making carbon spars

Discussion in 'Boat Design' started by peterchech, Aug 3, 2011.

  1. peterchech
    Joined: Aug 2010
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    Location: new jersey

    peterchech Senior Member

    I am going to make a carbon bowsprit, because it is light and stiff, but also because I've never worked with carbon fiber before and I'm curious. It will be for a 21' catamaran with a large beach cat rig.

    Can anyone give a ballpark figure for how many layers of 9oz 12k uni carbon should be laminated to give a strong but light spar?

    I plan on using a layer of glass cloth as the initial internal layer, as recommended by the gougeon brothers, wrapped around a piece of PVC pipe. Then I will cut a slit in it, remove it from the pipe, and wrap the carbon around that. What weight glass should I use for this?

    What about UV-resistance of the spar, do I need to coat with spar varnish or something?

    Thanks in advance for anyone's help.
     
  2. themanshed
    Joined: Sep 2009
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    themanshed Senior Member

    I made a bowsprit for my 20’ trimaran out of a PVC pipe. My first attempt was to wrap a cardboard tube with round carbon fiber tube cloth, but that did not work very well. Two problems the tube started to sag and the lay-up was heavy with epoxy. My second attempt was successful and gave me strong light bowsprit. Basically I cut the PVC pipe in half made a mold. Vacuum bagged carbon fiber cloth on the mold with a layer of Kevlar in the middle. I removed the molded halves, made two flange strips to attach the halves together, when wrapped one outside skin around the bowsprit after it was epoxied together. A rule of thumb is to make the piece at least as thick as a metal counterpart for carbon, and then I added 20% more. I can actually pick up the front of the hull by the end of the bowsprit. Below is a link to my website that shows some of the steps to build my bowsprit.

    http://themanshed.net/tms-20-trimaran/2-10-10-port-side-hull/?g2_page=2

    The bowsprit is internal on the bow and removal so I made a receiver for it by wrapping several layers of wax paper around it and did a layup with carbon fiber and a few layers of Kevlar to make an external tube that goes into the hull and though two bulkheads.

    http://themanshed.net/tms-20-trimaran/4-7-10-bulkheads/?g2_page=3

    This was my take on it. I’m still working on the hull and hope to have the outside carbon skin on it in the next month or so. I have to do most of the faring first as the outside skin is only two layers of 200gm carbon and one layer 6oz Eglass for protection. Not much to fare out on the skin.
    Good Luck
     

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  3. CatBuilder

    CatBuilder Previous Member

    Wow, interesting thread.

    So what do you finish that carbon bowsprit with to protect the epoxy from UVs and still have the cool, black carbon show through?

    Also, is there an issue with heat distortion of the epoxy at high temps with an all black carbon tube?
     
  4. themanshed
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    themanshed Senior Member

    Right now it is still raw carbon fiber as the boat is inside and still under construction. I'm not sure If I will leave it with just a UV coating since I can take it off and the boat will trailer. One thing for sure is that it will be "water cooled" with this water rocket!
     
  5. dinoa
    Joined: Oct 2007
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    dinoa Senior Member

    Jim Marske describes a great way of making composite tube using PVC pipe along with lots of other interesting stuff like using high modulus Graphlite in spar caps and attaching it to spar root end fittings.

    marskeaircraft.com/workshops

    You lay up over a PVC pipe with outside diameter that is close to the inside diameter of the pipe to be fabricated. The PVC pipe can be supported by placing a steel pipe inside to keep things straight.

    The plastic pipe is waxed and 45 deg bias cloth layed up. The cloth wrinkles are worked out with a gloved hand from center out. The 45 bias acting as a Chinese finger trap tightening the cloth.

    To seperate the tube the inside of the pipe is heated alternately at both ends with an air gun before it has fully cured thus expanding the pipe. Hold for 15 minutes then allow to cool. The PVC pipe shrinks away from the composite tube facilitating removal.

    I havent tried it but hats off to Jim for the brilliant idea.


    Dino
     
  6. CatBuilder

    CatBuilder Previous Member

    I need to make a bowsprit and davits. Thank you very much for the thread. If I can figure out appropriate carbon layups as compared to the specified aluminum, I think I might go for it.
     
