Carbon bow sprit info.

Discussion in 'Sailboats' started by New builder, Jul 22, 2015.

  1. New builder
    Joined: Jul 2015
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    New builder Junior Member

    Looking at putting a carbon bowsprit on a boat I want to build. Size of boat has not been decided yet.
    The tubing I see comes in various sizes and different cloth orientations.
    Does anyone know what the best orientation is. ???
    Also, I have read if you want 4 or 5 feet of sprit out front. You need 4 or 5 feet of sprit inside. So 1 to 1. An equal number out to an equal number in. Is this true ?
    If a sleeve is used inside the boat. Would the 1 to 1 rule still apply ?
    Hopefully there is some one that knows.
    Cheers.
     
  2. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    I think your cart is a very long way in front of your horse but...
    Good carbon spars are almost entirely unidirectional fibres running lengthways. Only a very small percentage of fibres are needed running axially.

    > An equal number out to an equal number in.

    Imagine applying that to free standing masts!
     
  3. messabout
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    messabout Senior Member

    I think that 4g is telling you that one to one ratio is not necessary. I concur.

    Why do you need a carbon bow sprit?
     
  4. rob denney
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    rob denney Senior Member

    The ratio between lengthwise, +/-45 and axial reinforcement is about 80%/15%/5%, but varies depending on the actual arrangement. Mostly dependant on the loads it will see (often means the 90 fibres aren't required) and the amount of torque it will experience (rudder tubes have more than masts).

    The amount of bury (distance between the supports for the prodder) also varies. Ideal is about 12% of the length, but we have successfully used as little as 6% (11m mast with 75mm bury). Quite a few variables for this as well.

    Any questions about your specific tube (or rig), let me know.

    rob
     
  5. JRD
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    JRD Senior Member

    What class or style of sailboat is it? How big is the sail. The bury length depends on the loads and strength of the tube, simple as that. Also do you want it to retract when you drop the sail?
    oh yes also it depends on how strong the hull is where you connect it, the shorter the bury, the higher loads on the hull. Its just a big lever really. As a guide you need to be able to lift the front of the boat holding the tip without excessive bend or breakage.
     
  6. New builder
    Joined: Jul 2015
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    New builder Junior Member

    Right now. I'm all I'm asking is what I stated in my original question. What kind of glass orientation is used when building a carbon fibre spinnaker pole ?

    I see different types of tubing available. Such as wound, straight, uni directional. Etc etc. And as I mentioned. The boat legnth hasn't been decided.

    So. Back to my question. If you were going to purchase a carbon tube. Let's say for a melges 24. What type of tube would you purchase. It will be very close to a melges style of boat.

    I hope that helps with the question.

    Thanks.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Composite structures are engineered for expected loading. There's no generic fiber orientation, though this said, most spars have a high percentage of longitudinal fiber orientation, for obvious reasons. Most of the tubes you're looking are are woven, which works and has uniform load dispersal, but not the ideal thing for a spar. Spars are best made from "warp" unidi fabrics, so you can control the weight, while maintaining the appropriate stiffness/strength necessary. In fact, these are the only reasons for carbon spars. Simply buying a woven tube for a spar, places half the fibers in the wrong orientation, which is self defeating and costly, plus heavier than necessary.
     
  8. New builder
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    New builder Junior Member

    Ok. How about this. Anyone know what the Melges 20 or the Melges 24 or similar type of boat use for a bow sprit ??..
    I know its carbon, but. Anyone know the inside or outside diameter ? The wall thickness. ? What type of Carbon cloth was used to manufacture it ?

    Thanks for all the replies so far.
     
  9. rob denney
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    rob denney Senior Member

    Either:
    filament wound, as long as the winder can get 0 degree fibres (most can't)
    uni over a mandrel and shrink wrapped
    pressure female moulded if money is no object

    All will perform similarly and the weight difference won't be noticable. The filament wound will be cheaper, the pressure mould more expensive

    All will have most of the fibre running lengthwise as per my previous post. None will use cloth except for the inner and outer layer, when it will be applied at +/-45 unless it is decorative.

    No idea about the Melges.
     

  10. timber
    Joined: Jul 2004
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    timber Junior Member

    I am curious about this, too. My boat is an i550, 18 LOA, 4.5 WL beam, 8' max. beam, 800lbs, 26 foot hoist of Asym, 500 Sq. ft. max asym sail, 250 sq. ft. upwind sail.
    Nominal 3.0" O.D. for sprit, 58" length from Bow.

    will have 80% of fibers oriented on long axis, knitted sleeve for rest of laminate.
    Will source from Soller Composites for materials but need help on amount of material and layup for adequate durability without unnecessary overbuild.
    Advice or ideas welcome.
     
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