Thickness of a sandwich composite panel, and a few other related questions?

Discussion in 'Materials' started by Peter Griebel, Feb 23, 2022.

  1. Peter Griebel
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    Location: Bangkok, Thailand

    Peter Griebel Junior Member

    Hi,

    I'm thinking about building a Souriceau 4.75., a smal costal cruiser designed by Eric Henseval. Since I'm located in Bangkok, it is impossible for me to locate marine grade plywood. The "marine" plywood that are used for boats here is of unknown quality, a risk I'm not ready to take.

    The alternative is using a PVC foam core instead, something that are more commonly available here. The NA Eric Henseval suggest the following foam core sandwich to replace the 9 mm plywood/
    fiberglass sandwich for the hull:

    Outside skin lamination: Fiberglass +/-45° , total of 600 gms
    Fome core: Divinycell PVC foam core 80 kg/m3 @ 15mm thickness
    Inside skin lamination: Fiberglass +/-45° , total of 600 gms

    Is there anyone who can help me with an estimate of how thick the finished sandwich panel will be? I'm not sure if it changes anything, but I thought I better mention that it is my intend to do a hand layup.

    When changing the thickness of the sandwich, it will of cause affect the dimensions of cross halving joins between the bulkheads and the longitudinals, and I would also have to add to the edge of the deck panels where they meet the hull, so an idea of the sandwich thickness will be very helpful.

    What is normal procedure when laying up the above sandwich? Should I use one layer of 600 gms cloth on each side, or two layers of 300 gms? Does it make a difference in terms of workload and the finished result?

    And lastly, does anyone have any recommendations on some books I should read before jumping into this endeavour?

    Is "Fiberglass Boat Building for Amateurs" by Ken Hankinson still the go to book on the subject, even though it is more than 30 years old?

    Thanks,

    Peter
     
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  2. fallguy
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    fallguy Senior Member

    600 gram glass is db1700 in imperial units

    there is no value in using 300 gram

    if you used 400g biax and were allowed to use 6 oz woven; it would be weaker, bit easier to finish

    hexcel also makes a 16-18 oz woven that finishes like a dream, but will never be as strong

    None of this is arbitrary and must be approved by the designer, but biax is more work than wovens to finish.

    When laminating foam by hand, nothing too special is required. But for 600g glass, you must wet the foam, because the glass will NOT wet down through well and you may not get enough resin into the foam.

    I recommend applying about 40% of the weight of the glass in resin to the foam. You can make a pvc roller that does not drink all your resins. I forget if it is 1.25" or 1.5" pvc. You may need a bit of tape on the roller frame to get it right. Do not place the pvc in acetone.

    use an acetone pail with a lid for your tools

    I recommend a 6"x1/2" bubble buster roller for consolidating or pressing out any air.

    the dimension of most db1700 or 600g glass is about 0.035" or approximately one millimeter when laid up

    You ought to consider using peelply as well; it will help flatten the finish of biax some.

    If any of the panels need to be bonded for length; the best way is a plastic stapler, but they are expensive for a small project and you may also look for plastic copulas. Raptor makes them.
     
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  3. fallguy
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    fallguy Senior Member

    The way to convert glass weight to resin needed.

    3# glass
    Resin is say 9.1#/gallon

    3/9.1 • 128 oz/gallon is 42oz resin at 100% resin to glass

    a lot depends on temperatures and resin viscosity, a cold resin is slower to gel, but you use more

    I have quite a bit of experience.

    Using foam changes things quite a bit as the foam is not very strong until glass both sides.

    Tell us more about the boat and the construction and we can offer more help.
     
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  4. fallguy
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    fallguy Senior Member

    Also, for hand lamination; all the work is done face up. So one panel takes two days.

    The reason I ask about construction is for some foam boats; the inside lamination is done before the foam is placed on the jigs. This is typical for boats specified in ply because the jig spacings are too wide and the foam will sag. Or the designer may tell you to ribband the jigs instead.

    Are you going to use epoxy and paint or ve and gel?
     
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  5. fallguy
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    fallguy Senior Member

    Also, a beautiful sailboat. I recommend you consider building a vac table Peter. It is not so hard to do and will improve your product. I can help you with the how. You are going to need a big flat table anyhow for those panels..

    It looks to me like you could laminate the insides of the panels and bond them to the stations a bit and do the outside in a single skin. Is this the plan?
     
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  6. Peter Griebel
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    Peter Griebel Junior Member

    Screenshot 2022-02-23 at 21.38.12.png Thanks Fallguy,

    Thats a lot of useful information, and I will read it many times over to make sure I got all of it. This is exactly why it is so useful to ask in a forum like this, had no idea that I could use plastic nails. I will try to see if I can find the specific products that you mention, here in Thailand.

