Microcatarmaran

Discussion in 'Fiberglass and Composite Boat Building' started by sebaseba, Apr 14, 2020.

  1. sebaseba
    Joined: Apr 2020
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    sebaseba Junior Member

    Yeah. I'm accepting it slowly, read the previous post. I'm looking into alternative creative solutions, maybe using things that aren't commonly used, but it's just research (for now) of possibilities. I like also the idea of honeycomb + foam structures. Seem it really adds to strength. I have a lot to learn. :)
     
  2. fallguy
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    fallguy Senior Member

    XPS is usually sold at the big box stores in low density versions.

    It has dual problems in shear and compressive strength. I use it for its intended purpose. Insulation. Yes, in a boat around the livewell or even as livewell sides with heavy glass so if it shears; I don't care.

    If you special order a higher density version that is say under 50psi shear; abrade the surface with 36 grit floor paper. This effectively modifies the surface area to maybe 125% which might be a stretch, but if you apply a thixo mix to it; it does better on shear. If you had a 30psi density and you get 125%; you pick up another 7 pounds or so this way. Never leave it raw edged. But mainly avoid it.

    The rubber lashing method is good precisely for the reasons I cited. If you get into some rough stuff; the lashing will give a bit. But it is also super simple. If you gave me a carbide cutter; some rubber inner tube; and a couple 2x4s; I could lash two canoes together in under an hour. They would work without stays even.

    If I didn't have the carbide cutter to slot under the gunwhale; I'd lash to the seat backs. Just remember, over the aka first; not through the lashing point first.
     
  3. fallguy
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    fallguy Senior Member

    8E9968A8-B650-4F0E-AB93-F01A843F3967.jpeg
    See rubber lashing around aka?

    Fish was released; there are two small whitefish in its belly causing distention.

    We use outriggers because water is 39F and going over can kill you with all the heavy clothing needed if it is 25F outside. But the concept is the same for lashing two canoes together.
     
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  4. upchurchmr
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    upchurchmr Senior Member

    There have been others discussing the problems of materials from your area.
    You have my sympathy.
    I personally like strip planking.
    Once you learn it doesn't take as long as it seems, but only if you are willing to paint - not varnish.
    If you are doing something like a canoe (smaller) you run into the problem of buying fiberglass/ epoxy.
    So nothing I know works.

    I wish you good luck .

    FYI, foam or honeycomb adds stiffness while reducing weight - if it is engineered properly. But that is a difficult design.
    It does not add strength if you have an equal weight design.
     
  5. sebaseba
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    sebaseba Junior Member

    upload_2020-5-1_13-5-49.png
    upload_2020-5-1_13-6-17.png
    upload_2020-5-1_13-6-51.png

    Interesting graphs I've found :)
     
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  6. sebaseba
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    sebaseba Junior Member

    upload_2020-5-1_14-28-39.png
    An another.
     
  7. sebaseba
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    sebaseba Junior Member

    OK, I think I made myself a nice setup in excel to calculate sandwich material properties.
    I think I now see why using styrofoam usually fails. Not sure if I'm calculating it right, but I think I undertand the gist
    Styrofoam has quite low shear strength. In order it to work, you have to make the core quite thick and making the fiberglass thicker doesn't help as much.
    The main limiting factor is the shear strength of styrofoam. That's why it turns into dust.
    Also XPS seems to be better than EPS and higher compresive strength EPS is better than lower compresive strength EPS.

    Comparing EPS200 to Divinycell H45 my calculations say that you need to increase core thickness by 60 % to get the same performance.
     
  8. upchurchmr
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    upchurchmr Senior Member

    While the point about strength is true, the benefit to a core sandwich is stiffness.
    Make your own test.
    Build your own sandwich panel 12" x 4" x 1" thick.
    Start with EPS.
    Add a wood block at one end the thickness of the core.
    Use a good thin plywood, or glass/ epoxy.
    Draw a vertical line on one side of the panel.
    Clamp the end with the wood block to a table.
    Load up weights on the free end but not so much that you break it at first.
    Look at the vertical line on the side of the panel.
    The previously vertical line will be distorted into an S shape.
    Repeat with a stiffer core and the same weight and the total deflection will be less. For the stiffer core the line would still be straight (or at least straighter).
    Now take the EPS sample and try to load until it breaks.

    If you can find some end grained balsa and you will see what a much better core does.

    Have fun.
     
