 3x the expected weight in order to see if your joint has a chance.

    You can tell I don't expect this to work easily, but you need to attack any known issues to prove (to yourself) the design you go with.

    There is a reason PVC is not used for places where there are loads. It is heavy, weak, and not stiff.

    Please report back your progress. Cleaver design has made lots of things work that experienced people doubt.
    If you succeed you can enjoy being right, and if not, others with similar proposals will know what happened - perhaps sparing them cost and effort.

    Good luck.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I hope he's not intended to use a bare copper cable, ( he does worry about impedence) you will be able to hear that fizzing in a salt environment.
     
  5. whitepointer23

    whitepointer23 Previous Member

    What sort of radio is the aerial for. My boat has an insulator on 1 backstay . I think that might have been the hf aerial.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    It is amazing how often PVC pops up as part of a structural idea, on this site. Even though it lacks any real ability to bear a load.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Someone beat me to it, but the saw horses can easily be protected with packaging tape (wax paper can melt the wax during the exotherm), so they're not going to stick.

    I'm not sure I understand the perceived problems and the need for PVC pipe. If this is just a conductor sheathing, why 2". I'd be inclined to simply use the fabric tubing alone over a mandrel. It would be a lot lighter, though you'd have more fabric and goo work. For that matter, you can buy precast 'glass sections and bond them together, for a hell of a lot less bother. You can also get structural pultruded tubing, which typically are 20' lengths, with the cheapest being UV protected polyester.

    [​IMG]

    This is 1" diameter UV'd polyester, 1/10" wall and runs about $4 a foot at full retail. The smallest I've seen is 1/4" (OD) with a 1/16" wall and these will be less than $2 a foot. I'm not sure of the size of your wire, but let's say you can stuff it into a 1/2" tube (1/8" wall), this will cost about $2.50 a foot. I'm sure they'll make you buy two 20' tubes (though most will cut to length for a fee), but this is still $100 in tube and all you have is a single splice. The net result is a structural tube, appropriately sized, minimum goo factor and windage, for probably less than playing around with PVC and fabric socks. FWIW . . .
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    I think that PVC pipe has become part of the family, and he's not parting with it.
     
  9. tom28571
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    tom28571 Senior Member

    It would have been better if the OP had clearly stated what he was working on from the beginning, which might have eliminated much of the confusion. A 35' length of PVC pipe is a limber noodle whether it is all one diameter or reduces from 2" to 1". A stretching fiberglass sleeve will certainly snug down on the whole thing without any real problem. Applying resin to that sleeve is not a big deal either.

    A real problem comes when he discovers that the stretch sleeve does not stiffen the noodle very much. The orientation of glass fibers on the 2" section will be way off the vertical and offer little in axial stiffness. The fibers on the 1" section will be much more aligned with the pipe axis and will stiffen it a fair amount.

    Whether any of this is adequate to support an antenna 35' in the air is questionable.
     
  10. philSweet
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    philSweet Senior Member

  11. VictorVictor
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    VictorVictor Novice fiberglass

    All responders:

    I am impressed with the quality of this forum's members and their numerous constructive comments and suggestions.

    One point to answer on why I am using strengthened pvc instead of just hoisting up a wire with a masthead pulley or using the backstay. The 35 foot tube will be used in other places, some even ashore as well as on another boat, so it needs to be portable. The radio is an amateur radio transceiver with multi band coverage. The antenna will have a number of different lengths of wire along side the pvc to provide a resonant quarter wave wire for those various frequencies.

    At this time I am going to discuss all the info and ideas you all have offered and will proceed after consideration and talks with others.

    Thank you all very much.

    Victor Victor
     
  12. gonzo
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    gonzo Senior Member

    An antenna like you are describing, regardless of material, will need standing rigging about the same as your mast. The common, and logical, solution is to put two insulators on the back stay and use is as the antenna.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    a 35 foot pole doesn't fit my idea of portable !
     
  14. PAR
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    PAR Yacht Designer/Builder

    The pultruded stock I mentioned above is also available in telescoping sections.

    [​IMG]
     

  15. gonzo
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    gonzo Senior Member

    It would be cheaper to simply buy a fiberglass tube if a tube was necessary. I don't understand what the PVC pipe is supposed to accomplish.
     
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