Own design project of A-Cat

Discussion in 'Fiberglass and Composite Boat Building' started by Vector77, Apr 8, 2014.

  1. petereng
    Joined: Jan 2008
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    petereng Senior Member

    Hi Vector - vertical planking like Ian uses is fine whether it be 9mm or 12mm. For the foam to be stable it needs to be heat shaped then seam glued and screwed to the ribands into the mould, then skinned on one side, then frames put in, then removed, turned over and the outside done. If you screw them into forms and only edge glue them together, then remove it from the mould it will spring into some unusual shape.

    ian and Fram publish images on how to do this process.
    cheers Peter S
     
  2. Vector77
    Joined: Apr 2014
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    Vector77 Junior Member

    Thank you Peter... Just I don't know... if I will put wrom from the plank (the form, lath or rod) to the herex core.. would it stay for the hardening time of glue?
    Or do you think it si better to put worm thru the herex core to the form, lath/rod?

    I know that then I will put cloth on the inside surface and then on the outside...
     
  3. Vector77
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    Vector77 Junior Member

    Also I have a one question...

    I read somewhere, that 3kg/m2 of carbon fibre is 3 mm thick.

    Does it mean, that 5 mm thick profile is made by 5 kg/m2 of carbon fibre?

    And that 5kg/m2 of carbon fibre is 2,5 kg of pure carbon cloth and 2,5 kg is resin?

    Thanks...

    I will need build beams for the hulls... so I thought that profile by diameter 100 mm and 5mm thick of the surface would be OK...

    I made calculation that surface of beam with diameter 100 mm, 5 mm thick and 2,3 lenght need 2,5 kg/m2 of carbon cloth and 2,5 kg/m2 of resin...

    Right?
     
  4. petereng
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    petereng Senior Member

    Hi Vector = hand laminated carbon fibre with a 1:1 ratio of resin to carbon by weight has a density of around 1400kg/m3 so 1mm thick areal mass is 1.4kg/m2. There are lots of videos and books on construction methods. look on the west system site. They have good construction info. You need to do a lot of reading yet! Peter
     
  5. Vector77
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    Vector77 Junior Member

    petereng: thank you for your comment. I will make laminate by hand.. but I will also use vacuum pump to exhaust waste of resin.

    Here is my calculation of the weight of hulls (2 hulls weight together)

    surface of one hull - 6,6 m2 - 2 - 13,2m2 plus reinforcement (rib, mirror etc.) 15 m2

    HEREX/AIREX C71.75 - 80 kg/m3, weight of 9mm C71.75 is around 11,25 kg


    Inter surface of hulls:
    Multiaxial cloth 320 kg/m2 + resin = c. 700g/m2 x 15 m2 of surface area = 10,5 kg


    Exterior surface of hulls:
    Multiaxial/Biaxial/standard cloth of fibre 400g/m2 + resin = c. 800g/m2 x 15 m2 of surface area = 12 kg

    So total weight of the pure hull woudl be 33,75 kg

    Is there any chance to save some weight?

    I calculate plus extra 5 kg for filler, epoxy primer and TopCoat...

    I will use lightweight epoxy filler (I distribute it...) and lightweight epoxy primer... and standard polyuretane TopCoat...

    Beam:
    For the building and better orientation with this prototype... I will buy 2x2,3 length ALU tube... distance 100 mm and thick of the profile would by 3 or 5 mm... But I think also about 90 mm distance and 5 mm thick.. which would be fine for testing of the hulls on the water?
    During the time I would like to make carbon tubes... but at this moment I would like to see boat "together" with hulls and somethink between of it...

    Thanks for comment

    I have a lots of work to do... and lots of reading... thanks for your time and help ;)
     
  6. petereng
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    petereng Senior Member

    you need to check all your numbers and then make some judjmnets on if these are obtainable. You probably need to make some small test panels to confirm your construction weights then you can look at things and decide how to loose weight.List your parts by wight so you can look at your heavy bits first. You stilol hav a long way to go.