  7. peterchech
    Joined: Aug 2010
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    Location: new jersey

    peterchech Senior Member

    Great pics of the process on your site manshed. Worth a thousand words, and you make it look like something even I can do ;-)

    But could you explain what exactly the flange is? How exactly do you join the two halves?
     
  8. themanshed
    Joined: Sep 2009
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    themanshed Senior Member

    I made a 2 small lay ups in the mold about 2 inches wide the length of the mold. They were not vacuum bagged just a hand lay up. This gave me a curved "flange" that matched the shape of the bowsprit. I used a thicked epoxy and glued half of the width of the flanges to both of the inside edges of one of the bowsprit molded pieces. This was to act as a backing plate or lip for other bowsprit to sit on as they were joined and glued. Now I have more glued surface then I would have I just edge glued the two halves, this combined with the final outside wrap of one carbon skin gave me a light strong bowsprit.

    One picture has flange strip in the background, the other is the second flange clamped in place waiting to "set-up".
     

    Attached Files:

  9. Hussong

    Hussong Previous Member

    It's far, far easier to wrap carbon tow, uni-cloth, or whatever, around an existing carbon tube, such as a windsurfer mast, than to build one from scratch. The form is already established, it is easy to get a simple engineering opinion as to how much carbon and where, at very few dollars from a qualified source and the process is infinitely easier to do for the average homebuilder guy.

    There are many examples for this process on the Internet and most of those who have already done so will share their experience with you after a simple email and question.

    Always better to not re-invent the wheel.
     
  10. themanshed
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    themanshed Senior Member

    I know people who have used sections from windsurfer masts, usually they are tapered, sectional, thin, and not the correct width. One of the problems with a wrap is getting your core out. I researched this option before I decided to make own mold.
     
  11. Hussong

    Hussong Previous Member

    What I was offering does not involve the removal of the core tube, be it windsurf mast, or straight carbon tubing. Simply rough the surface and apply even layers of material until the stick is strong enough for the intended use. You can wrap heat shrink plastic wrap around the fresh laminates, shoot it with a hair dryer to drive out the excess resin and hang it up to cure.

    Un wrap it, test it for proper bend and sand smooth. A two-piece stick is no problem. Just glue the two pieces together and cut to proper length.

    The makers of filament wound tubes have all sorts of factory seconds that they'd just love to unload at really good prices, so a nice prodder is available to virtually anyone who is willing to do a little experimenting.
     
  12. themanshed
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    themanshed Senior Member

    That way works I tested it but was not happy with the results and I used a heat gun. The shrink wrap plastic trick does not give a true surface compared to a molded surface. You are not going to squeeze out extra epoxy from a 10 foot run with a shrink wrap, better results from hand with a squeegee but it is hard to squeegee round, and not to the degree of a vacuum bag. I got a heavy uneven lay-up not what I wanted for a bowsprit. I guess it depends where your acceptance threshold lays.

    Other things to remember less epoxy or resin means a stronger layup. The orientation of the fiber is also important. You want the orientation of the fiber to be lengthwise in the pole to run horizontal - end to end. I would question the orientation in any pre-made pole or tube not designed for this type of load.

    The use of a core - then a build-up usually gives you more weight then you want and the cost will be higher than if you made the mold out of less than $20 of materials. Time saving is null by the time you surf the web, contact the vendor(s), shipping, then make the piece actually do what you want - to modify it.

    From my experience you have two choices Buy It or Build It.
     
  13. peterchech
    Joined: Aug 2010
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    peterchech Senior Member

    :D:D:D:D:D
     
  14. themanshed
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    themanshed Senior Member

    Going to be working in Atlantic City this fall how is the sailing in that area?
     

  15. peterchech
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    peterchech Senior Member

    I've heard that Atlantic City Bay is a great place to sail but have never actually sailed it. At least the water will be warm that time of year (stays warm to about mid october usually) although nothing compared with s. florida lol. Should be good winds in the fall too as the summer up here can be light at times...

    If you want a ride on an outrigger canoe I sail about an hour north of AC in Sandy Hook Bay, which is also a pretty interesting place to sail. It is kind of low-speed edge of your pants sailing if you can imagine, never faster than 9 knots but you FEEL like you are on hydroptiere lol
     
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