How many layers to bullet proofness?

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

  1. apex1

    apex1 Guest

    Any loose fabric stops any bullet, no matter steel or even uranium core. Like capt. vimes already mentioned, there have to be several loose curtains of fabric (preferrably Kevlar / Aramid) and you can even stop a 9cm grenade.

    Boat hulls, built within sensible weight limits, are NOT bulletproof, no matter which material you would use. (the best results you can achieve with wood epoxy btw!)

    A example: 4 "layers" of Kevlar 300gsm hung loose one after the other, can stop most handguns bullets, even 357 magnum core lokt!
    The same fabric glued together with epoxy does not stop a 38 wad cutter.

    The fact that the curtain gives way to the bullet makes the effect. You can use plain canvas too, though not as effective as Aramid.

    In test setups for forensic investigations a simple wooden box, stuffed with cotton, is used to catch the bullet intact (no deformation). These boxes are less than 60cm or 2ft deep!


    No, not even a rule of thumb! It is nonsense!
  2. gunship
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    gunship Senior Member

    its a james bond clock ;P
  3. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Good grief ! Are you guys preparing war boats for what ?

    So the Germans have wad cutters now also :D

    Best bullet proofing is to hang all your clothes, blankets, life jackets all around you when you hide in the hull.
    The advantage of this is they will have less wrinkles in them, the wet ones will eventually dry if you don't keep wetting them, and
    of course they will protect you from bullets :D
    Just remember when the life jacket gets a puncture you will sink :D

    What are you going to stop the RPG's with ? Use a cricket bat, you can hit them right back with it. If you miss you're in **** I mean water. Probably both.
    Best cricket bats men are those aboard :D
  4. aranda1984
    Joined: Jan 2010
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    aranda1984 aranda1984

    No, not even a rule of thumb! It is nonsense![/QUOTE]

    Hi Richard.

    I don't do fiberglass, I guess, I should have kept quiet, but this is where I got my information from. I can't remember the source, but I found this in my data base.

    Laminating layers of glass and resin to make a boat hull
    The most popular boatbuilding material is a mixture of fine glass strands and cured polyester resin known as fiberglass, glass-reinforced plastic (GRP), or fiber-reinforced

    (Note, the actual pictures have been stripped by the Control C/ Control V transfer...)

    Common fiberglass materials include the following (top to bottom): Chopped-strand mat, in which randomly oriented glass strands of irregular length are either glued to a scrim backing or loaded into a chopper gun for professional application. Woven roving comprises bundles of continuous glass strands assembled into a coarse weave. In unwoven roving the bundles are stitched together parallel to one another to give great strength along the axis of the bundles. If the unwoven roving shown here were cross-stitched to a second layer oriented 90 degrees to this one, the result would be a biaxial roving with greater strength in two directions than even a woven roving of the same weight provides. The fiberglass cloth at bottom has a finer weave and a lighter weight than woven roving. Professional builders use it in specialized applications but rarely in hull construction. For do-it-yourself repairs, however, you’ll have an easier time and get better results if you use mat and cloth rather than mat and roving.
    plastic (FRP). Its success stems from the fact that one set of molds can produce hundreds of identical hulls, decks, cockpits, and cabin tops. Most boat builders use the same laminate—alternating layers of chopped strand or mat (1½ to 3 oz. per square yard) and woven roving (24 oz. per square yard) wetted out with standard polyester resin. Vinylester resin is more expensive than polyester but less permeable to moisture and more resistant to osmotic blistering or “boat pox.” Some expensive boats use vinylester throughout the layup; in other boats, it’s used only in the surface layer of the laminate, where it bonds very well to the polyester resin beneath it. A skin coat (just beneath the gelcoat) consisting of 3 ounces of chopped strand or mat wet out with vinylester resin greatly reduces the odds of blistering. A skin coat is always a good idea no matter the resin because it prevents “print-through” of the coarse woven-roving pattern onto the gelcoat. Epoxy resin, which is stronger and more flexible than polyester, is not normally used for production hulls because it is more expensive, but it’s widely used for repair work and special projects. Epoxy adheres well to the old polyester resin in boat hulls and gelcoats, but polyester does not fare so well when applied to old epoxy. The two layers mentioned previously (mat and roving) constitute one ply and measure about 3/32 inch (2.4 mm) in thickness. Such a laminate weighs about 94 pounds per cubic foot (1,506 kg per cu m). The glass fibers should comprise about 35 percent of that weight.

    The thickness of a fiberglass hull in inches should roughly equal the waterline length in feet divided by 150, plus 0.07.

    The topsides are usually 15 percent thinner than average, whereas the hull at the waterline and below is 15 percent thicker.