    Peter
     
  7. david r.
    Joined: Nov 2012
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    david r. New Member

    Hi,
    This is my first post here.
    Vector has an interesting project, and i have a little advice based on my own cat project that is only slightly more than half the size of his boat.
    No offense but, unless you are a very industrious person with free time and funding, you should give that herex or airex sheet foam back to your friend; take your money and buy a used catamaran and sail around in your free time.
    If you do go through with the project, you should plan out the completed boat before you start. Are you going to buy the rig? Are you going to buy the rudder system and dagger boards? How will you engineer the load paths in the hulls with bulkheads and re-enforcements? Where are you going to put the mast and trunks?, etc.
    As for the weight; 75lb hulls in wood be heavy even for a wood boat. I used stro/corecell/glass/epoxy/and carbon re-enforcements, and got 25 lb hulls 9'8" in length. The 1# styro that i shaped the hulls from is still in there.
    When i imagine a second boat for me, i would start by making the daggerboards, trunks, and rudder system first. The rudders T foil, and the daggerboards would be 1 of the 3 main types for hydro foiling that are popular. A future decision that is waiting for more data.
    Speaking of rudders, you should build your transoms strong, as a T foil rudder can load up if you put it to work.
    The French guy on you tube with the black foiling A cat seems to have used large carbon tubes for his beams. Maybe you can buy tubes instead of building them from scratch. Those boats are build as a one piece unit in carbon, so you idea of building hulls with saddles for alu. beams, then later switching to carbon is not an optimum use of carbon in the end.
    thanks, good luck, happy sailing
     
  8. Vector77
    Joined: Apr 2014
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    Vector77 Junior Member

    David: Thank you for your post... I sailed many catamarans... F18, 18HT, F20... bigger like Eome 35 (Czech catamaran where I helped with development and builidng).

    This catamaran is only for myself. I decided to make hulls and beams separately just with mechanical join.

    Finally here are some pictures (please - daggerboards/foils are at this moment only for demonstration).

    To your questions:
    1) Rudder system - I would like to use some rudder system from Dart or Hobbie catamaran... only the rudder would be designed by my self (or maybe I would by some on internet)
    Also rudders would be with T foil profile... (on the render isn't - just for ilustration...

    2) Daggerboard - I think I would like to use "C" shape od daggerboard and then maybe combinate with J board....

    3) Mast - probably I would make it by my self by carbon or I will by mast of dart 18 (same size) or buy it from local carbon-fibre manufacture which is specialised on that...

    Please could anybody tell me with version of the sandwitch would be better? Could I use 9mm HErex with 300g/m2 carbon fiber (or fiber glass) biaxial from both sides or shell I use 600g/m2 from both sizes?

    I build with my friend Farrier trimaran by 1,2 mm Airex 70.75 and 600g/m2 from both sizes.... it was OK.. but this moat is smaller.. so?

    Thanks
     

    Attached Files:

  9. Vector77
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    Vector77 Junior Member

    Also Here are separately profiles of the hull...
     

    Attached Files:


  10. david r.
    Joined: Nov 2012
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    david r. New Member

    Since you have built a boat before, i guess you know what you are getting into.
    Most of my foam sandwich experience comes from building boards, and sailing beach cats.
    There are various densities of hard foam, herex and airex are at opposite ends of the pliability scale, so it's hard to give any advice. plus there is the language barrier.
    Anyway, from my experience the lightest usable combo is obviously 1/8" hard foam with 2 oz. glass on both sides, but that would be too light for a 18' cat. The bottom of a windsurfer can be done with 1/4" hard foam and 4oz. cloth on each side, but many of them have 4oz. under and 6oz. on top of the bottom skin. Although a big course racer can be done with 1/8" bottom foam with 2oz. under and 4oz. on the outside. Decks are 1/8 foam with 4oz. under and all sorts of re-enforcement on the outside. Normally glass under and carbon on the outside.
    So i am saying that i think your foam is thicker than it needs to be, so you should glass it light (with carbon if you have the dough to throw around). Re-enforce the high stress areas with carbon any way. Make some test panels, look at other cats. I think most beach cats use between 1/8 or 1/4" had foam. You have 1/3" hard foam. A very light glass job would hold together if done right, but it will puncture easily from sharp rocks.
    If you are not trying to build a competitive race boat, the weight won't matter that much except for when you move the boat on land.
    If you plan to switch the daggerboards latter, you should try to plan it so that you don't have to change the trunks as well.. Also i think that the boards and mast go further forward on a foiler, so there is that to consider. Changes going on in that class.
    good luck.
     
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