    Here are some data on the boat:

    Hull length: 4,75 m
    Length at DWL: 4,75 m
    Beam max. : 2,20 m
    Draft min./max.0,57 m / 1,35 m
    Retractable keel with tackle (easy and simple system)
    Total Area to windward: 18 m2
    Displacement:530 kg
    Keel ballast: 140kg with 120kg of bulb
    Unsinkable with flotation foam under berths
    Trailerable
    Can beach.
    Hull with 5 chines
    European Conception Category: C2 D3

    Here is a link to a picture gallery shoving a finished boat: SOURICEAU 4-75 http://www.jmliot.com/folio/569/souriceau-4-75.html

    The boat is built upside-down, on a male plug, but can also be build directly on the bulkheads. For the hull is used 9 mm plywood with 300 gms of fiberglass ( that's what will be replaced with the above mentioned foam core sandwich). The bulkheads are originally intended to be 4 mm plywood.

    Screenshot 2022-02-22 at 20.05.42.png


    This image is of a build from the Netherlands by Niels Helleman. I borrowed the picture from Niels Helleman's blog that can be found here: Amateurjachtschipper bouwt microcruiser: Het dichten der romp http://nielshelleman.blogspot.com/2013/04/het-dichten-der-romp.html

    Niels Helleman build his boat directly on the bulkheads as can be seen on the picture. Excellent craftsmanship, I can only hope that I manage to get close to this level.
     
  7. Peter Griebel
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    Peter Griebel Junior Member

    [QUOTE=" It looks to me like you could laminate the insides of the panels and bond them to the stations a bit and do the outside in a single skin. Is this the plan?[/QUOTE]

    Yes that was also what I have been thinking, but to be honest I have no experience working with PVC foam, so haven't really come to a conclusion on that. I will probably start laminating the bulkheads and longitudinals first, to start with the smallest pieces, and get a little experience before doing the hull panels. Screenshot 2022-02-23 at 21.49.34.png

    Regarding the vac table, it seems like a big extra project for a small one of build. Would you vacuum infuse both the bulkheads and the hull panels? If yes, then I would need a 5 meter long vac table. I was considering to build a table big enough for the bulkheads, and the do the long hull panels on the tiled floor, is that a bad idea?


    Oh, and one more thing I'm concerned about is the high temperatures and humidity here. I have read that the room temperature should be no more than 32 degrees, is that correct? If I work outside I would have to work in the evening and let it cure over night. The temperatures would then be around 30 degree Celsius (86 deg F). The other choice would be to do it inside my house using air-con.
     
  8. fallguy
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    fallguy Senior Member

    Well, a couple ways you can go, but the designer should be on board.

    Foam will not span the bulkheads without laminate. A two sided lamination will not be solid enough for long spans until about 5-7 days. Building on a jig might be better, then flip and remove some or all the jig and replace with spanners and fit bulkheads. Bulkheads must NEVER be larger than the hull. Building them ahead of time is always a danger of this, as long as you understand pushing out the hull is an agriegous, unrecoverable error; you'll be fine.

    You may have problems trying to laminate large panels at 86F unless you buy tropical 2 hour epoxy resin. You ought to learn some strategies first. One strategy is mixing a bottom batch of say 40% of the need and then applying it and rolling the fabric off a tube and then a quick consolidation pass and then mix and pour the 60% batch..this way, the first batch can gel, but you won't lose the batch in a bucket...86F is pretty warm and epoxies are rated at 100g mass; so a narrow cylinder of 2 pounds of epoxy is as much as 9 times a bigger mass than the rating, for example. Even using a bigger one gallon bucket will slow gel times. And keeping the epoxy in a cool place, and neber allowing the sun to beat on it, etc.

    If not epoxy, I am not your expert on dealing with warm temps using vinylester.

    Another thing to watch out for in your situation is blush. A greasy stuff on the surface. Worse in high heat and humidity. Certain epoxies are better. Silvertip by Systems 3 makes a tropical epoxy and is very unlikely to blush.

    You could also order plywood from the US. I know a highly reputable company if you have second thoughts about foam.

    I think you ought to build on stations and not bulkheads.
     
