glass core strength comparisons

Discussion in 'Materials' started by jpuseyjr, Mar 31, 2013.

  1. jpuseyjr
    Joined: Mar 2013
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    jpuseyjr Junior Member

    I will eventually be building a power cat - not sure of the size etc. At this point I am just curious about solid glass, glass (different coring) core materials, strengths etc.

    Trying to optimize the build for strength, weight, cost etc.

    I have read alot of different forums and specs and there are so many it can be overwhelming and many are marketing ploys I would say.

    In reference to strength to weight - I keep reading that a cored hull is stronger than a solid hull of same thickness (in general - I know there are other things to take into consideration - such as type of glass etc). What about the stength of cored in reference to a solid hull? I am assuming a solid hull is stronger (same thickness) - but could you effectively make the hull thinner and still be as safe?

    My eventual build will be using more round construction instead of straight 90 degree edges - it would a be a little more difficult in the build but overall be a stronger hull. Actually, that should be a question....

    Being I am looking at more of a rounded hull design - strcutural foam would really complicate the build - but what about coremat XM 10 - anyone have any experience with this stuff - I know it eats resin but comparible coring vs coring doesn't look all that bad of you compare thicknesses - this is what I come up with so far

    (just for weight comparisons)
    3/8 inch foam core with 18 oz roving both sides - thickness 0.433 inches - weight .641lb/sqft

    xm 10 - just with resin - thick 0.394 inches -weight 1.398 lbs sq/ft

    glass - 10 layers 24oz wr - thick 0.4 inches - weight 3.340 lbs sq/ft

    Any thoughts - here - I know an actual layup would be different - just trying some comarisons of products vs - weight - thickness etc?
  2. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    With any multihull you are going to want to use a core, I have owned several cats that were solid glass but by necessity they were very thin skinned so not very resistant to puncture. It is better to use a fairly thick core and thin skins to get good stiffness with minimal weight and maybe taper out to a solid glass strip down the centerline where you will sit on the beach, but make it solid.

  3. tunnels

    tunnels Previous Member

    solid will be heavy
    Cored is lighter !!
    Theres more than one kind of strength to consider .
    Why are people so hung up and worried about puncture resistance ???
    i have been boating since i was twelve years old and neither my father or myself have ever come close to putting a hole in the boats we have owned over more than 60 years !! hitting things and putting holes in boats is the drivers responsability !! if you not watching where you going and thinking about what you doing you shouldnt be behind the wheel !!
    Kevlar is you puncture resistant material . No its not bullet proof !!
    Core matt has no place in the construction of boat hull bottoms it will not take the continual pounding or flexing and will eventually shear from end to end !!
    Hull Top side , decks and interior panels etc core matt is ok !!,BUT hull bottoms NO no no !!
    Same with Foam cores !!! you really have to do your home work on that subject !!it will depend on the speed the boat will be travelling at as to what core is better suited !! The shape of the hull also is a limiting factor in all this .
    topsides are not to much of a problem , Its the bottom thats the trick part!!! Balsa !! again do your home work !! and compare and you make up your own mind when you've read all the information !!

    Dont know what speeds you looking at or what size boat but theres a great long list of differant glass materials availible . Same with resins to go with the glass . Polyester is the most widely used !!,Vinylester is a far better and tougher resin . And then theres epoxy !!,but as you go up the scale with better resins so does The price go up as well !!, so lots of just basic things to consider . The mix and match of resins and glasses and cores is a tricky one .
    Remember All materials have limitations !!! Resins glasses and cores !! its knowing what is best suiter to what conditions !!

    Introduce speed and you have to really take lots things into consideration with the boats construction in the way of stringers ,frames ,bulkheads along with twisting and raking and flexability !! .
    DEpending on the desisgn and what the deck is like this is what takes a lot of the twist and flex in cats so not only the hull construction but the deck to consider along with it !!.
    Inboard ?? outboards ?? what kind of power you looking at ??what kind of seas you going to use it in ??
  4. jpuseyjr
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    jpuseyjr Junior Member

    I know that there alot of other 'things' to consider..... I am trying to take this one step at a time without complicating things too much. I am just looking for ideas for material comparisons. I will throw a basic idea of what I have in mind and it will probably not come to light for another 10 years or so, with a million and one changes between here and there, as this is going to be our retirement RV so to speak.

    So lets back up a bit and look at the overall picture of what we are looking at. I am not worried about the architechtural engineering at this point nor the physical building. These are issues I have lots of experience with and will deal with later.

    We are looking at a live aboard power cat, outboard powered, cruise speed of about 17knots. We will not be doing ocean crossing and we live in florida - gulf side but will be going from port to port way down the road - maybe to bahamas ocassionally. But for the most part only moving around once a month or so and most of the time will be anchored in a protected bay, in freshwater 90% of the time. We are very conscience of the water and don't like getting a beating in heavy seas. I have been boating, and owned many larger boats not quite what you would call a yacht - we frequently go well beyond 40-50 miles offshore here in the gulf and very comfortable doing so. Prior preparation prevents piss poor performance........

    So I have looked at many designs - but with living in florida we have many issues that will limit the resonable costs of owning a full blown yacht.

