Skin On Frame Catamaran

Discussion in 'Boat Design' started by ElGringo, Sep 14, 2016.

  1. ElGringo
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    ElGringo Senior Member

    But Manfred, I don't even know what that is.
     
  2. Rurudyne
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    Rurudyne Senior Member

    Hey, thanks!

    Found this about the boat standing up to rain: http://youtu.be/dCOmobDXPpI

    ... but then ...

    ... and thanks as well! ... also snow is another matter entirely!

    I note that the coroplast's structure, which should offers one insulation value, may be responsible for the inability to melt off roof accumulation by means of interior heat.

    And it isn't really cheap, Home Depot wants $173 and change for a 4x8 5 pack.

    But what I had in mind was more along the lines of SOF rather than frame with a skin. By this I mean that with SOF the skin is not simply attached the frame but is shrunk to the frame. It provides some of the strength.

    Consider a roof whose internal structure is somewhat like a large SOF stand-up paddle board in place of the Coroplast covered roof of the boat shown in those videos. I'm thinking it should have more strength to hold its shape under load, better resisting buckling as the aluminum roof rafters supporting the Coroplast roof apparently did.
     
  3. Rurudyne
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    Rurudyne Senior Member

  4. Manfred.pech
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    Manfred.pech Senior Member

    Thank you for the links. Here is another one: https://www.boats.com/reviews/crunching-numbers-displacementlength-ratio/

    The best and cheapest way is to buy a well tested design of one of the designers here. But if you are are a risky guy and want an expencive experiment which can ruin you, make a list of all you want to carry with you and the weight of it. Then try to "design" a boat which can carry (float) all your goods including yourself and the weight of the vessel. Helpful might be "Delftship" or "Freeship" (Google). You can discuss the results here.
     
  5. ElGringo
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    ElGringo Senior Member

    Rurudyne, These guys make sandwich panels, and you can order them with whatever skins and foam thickness you want. Look around on the site a bit as it is not real easy to find everything. http://singcore.com/product/sing-panels They may not sell direct to you but they have a form you can take to Lowes and get them to order for you.
     
  6. ElGringo
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    ElGringo Senior Member

    Manfred, I will go to that website and learn what I can. It seems I am always thanking you because you are kind enough to come to the aid of fools like me.
     
  7. ElGringo
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    ElGringo Senior Member

    Manfred, if I did it right, it is 77.94 and would be considered an ultralight.
     
  8. Manfred.pech
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    Manfred.pech Senior Member

    Astounding.
     
  9. Rurudyne
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    Rurudyne Senior Member

    Here's an interesting little website:

    http://www.sheldrake.net/surfboards/look.xhtml

    Something like a Phlatprinter (now in 3rd version) might be good for helping to adapt this idea ... probably in light marine plywood rather than cardboard.
     
  10. ElGringo
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    ElGringo Senior Member

    Manfred, the "Astounding" part is that I'm not smart enough to know why I need to know the displacement/length ratio. I looked around that website for a long time and what I really thought was whaaaat does that mean? Do you guys really know all that stuff? Do you need to know it before you glue some sticks and nylon together? Will I sink if I don't know it?

    I did find some information on another website that just can't be true, it was a boat speed calculator and it claims my little boat will go 34 mph with a 10 hp motor. I don't believe that.
     
  11. Rurudyne
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    Rurudyne Senior Member

    It's my understanding that such calculations will work best over a particular range of DLR etc and outside if that range they suffer.

    That said, a long narrow hull can without planing achieve higher speeds. I believe that when length is 6 times beam a properly fashioned hull might achieve twice the square root of its LWL in feet, in knots. At least based on a equation I remember ... something like LWL / (3 x BWL) times the square root of LWL (apparently for LWL/BWL > 4:1) but my mind's kinda fuzzy right now because I've been moving fairly heavy tools from one place to another in the heat of the Texas day.
     
  12. Manfred.pech
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    Manfred.pech Senior Member

    El G. I tried to motivate you to get a well tested design from a designer here who has done already all the math which is useful for a good boat. I have wasted a lot of money and time for own "designs" which have not been successful. One of them:

    [​IMG]
     
  13. ElGringo
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    ElGringo Senior Member

    Manfred, I know it would be a better boat, but I also know that it would weigh a lot more than 4 to 6 hundred pounds. I think I can load and unload a boat of that weight from a boat trailer backed into the water without winding up in the hospital again. I have reached a place in my life where nothing else can be done except pain medicine and I don't like it because I can not think or function. So I tolerate the pain and do what little I can. I believe that I can and will build a SOF catamaran of around 16 feet in length and powered by a 5 to 10 horse motor. I have a large room, 36' X 36' added to the back of my home which has heat and cooling. It stays 72 degrees year round and other than two desks and computers it is not used for anything. I can work for about 30 minutes and then have to rest for about the same, but if I live long enough, I'll get it done.
    You have been more help on this website than anyone else and again I thank you.
     
  14. upchurchmr
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    upchurchmr Senior Member

    Do you have an idea about what you would do for the deck of the cat?
    A flat platform, with chairs?
    How you get the weight of the deck, motor, and people transfered into the hulls will affect how you need to build the hulls.
    Any idea of how much weight you want to carry?
     

  15. ElGringo
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    ElGringo Senior Member

    Upchurch, Probably three 4 X 8 plywood sandwich panels built of 1/8" ply, 1 X 2's and foam. If the hulls were 18" wide and the beam 8' I would only have to deal with a 5' open span. The fwd. and aft ends of the deck would have a plywood box beam bonded to them and probably two smaller box beams bonded to the outside edge on top of the deck. The aft beam would support the motor. I may be way off on my thinking but I don't see why the boat would weigh more than 400 pounds with the motor, and maybe less. Then add me, something to set on, and maybe an ice chest, for a load of 250 pounds.

    I could go buy a boat but it would not be the same to me.
     
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