Substitute Carbon Fiber for fiberglass on small boat?

Discussion in 'Materials' started by waterbear, Jun 28, 2017.

  1. waterbear
    Joined: Mar 2016
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    Location: Alameda, CA

    waterbear Junior Member

    I'll try to keep this short. I'm building a large flat bottomed rowboat and I have a little bit of carbon fiber on hand, and I'd like to know if I can substitute the carbon for some of the glass, or use it strategically to stiffen the boat.

    I'm not interested in reducing the weight, just interested in not wasting the materials I have on hand. I have about 50' of 6oz 6" woven tape, and about 1 square meter of 12oz biaxial.

    I was thinking of either taping the inside of the chine with carbon, or maybe putting tape over the 3/4 x 1 inch stretchers on the floor to further stiffen the floor.

    More details:

    1. I'm building this 23'x5' flat-bottomed open rowboat:

    Duckworks - Marietta Yawl http://www.duckworksmagazine.com/08/designs/marietta/index.htm

    2. The scantlings are as follows: 3/8" bottom, 1/4" sides, 3"x 3/4" softwood frames.

    3. The chine is to be taped on the inside with woven 7" 7.5oz and 5 in 7.5oz tape. The outside is taped with 6oz tape, with 6oz cloth on the sides overlapping the chine, and 10oz cloth on the bottom overlapping the chine.
     
  2. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    I doubt it's going to matter on a row boat. If you were to switch and use 1/2 carbon for 1/2 fiberglass on a speed boat the different stiffness properties might be a problem because all the load would be taken by the carbon first, if that failed, the weaker glass would go next. But on a row boat, I doubt it's a problem
     
  3. waterbear
    Joined: Mar 2016
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    waterbear Junior Member

    Ok, thanks. It sounds boat would ultimately be stronger, but less stiff if all the taping were done with fiberglass?
     
  4. jorgepease
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    jorgepease Senior Member

    So if you are doing all the ply in carbon and not mixing glass and carbon then your panels are stronger. Taping with glass tape won't hurt anything.
     
  5. waterbear
    Joined: Mar 2016
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    waterbear Junior Member

    Ok, interesting, but not feasible with the tiny amount of carbon on hand.
     
  6. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    I really think you will be okay on that boat but there ares some NA's on here who will know better than me.
     
  7. waterbear
    Joined: Mar 2016
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    Location: Alameda, CA

    waterbear Junior Member

    Ok, thanks, I won't worry about it unless someone more knowledgeable says otherwise. I'll probably just put some tape on top of the stretchers to stiffen the floor and maybe put some extra carbon into the bow area.

    The floor has unsupported areas as large as 3.25' x 3.5', with the bottom being 3/8ths plywood and 10oz glass on the oustside bottom. There are two 3/4" x 1" transverse stretchers about 12 inches apart to stiffen the panel, but the whole assembly doesn't sound very stiff to me. I know it's not a performance or strength issue, it's just nice to have a solid feeling floor in a boat.
     

  8. Mike Inman
    Joined: Oct 2018
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    Location: Jacksonville, Florida

    Mike Inman Junior Member

    The magic of carbon vs glass is that it is stronger so you can use less - using less fiber means needing less encapsulant which means less weight. If you end up using the same amount of fiber either way, the carbon end product will be stiffer, but no lighter. As mentioned above, mixing the two isn't inherently bad, but should be done thoughtfully so weird differentials in stiffness don't make something undesirable happen - not much of a concern in a rowboat, though I'm thinking just now that stiffening around the oarlocks wouldn't be a bad thing...
     
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