General Composites Construction questions

Discussion in 'Fiberglass and Composite Boat Building' started by Mark C. Schreiter, Nov 17, 2020.

  1. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member

    Hello,

    Ill do my best to reduce the amount of words here so I apologize upfront for my brevity.

    I have several years working in an aviation composites shop doing wet layups, vacuum bagging, prepreg, mold making and so on. i'm not an expert but I'm not scared of composites.

    I want a boat and my wife hates boats. Money is not a huge issue but Its very hard to spend it on something my family hates.

    Im looking for a flats boat in the 15ft range, mainly because I will be using it to fish alone and on occasion bring my wife and daughter to a sand bar and I want a project that I can work on that will fit in my garage. My boat needs to be as simple as possible. tiller motor, no electronics, self bailing, minimal compartments and so on. my requirements I feel are inline with my lack of experience boating. I grew up around boats with my parents but I was much too cool to care about them at the time. I have regrets.

    so I've been looking for about a year online with very little results. there are boats out there but people are asking insane prices for rotten projects. Or i'll find the right boat with the wrong motor. Im pretty stubborn and I refuse to buy something and try to resell online.

    now, recently I picked up plans for an all composite core 15ft flats boat with a tunnel hull, sponsons and what appears to be the perfect shape for my fishing in the flats needs. the only problem is the cost of materials. the plans call for 5lbs diviny cell for at almost $200 for 1 4x8 sheet and ill need about 18. yes I could build it out of wood and glass but again im stubborn and that's just not gonna happen.

    I found a company called Carbon core and they make a 4lbs density foam that is half the cost and is a marine grade core material. i've spoke with them and they lead me to believe that there foam is a direct competitor to divinycell.

    onto my questions, if I used a 4lbs core material on the hull when the plans call for a 5lbs, would or should I add another layer of 1708 glass?

    the hull plans call for 2 layers of glass, foam core and two more layers of glass ( 1708 and a 12oz biaxial, i believe). what about a solid laminated hull bottom? what would my laminating schedule look like? maybe 6 or seven layers of glass on the hull bottom and foam core the sides? Id alos foam pore every cavity possible.

    the foam core boat final weight is around 400lbs and the wood cored boat is around 600 so I figure as long as i keep my weight under ?? 700 or so lbs I should be in ok shape.

    Yes I know I shouldn't mess with the plans and the designer put tons of time and effort and money into them. I don't mean to insult the designer and I don't think I can do it better but I'm just looking to do it cheaper.

    At this point Im more than ok with sacrificing weight for speed and performance and any combination of the three. Id like to boat to float at least 500lbs and go forward and backwards.

    any assistance is greatly appreciated. Im do not want to start a debate on materials or talk about how I should just buy a new boat or anything non constructive. Id like to determine a way to build the boat of my current dreams at a more reasonable to me cost.

    thank you in advance,

    -Mark
     
  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    4 lb core from 5# core should be negligible...sort of

    Adding 1708 in hand lamination is 50 ounces per yard. Way major overkill for the delta in density.

    But.

    The density is not the issue. The flexural behavior and other things are also important.

    All the attributes of the core need to be compared. Things like sheer strength are vital.

    Also, I have calculated waste rates of epoxy at about 30% for wet bagging. The core and glass cost less in my build than the epoxy by about half.
     
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  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    How do you see yourself needing 18 sheets of 8x4 Divinycell for a 15 foot boat ? Sounds like enough to build two of them.
     
  4. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member

    18 sheets could be a little high, might be slightly less do to my specific build but not by much. I’m looking at at least 13 sheets for certain. If all goes well up to that point than I’d consider things like center console, live well, cooler, hatches and so on.

    the entire hull is sandwich construction. 2 layers of glass, foam and 2 more layers of glass. The stringers call for 2 layers of foam with a single layer of glass in between, the bulkheads call for 3 layers of foam with glass in between. The sole is sandwich construction, as well as the deck. The plans call for hatches, center console and so on, polling platform, transom, gunwales, rod holder brackets and you get the point. It all ads up.

    with foam and shipping alone I’d be on the high side of $4,000. Pick up a used motor and I could splash it for maybe $10,000. That’s using all the recommended materials though. I’ve been using UScomposites for epoxy and cloth for personal projects from surfboards to skateboards to car parts and have had super solid results and it’s half the cost of West Systems epoxy.

    $10,000 is just a bit much for something I built in my garage.

    Perhaps a big reason is that I know myself well and my ADHD gets the best of my and projects tend to get shelved. I don’t want to end up shelving a pricy “fun” project.
    -Mark
     
  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Two bottom each side..
    Two for the sides.
    Two for the decks.
    Two for the bulkheads
    Two for the benches
    One for the splashwell area.

    I get like 11.

    You buy a raptor stapler and a box of staples and use all the pieces. The raptor costs about 250$, but pays for itself if you build a few panel equivalents from scraps.