    Powerboats need hulls that are thicker than normal by 1 percent for every knot in speed over 10 knots. Despite its popularity, GRP has some major drawbacks. It lacks the warmth and personality of wood and weighs about three times as much for the same volume of material. It is the floppiest of all boatbuilding materials; therefore, to provide the stiffness a boat requires, most solid fiber-glass hulls should have five or more longitudinal stringers on each side of the inside of the hull. Bulkheads also provide stiffness, as do the molded, ribbed fiber-glass grids often placed under the cabin sole in fiberglass construction. Early fiberglass boats of the 1960s and 1970s were often over-built by manufacturers who were just making the transition from wood and still unsure of fiberglass’s strength. Most of those early boats are still around, and when they are well maintained and updated, they can make great bargains on the used-boat market. Recent boats—especially at the high end—are not just built but also engineered. Most now have foam or balsa cores sandwiched within inner and outer laminates of fiberglass for stiffness and lightness. High-performance boats may have super-lightweight honeycomb cores encased in laminates of vinylester or epoxy resin in which the fiberglass reinforcement is replaced in high-stress areas with Kevlar or carbon fiber. Such hulls are usually laminated with vacuum bagging to remove all excess resin for the very lightest weight. Fiberglass decks are almost always cored construction these days because stiffness in that location is at a premium and cannot be gained from convex curvature in a relatively flat expanse. A “squishy” deck that yields underfoot is often an indication that moisture has invaded and rotted a balsa core—often through fastener holes. Spider-web crazing or local swelling in the deck gelcoat may indicate the same thing. Beware: the repair can be expensive. Fiberglass is long-lasting but not maintenance-free. The gelcoat surface eventually chalks, degrades, and requires painting. Water vapor passing through the outer layers of the underwater hull can cause blistering (osmosis) and delamination—expensive repairs.See also Blisters in GRP; Gelcoat; Plastics.

    If you disagree and you have lots of technical and practical experience, I would like you to correct me, so that we will all know the right answer.


    Stephen I. M.
  5. Boston

    Boston Previous Member

    the hind 24 soviet attack helicopter wind screen could supposedly withstand multiple 50 cal hits and it was laminated acrylic
    ( or at least thats what my military friends in Afghanistan tell me )

    in a nut shell
    I think you wasting your time trying to bullet proof a pleasure craft
  6. capt vimes
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    capt vimes Senior Member

    the russian hind 24 was/is armoured to withstand .50 cal bulltes... thats right BUT:
    the fuselage had/has this armourement and only on its bottom... definetely not the windscreen!
    this is simply impossible...

    nobody answered my question so far...
    what is the best material - ok, not a good word, lets call it matter - to stop and destroy bullets?
    any one? ;)
  7. powerabout
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    powerabout Senior Member

    exploding armour

    I have seen photos of a series of crew supply vessels ( with holes in them)and one model is being shipped to Nigeria.
    They had some Governement help making them bullet proof.
    All that happend was the the other side got bigger guns so the next boat was more bullet proof etc etc...
  8. Boston

    Boston Previous Member


    and I just looked it up but Ill go do it again to make sure
    the windscreen is said to stop a 50
    its 5 in the am
    but Ill post were it says that soonest
  9. capt vimes
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    capt vimes Senior Member

    not for non-explosives... a rifle bullet goes through explosives - even if triggering it - like through butter...
    explosives are a means to prevent hollow charges (fired from a RPG i.e.) from penetrating the steel underneath...

    8.4 cm hollow charges cut through 100 cm of armour steel... add some explosives on the outside... the hollow charge will have no effect at all...
  10. capt vimes
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    capt vimes Senior Member

    sand is good...
    but... think liquid... ;)

    you are right... the plane part to the front is really said to stopp a .50 round...
    wow - didn't know that... my apologies...
    impressive helicopter... ;)

    Attached Files:

  11. gonzo
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    gonzo Senior Member

    I think it sucks that this thread hijicking is happening so often. Why don't you guys answer the question in the thread?
  12. capt vimes
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    capt vimes Senior Member

    i think it has been answered... and
    don't you dare hijacking this threat... ;)
  13. SamSam
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    SamSam Senior Member

    This happens a lot. I don't think it's hyjacking so much as not paying attention to detail.

    What happens even more is people ask questions that can't be answered too precisely. A 31' power boat is shown but specs asked for a sailboat of no specific size. The actual questions asked were...
    A 31' boat like pictured might have 3/8" of glass at the gunnels gradualy increasing to trhe chines and at some places on the bottom may be 1" thick, for a solid layup with no sandwich. How many layers depends on the type of cloth and how applied ie hand layup, vacuum bagging, etc.

    Here's a chart from Ken Hankinson's book "Fiberglass Boatbuilding For Amateurs".....
  14. Marco1
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    Marco1 Senior Member

    We use to make bullet proof doors for banks by laminating several layers of aluminium and plywood glued with a good quality contact glue. And yes we tested them with ACP 45 and 308 winchester, and both would only go 1/3 of the way through the 40mm door.
    I agree with the observation that a solid resin kevlar compund will not stop any serious projectil. Only several layers of different density material that can slide over each other and mold to the projectile offering a variable resistance would be able to stop a projectile of anything over 40 grains at reasonable speed.

  15. Boston

    Boston Previous Member

    I believe sand was the appropriate answer
    cheapest way to stop a bullet

    the impact resistance of a vest is due to its ability to absorb energy
    the harder a material is the harder it is to dissipate that energy so vests tend to be thick and made of loosely attached layers
    completely the oposite of a GRP hull

    we killed that question ages ago Gonz :cool:
    you gotta keep up mate :D

    no more beer for you :p
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