General Composites Construction questions

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

  1. Mark C. Schreiter
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    Mark C. Schreiter Junior Member

    off memory I believe the bulkheads serve as supports for the casing deck at the bow and stern as well. The hull has a tunnel on the bottom and I think they’re called “sponsons” where the motor is recessed a foot into the hull. So there are some structures there that they call bulkheads because it has a “false transom” and the stringers provide support for the sole.

    I thought self bailing would be an easy way out to simplify the boat? Maybe I’m not 100 on what exactly it would look like on this boat.
     
  2. Mark C. Schreiter
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    Mark C. Schreiter Junior Member

    im not telling you anything. I’m just passing alone what I read in the plans. It would make more sense if the plans were talking about the final product and not the actual bill of materials. Witch I’m assuming they are talking about final product.

    Regardless the epoxy is not my worry when it comes to cost. As stated I like USComposites thin epoxy that is $1000 for 20 gal of resin and 6 gal of hardener.
     
  3. fallguy
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    fallguy Senior Member

    Also, a plastic honeycomb with veil each side is not suited for vac.

    I have used plascore and it is resin thirsty and uses somewher e about 1 oz per sq foot additional epoxy to wetout.
     
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  4. fallguy
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    fallguy Senior Member

    A lot of the guys on the forum will tell you self bailing is a bit complex to get the height of the scuppers right.
     
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  5. bajansailor
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    bajansailor Marine Surveyor

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  6. Rumars
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    Rumars Senior Member

  7. fallguy
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    fallguy Senior Member

    Noahs does a good job on freight. Great prices on glass. Basically, you try to buy a lot of stuff and the cost drops.

    The pvc 80 is a good product, smaller sheets than the M foam and only an issue if dark paint.

    One thing to know is all foam core is special ordered. If you want holes for vacuum; scored for infusion; solid for wet layup. All custom ordered and no returns.

    I bought all my glass and foam from them. I bought all my epoxy from BBC is Florida.
     
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  8. Mark C. Schreiter
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    Mark C. Schreiter Junior Member

  9. Mark C. Schreiter
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    Mark C. Schreiter Junior Member


    Im wondering why foam is cut to such odd sizes considering a standard sheet of most construction materials is 4x8?

    what's your opinion on taking the time to vacuum bag such a small boat? from what I think I know, vac bagged parts can be stronger, stiffer and lighter but is it really worth it for a 15 foot boat or are the benefits negligible? the plans want you to cut the stringers, bulkheads, sole and basically all the foam parts and laminate them before install and then basically tab them in. if I bagged them i would only be able to do a couple parts at a time and would add on at least a month but if my biggest gain is negligible than id probably omit it. you can "wet Layup" the boat and they say it only ads about 40 lbs to the final weight. im fine with that. curious of you opinion though.
     
  10. fallguy
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    fallguy Senior Member

    wet bagging is a **** ton of work and way slower for that 15 footer

    I don't know the build specifics, but consider you cannot torture a fully skinned panel much.

    So, it is possible that only half the panel is built on the table. The. The rest of the boat is hand glassed on the entire boat bottom? Or big bagged which is a **** ton of work for one guy; probably impossible with onehour epoxy.

    The reason the sizes vary is a mystery to me. I have only one idea. The chemicals are made into a puck and that puck must have limitations on how large it can expand? The expanded foam is then perhaps trimmed to the highest yielding size?

    No way would I build a Merten's small boat in foam. The build speed with plywood is significantly faster. To be honest, if I was to start over. All of my work would be done with infusion. Wet bagging is stressful. Wet bagging also has higher waste rates than infusion. The issue is you don't have 60 minutes to play with and minimize resin use. From the time you mix; you have about 50 minutes to get the parts in the bag before gelation. This includes wetting both sides for a two sided layup; wetting the downside core. Wetting the topside laminate which is the same size. Peelply laid nicely. Release and breather and bagging. Removal of gum tape backers on 3 sides. Laying the bag well. Pleating. All must be done before gel or you entrain air.

    Here is a 33.5' panel in the bag. These used a tropical epoxy that was post cured as a whole hull in an oven. Our times ranged from 110 to 63 minutes on these large panels with 120 minute epoxy. Two of the 8 large panels were rejected; likely due to the bottom side gelling too fast on us and entraining air. Those pieces were used in other less exposed areas of the build. I am in my 4th year of full time work. The 33 foot panels were built with a three person crew. For 16 foot panels, you need two people for wet bagging.
     