    1) Hurricanes - can't pull a 20 ft X 42 ft catamaran out of the water easily or quickly....
    2) Mooring - not easy to find a slip around here that will accomodate a 20ft wide cat... if you do, your looking at 2 slips and $$$$$ - 800/month.
    3) Haul outs and bottom painting - Most places here locally will not accomodate something of this WIDTH - and then you are at their mercy $$$$$.

    Taking this into consideration - a 20 X 42 ft cat doesn't really seem to fit thte bill. I have looked at many designs but the one that really strikes my interest is the prowler VT schioning designs ------ but again -18 ft wide - I am looking into the feasability of something similar. 14 X 35 ish.... semi discplacement hull. I can haul - with permits - 14 feet wide. I live near the coast so not driving long distances and would probbaly only be hauled out 5-6 times a year - so no big deal - alleviates the slips - and haul outs - and the big one HURRICANES....

    Things we DON'T need..... 4 beds - super high clearances inside - like the lofted ceilings and 6-6 clearance in the sponsons - Living accom's - 1 queen size bed up front Between sponsons - storage - head - everything else on the main deck - don't need fly bridge - I have done some basic drawings and it should fit will withing the 13'6" road height requirement. I have looked at the kit kat out of st pete but not thrilled with the - honeycomb core - not thrilled with the end grained blasa --- which this brings me back to my original question of --- materials/cost/weight/and (less) construction difficulties....

    Looking at definatetly using vinylester resin with maybe an epoxy outer (paint). But definately not poly. But again coring - I will wory about the architecture of it later - just trying to get ideas now...
    Just throwin this out there as a lay up - 1 oz Mat/24oz wr/24ozwr/CORE?????/24OZWR. This puts me at .144 inches in thickness and a weight of 1.209 lbs/sq ft - if I add 1 inch corecell - If i remember correctly (?6lbs a sheet) comes to about .1875 lbs/sqft - Have to go back and look though. This would bring the whole layup to - 1.144 inches in thickness with a weight of 1.3965 lbs/sq ft.

    Again I am not using this as engineering specs or actual layup I will consult with an enginner for all that later - right now I am looking to see if I am on the right track. What about other cores? forget wood - I think foam is about the best/easy working - but expensive - Not sure about the coremat XM 10 thats why I was asking - coremat xm 10 vs foam vs solid - I am also thinking of solid below waterline and cored above.... These are all just ideas right now hopefully becoming a reality - just like to be informed when I go to talk to someone who is trying to sell me something that they may have in interest in .

    Thank you for any input
  5. tunnels

    tunnels Previous Member

    ok that news sure changes few things !! size is big but its not fast !
    Glass if you want to save weight you would not want to be using woven roving !! and sure as hell no core matt any where .:eek:
    yes can use Foam cores just about every where !! along with triaxles and double bias glass and you should be looking at resin infusion of all the panels using epoxy resins !! ;)
    And dont poo poo Balsa its got a lot better propoties than Foam in more ways then one ,and for me as having worked with glass etc for many years and just done a 25 mtrs lake boat 25 mm thick balsa was number one choice and won hands down over any of the foams !!
    Dont blame the materials for failures its 90% bad workmanship that makes things fail and 10% bad choice of combination of materials . :confused:
    Also be very careful getting caught up in the weight saving thing .
    You scimp on materials building the hull and deck to save a few kilos and then fill the boats with tons of useless junk that really just creature comforts and for show !!.:p
  6. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Tunnels, when you have a multihull of any sort, beaching it on purpose is a reality,but so is the possibility of puncturing the hull bottoms if you settle on a sharp rock, a solid foot wide strip down the keel line is worth considering. I agree that puncturing in normal use is not much of an issue and a lot of cored boats have much heavier skins than they need

  7. jpuseyjr
    Joined: Mar 2013
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    jpuseyjr Junior Member

    Thanks for the input and replies - not knocking the balsa - just a personal preference of mine. Was hoping to stay away from the epoxy if at all possible - I have looked at alot of specs with epoxies and such and don't see a huge advantage over vinylester for the price difference. I do see the advantage of extra glass on the bottom of the hulls.
    What about the different foam cores - divinycell vs coremat? Huge difference in price - are htey all that different - again for the price/strength, etc?

    I gues sif I go foam boards I will have to ditch the idea of rounder hulls and stick with the 90 degree corners --


  8. tunnels

    tunnels Previous Member

    YOU cannot compare core matt and foam they are two absoluty and completely differant materials used for differant things in differant places !!dont get confused by all your reading !! divinicell vs core matt !! you cant compare the two !! the weight differance of a equivlent thickness of each is not even in the same book !! You are totally confused on that one !!

    Yes i do agree in what you say about epoxy and vinylester but also dont dismiss Polyester either !! there nothing wrong with a good polyester resin for unterior use or even making the deck !. The price is always better and its easy to use !
    Like i said do your home work on the glasses that are availible to you and get your head round there uses !! all materials have there special properties and places where they can be use . but you need to know where they should not be used as well !!. :cool:

    NO you can use foams for curved surfaces but depends on the thickness of the core you pick on to use as to what sort of corners you looking at !!SHARP OR ROUNDED ?? Its best to vac bag all and any cores into place !! always !! tight corners dont need cores depended on there shape !! a crease or corner has its own natural strength so a core can actually become a weak place where delamination can and will take place in a stressed situation !!
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