How many layers to bullet proofness?

Discussion in 'Boat Design' started by ScottK, Feb 1, 2010.

  1. ScottK
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    ScottK Landlubber

    I read that the Ocean Master fiber glass boats claim to be bullet proof by using 14 to 20 layers of fiber glass. How many layers of fiberglass does a normal sailing yacht use?

    The above bullet proof hulls actually do mean they can stop a bullet.

    I have never built a boat before, so this may be a silly question to you. And I am not sure if they are using sandwich construction or one layer.

    And I don't expect anyone to answer how many layers it takes to stop a bullet, being that there are too many variables. I just want to know how many layers is normal?

  2. gonzo
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    gonzo Senior Member

    Fiberglass is good at puncture resistance. They don't say layers of what wieght or type they use, but it is possible. 9mm bullets if they are lead have little penetration on hard surfaces. The large caliber rifle round they claim has no data for type or distance so means nothing.
  3. hoytedow
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    hoytedow Carbon Based Life Form

    A lot depends upon the particular bullet. I know that several bullets are capable of going through 20 fg layers as though it were cheese.
  4. gonzo
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    gonzo Senior Member

    Armor piercing of medium caliber would.
  5. capt vimes
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    capt vimes Senior Member

    bulettproof vests are maid of layers of aramid - as far as i remember - loosely connected...
    a ship hull is build of the same fibres (sometimes - usually its either carbon or glass) but they are covered, soaked and backed in resin... giving a solid, sturd and stiff structure... not bulletproof at all - no matter how much layers of fibre you have in there...
    of course - make a hull thick enough and it will eat up bullets in the end... ;)

    what makes the vests bulletproof is the LOOSELY layers - eating up the energy layer by layer - you will not find that in a ships hull... a backed composite hull is stiff as no other material and hence loosing its capability to soak up energy in a short distance...
  6. messabout
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    messabout Senior Member

    If these boats are truly bulletproof, then the Somalian pirates will surely want a few of them.
  7. capt vimes
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    capt vimes Senior Member

    is it just me or do anybody else see the misconception here?

    bulletproof is NOT bulletproof!
    define your requirements first...

    soft vests are to stop mainly sidearms (pistols and such) and sharpnels and NOT rounds fired from a rifle, long barreled firearm...

    you want protection for those high energy rounds fired from a rifle... you need to combine different techniques...

    soft layers of aramid/glass/carbon (good enough to keep of a 9 mm bullet from a clock) with heavy plates of ceramic placed in there... a vest proof to sniperfire weighs 25 kg - for your rump only - and has dozens of layers of aramid AND ceramic plates all over in it...

    a ship hull now could be considered (becaused it is backed in resin) to be one of those ceramic plates... BUT without the loose layers of aramid these plates do not even stop a 9 mm round from a clock! ;)
  8. Steve32
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    Steve32 Junior Member

    1 inch thick piece of lexan is bullet proof so they say but why are you asking? for the fear of pirates? they use RPG's to stop a ship. as far as bullet proof i once shoot my old 44 magnum marlin rifle through a 1/4" steel plate that was leaning against an old fibreglass boat and it made it through the boat too. maybe some kevlar would help!
  9. powerabout
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    powerabout Senior Member

    I rigged an offshore boat once for the builder once.
    It had one heavy layer of Kevlar.
    When I cut the transom out for the Sterndrive he reconned it was so strong it was bullit proof.
    So out with the 12 gauge and bang, straight through 4 layers of half inch ply multple layers of glass and the kevlar...
    kinda surprised me as well....

    Having repaired few racing beach cats built with kevlar ( which is only there for impact protection) I can tell you its much much better than std glass even with carbon when another cat is trying to cut it in half...
    as for bullets, I guess they make vests out of it.
    PBO would be better and M5 is so good the US military has bought exclusive rights from the Jap company so we cant get it
  10. powerabout
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    powerabout Senior Member

    i didnt know a clock was so dangerous?
  11. Boston

    Boston Previous Member

    having worked in the glass industry for quite some time I can assure you that a 1 inch piece of acrylic is bullet proof up to about something less than say a 45 but if you add shatter resistant film it can take the 45 as well but will break

    laminated glass with shatter proof film can handle multiple rounds but also ends up broken
    depends on the thickness
    annealed and 5 layers of 1/4 inch will stop a riffle round but just barely

    none of which is very practical on a boat with a weight budget
  12. capt vimes
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    capt vimes Senior Member

    ok - now i gonna steal that thread... ;)

    what makes something bulletproof... (this is not a question and if so just a retorical one ;))

    the material?
    or the way it is mashed together?
    what is the best, cheapiest and by now means hard-to-come-by material?

    i will answer the first two...
    1.) the material...
    no - any material in the right amount will stop a bullet... consider a one mile thick plank of balsa - it will stop a bullet!

    2.) construction (materials combined, mashed together)

    you want to eat up the energy of a bullet (we are not talking explosive projectiles like from an RPG here...) in as a short way as possible...
    kevlar and aramid have proofen to do these things IF kept in - rather a lot of - loose layers... but the ammount those layers can eat up is limited by the layers and therfore the weight and thickness one can bear is also limited - hence the proofness is limited...

    to increase the "proofness" against higher engeretic projectiles you need some hard, solid material in between... more to the front actually
    what does this material now provide?
    it destroys the projectile but with the sideeffect that the whole energy (we are talking about some thousands joule here) is directly transferred to the support structure (the body ;)) AND a hell of broken up bits and shrapnells is going the way of the support structure.... ;)
    so - some more kevlar/aramid layers are to be placed in between to stop those fragments from penetrating your skin/body...

    you got hit by a siper in the chest wearing one of those vests... you will survive but you will have multiple rip fractures...

    kevlar/aramid - good to stopp bullets if kept loose like curtains... no proof whatsoever if covered in resin...
    ceramic/steel (that one tanks make out of it) - good to stopp bullets but it will crack your bones and knock you into the ground... not just down...

    what now is the best material to effectively slow down and destroy bullets?
    be vary - trickquestion... :D ;)
  13. kistinie
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    kistinie Hybrid corsair

    i 'm afraid that with uranium 12.7 bullets and upper it is a lost battle.
    Hopefully they are expensive !
    What a nice planet ...
  14. troy2000
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    troy2000 Senior Member

    I have a collection of Mosin Nagants--Russian bolt-action military rifles--in 7.62x54R, which is roughly equivalent to a .30-06. When I buy a case of old Soviet-bloc steel-core, the rounds pretty much go through anything I shoot them at. I make very, very sure I have a hill for a backstop, and soft soil to prevent ricochets.

  15. aranda1984
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    aranda1984 aranda1984

    The statement of bullett proof in this case is not to be taken for real bulletts from guns.

    By the way, there is a simple formula kicking around for fiberglass thickness for a boat hull:

    I think it is : Water line length in feet / 150 + 0.07.

    Abover waterline is about 15% less.

    So a 75' long boat would have a 0.535" thick hull under water and a 0.428" thick hull on top...

    For power boats, add 1% extra for every knot over 10!

    Depending on the shape of the hull, the same thickness is weeker on the flat bottom then on a deep V or round bottom!

    This is over simplified!
    This is a rough guide line!

    Add some clever tricks with ribs and bulk heads and this is a "bullet proof" hull, until it meets a bullett or a sharp rock!
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