  9. sebaseba
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    sebaseba Junior Member

    Yes. I did calculations for balsa and it seems very good. Maybe I'll use EPS or XPS where it doesn't need to be stiff and balsa or even plywood where it needs to be.

    Also I'm thinking of maybe going beyond 3 m of length, but I need to ask wtf I need to do then in order to register the boat.

    Some say you just need boat plans, bills of materials, a statement that you built it yourself and a certificate of comformity to standards. The last one is the problematic one. Some say that if you build it for yourself (you can't rent it out or sell it for 5 years) it can be self-signed, some say you have to hire a certification authority. Some even say that you have to hire them before starting and that they can come to check the construction before it's finished and such checks cost 500 €. Meh.
     
  10. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Registration does sound a bit of a mess. Unless you get really lucky here you better ask in a slovenia boating forum.

    Have you read this and the PDFs?
    Boat registration / Permits / Slovenia Business Point http://eugo.gov.si/en/permits/permit/12623/showPermit/

    From this info about croatia (same regulations?) you might be able to talk with any harbor master or port authority for info. Big question is if you can make your own "certificate of construction" for seaworthiness.

    Maybe it's easier to register your boat in another EU country haha
     
  11. sebaseba
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    sebaseba Junior Member

    I've sent an email today to the Slovenian Maritime Administration. I'll see what they'll say.

    Yes, there's a Slovenian forum on boating. Features also a section named "fixing, building and restoration" (of boats), but it's predominantly about fixing and maybe restoration. There is ocassionaly someone talking about building, but other members mostly are full of pessimism and conflicting information. I started to read, but quickly stopped for the sake of my psychological well-being. Also information seems to be old, although I doubt much has changed.

    I know it was very common to build your own boat in ex-Yugoslavia times. The process was simpler, less bureocracy. :)
    Many were built out of ferro-cement. But also wood and GRP.

    I know there are two associations building & restoring wooden boats (the second I'm not sure if it's an official association or just a bunch of people together):
    * Društvo Bracera Associazione Brazzera https://sites.google.com/site/braceradrustvo/ and their event Regata starih bark: lesenjače znova napele jadra in preplavile slovensko morje https://www.rtvslo.si/zivljenjski-slog/retro/regata-starih-bark-lesenjace-znova-napele-jadra-in-preplavile-slovensko-morje/500687
    * Rebra bodo hrastova, paluba iz macesna https://www.slovenskenovice.si/novice/slovenija/clanek/rebra-bodo-hrastova-paluba-iz-macesna-73106

    But building boats using pre-1950 plans and using traditional materials is from what I understood a special class, exempt from rules.

    Well I could always sail in Italy. There I think you don't need to register the boat up to 10 m. Not sure. But Italy is special. It's similar for airplanes. You don't need any license to drive or to register it, but you are disallowed to use the radio then. lol.
     
  12. Dejay
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    Dejay Senior Newbie

    Well lets hope you get good news. Might be better to call though and chat a bit.

    In Germany from what I've read below 15m you just need an IBS (international boat paper) it's just 32€ online with the ADAC. I don't know what the rules are for sailing and keeping a boat registered in a foreign country for extended periods. Or if you even can. I guess that would be too easy haha.

    Of course 3 meters can be done, just a bit slow. Just build an easy and cheap to build plywood catamaran. I'm a total novice, but maybe a planing monohull sailboat would be better if you want some speed. Or a small hydrofoiling sailboat. Hydrofoils aren't limited in the speed by the length of the boat. Much more complex of course.
     
  13. sebaseba
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    sebaseba Junior Member

    I know for cars if you do the technical (MOT) check in an another EU country, the other EU country must approve that too. Some do that here, they go to Croatia to do it, because they are more likely to pass there. Maybe it works the same for boats. I do the certification in Germany and just register here. :) :)

    I'm thinking of maybe doing a catamaran, that has the "canoes" out of 3 pieces. You remove the center piece and you have a 3 m boat, you add it, you have a 5 m boat. That way it would be max. legit for rivers & lakes and it could be shortened to 3 m for sea. That would be kinda neat. Also easier to store and transport.
     
  14. sebaseba
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    sebaseba Junior Member


  15. sebaseba
    Joined: Apr 2020
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    sebaseba Junior Member

    OK, I got a reply on the e-mail and they said it's very simple but that I should call them tomorrow so that they fully explain to me everything. \o/
     
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