Need Help with Sunshade Design

Discussion in 'Boat Design' started by Charly, Feb 11, 2013.

  1. Charly
    Joined: Dec 2009
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    Location: st simons island ga

    Charly Senior Member

    Hello everybody.

    I have been thinking lately about building a shade for my catamaran build (36' daycharter Kurt Hughes).

    The plans do not come with a stock option for an awning/bimini/dodger arrangement, since the needs and preferences of each builder are probably widely varied, So, I have struck out on my own here, :D, and made a very amateurish attempt at a drawing to illustrate what I think I want.

    Here is a summary:
    Ample shade protection for all those seated on the bench seats that run fore and aft, for 8 feet, underneath the boom.

    A versatile system that can be expanded, or contracted to suit the weather requirements, by adding or subtracting canvas sections, maybe even expanding to cover the helmsman and the whole deck at times.

    A sleek look, with stiff canvas panels that create very little windage, and with low tech lashings etc to hold the canvas on, preferably with some kind of "vent" arrangement to spill excess wind when needed- especially uplift.

    A hinged dodger that can fold down, allowing the forward part of the top to become a wind'spray shield, when needed.

    It must be strong and light , of course, and inexpensive materials as much as possible.

    I would really appreciate any advice, comments, anecdotes, ideas or opinions, especially as to materials selection for the frame.

    edit;
    the proposed frame is drawn in green. The dodger part would be supplemented with a piece of canvas that would somehow be fastened already to the main beam on one edge, and that would then be un folded or unrolled up to cover the forward section that is left exposed after the eyebrow has dropped down and been secured. No eisenglass in it, I reckon, since you cant see through the stuff anyway...
     

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  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Ive never operated a cat.
    For the sun you need overhead protection and protection from low angle sun and reflection. My sun awnings have roll down curtains that touch the lifelines when deployed. The bigger the awning, the cooler the boat and crew.

    Windows in an awning are a waste of money...then sun burns thru.


    Make your canvas work a light colour...dark get too hot and bleaches out with age. I prefer the light silver sunbrella fabric.
     
  3. Submarine Tom

    Submarine Tom Previous Member

    I'm not a trimaraner, oops I mean cat'er.

    Keep it simple, try over the boom with some support lines to the rigging.

    Surely you've done this before. It should give you a good idea what you need / want.

    Sunbrella is an excellent product. Choose a bright colour you like.
     
  4. Alex.A
    Joined: Feb 2010
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    Location: South Africa

    Alex.A Senior Member

    Shade cover

    Something non permanent?
     

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  5. yipster
    Joined: Oct 2002
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    Location: netherlands

    yipster designer

    true but qualitys varie, for example Eisenglass, strataglass, isingglas although more expensive last in better gauge sizes for a long time
     
  6. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    The high quality windows will last a few years. UV eventually takes its toll.

    I was talking about widows letting in heat and the top of your head burning up.

    The OP might investigate roller fulrer style curtains housed in a large diameter tube. Many superyachts are doing this
     
  7. charlyIII
    Joined: Oct 2012
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    Location: st simons island ga

    charlyIII Junior Member

    Thanks for the input

    Cant run it over the boom, even at anchor, because it is set up w/ lazy jacks. It must be functional under sail.

    Side curtains will be a must also, but they shouldn't be much of a problem to add to the structure once I figure out how to build it. mosquito nets could of course be added also later.

    The main issue, as I see it, is a frame that is light and stiff, and that will not rack or collapse. The roof will need camber, to shed water... but not too much camber, because headroom and visibility is a definite problem as well. For this reason I will not be able to have any kind of "collar ties" to resist the side frames tendency to bow out, and to help hold the sides parallel to each other, so the roof frame members must be able to hold their shape. I thought of making two smaller versions of a "radar arch" one fore and one aft, out of okume/ balsa/ okume sandwich for this reason.

    I think the dodger part will work once I get the hinge and pivot mechanisms figured out.

    I could build a mock up out of pvc. I was wondering if I could then just cover the pvc pipes w/epoxy/glass and be done with it? but I don't know about the strength and weight of such an arrangement. Anyone tried that?
     
  8. charlyIII
    Joined: Oct 2012
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    Location: st simons island ga

    charlyIII Junior Member

    Yikes.

    I wonder what kind of material those frames are made of?
     
  9. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Plenty of camber in the roof. Heat rises so the farther away from the top of your head the better.

    Youre petty craft with composites. Why not go with a composite frame roof. Use pvc are the core becaase its easy to shape and bend with heat. Carbon and eglass sleeves are cheap. Unidirectional fiber easy to work with.

    Large diameter tubes for verticles and small diameter tubes for horizontals then you can " Socket " them together.

    A similar method like that used for catamaran trampoline tracks could be incorporated for curtains .
     
  10. Submarine Tom

    Submarine Tom Previous Member

    You may find a better (more helpful) audience on the Multi Hull page.

    I would consider quality tent poles that break down (colapse).

    Sounds a bit like you're reinventing the wheel.

    What have others done successfully?
     
  11. Charly
    Joined: Dec 2009
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    Location: st simons island ga

    Charly Senior Member

    Tom,

    Yes. And what failures and why?

    I consider this to be an "Apocalypse" boat. It was the designer's article "Apocalyptic Boatbuilding" that gave me the final push to actually build the thing. I have faithfully followed the plans, but this build has been a grand excercise so far in economizing, simplifying and making do. This generally means more labor (which is free, in my case), and getting every conceivable ounce of use out of the materials. So, I am attempting to accomplish this phase of the build with the simplest and most inexpensive material. There was a thread a while back, in which Frosty was wondering why someone couldn't just make a pvc pipe frame and cover it with glass. I think he actually did it on his boat. He is gone now, but I would very much like to know the outcome, or if any others have done it, and what might be the downside to that particular method in this application.

    I think this is the appropriate folder for this topic, no? I was hoping to stimulate some of the more design/engineer oriented members here to speak out, though much of their language is above my head, I am sure that I -and others- could learn something. I appreciate all inputs.
     
  12. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    cheapest thing you can do is build a wood canopy frame. If you laminate hoops and use brass hardware it can look attractive and be functional, though not particularly light, it would be inexpensive (but fairly labor intensive to build). You can even use inexpensive tarps for the canopy, and than stall a custom fabric one when your budget allows.

    If you make it high enough to be close to the underside of the boom you will also increase the efficiency of the main sail by acting as an end plate.

    [​IMG]

    [​IMG]
     

  13. Charly
    Joined: Dec 2009
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    Location: st simons island ga

    Charly Senior Member

    It will definitely have to be as close as possible to the boom. It looks like the height from bottom of the boom to top of the bridgedeck is about 67 inches, which will make for some sore necks I'm afraid. I haven't talked to the designer yet about raising the gooseneck height a bit, but I imagine he would frown on it.

    Petros, are you talking about hoops like mast hoops or like hoops on a shower curtain? I was thinking it would be simpler to just put some heavy grommets in the sunbrella, and lash it to the frame.

    Actually what I had in mind is very similar to the top photo ("Sirius" a sister ship) I just wanted something with a little more curves to it, along with the other options mentioned in the OP.
     
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