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  11. fallguy
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    fallguy Senior Member

    Build Mertens Phantom 15 in plywood. Those are really great boats he has over there. The foam is probably 200 pounds lighter for triple the cost and triple the build time..not worth it because the boat only seats so many anyhow

    if you want some foam fun, build the td3
     
  12. Rumars
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    Rumars Senior Member

    Foam sizes are often metric, and translate poorly to imperial. There also is a need for sheets that are long and not very wide that are used for planking so you have sizes like 2m×0.5m (~20×79inches) wich is 1sqm and that is very nice for us metric folks that buy foam by the square meter and calculate our hull surface in sqm.
    Fiberglass is also nice in metric, the weight in gr/sqm is almost equal to the finished laminate thickness, 600gr/sqm makes ~0.6mm.
     
  13. Mark C. Schreiter
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    Mark C. Schreiter Junior Member

    Agreed that its a ton of work but i'm a glutton for pain and whatever keeps me out of the house and away from the TV is awesome by my book.

    the epoxy I use kicks off pretty fast in the mixing container but it takes a couple hours to gel on me when laid up on the glass. i would need to mix the resin in small batches and feed my wife a bottle of wine in order to convince her to help me laminate. but the parts ( other than the hull) are all flat panels, so as long as i'm careful i could reuse the bagging film and bagging tape a couple times. basically make a table out of plywood lay down plastic to avoid bonding anything directly to the table, baggage tape along the 4 outside edges and apply bagging material to one side of the table, prepare one side of the foam, g;*** it, peel ply, bleeder/breather, seal bag and pull vacuum. this would save time and work. also if I bagged it all, i would only do 1 side at a time.

    the build is roughly planned as below, although i'm sure im missing a step or two.
    1. they want you to build a base that will serve as a vacuum table and later a support for your buck. the table is 4, 4 x 8 sheets of ply wood.
    2. cut out all the foam parts from the foam and bond via butt joint the parts together that are to big to fit on 1 sheet.
    3. for the stringers, bulkheads and a few other parts, vacuum bag one side of your part on the table, flip over and do the other side.
    4. set all those parts aside and build the buck or male (ish) mold. basically this consists of a handful of plywood frames laid out like a strongback design ( I think thats what its called) and then you run stips of wood 1/2" thich by 1 or 2" wide from bow to stern. this gives a general shape of the boat.
    5. cut out the foam for the hull bottom and sides. this is bare foam and no glass. the boat has mostly a flat bottom so the foam layout should not be to complicated. use drywall screws to anchor the foam to the mold.
    6. thickened epoxy at the seams and fiberglass tape on top of that. when that cures you can remove the screws and the hull should hold shape.
    7. 2 layers of glass on the outside. you can do finish work or at least start it at this point but to complete the tunnel hull you have to flip the boat over and do that first, for some reason.
    8. flip boat, work the tunnel, transom and false transom out of foam and fiberglass.
    9. fit the stringers and bulkheads into place, fliet the seams and tab everything in.
    10. bond the preglassed sole and decks with thickened epoxy and i think tab them in but I cant remember off hand. Im sure ill end up tabbing them in though either way.
    11. prep, paint, add power.
     
  14. fallguy
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    fallguy Senior Member

    The only thing that worries me about Mertens conversions to foam from ply are behavior of things like bottoms. The bottoms will sag as you described. Then tons of fill work to avoid a hook type bottom. Foam has much lower flexural rigidity than ply.

    What about gunwhales? Core cannot have any raw edges. So gunwhales made of coosa? Or are you gonna decore and recore all holes?
     
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  15. Mark C. Schreiter
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    Mark C. Schreiter Junior Member

    The Gunwhales are attached or part of the for and aft decks, made from foam and go on in one shoot and have two or three frames to help support them as they are meant to be wide and strong enough to walk on. I haven't thought about the edges to much yet but I think, I would ideally like to rout out maybe a 1/2 inch into the foam or so and fill it with thickened epoxy. then I can create a nice rounded over radius to the edges.

    I also have a very thin kerf saw blade for my table saw that I use to cut fret slots for guitar necks when I was into building guitars. so for where the foam will have to contour instead of buying the slotted foam i would make the relief cuts myself.
     
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