Ulua strip-plank hull glass schedule

Discussion in 'Boat Design' started by abosely, Oct 27, 2015.

  1. abosely
    Joined: Mar 2015
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    abosely Senior Member

    Building a Dierking Ulua strip-plank outrigger with my nephews so we have something to play with while building Narai since it's a rather long term build.

    Using 3/4" x 1/4" VG D-F cove & bead strips. As most people finish them clear 6oz glass cloth on both sides (totally encapsulated) of is recommended. I'm painting it so that's not a factor.

    It is intended as an expedition/working type boat and not real concerned with the lightest weight or highest performance possible, but rather ruggedness.

    A lot of the places it will be at are rocky or all lava rock, so want to optimize hull against puncture and impact damage as much as reasonably possible.

    Towards that end will use S-Glass cloth. At this point thinking of using 9oz satin weave S-Glass on both sides of hull and a strip of Xynole along keel. Using System Three SilverTip Laminating resin if that matters.

    Would it be better to use two layers of lighter cloth or add an additional layer of cloth in addition to 9oz cloth on both sides of lower hull that comes up 4" or 5" above water line or what would be a good glass schedule to get most protection from puncture & impact damage that is practical?

    Cheers, Allen
  2. messabout
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    messabout Senior Member

    Puncture resistance will be better served by more glass thickness, and strength, inside the boat, not outside. Not to say that outside protection is to be ignored. If you are going to ram into rocks you need a tough skin along with a stiff skin section.
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Agreed, 'glass isn't the best choice for puncture or abrasion resistance. Xynole is about the same cost as 8 ounce cloth, so consider this instead for abrasion resistance. Puncture resistance with fabrics is best internally as mentioned, so consider something good at it, like Kevlar.
  4. DCockey
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    DCockey Senior Member

    That depends on the area of the concentrated load relative to the thickness of the hull and core stiffness. If the area is enough then the strength of the outer skin will determine if there is a failure.

    With the load spread over a larger area the maximum stress on the outer skin will be compressive while maximum stress on the inner skin will be tensile.
  5. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Couldnt see what size the boat is from the post. if its a small 12-16 ft canoe, then two layers of 6 oz is a good start, with rubbing strips of Xynole or Dynel ( keel anD chines) is the minimum. You have to watch the weight though.

    If its larger, then you will have more weight to impact the rocks with .

    Some interesting comments here indicate that Kevlar isnt all that good for puncture resistance, so it would be better to put it under S glass.

    "Fundamentals of Composites Manufacturing - Materials, Methods and Applications (a Society of Manufacturing Engineers textbook),

    Kevlar's impact strength is low compared to S-2 glass. Even E-glass may fare slightly better.
    However, kevlar is unique in its toughness. Its resilience and ability to be taken far beyond its limits without severely damaging it is unparalleled by the other reinforcing fibers. Kevlar fibers will not tear even if the laminate has cracked completely. However, they tend to delaminate from the other plies. This is due to the low Interlaminar Shear Strength of Kevlar fibers.

    Thus, impact strength and impact performance are very different concepts. Another consideration is that kevlar or glass are very easy to repair after catastrophic failure. Carbon will tend to shatter, making repairs difficult or impossible.

    Putting S-glass or S-2 between layers of high-modulus carbon or Boron fibers will increase the impact resistance, resiliency, tensile strength without adding much weight. Additionally, the glass somewhat dampens the brittleness of the carbon fibers.

    Innegra-S fibers promise better impact resistance as well as impact strength"
  6. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Instead of satin weave why not Biaxial. It's easier to apply, you get better glass resin ratio and it's stronger.

    BR Teddy

  7. abosely
    Joined: Mar 2015
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    abosely Senior Member

    What about this?

    For inside hull, one layer of 5oz Kevlar with one layer of 9oz Bi-axial S-Glass. Kevlar for puncture resistance and S-Glass for compression, stiffness and ease of finishing.

    Outside of hull, two layers of 9oz Bi-axial S-Glass and one layer of Xynole up past water line 8" or so for abrasion resistance. The two layers of S-Glass to help create 'hard' skin over D-F to help minimize crushing/denting wood and over all strength.

    Cheers, Allen
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