Layup schedule help

Discussion in 'Fiberglass and Composite Boat Building' started by Scuff, Sep 5, 2017.

  1. Scuff
    Joined: Nov 2016
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    Scuff Junior Member

    Hi,

    First post but I’ve been a lurker for a while. I recently purchased plans for a 27’ sailboat. The designer provided two layup schedules using polyester resin. One is for Woven roving and the other for biaxial cloth, both use a 5/8” PVC core. I would like to use the biaxial schedule and epoxy in lieu of the polyester resin. The layup specifies 17oz biaxial cloth with a mat backing. My understanding is the mat isn’t needed when using epoxy. The schedule specifies a thickness and three material weight values (Fiber volume, Area – oz/ft^2, Total lb/ft^2). Can someone help me with determining the layup without the mat backing? Any advice is appreciated. Thanks in advance.
     
  2. jorgepease
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    jorgepease Senior Member

    170 oz with a 5/8 core ... for which part of the boat?
     
  3. Scuff
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    Scuff Junior Member

    This is for the hull and decks by my understanding. The plans came with a drawing showing the layup which showed 1/2" pvc core with a note to see current print out. The printed sheets both show a 5/8" core and a choice of either 24oz WR or DBM1715 .. I don't find any 1715 listed in any of the fiberglass supply companies guessing that's the biax with a 1.5 oz mat? Thanks.
     
  4. jorgepease
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    jorgepease Senior Member

    sorry I read wrong, thought 170 oz )) ... So how many layers of 17 does it say? For foam core 17 oz doesn't sound enough, double that on each side or even more sounds more like it
     
  5. Scuff
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    Scuff Junior Member

  6. jorgepease
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    jorgepease Senior Member

    I doubt the mat will make much difference either but doesn't hurt to ask the designer. Also ask about alternating cloth ie: +- 45 and 0-90
     
  7. Scuff
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    Scuff Junior Member

    Hi I asked the designer and it is a single layer of 1715 dbm. My understanding is that is a +/- 45. There are additional reinforcements on keel, bow etc. If using epoxy and divynicel or corecell is there any need for the mat layer next to the core? Could I also not use a mat backing on the dbm as well? Designer said not to alter the layup schedule regardless of resin choice but my understanding is the mat is just extra weight and cost with the epoxy.
     
  8. jorgepease
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    jorgepease Senior Member

    170z on foam core for. 27 foot sailboat sounds really light, like a schedule for plywood but designer is the guy that has to stand by his plans ) ... I wouldn't go less than at least double that, don't care what is spec'd. Stiffness will be ok but not much in the way of impact protection.
     
  9. AusShipwright
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    AusShipwright Junior Member

    Fibreglass mat in combo with epoxy resin isn’t compatible as the binder that holds the individual strands of the mat together can’t be broken down by the epoxy resin
     
    tinhorn likes this.
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Quite a few have made that error over the years. Not a pleasant discovery, I have known not to do it, but many are not wise to it.
     
  11. Scuff
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    Scuff Junior Member

    Thanks for the info on not using mat. I guess that confirms that the layup was used with polyester or vinylester. I would just eliminate the mat from the schedule?
     
  12. AusShipwright
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    AusShipwright Junior Member

    Correct. Your laminate schedule for the decks sounds ok, although on the hull, one layer of 17 oz. DB is definitely to light. Without knowing the internal framing layout of the hull, I'd say at least 2 layers 17 oz DB +- 45 either side of the core or even quadra-axial would be better suited as you wouldn't have to worry about the orientation of the fibres when laying them in the mould.
     
  13. fallguy
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    fallguy Senior Member

    I am building a 32' powercat with speeds around 23kts. The lamination is 22 oz triax double both sides bottom and single 22 oz triax each side 12mm corecell. I, personally don't see why anyone would suggest mat to the inside. Mat is typically used gelcoat side to avoid print through. No mat!

    Two layers of 17oz fabric seems like major overkill if we are talking the entire hull. That is going to add a quite a bit of weight. I am sorry, mostly because I am not qualified to answer, but I seriously doubt 34oz schedule is needed.

    For a 30 yard layup one side; you are adding 120 pounds to the hull for hand layup if my math is right. Do it both sides 240. A big mistake. The boat will probably never maker her lines.

    If you want to improve on the layup; doubling the 17oz is not what I would want for...

    For one thing; intended use isn't even known.

    Corrections from experts welcome.

    Very confusing answer; I'd rather not catch any flack for pointing out uncertainty.

    Kind regards to the op, but before you double the layup; better understand consequences.
     
  14. gonzo
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    gonzo Senior Member

    The mat will increase the stiffness of the laminate besides increasing the strength. Epoxy resin has more elongation, which is good for impact. However, it also makes the laminate less stiff. Why don't you ask the designer? Also, what is the advantage of epoxy in this application? Polyester is easier to work with and less prone to failure due to mix ratio mistakes.
     

  15. AusShipwright
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    AusShipwright Junior Member

    @fallguy like I said without knowing the internal framing that was an initial estimate and aimed at a minimum skin thickness of 2mm.

    The laminate for the hull will depend on the unstiffened panel size, lay-up method and as you mentioned intended use.
     
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