    In boat building, butt joints are accepted.
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I missed the sole and stringers; so he is close..but the transom requires coosa. Wait until you buy one of them and freight!

    I think you can get Gurit M for like $150 a panel. So 2250, plus coosa at say 400. You probably need some high density? Like 400 more. Freight qt $400. $3500 for core. Glass is say $1000. Epoxy is going to cost you like $7000. Raw hull costs are about $12,000. My raw hull costs for a 32' cat are about $30k epoxy,$12k glass,$15k core. It is light, but close. About $70,000 for raw hulls. Wet bag build.

    Small boats in foam are at a huge diseconomy versus okume plywood.

    Okume plywood say $60 a sheet at to keep it easy. $1000, glass is say 2x12oz biax or cost is maybe 400? Epoxy is about maybe 10 gallons say $1000. Raw hull say $2500 or about 20% the cost of foam and builds about 3 times faster.

    Pretty terrifying spending $70,000 and not having mich of a boat. Wife would have been pretty mad if I had quit.
     
  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Do you realize how much paint costs? Even the paint for a small 15' boat is gonna cost like $500.
     
  8. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member


    On second thought I think you guys are closer than me. After glancing at my notes the divinycell comes in 4x8 sheets and the plans call out for 12 sheets and an additional sheet of Coosa board for the transom.

    I was looking at the Carbon Core foam and those are not the standard 4x8. I think they’re closer to. 3.5 x 7.5 or something strange like that. The plans have all the parts laid out to minimize waste but using 4x8 sheets. So I was planning on butt joining the odd sized sheets to make them standard sizes. And there were a few places that I would like to add extra thickness due to the density of the carbon core foam being less than the plans call for. Mainly the stringers and bulkheads.

    So divinycell would be 12 sheets of 5lbs and if i got carbon core foam maybe 15 sheets. Plus additional if I wanted hatches, polling platform and things like that.
     
  9. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Which design are you planning on building Mark?
    Can you provide any links please?
     
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  10. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    4x8 sheet of foam is 32sqft on one side, covered with one layer of 1708 +1 layer 12oz biax. Foam price is dictated by thickness and type, so no info here. If foam is to expensive balsa can be used but is heavier. 13 pieces needed (12 PVC, 1 Coosa).
    1708 comes in 4ft 2in wide rolls, needs 8ft×13pieces×2= 208ft = 69 yards
    12oz biax same as above
    Resin: let's say one gallon covers 12sqft of 1708+12oz biax on foam. Total area is 32sqft×13= 416sqft /12= 34.6 gallons.
    So I look at the US composites site, one full roll of each of the fiberglass weights is ~1000$. 40 gallons (mixed) of their 635 epoxy with medium hardener is 1600$. The same amount of 435 standard polyester is 1024$.
    Total is foam 3000 + epoxy 1600 + fiberglass 1000 + freight = 6000? Add fairing and painting and consumables maybe another 1500.

    What thickness and type of foam is specified in the plans? And is the layup really 1708+12oz biax? I ask because the numbers don't add up if the whole completed boat is 400lbs, since one gallon of epoxy alone is about 9lbs.
     
  11. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member

    Plus all the filler, high build primer, sealer and prep materials.

    I’m not to worried about all that because the finishing work is closer to the end and I can sort of launder the money at that point.

    I’m also not planning on building it over a weekend. the plans say 400 hours for an average build if I recall correctly. I would need all the pricy bits upfront though. Foam sandwiches for the stringers and bulkheads are the first steps in the build.
     
  12. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    For a cored 15 foot boat, stringers can be dispensed with, ditto bulkheads, just use a thwart toward each end, that doubles as a bulkhead/seat. With a reasonably flat bottom, and nothing to kick your toes on, in between. You can have the forward one at the same level as your casting platform. As for self-bailing, I would omit that, in such a small boat. KISS ! :D
     
  13. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member

    The plans call for 12 sheets of 4x8, 1/2 inch 5lbs density foam plus 1 inch 4x8 can’t remember what they use her but you can use coosa board.

    The exact cloth used is 150 yards of biaxial 12 oz. 45/45 and 0-90, with or without mat plus 150 yards woven 9 oz. the cloth is estimated at 50” wide and is to be cut into strips for tabbing as well. Or buying glass tape and fewer yards of the biaxial is an option. If you cold mold or wet layup they say you should use 15 gallons of epoxy give or take and vacuum bagging you should be around 10 gallons.
     
  14. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member

    the plans I have are from boat builders central for the phantom 15.
     
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  15. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I get a kick out of someone telling me I can use less epoxy wet bagging than hand laminating.

    The epoxy use is more wet bagging and less ends up in the final part.

    I have about 300 gallons experience that affirms it takes more epoxy to wet bag efficiently than less than hand laminating.
     
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