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  9. rxcomposite
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    rxcomposite Senior Member

    Peter
    Just a few quick observations.
    1. H80 is more than adequate for the job at 15 mm thick. It has a shear strength of 1.1 N/mm2. H60 will do. You need only 0.70 shear strength. Use H60.
    2. 600 gr/m2 biax is inadequate. Might work for a paddleboard. It is only 0.7 mm thick. Skin thickness has a minimum. At 1.1 mm minimum, it is still a "no step" zone. Minimum is 1.5 mm outside, 1.4 mm inside, bottom laminate, That is to allow for resistant to puncture.
    3. Total thickness is 15 mm + 1,5+1.4,
     
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  10. fallguy
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    fallguy Senior Member

    Peter-rx is a highly experienced fellow and his words are gold, I find his laminating schedules to be solid. I did not want to comment against your designer specs, but...

    my catamaran cabin walls are made of 600gr biaxial glass; it really should never see waves and is on 12mm core

    rx is correct that your laminate plan at 600g is really, really light

    for example; you would not stand on a 600g 15mm panel over a span of say 24" and expect it to not fail or bend a lot; perhaps past maximums

    however, two layers of 600g is really excessive and simply too much for the speeds you will encounter and for a nearshore vessel

    something in the middle would be better; perhaps a 850-900g glass

    I will not enter into polemics or argue with rx, but a 34 oz laminate both sides for your boat is too much,17 oz too little based on my experience with these panel weights.

    Two layers of 400g glass is really pretty strong.
     
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  11. rxcomposite
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    rxcomposite Senior Member

    I am following ISO min standard. I am not questioning his design. In fact, the OP said "suggested". I just refined it.
     
    Last edited: Feb 24, 2022
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  12. rxcomposite
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    rxcomposite Senior Member

    There is. When it is biax, it means 2 direction. But there is a difference. A 0/90 degree woven roving laid up at +45-45 has a higher modulus than a stitched or uni laid at +45-45. Choose carefuly.

    Personally, I would choose a WR laid up at 0/90 outside and if needed to add bulk, Biax can be inside, nearer the core. It is good for torsion inspite of its lower modulus. Thus_ core, biax, WR.
     
    Last edited: Feb 24, 2022
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  13. Peter Griebel
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    Peter Griebel Junior Member

    Thanks for the replies from both Fallguy and rxcomposite :)

    That is a lot more glass than the original plywood design where the outside skin is only a 300 gms biaxial on a 9 mm plywood.

    So if I understand Rxcomposite correctly, I have to go up to at least 1300 gms of biaxial, right?

    Some of the biaxial fabrics that I see in high weights, are a combination of biaxial and chop strand, is that fine? UTEC's highest weight biaxial fabric is a 1250 gms with a distribution between biaxial/chop strand of 800/450. Would it be an idea to use that and then add a women fabric on top? and in that case how many grams of woven? Or is there a better solution?

    I think a solution where the outside and inside skin have same thickness is optimal, as it minimise the amount of different fabrics that I would need to buy.

    I will go back to the NA and talk with him again. The numbers he suggested was just as a rule of thumb, so was not to be taken as a final answer I guess. For a newbie as me, this whole conversation is very helpful, also in terms of me being better prepared for talking with the NA.
     
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  14. rxcomposite
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    rxcomposite Senior Member

    Yup. plywood is already structural. You are just enhancing it by encapsulating and it will come out to be bulletproof. With foam cores, it is weak so the skin bears all the loads. But it is lighter. Quick compare, plywood would be in the 450-500 kg/m3, Foam core in the 60-100 kg/m3.
     
    Last edited: Feb 24, 2022
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  15. fallguy
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    fallguy Senior Member

    Rx did not suggest 1300g biax. He did suggest a biax and uni? out, which will finish better.

    I don't want to speak for him, but I will speak for me.

    Something on the order of 600g biax with a 300 gram woven, or 600g biax with a 400g woven if one exists would be something I'd test. What test? Measure the distance between midship bulkhead maximums and stand on the panel. Simple. 200# point load it. You do have multiple hard chines and the panels to the sea are not so big it looks like.

    RX will advise a thicker layup; most likely on the order of 600g biax and 600g woven. But I would not go to ISO unless required. So much also depends on planned use. Are you crossing oceans, for example? North Sea? I'd add more glass if so. Might even go more core..

    For blue sea plans, I'd go say 600g biax and 600g hexcel uni.

    something like this one, but it is late and I did not review it well

    triaxial glass like a 950 should also at least get beat up on by rx; my hardchine powerboat uses 850-950 triax on 12mm core

    Here is a heavier hexcel uni. Also won't wet tops down; fyi.

    Hexcel HiMax Fiberglass E-Glass Unidirectional Fabric 48.42″/1230mm 17.7oz/600gsm - Composite Envisions https://compositeenvisions.com/product/hexcel-himax-fiberglass-e-glass-unidirectional-fabric-48-42-1230mm-17-7oz-600gsm/
     
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